Denticle rows on larval appendages in twelve species of Phytoseiidae (Parasitiformes: Mesostigmata)

Denticle rows on larval appendages in twelve species of Phytoseiidae (Parasitiformes: Mesostigmata) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Denticle rows on larval appendages in twelve species of Phytoseiidae (Parasitiformes: Mesostigmata) Fang-Xu Ren, Xin-Ju Wei, Min Ma, Qing-Hai Fan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4506139/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The presence of denticles on appendages such as the palpi and legs is rarely documented in phytoseiid mite larvae. To address this gap, we studied twelve species across six genera of Phytoseiidae: Amblydromalus limonicus , Amblyseius herbicolus , Amblyseius orientalis , Amblyseius taiguensis , Euseius utilis , Neoseiulus benjamini , Neoseiulus californicus , Neoseiulus setarius , Neoseiulus womersleyi , Neoseiulus zwoelferi , Phytoseiulus persimilis and Phytoseius hongkongensis . We identified and described the denticles on the palp, basis capitulum, and specific leg segments of these species, discussing their functional significance. Acari mite morphology function palpi legs Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Phytoseiidae (Acari: Mesostigmata) comprises about 2557 valid species primarily inhabiting in vegetation ecosystems worldwide (Demite et al. 2024 ). Renowned for their predatory behavior and adaptable morphological characteristics, these mites exhibit distinctive traits such as their diminutive size and fewer idiosomal and leg setae, setting them apart from other mesostigmatid mites typically inhabiting soil environments (Walter and Proctor 2013 ). While denticle rows within the deutosternum are commonly utilized in the taxonomy of Mesostigmata, those located on other body parts, particularly appendages like legs and palpi, have often been ignored or undocumented. During our observation of phytoseiid mite larvae, we found rows of denticles on the dorsal surfaces of the palp, basis capitulum, and some leg segments. These denticles exhibit remarkable morphological diversity among various species. Upon reviewing existing literature, we noted that denticle presence in larval stages had previously been mentioned or illustrated for a limited number of species, such as Promegistus armstrongi Womersley (Promegistidae) (Seeman 2012 ), Vulgarogamasus kraepelini (Berlese) (Parasitidae) (Teodorowicz et al. 2012 ), and Sejus hinangensis Hirschmann and Kaczmarek (Sejidae) (Trach and Tolstikov 2016 ), as well as phytoseiid mites, Neoseiulus subsolidus (Beglyarov) and Neoseiulus neoagrestis Khaustov & Döker (Phytoseiidae) (Khaustov et al. 2022a , b ). While previous studies have provided valuable information on the denticles on larval appendages of a few Neoseiulus species, a comprehensive examination of denticle diversity and variation remains absent. This manuscript aims to fill this gap by undertaking a comprehensive examination of the morphology and functional importance of denticles on larval phytoseiid appendages. Through morphological analyses, we seek to shed light on the adaptive significance and functional roles of these structures in phytoseiid mites. Materials and methods Twelve species from six genera were examined. The fresh specimens selected for observation were sourced from established laboratory populations, i.e., Amblydromalus limonicus (Garman and McGregor) and Amblyseius herbicolus Chant from Auckland, New Zealand; Amblyseius taiguensis Liu, Ma and Fan, Euseius utilis Liang and Ke, Neoseiulus benjamini Schicha, Neoseiulus setarius Ma, Meng and Fan, Neoseiulus womersleyi Schicha, Neoseiulus zwoelferi Dosse from Shanxi province, China; Phytoseius hongkongensis Swirski from Shaanxi province, China; Amblyseius orientalis Ehara, Neoseiulus californicus McGregor and Phytoseiulus persimilis Athias-Henriot from Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China. The voucher specimens used were deposited at the Entomological Microscopy Laboratory, College of Plant Protection, Shanxi Agricultural University, Taigu, Shanxi, China and New Zealand Arthropod Collection (NZAC), Auckland, New Zealand. Optical microscopy Specimens were mounted in modified Hoyer’s medium (Faraji and Bakker 2008 ) on microscope slides. A compound microscope (Nikon Eclipse 80i) with differential interference contrast (DIC) was used to measure and photograph specimens. Illustrations were made by means of a drawing tube (Nikon Y-IDT) attached to the microscope and edited with Photoshop 2024. Scanning electron microscopy The larvae of N. zwoelferi were immersed in a solution containing 2.5% w/v glutaraldehyde in phosphate-buffered saline (pH 7.4) for 8 hours to achieve fixation. Following fixation, the specimens were rinsed with phosphate-buffered saline and then dehydrated in a series of ethanol solutions (30%, 50%, 70%, 80%, 90%, 95%, and two rounds of 100% v/v), with each step lasting 10 minutes. Subsequently, the specimens underwent critical point drying using a JFD-320 freeze-drying device. Following this, the prepared specimens (n = 10) were affixed to stubs using double-sided carbon tape and coated with gold using an FC-1600 sputter coater. Observations and photography of the coated samples were performed using a JSM-6490LV scanning electron microscope. Results The palpfemur and basis capitulum of all species were observed to have a row of denticles. All species (except P. hongkongensis ) had denticle rows or loops on trochanters I and II. Femur I exhibited a short denticle row exclusively in N. womersleyi , while femur II had two to three rows or loops of denticles in all species. Denticle rows were found on femur III only in N. womersleyi and N. zwoelferi . All these denticles were positioned dorsally. Palp (Figs. 1 – 3 ) Each femur has a row of denticles at the level of and medial to seta d2 (Figs. 1 a, 2 a & 3 ). These denticles are relatively stable in position, with their extension direction being mostly horizontal. The number of the denticles varies among species. E. utilis and P. hongkongensis have 5 (5–7) and 5 (5–6) denticles, respectively, while N. benjamini has 15 (14–17), N. setarius has 13 (10–17), and N. zwoelferi has 14 (10–17) denticles. An exceptionally large tooth was observed posterior to d2 in A. taiguensis (Fig. 3 d). The number of denticles influences the arrangement of the small denticles, with species possessing more denticles having a denser and more orderly arrangement, while species with fewer denticles show a relatively disordered arrangement, such as P. persimilis . Regarding the overall shape of the denticle rows, there are differences