Ultrastructure on head and trunk of green lacewing larvae associated with debris-carrying behavior

Ultrastructure on head and trunk of green lacewing larvae associated with debris-carrying behavior | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 29 April 2025 V1 Latest version Share on Ultrastructure on head and trunk of green lacewing larvae associated with debris-carrying behavior Authors : Jun Lu 0009-0009-4122-6093 , Hongyu Li , and Xingyue Liu [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.174590650.03598161/v1 338 views 149 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Green lacewings (Neuroptera: Chrysopidae) are a group of well-known predatory insects, with important value as natural enemies in biocontrol of agricultural pests. Debris-carrying behavior is a spectacular biological trait in many green lacewing larvae, being an essential mechanism to prevent cannibalism or evade predators. However, the ultrastructure that might be associated with the debris-carrying behavior has yet been observed and compared with those larvae lacking this behavior. Here we observe and describe the fine structure on the head and trunk of green lacewing larvae with or without debris-carrying behavior using SEM (Scanning Electron Microscope). A total of five types of sensilla were found on antennae and mouthparts, including SCh3 (Sensilla chaetica 3), ST1 (Sensilla trichoidea 1), and SB3 (Sensilla basiconica 3) on the mouthparts, and SCh2 (Sensilla chaetica 2) and ST4 (Sensilla trichoidea 4 ) on the antennae. However, no significant difference of these sensilla could be found between the two types of larvae. The SMS (Submedian seta) on the dorsum of trunk is curved at tip in the debris-carrying larvae, while it is straight in the naked larvae. Besides, all debris-carrying larvae possess scale-like setae with spinous tip. However, the two species with naked larvae respectively possess scale-like setae and slender hair-like setae on the dorsum of trunk. The SMS with hook-like tip is the single structure only present in the debris-carrying larvae. The potential function of sensilla on head and setae on trunk in relation to the debris-carrying behavior is discussed. Ultrastructure on head and trunk of green lacewing larvae associated with debris-carrying behavior Jun Lu, 1 Hongyu Li, 1 Xingyue Liu 1 1 Department of Entomology, College of Plant Protection, China Agricultural University, Beijing, China E-mail address: Jun Lu: [email protected] Hongyu Li: [email protected] Correspondence: Xingyue Liu, Department of Entomology, College of Plant Protection, China Agricultural University, Beijing 100193, China. Email: [email protected] Keywords: Scanning electron microscopy | green lacewing larvae | sensilla | debris-carrying behavior | seta ABSTRACT Green lacewings (Neuroptera: Chrysopidae) are a group of well-known predatory insects, with important value as natural enemies in biocontrol of agricultural pests. Debris-carrying behavior is a spectacular biological trait in many green lacewing larvae, being an essential mechanism to prevent cannibalism or evade predators. However, the ultrastructure that might be associated with the debris-carrying behavior has yet been observed and compared with those larvae lacking this behavior. Here we observe and describe the fine structure on the head and trunk of green lacewing larvae with or without debris-carrying behavior using SEM (Scanning Electron Microscope). A total of five types of sensilla were found on antennae and mouthparts, including SCh3 (Sensilla chaetica 3), ST1 (Sensilla trichoidea 1), and SB3 (Sensilla basiconica 3) on the mouthparts, and SCh2 (Sensilla chaetica 2) and ST4 (Sensilla trichoidea 4 ) on the antennae. However, no significant difference of these sensilla could be found between the two types of larvae. The SMS (Submedian seta) on the dorsum of trunk is curved at tip in the debris-carrying larvae, while it is straight in the naked larvae. Besides, all debris-carrying larvae possess scale-like setae with spinous tip. However, the two species with naked larvae respectively possess scale-like setae and slender hair-like setae on the dorsum of trunk. The SMS with hook-like tip is the single structure only present in the debris-carrying larvae. The potential function of sensilla on head and setae on trunk in relation to the debris-carrying behavior is discussed. \papertype Original Article 1 | Introduction Chrysopidae (green lacewings) are a cosmopolitan and species-rich family of Neuroptera, currently with 1461 species worldwide (Oswald, 2025). The vast majority of green lacewing larvae feed on agricultural pests, such as aphids and scale insects, while adults feed mainly on pollen and nectar, except a few species, such as Chrysopa pallens, with predatory feeding habits in both adults and larvae (Albuquerque et al., 2012). Being among the important natural enemy insects, green lacewings are often used for agricultural pest control because of their large food consumption and strong reproductive capacity (Loru et al., 2014; Sousa et al., 2016; Lai & Liu, 2020). Based on morphology and behavior, the green lacewing larvae are divided into two types: debris-carrying larvae and naked larvae (Tauber et al., 2014). The debris-carrying larvae consist of the species that can use exogenous organic or inorganic material to shield or camouflage body, and generally the larval body shape is globose and humped; while the naked larvae refer to those without inorganic material and exogenous organic on the dorsum of the larval body that is fusiform and flat (Tauber et al., 2014). Currently, there are 27 genera with records of debris-carrying larvae (Breitkreuz, 2018). Owing to the debris-carrying behavior, the larvae could hide from predators (Anderson et al., 2003). Carrying debris may also prevent cannibalism among conspecific larvae, and the application of the debris-carrying larvae in biocontrol, e.g., Mallada basalis (Cheng et al., 2012), may enhance the effectiveness of production of natural enemies. The debris-carrying behavior is thought to be a form of camouflage. A well-known case in insects refers to the assassin bugs Paredocla spp. and Acanthaspis spp. that build a camouflaged “backpack” of sand, dust, and the corpses of prey (e.g., ants) for protection and ambush predation (Brandt & Mahsberg, 2002). The debris-carrying behavior of green lacewing larvae is generally similar to that of the assassin bugs. The “backpack” formed by the corpses of aphids can prevent the ants to recognize and attack the green lacewing larvae as physical and chemical isolation (Hayashi et al., 2014). Unlike the assassin bugs that mainly immobilize corpses through sticky secretions of the seta on the abdomen, the green lacewing larvae primarily use the hook-like hairs on the back of body to anchor and carry the debris (Canard et al., 1984; Tauber et al., 2014; Brandt & Mahsberg, 2002). The debris-carrying behavior of green lacewings and allied groups of the superfamily Chrysopoidea can be traced back to the Early Cretaceous (Pérez-de la Fuente et al., 2016, 2018) b ased on recent findings of the debris-carrying chrysopoid larvae from amber inclusions, with a wide variety of fragments, including fern trichomes, arthropod prey, etc. Considering the extant green lacewings, more diverse fragments as the debris carried have been found, such as prey carcasses (e.g., arthropod exoskeleton, snail shell), dried leaves or trichomes, silk of spiders or mites, and particles of sand or soil (Tauber et al., 2014). The morphological structures associated with the debris-carrying behavior between the extant and fossil species distinctly differ. In the larvae of extant green lacewings, the seta on the back is not bifurcated, and the length is shorter than that of the fossil species; however, the seta is longer, bifurcated, with trumpet-shaped tip in the fossil species (Pérez-de la Fuente et al., 2016; Tauber & Garland, 2014). So far, ten types of specialized setae have been reported in the debris-carrying larvae. Two types are present in the fossil species, while the other eight types are developed in the extant species, and their function may be different depending on the debris carried (Pérez-de la Fuente et al., 2018). For comprehensive understanding on the function of the structure involved in the debris-carrying behavior, it is essential to observe and describe their ultrastructure, which, however, is still lacking in Neuroptera. The SEM (Scanning Electron Microscope) observation on the assassin bug species Acanthaspis cincticrus and Acanthaspis collaris, with similar debris-carrying behavior to green lacewing