among species. In some species, the small denticles are observed to grow on a plate-like structure. Among these, N. zwoelferi is the most prominent, with the entire plate-like structure clearly observable. Some species show a clear tendency for this, such as N. setarius , N. womersleyi and P. persimilis . However, for some species, the presence of the plate-like structure is difficult to observe, such as N. californicus and N. benjamini . Denticle rows were absent on the trochanter, tibia and tarsus in all species. Basis capitulum (Figs. 1 – 3 ) On the dorsal surface of the basis capitulum (dorsal extensions of the palpcoxae), there is one or two rows of small denticles (Figs. 1 a, 2 a & 3 ) at each side, with significant variation among different species. The species with the fewest denticles include P. hongkongensis with 8 (5–11) denticles and P. persimilis with 9 (6–11) denticles, while N. zwoelferi has the most denticles with 23 (18–28). N. benjamini also has 23 (21–26) denticles. Some species show the presence of small denticles on the lateral side of the basis capitulum (Figs. 1 a, 2 a, 3 a–e, h–j). However, due to slide preparation reasons, the count of lateral denticles is not as clear, and some lateral denticles might not have been observed. The observed small denticles are located on the outer side of the dorsal denticles and are slightly inclined towards the palp direction. For most species, the number of these denticles is around 7. Among the available six specimens of A. orientalis , only one specimen exhibited lateral denticles, with 3 denticles. Leg I (Figs. 1 b, 2 b, 4 b & 5 ) The presence of denticles on coxa I was only observed in N. zwoelferi (Figs. 4 b, 5 j) which featured two rows of denticles situated on the dorsal and dorsoposterior areas. These two rows of denticles were nearly horizontal, with a distinct gap between them. In all species, except for P. hongkongensis , trochanter I displayed a dorsal row of denticles. These denticles exhibited various shapes, primarily falling into three categories: elliptical, hook-shaped and arc-shaped. The number and shape of denticles showed a close correlation, with elliptical denticles being the most abundant, typically numbering between 30 to 40, while arc-shaped denticles ranged from 10 to 20. Species with an elliptical row of denticles included A. limonicus , A. herbicolus , A. orientalis (partially), N. setarius , and N. zwoelferi , while hook-shaped ones were found in A. orientalis (partially), and curved denticles were observed in E. utilis , N. benjamini , N. californicus , N. womersleyi and P. persimilis . A. orientalis exhibited both elliptical and hook-shaped arrangements among the available specimens. Femur I denticles exist exclusively in N. womersleyi , situated between ad1 and pd1 (Fig. 5 i), noticeably larger than those found on trochanter I. Denticle rows were absent on the genu, tibia, and tarsus in all species. Leg II (Figs. 1 c, 2 c, 4 a & 6 ) As in leg I, denticle rows were also absent on the genu, tibia and tarsus of leg II in all species. The presence of denticles on coxa II was exclusive to N. womersleyi (Fig. 6 I) and N. zwoelferi (Fig. 6 j), which positioned on the dorsoposterior area of coxa II. Trochanter II has a single row of small denticles, dorsomedial to pl , present in all species except for P. hongkongensis . Among them, N. setarius has the most denticles with 19 (16–23), N. zwoelferi has 18 (15–21), and E. utilis has the fewest with 9 (7–12). Femur II can have up to 3 rows of small denticles, namely D1 , D2 , and D3 ; D1 positioned between or slightly posterior to level of ad1 and pd1 ; D2 if present, positioned slightly anterior to level of ad2 and pd2 ; D3 if present, positioned posterior to pd2 . This feature shows some differences across different genera. For example, Amblyseius species has 3 rows of denticles ( D1 , D2 and D3 ), while A. limonicus , E. utilis , Neoseiulus species, and P. persimilis have only D1 and D3 , and P. hongkongensis has D1 and D2 . Within species, there are also differences in the number of denticles. For instance, N. setarius has 13 (11–16) denticles in D1 and 8 (7–10) in D3 , while N. zwoelferi has 7 (5–9) in D1 and 12 (10–15) in D3 . Leg III (Figs. 1 d, 2 d, 4 a & 7 ) A row of denticles, D3 , are exclusively present on the femur of N. womersleyi (Fig. 7 a) and N. zwoelferi (Figs. 4 a & 7 b), with no observation of denticles in other species (Figs. 1 d & 2 d). Function of denticles on larval appendages The denticles on the palps and legs in larval stage disappeared in nymphs and adults, leading to the conclusion that this feature is specific to larvae. As described and illustrated above, the locations where these small denticles appear are relatively consistent across species, indicating a stable feature with significance for larval mites. Regarding the function of the denticle rows, assumptions can be made. The denticles, with their small size ranging from 0.2 to 1.8 µm in height and 0.3 to 1.7 µm in width, positioned on the dorsal side of the proximal segments of limbs, are unlikely to serve as a defensive mechanism against predators. Similarly, they are also unlikely to be related to feeding or locomotion for the same reasons. Since no auxiliary eggshell-breaking features have been identified in these species, the denticle rows might have a cutting function during the activities of larval mites, potentially aiding in tearing open epidermis (approximately 1.0–2.0 µm) and eggshell (Fig. 8 ) which is approximately 1.7–2.1 µm (Di Palma & Alberti 2001 ). Given their exclusive presence in the pre-hatching and larval stage, it is plausible that if this feature serves a practical purpose, it would likely come into play during this period of life stage. Hatching of Phytoseiulus persimilis ( Fig. 8 ) To support the hypothesis, observations were conducted on hatching of P. persimilis . Initially, the newly laid eggs were translucent, plump, and smooth. Over time, their color gradually changed to light yellow, and the contents became cloudy. As hatching neared, lively movements within the egg, resembling small bubbles, were observed, gently swaying back and forth. The idiosoma of the embryonic mite was curled inside the eggshell, with chelicerae, palpi and three pairs of legs tucked close to its ventral side. When the eggshell cracked, fluid was released, causing the shell to lose its shine and shrivel rapidly. Concurrently, the mite's body expanded. First, the palpi extended outward and began to explore. Then, the palpi and the first pair of legs extended outward. When the first pair of legs extended, the second and third legs were not yet fully extended. The rest of the body followed and emerged afterward. With the first and second pairs of legs extending forward and the third pair extending backward, the eggshell split further. Although these observations were essential, they unfortunately did not provide robust evidence to demonstrate that denticle rows play a role in the hatching process. Discussion These denticle rows are likely to be ancient characteristics (plesiomorphy) expressed only during the larval stage. Similar features have been observed in the larvae of all three suborders of Mesostigmata, i.e., Sejida: S. hinangensis Hirschmann (Sejidae) (Trach and Tolstikov 2016 ), Trigynaspida: P. armstrongi Womersley (Promegistidae) (Seeman 2012 ), and Monogynaspida: N. neoagrestis Khaustov & Döker and N. subsolidus (Beglyarov) (Phytoseiidae) (Khaustov et al. 2022a , b ). Trach and Tolstikov ( 2016 ) described two rows of denticles on dorsal palpfemur, and two enlarged denticles at anterodistal corner of palpgenu of S. hinangensis and Kaczmarek (Sejidae). In the description of larva and deutonymph of P. armstrongi , Seeman ( 2012 ) noted that coxae of all legs (I–III), trochanters and femora II–III with rows of fine denticles in larva and these were absent in the deutonymphal stage. Khaustov et al. ( 2022a ) illustrated the denticle row beside d2 on palpfemur, and an arc-shaped denticle row posterolateral to pd2 on femora II and a denticle row lateral to pl on trochanter II in larva of N. subsolidus (Beglyarov). Khaustov et al. ( 2022b ) illustrated similar denticle row beside d2 on palpfemur and also a denticle row between ad1 and pd1 on femora I and II each in larval N. neoagrestis . Since the true function of these denticle rows remains undetermined, further investigation using other techniques may fill this gap and provide insight into their adaptive significance in the development and survival of larvae. This research could contribute to a deeper understanding of the functional morphology of appendages in Mesostigmata. Declarations Acknowledgements We would like to express our gratitude to Mr. Yu Liu and Ms. Juan Wang from the College of Plant Protection at Shanxi Agriculture University in China, as well as to Dr. Xuenong Xu, Dr. Endong Wang and Mr. Chuantao Huang from the Institute of Plant Protection, Chinese Academy of Agricultural Sciences, China, for providing some specimens and invaluable assistance for this research. QF extends deep appreciation to his colleagues at the Plant Health & Environment Laboratory, Ministry for Primary Industries, New Zealand, for their continuous encouragement and support throughout this study. Funding This work was partially funded by the State Key Laboratory for Biology of Plant Diseases and Insect Pests (SKLOF202215), and Min Ma was supported by China Scholarship Council. Author Contributions All authors contributed to the conception and design of the study. Materials were prepared by Fang-Xu Ren and Xin-Ju Wei. Data collection and analysis were performed by Fang-Xu Ren, Min Ma and Qing-Hai Fan. The first draft of the manuscript was written by Fang-Xu Ren and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Data availability The datasets generated and analysed during the current study are available from the corresponding author on reasonable request. Research involved in Human or animal rights This article does not contain any studies with human participants or vertebrate animals performed by any of the authors. Conflicts of interest The authors declare that they have no known conflicts of interest. No competing claims are known. Potential reviewers Dr. Edward A., Ueckermann, Unit for Environmental Sciences and Management, North-West University, South Africa. E-mail: [email protected] Dr. Gilberto José de Moraes, Entomologia e Acarologia, Universidade de São Paulo, Brazil. E-mail: [email protected] Dr. Ismail Döker, Agricultural Faculty, Cukurova University, Türkiye. E-mail: [email protected] References Demite PR, Moraes GJ de, McMurtry JA, Denmark HA, Castilho RC (2024) Phytoseiidae database. Available from: http://www.lea.esalq.usp.br/phytoseiidae. Accessed 25 May 2024 Di Palma A, Alberti G (2001) Fine structure of the female genital system in phytoseiid mites with remarks on egg nutrimentary development, sperm-access system, sperm transfer, and capacitation (Acari, Gamasida, Phytoseiidae). Exp Appl Acarol 25: 525–591. https://doi.org/10.1023/A:1014741808835. Faraji F, Bakker F (2008) A modified method for clearing, staining and mounting plant-inhabiting mites. Eur J Entomol 105 (4): 793–795. https://doi.org/10.14411/eje.2008.105 Khaustov VA, Döker I, Joharchi O, Khaustov AA (2022a) Morphological ontogeny and complementary description of Neoseiulus subsolidus (Beglyarov) (Acari: Mesostigmata: Phytoseiidae). Zootaxa 5187 (1): 249–269. https://doi.org/10.11646/zootaxa.5187.1.14 Khaustov VA, Döker I, Joharchi O, Kazakov DV, Khaustov AA, Moradi M, Fang XD, Klimov P (2022b) A new, broadly distributed species of predacious mites, Neoseiulus neoagrestis sp. nov., (Acari: Phytoseiidae) discovered through GenBank data mining and extensive morphological analyses. Syst Appl Acarol 27 (10): 2038–2061. https://doi.org/10.11158/saa.27.10.14 Seeman OD (2012) Larva and deutonymph of Promegistus armstrongi Womersley (Acari: Mesostigmata: Trigynaspida: Promegistidae). Memoirs of the Queensland Museum Nature 56 (1): 255–269. Teodorowicz E, Gwiazdowicz DJ, Kamczyc J (2012) Description of larva and protonymph of Vulgarogamasus kraepelini (Acari: Parasitidae). Biologia 67/3: 540–545. https://doi.org/10.2478/s11756-012-0033-x Trach VA, Tolstikov AV (2016) Description of larva of Sejus hinangensis from the Far East of Russia. Acarina 24 (2): 175–179. https://doi.org/10.21684/0132-8077-2016-24-2-175-179 Walter DE, Proctor HC (2013) Mites: ecology, evolution and behaviour—life at a microscale. 2nd Edition. Springer, Netherlands, 494 pp. https://doi.org/10.1007/978-94-007-7164-2 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4506139","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":312147715,"identity":"f4e2cf06-d088-4193-bb11-d58011c01344","order_by":0,"name":"Fang-Xu Ren","email":"","orcid":"","institution":"Shanxi Agriculture University","correspondingAuthor":false,"prefix":"","firstName":"Fang-Xu","middleName":"","lastName":"Ren","suffix":""},{"id":312147717,"identity":"a2b4e266-2770-44aa-a311-6f58bb8189a1","order_by":1,"name":"Xin-Ju Wei","email":"","orcid":"","institution":"Shanxi Agriculture 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10:37:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":97906,"visible":true,"origin":"","legend":"\u003cp\u003ePalp and basis capitulum of larvae. \u003cstrong\u003ea\u003c/strong\u003e \u003cem\u003eAmblydromalus limonicus\u003c/em\u003e. \u003cstrong\u003eb\u003c/strong\u003e \u003cem\u003eAmblyseius herbicolus\u003c/em\u003e. \u003cstrong\u003ec\u003c/strong\u003e \u003cem\u003eA. orientalis\u003c/em\u003e. \u003cstrong\u003ed\u003c/strong\u003e \u003cem\u003eA. taiguensis\u003c/em\u003e. \u003cstrong\u003ee\u003c/strong\u003e \u003cem\u003eEuseius utilis\u003c/em\u003e. \u003cstrong\u003ef\u003c/strong\u003e \u003cem\u003eNeoseiulus benjamini\u003c/em\u003e. \u003cstrong\u003eg\u003c/strong\u003e \u003cem\u003eN. californicus\u003c/em\u003e. \u003cstrong\u003eh\u003c/strong\u003e \u003cem\u003eN. setarius\u003c/em\u003e.\u003cem\u003e \u003c/em\u003e\u003cstrong\u003ei\u003c/strong\u003e \u003cem\u003eN. womersleyi\u003c/em\u003e. \u003cstrong\u003ej\u003c/strong\u003e \u003cem\u003eN. zwoelferi\u003c/em\u003e. \u003cstrong\u003ek\u003c/strong\u003e \u003cem\u003ePhytoseiulus persimilis\u003c/em\u003e. \u003cstrong\u003el\u003c/strong\u003e\u003cem\u003e Phytoseius hongkongensis\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4506139/v1/43240c14def38025f403e072.png"},{"id":58281746,"identity":"af2ac60a-b14a-4086-80ac-7c69f9105746","added_by":"auto","created_at":"2024-06-13 11:01:42","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":618363,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eNeoseiulus zwoelferi \u003c/em\u003e(larva). \u003cstrong\u003ea\u003c/strong\u003e coxa, trochanter and femur of legs I–III. \u003cstrong\u003eb\u003c/strong\u003e coxa and trochanter of leg I. (Denticles rows are indicated by arrows).\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4506139/v1/79243834882e15829f1ecb6d.png"},{"id":58280420,"identity":"bbbc22ff-a2b9-46ac-abfc-65f7ce3ddd43","added_by":"auto","created_at":"2024-06-13 10:45:42","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":213337,"visible":true,"origin":"","legend":"\u003cp\u003eLeg Ⅰ of larvae (excluding genu, tibia and tarsus). \u003cstrong\u003ea\u003c/strong\u003e \u003cem\u003eAmblydromalus limonicus\u003c/em\u003e. \u003cstrong\u003eb\u003c/strong\u003e \u003cem\u003eAmblyseius herbicolus\u003c/em\u003e. \u003cstrong\u003ec\u003c/strong\u003e \u003cem\u003eA. orientalis\u003c/em\u003e. \u003cstrong\u003ed\u003c/strong\u003e \u003cem\u003eA. taiguensis\u003c/em\u003e. \u003cstrong\u003ee\u003c/strong\u003e \u003cem\u003eEuseius utilis\u003c/em\u003e. \u003cstrong\u003ef\u003c/strong\u003e \u003cem\u003eNeoseiulus benjamini\u003c/em\u003e. \u003cstrong\u003eg\u003c/strong\u003e \u003cem\u003eN. californicus\u003c/em\u003e. \u003cstrong\u003eh\u003c/strong\u003e \u003cem\u003eN. setarius\u003c/em\u003e.\u003cem\u003e \u003c/em\u003e\u003cstrong\u003ei\u003c/strong\u003e \u003cem\u003eN. womersleyi\u003c/em\u003e. \u003cstrong\u003ej\u003c/strong\u003e \u003cem\u003eN. zwoelferi\u003c/em\u003e. \u003cstrong\u003ek\u003c/strong\u003e \u003cem\u003ePhytoseiulus persimilis\u003c/em\u003e. \u003cstrong\u003el\u003c/strong\u003e\u003cem\u003e Phytoseius hongkongensis\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4506139/v1/dbb9a0c09dea5fdbfb523e4d.png"},{"id":58279936,"identity":"14fbcfad-6209-4448-8251-7e2ee80de8e3","added_by":"auto","created_at":"2024-06-13 10:37:42","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":196965,"visible":true,"origin":"","legend":"\u003cp\u003eLeg ⅠI of larvae (excluding genu, tibia and tarsus). \u003cstrong\u003ea\u003c/strong\u003e \u003cem\u003eAmblydromalus limonicus\u003c/em\u003e. \u003cstrong\u003eb\u003c/strong\u003e \u003cem\u003eAmblyseius herbicolus\u003c/em\u003e. \u003cstrong\u003ec\u003c/strong\u003e \u003cem\u003eA. orientalis\u003c/em\u003e. \u003cstrong\u003ed\u003c/strong\u003e \u003cem\u003eA. taiguensis\u003c/em\u003e. \u003cstrong\u003ee\u003c/strong\u003e \u003cem\u003eEuseius utilis\u003c/em\u003e. \u003cstrong\u003ef\u003c/strong\u003e \u003cem\u003eNeoseiulus benjamini\u003c/em\u003e. \u003cstrong\u003eg\u003c/strong\u003e \u003cem\u003eN. californicus\u003c/em\u003e. \u003cstrong\u003eh\u003c/strong\u003e \u003cem\u003eN. setarius\u003c/em\u003e.\u003cstrong\u003e i\u003c/strong\u003e \u003cem\u003eN. womersleyi\u003c/em\u003e. \u003cstrong\u003ej\u003c/strong\u003e \u003cem\u003eN. zwoelferi\u003c/em\u003e. \u003cstrong\u003ek\u003c/strong\u003e \u003cem\u003ePhytoseiulus persimilis\u003c/em\u003e. \u003cstrong\u003el\u003c/strong\u003e\u003cem\u003ePhytoseius hongkongensis\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-4506139/v1/505d854ccf5edb6c285ef99d.png"},{"id":58280424,"identity":"13f00f8f-91ae-4180-b753-90b0a9f41f1b","added_by":"auto","created_at":"2024-06-13 10:45:42","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":36820,"visible":true,"origin":"","legend":"\u003cp\u003eLeg IIⅠ of larvae (excluding genu, tibia and tarsus). \u003cstrong\u003ea\u003c/strong\u003e \u003cem\u003eNeoseiulus womersleyi\u003c/em\u003e. \u003cstrong\u003eb\u003c/strong\u003e \u003cem\u003eN. zwoelferi\u003c/em\u003e\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-4506139/v1/7f79ad347a120e2d68e8643b.png"},{"id":58279937,"identity":"1b886043-1daf-46bd-ac65-f8a1b4c3f9e7","added_by":"auto","created_at":"2024-06-13 10:37:42","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":980021,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eAmblyseius herbicolus\u003c/em\u003e, larva in almost mature eggs. \u003cstrong\u003ea\u003c/strong\u003e \u0026amp; \u003cstrong\u003ec\u003c/strong\u003e dorsal views. \u003cstrong\u003eb \u003c/strong\u003e\u0026amp; \u003cstrong\u003ed\u003c/strong\u003e ventral views\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-4506139/v1/8532de396d3a5ad46921d56e.png"},{"id":58496333,"identity":"68089f94-628b-4488-a6be-48b6c20b9515","added_by":"auto","created_at":"2024-06-17 12:15:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6094257,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4506139/v1/403b3d3f-6264-4927-8ea2-7e1425c4edc8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Denticle rows on larval appendages in twelve species of Phytoseiidae (Parasitiformes: Mesostigmata)","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePhytoseiidae (Acari: Mesostigmata) comprises about 2557 valid species primarily inhabiting in vegetation ecosystems worldwide (Demite et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Renowned for their predatory behavior and adaptable morphological characteristics, these mites exhibit distinctive traits such as their diminutive size and fewer idiosomal and leg setae, setting them apart from other mesostigmatid mites typically inhabiting soil environments (Walter and Proctor \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWhile denticle rows within the deutosternum are commonly utilized in the taxonomy of Mesostigmata, those located on other body parts, particularly appendages like legs and palpi, have often been ignored or undocumented. During our observation of phytoseiid mite larvae, we found rows of denticles on the dorsal surfaces of the palp, basis capitulum, and some leg segments. These denticles exhibit remarkable morphological diversity among various species. Upon reviewing existing literature, we noted that denticle presence in larval stages had previously been mentioned or illustrated for a limited number of species, such as \u003cem\u003ePromegistus armstrongi\u003c/em\u003e Womersley (Promegistidae) (Seeman \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), \u003cem\u003eVulgarogamasus kraepelini\u003c/em\u003e (Berlese) (Parasitidae) (Teodorowicz et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), and \u003cem\u003eSejus hinangensis\u003c/em\u003e Hirschmann and Kaczmarek (Sejidae) (Trach and Tolstikov \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), as well as phytoseiid mites, \u003cem\u003eNeoseiulus subsolidus\u003c/em\u003e (Beglyarov) and \u003cem\u003eNeoseiulus neoagrestis\u003c/em\u003e Khaustov \u0026amp; D\u0026ouml;ker (Phytoseiidae) (Khaustov et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003eb\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWhile previous studies have provided valuable information on the denticles on larval appendages of a few \u003cem\u003eNeoseiulus\u003c/em\u003e species, a comprehensive examination of denticle diversity and variation remains absent. This manuscript aims to fill this gap by undertaking a comprehensive examination of the morphology and functional importance of denticles on larval phytoseiid appendages. Through morphological analyses, we seek to shed light on the adaptive significance and functional roles of these structures in phytoseiid mites.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eTwelve species from six genera were examined. The fresh specimens selected for observation were sourced from established laboratory populations, i.e., \u003cem\u003eAmblydromalus limonicus\u003c/em\u003e (Garman and McGregor) and \u003cem\u003eAmblyseius herbicolus\u003c/em\u003e Chant from Auckland, New Zealand; \u003cem\u003eAmblyseius taiguensis\u003c/em\u003e Liu, Ma and Fan, \u003cem\u003eEuseius utilis\u003c/em\u003e Liang and Ke, \u003cem\u003eNeoseiulus benjamini\u003c/em\u003e Schicha, \u003cem\u003eNeoseiulus setarius\u003c/em\u003e Ma, Meng and Fan, \u003cem\u003eNeoseiulus womersleyi\u003c/em\u003e Schicha, \u003cem\u003eNeoseiulus zwoelferi\u003c/em\u003e Dosse from Shanxi province, China; \u003cem\u003ePhytoseius hongkongensis\u003c/em\u003e Swirski from Shaanxi province, China; \u003cem\u003eAmblyseius orientalis\u003c/em\u003e Ehara, \u003cem\u003eNeoseiulus californicus\u003c/em\u003e McGregor and \u003cem\u003ePhytoseiulus persimilis\u003c/em\u003e Athias-Henriot from Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China. The voucher specimens used were deposited at the Entomological Microscopy Laboratory, College of Plant Protection, Shanxi Agricultural University, Taigu, Shanxi, China and New Zealand Arthropod Collection (NZAC), Auckland, New Zealand.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eOptical microscopy\u003c/h2\u003e \u003cp\u003eSpecimens were mounted in modified Hoyer\u0026rsquo;s medium (Faraji and Bakker \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) on microscope slides. A compound microscope (Nikon Eclipse 80i) with differential interference contrast (DIC) was used to measure and photograph specimens. Illustrations were made by means of a drawing tube (Nikon Y-IDT) attached to the microscope and edited with Photoshop 2024.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eScanning electron microscopy\u003c/h2\u003e \u003cp\u003eThe larvae of \u003cem\u003eN. zwoelferi\u003c/em\u003e were immersed in a solution containing 2.5% w/v glutaraldehyde in phosphate-buffered saline (pH 7.4) for 8 hours to achieve fixation. Following fixation, the specimens were rinsed with phosphate-buffered saline and then dehydrated in a series of ethanol solutions (30%, 50%, 70%, 80%, 90%, 95%, and two rounds of 100% v/v), with each step lasting 10 minutes. Subsequently, the specimens underwent critical point drying using a JFD-320 freeze-drying device. Following this, the prepared specimens (n\u0026thinsp;=\u0026thinsp;10) were affixed to stubs using double-sided carbon tape and coated with gold using an FC-1600 sputter coater. Observations and photography of the coated samples were performed using a JSM-6490LV scanning electron microscope.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eThe palpfemur and basis capitulum of all species were observed to have a row of denticles. All species (except \u003cem\u003eP. hongkongensis\u003c/em\u003e) had denticle rows or loops on trochanters I and II. Femur I exhibited a short denticle row exclusively in \u003cem\u003eN. womersleyi\u003c/em\u003e, while femur II had two to three rows or loops of denticles in all species. Denticle rows were found on femur III only in \u003cem\u003eN. womersleyi\u003c/em\u003e and \u003cem\u003eN. zwoelferi\u003c/em\u003e. All these denticles were positioned dorsally.\u003c/p\u003e \u003cp\u003e \u003cem\u003ePalp\u003c/em\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eEach femur has a row of denticles at the level of and medial to seta \u003cem\u003ed2\u003c/em\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ea \u0026amp; \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e). These denticles are relatively stable in position, with their extension direction being mostly horizontal. The number of the denticles varies among species. \u003cem\u003eE. utilis\u003c/em\u003e and \u003cem\u003eP. hongkongensis\u003c/em\u003e have 5 (5\u0026ndash;7) and 5 (5\u0026ndash;6) denticles, respectively, while \u003cem\u003eN. benjamini\u003c/em\u003e has 15 (14\u0026ndash;17), \u003cem\u003eN. setarius\u003c/em\u003e has 13 (10\u0026ndash;17), and \u003cem\u003eN. zwoelferi\u003c/em\u003e has 14 (10\u0026ndash;17) denticles. An exceptionally large tooth was observed posterior to \u003cem\u003ed2\u003c/em\u003e in \u003cem\u003eA. taiguensis\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The number of denticles influences the arrangement of the small denticles, with species possessing more denticles having a denser and more orderly arrangement, while species with fewer denticles show a relatively disordered arrangement, such as \u003cem\u003eP. persimilis\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eRegarding the overall shape of the denticle rows, there are differences among species. In some species, the small denticles are observed to grow on a plate-like structure. Among these, \u003cem\u003eN. zwoelferi\u003c/em\u003e is the most prominent, with the entire plate-like structure clearly observable. Some species show a clear tendency for this, such as \u003cem\u003eN. setarius\u003c/em\u003e, \u003cem\u003eN. womersleyi\u003c/em\u003e and \u003cem\u003eP. persimilis\u003c/em\u003e. However, for some species, the presence of the plate-like structure is difficult to observe, such as \u003cem\u003eN. californicus\u003c/em\u003e and \u003cem\u003eN. benjamini\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eDenticle rows were absent on the trochanter, tibia and tarsus in all species.\u003c/p\u003e \u003cp\u003e \u003cem\u003eBasis capitulum\u003c/em\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eOn the dorsal surface of the basis capitulum (dorsal extensions of the palpcoxae), there is one or two rows of small denticles (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ea \u0026amp; \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e) at each side, with significant variation among different species. The species with the fewest denticles include \u003cem\u003eP. hongkongensis\u003c/em\u003e with 8 (5\u0026ndash;11) denticles and \u003cem\u003eP. persimilis\u003c/em\u003e with 9 (6\u0026ndash;11) denticles, while \u003cem\u003eN. zwoelferi\u003c/em\u003e has the most denticles with 23 (18\u0026ndash;28). \u003cem\u003eN. benjamini\u003c/em\u003e also has 23 (21\u0026ndash;26) denticles. Some species show the presence of small denticles on the lateral side of the basis capitulum (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ea\u0026ndash;e, h\u0026ndash;j). However, due to slide preparation reasons, the count of lateral denticles is not as clear, and some lateral denticles might not have been observed. The observed small denticles are located on the outer side of the dorsal denticles and are slightly inclined towards the palp direction. For most species, the number of these denticles is around 7. Among the available six specimens of \u003cem\u003eA. orientalis\u003c/em\u003e, only one specimen exhibited lateral denticles, with 3 denticles.\u003c/p\u003e \u003cp\u003e \u003cem\u003eLeg I\u003c/em\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb \u0026amp; \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e)\u003c/p\u003e\u003cp\u003eThe presence of denticles on coxa I was only observed in \u003cem\u003eN. zwoelferi\u003c/em\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ej) which featured two rows of denticles situated on the dorsal and dorsoposterior areas. These two rows of denticles were nearly horizontal, with a distinct gap between them. In all species, except for \u003cem\u003eP. hongkongensis\u003c/em\u003e, trochanter I displayed a dorsal row of denticles. These denticles exhibited various shapes, primarily falling into three categories: elliptical, hook-shaped and arc-shaped. The number and shape of denticles showed a close correlation, with elliptical denticles being the most abundant, typically numbering between 30 to 40, while arc-shaped denticles ranged from 10 to 20. Species with an elliptical row of denticles included \u003cem\u003eA. limonicus\u003c/em\u003e, \u003cem\u003eA. herbicolus\u003c/em\u003e, \u003cem\u003eA. orientalis\u003c/em\u003e (partially), \u003cem\u003eN. setarius\u003c/em\u003e, and \u003cem\u003eN. zwoelferi\u003c/em\u003e, while hook-shaped ones were found in \u003cem\u003eA. orientalis\u003c/em\u003e (partially), and curved denticles were observed in \u003cem\u003eE. utilis\u003c/em\u003e, \u003cem\u003eN. benjamini\u003c/em\u003e, \u003cem\u003eN. californicus\u003c/em\u003e, \u003cem\u003eN. womersleyi\u003c/em\u003e and \u003cem\u003eP. persimilis\u003c/em\u003e. \u003cem\u003eA. orientalis\u003c/em\u003e exhibited both elliptical and hook-shaped arrangements among the available specimens. Femur I denticles exist exclusively in \u003cem\u003eN. womersleyi\u003c/em\u003e, situated between \u003cem\u003ead1\u003c/em\u003e and \u003cem\u003epd1\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ei), noticeably larger than those found on trochanter I. Denticle rows were absent on the genu, tibia, and tarsus in all species.\u003c/p\u003e \u003cp\u003e \u003cem\u003eLeg II\u003c/em\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea \u0026amp; \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eAs in leg I, denticle rows were also absent on the genu, tibia and tarsus of leg II in all species. The presence of denticles on coxa II was exclusive to \u003cem\u003eN. womersleyi\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eI) and \u003cem\u003eN. zwoelferi\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ej), which positioned on the dorsoposterior area of coxa II. Trochanter II has a single row of small denticles, dorsomedial to \u003cem\u003epl\u003c/em\u003e, present in all species except for \u003cem\u003eP. hongkongensis\u003c/em\u003e. Among them, \u003cem\u003eN. setarius\u003c/em\u003e has the most denticles with 19 (16\u0026ndash;23), \u003cem\u003eN. zwoelferi\u003c/em\u003e has 18 (15\u0026ndash;21), and \u003cem\u003eE. utilis\u003c/em\u003e has the fewest with 9 (7\u0026ndash;12). Femur II can have up to 3 rows of small denticles, namely \u003cem\u003eD1\u003c/em\u003e, \u003cem\u003eD2\u003c/em\u003e, and \u003cem\u003eD3\u003c/em\u003e; \u003cem\u003eD1\u003c/em\u003e positioned between or slightly posterior to level of \u003cem\u003ead1\u003c/em\u003e and \u003cem\u003epd1\u003c/em\u003e; \u003cem\u003eD2\u003c/em\u003e if present, positioned slightly anterior to level of \u003cem\u003ead2\u003c/em\u003e and \u003cem\u003epd2\u003c/em\u003e; \u003cem\u003eD3\u003c/em\u003e if present, positioned posterior to \u003cem\u003epd2\u003c/em\u003e. This feature shows some differences across different genera. For example, \u003cem\u003eAmblyseius\u003c/em\u003e species has 3 rows of denticles (\u003cem\u003eD1\u003c/em\u003e, \u003cem\u003eD2\u003c/em\u003e and \u003cem\u003eD3\u003c/em\u003e), while \u003cem\u003eA. limonicus\u003c/em\u003e, \u003cem\u003eE. utilis\u003c/em\u003e, \u003cem\u003eNeoseiulus\u003c/em\u003e species, and \u003cem\u003eP. persimilis\u003c/em\u003e have only \u003cem\u003eD1\u003c/em\u003e and \u003cem\u003eD3\u003c/em\u003e, and \u003cem\u003eP. hongkongensis\u003c/em\u003e has \u003cem\u003eD1\u003c/em\u003e and \u003cem\u003eD2\u003c/em\u003e. Within species, there are also differences in the number of denticles. For instance, \u003cem\u003eN. setarius\u003c/em\u003e has 13 (11\u0026ndash;16) denticles in \u003cem\u003eD1\u003c/em\u003e and 8 (7\u0026ndash;10) in \u003cem\u003eD3\u003c/em\u003e, while \u003cem\u003eN. zwoelferi\u003c/em\u003e has 7 (5\u0026ndash;9) in \u003cem\u003eD1\u003c/em\u003e and 12 (10\u0026ndash;15) in \u003cem\u003eD3\u003c/em\u003e.\u003c/p\u003e \u003cp\u003e \u003cem\u003eLeg III\u003c/em\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea \u0026amp; \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA row of denticles, \u003cem\u003eD3\u003c/em\u003e, are exclusively present on the femur of \u003cem\u003eN. womersleyi\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea) and \u003cem\u003eN. zwoelferi\u003c/em\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea \u0026amp; \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb), with no observation of denticles in other species (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed \u0026amp; \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003ed).\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eFunction of denticles on larval appendages\u003c/h2\u003e \u003cp\u003eThe denticles on the palps and legs in larval stage disappeared in nymphs and adults, leading to the conclusion that this feature is specific to larvae. As described and illustrated above, the locations where these small denticles appear are relatively consistent across species, indicating a stable feature with significance for larval mites.\u003c/p\u003e \u003cp\u003eRegarding the function of the denticle rows, assumptions can be made. The denticles, with their small size ranging from 0.2 to 1.8 \u0026micro;m in height and 0.3 to 1.7 \u0026micro;m in width, positioned on the dorsal side of the proximal segments of limbs, are unlikely to serve as a defensive mechanism against predators. Similarly, they are also unlikely to be related to feeding or locomotion for the same reasons.\u003c/p\u003e \u003cp\u003eSince no auxiliary eggshell-breaking features have been identified in these species, the denticle rows might have a cutting function during the activities of larval mites, potentially aiding in tearing open epidermis (approximately 1.0\u0026ndash;2.0 \u0026micro;m) and eggshell (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e) which is approximately 1.7\u0026ndash;2.1 \u0026micro;m (Di Palma \u0026amp; Alberti \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Given their exclusive presence in the pre-hatching and larval stage, it is plausible that if this feature serves a practical purpose, it would likely come into play during this period of life stage.\u003c/p\u003e \u003cp\u003e \u003cb\u003eHatching of\u003c/b\u003e \u003cb\u003ePhytoseiulus persimilis\u003c/b\u003e \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e\u003c/p\u003e \u003cp\u003eTo support the hypothesis, observations were conducted on hatching of \u003cem\u003eP. persimilis\u003c/em\u003e. Initially, the newly laid eggs were translucent, plump, and smooth. Over time, their color gradually changed to light yellow, and the contents became cloudy. As hatching neared, lively movements within the egg, resembling small bubbles, were observed, gently swaying back and forth. The idiosoma of the embryonic mite was curled inside the eggshell, with chelicerae, palpi and three pairs of legs tucked close to its ventral side. When the eggshell cracked, fluid was released, causing the shell to lose its shine and shrivel rapidly. Concurrently, the mite's body expanded. First, the palpi extended outward and began to explore. Then, the palpi and the first pair of legs extended outward. When the first pair of legs extended, the second and third legs were not yet fully extended. The rest of the body followed and emerged afterward. With the first and second pairs of legs extending forward and the third pair extending backward, the eggshell split further.\u003c/p\u003e \u003cp\u003eAlthough these observations were essential, they unfortunately did not provide robust evidence to demonstrate that denticle rows play a role in the hatching process.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThese denticle rows are likely to be ancient characteristics (plesiomorphy) expressed only during the larval stage. Similar features have been observed in the larvae of all three suborders of Mesostigmata, i.e., Sejida: \u003cem\u003eS. hinangensis\u003c/em\u003e Hirschmann (Sejidae) (Trach and Tolstikov \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), Trigynaspida: \u003cem\u003eP. armstrongi\u003c/em\u003e Womersley (Promegistidae) (Seeman \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), and Monogynaspida: \u003cem\u003eN. neoagrestis\u003c/em\u003e Khaustov \u0026amp; D\u0026ouml;ker and \u003cem\u003eN. subsolidus\u003c/em\u003e (Beglyarov) (Phytoseiidae) (Khaustov et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003eb\u003c/span\u003e). Trach and Tolstikov (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) described two rows of denticles on dorsal palpfemur, and two enlarged denticles at anterodistal corner of palpgenu of \u003cem\u003eS. hinangensis\u003c/em\u003e and Kaczmarek (Sejidae). In the description of larva and deutonymph of \u003cem\u003eP. armstrongi\u003c/em\u003e, Seeman (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) noted that coxae of all legs (I\u0026ndash;III), trochanters and femora II\u0026ndash;III with rows of fine denticles in larva and these were absent in the deutonymphal stage. Khaustov et al. (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022a\u003c/span\u003e) illustrated the denticle row beside \u003cem\u003ed2\u003c/em\u003e on palpfemur, and an arc-shaped denticle row posterolateral to \u003cem\u003epd2\u003c/em\u003e on femora II and a denticle row lateral to pl on trochanter II in larva of \u003cem\u003eN. subsolidus\u003c/em\u003e (Beglyarov). Khaustov et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e) illustrated similar denticle row beside \u003cem\u003ed2\u003c/em\u003e on palpfemur and also a denticle row between \u003cem\u003ead1\u003c/em\u003e and \u003cem\u003epd1\u003c/em\u003e on femora I and II each in larval \u003cem\u003eN. neoagrestis\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eSince the true function of these denticle rows remains undetermined, further investigation using other techniques may fill this gap and provide insight into their adaptive significance in the development and survival of larvae. This research could contribute to a deeper understanding of the functional morphology of appendages in Mesostigmata.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe would like to express our gratitude to Mr. Yu Liu and Ms. Juan Wang from the College of Plant Protection at Shanxi Agriculture University in China, as well as to Dr. Xuenong Xu, Dr. Endong Wang and Mr. Chuantao Huang from the Institute of Plant Protection, Chinese Academy of Agricultural Sciences, China, for providing some specimens and invaluable assistance for this research. QF extends deep appreciation to his colleagues at the Plant Health \u0026amp; Environment Laboratory, Ministry for Primary Industries, New Zealand, for their continuous encouragement and support throughout this study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was partially funded by the State Key Laboratory for Biology of Plant Diseases and Insect Pests (SKLOF202215), and Min Ma was supported by China Scholarship Council.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the conception and design of the study. Materials were prepared by Fang-Xu Ren and Xin-Ju Wei. Data collection and analysis were performed by Fang-Xu Ren, Min Ma and Qing-Hai Fan. The first draft of the manuscript was written by Fang-Xu Ren and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResearch involved in Human or animal rights\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis article does not contain any studies with human participants or vertebrate animals performed by any of the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known conflicts of interest. No competing claims are known.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePotential reviewers\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDr. Edward A., Ueckermann, Unit for Environmental Sciences and Management, North-West University, South Africa. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eDr. Gilberto José de Moraes, Entomologia e Acarologia, Universidade de São Paulo, Brazil. E-mail: [email protected]\u003c/p\u003e\n\u003cp\u003eDr. Ismail Döker, Agricultural Faculty, Cukurova University, Türkiye. E-mail: [email protected]\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eDemite PR, Moraes GJ de, McMurtry JA, Denmark HA, Castilho RC (2024) Phytoseiidae database. Available from: http://www.lea.esalq.usp.br/phytoseiidae. Accessed 25 May 2024\u003c/li\u003e\n\u003cli\u003eDi Palma A, Alberti G (2001) Fine structure of the female genital system in phytoseiid mites with remarks on egg nutrimentary development, sperm-access system, sperm transfer, and capacitation (Acari, Gamasida, Phytoseiidae). Exp Appl Acarol 25: 525\u0026ndash;591. https://doi.org/10.1023/A:1014741808835.\u003c/li\u003e\n\u003cli\u003eFaraji F, Bakker F (2008) A modified method for clearing, staining and mounting plant-inhabiting mites. \u003cem\u003eEur J Entomol\u003c/em\u003e 105 (4): 793\u0026ndash;795. https://doi.org/10.14411/eje.2008.105\u003c/li\u003e\n\u003cli\u003eKhaustov VA, D\u0026ouml;ker I, Joharchi O, Khaustov AA (2022a) Morphological ontogeny and complementary description of \u003cem\u003eNeoseiulus subsolidus\u003c/em\u003e (Beglyarov) (Acari: Mesostigmata: Phytoseiidae). \u003cem\u003eZootaxa\u003c/em\u003e 5187 (1): 249\u0026ndash;269. https://doi.org/10.11646/zootaxa.5187.1.14\u003c/li\u003e\n\u003cli\u003eKhaustov VA, D\u0026ouml;ker I, Joharchi O, Kazakov DV, Khaustov AA, Moradi M, Fang XD, Klimov P (2022b) A new, broadly distributed species of predacious mites, \u003cem\u003eNeoseiulus neoagrestis \u003c/em\u003esp. nov., (Acari: Phytoseiidae) discovered through GenBank data mining and extensive morphological analyses. Syst Appl Acarol 27 (10): 2038\u0026ndash;2061. https://doi.org/10.11158/saa.27.10.14\u003c/li\u003e\n\u003cli\u003eSeeman OD (2012) Larva and deutonymph of \u003cem\u003ePromegistus armstrongi\u003c/em\u003e Womersley (Acari: Mesostigmata: Trigynaspida: Promegistidae). \u003cem\u003eMemoirs of the Queensland Museum Nature\u003c/em\u003e 56 (1): 255\u0026ndash;269.\u003c/li\u003e\n\u003cli\u003eTeodorowicz E, Gwiazdowicz DJ, Kamczyc J (2012) Description of larva and protonymph of \u003cem\u003eVulgarogamasus kraepelini \u003c/em\u003e(Acari: Parasitidae). Biologia 67/3: 540\u0026ndash;545. https://doi.org/10.2478/s11756-012-0033-x\u003c/li\u003e\n\u003cli\u003eTrach VA, Tolstikov AV (2016) Description of larva of \u003cem\u003eSejus hinangensis\u003c/em\u003e from the Far East of Russia. Acarina 24 (2): 175\u0026ndash;179. https://doi.org/10.21684/0132-8077-2016-24-2-175-179\u003c/li\u003e\n\u003cli\u003eWalter DE, Proctor HC (2013) Mites: ecology, evolution and behaviour\u0026mdash;life at a microscale. 2nd Edition. Springer, Netherlands, 494 pp. https://doi.org/10.1007/978-94-007-7164-2\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Acari, mite, morphology, function, palpi, legs","lastPublishedDoi":"10.21203/rs.3.rs-4506139/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4506139/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe presence of denticles on appendages such as the palpi and legs is rarely documented in phytoseiid mite larvae. To address this gap, we studied twelve species across six genera of Phytoseiidae: \u003cem\u003eAmblydromalus limonicus\u003c/em\u003e, \u003cem\u003eAmblyseius herbicolus\u003c/em\u003e, \u003cem\u003eAmblyseius orientalis\u003c/em\u003e, \u003cem\u003eAmblyseius taiguensis\u003c/em\u003e, \u003cem\u003eEuseius utilis\u003c/em\u003e, \u003cem\u003eNeoseiulus benjamini\u003c/em\u003e, \u003cem\u003eNeoseiulus californicus\u003c/em\u003e, \u003cem\u003eNeoseiulus setarius\u003c/em\u003e, \u003cem\u003eNeoseiulus womersleyi\u003c/em\u003e, \u003cem\u003eNeoseiulus zwoelferi\u003c/em\u003e, \u003cem\u003ePhytoseiulus persimilis\u003c/em\u003e and \u003cem\u003ePhytoseius hongkongensis\u003c/em\u003e. We identified and described the denticles on the palp, basis capitulum, and specific leg segments of these species, discussing their functional significance.\u003c/p\u003e","manuscriptTitle":"Denticle rows on larval appendages in twelve species of Phytoseiidae (Parasitiformes: Mesostigmata)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-13 10:37:37","doi":"10.21203/rs.3.rs-4506139/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"34634533-e1b5-402f-ad8c-99cad8afae42","owner":[],"postedDate":"June 13th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-17T12:07:24+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-13 10:37:37","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4506139","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4506139","identity":"rs-4506139","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}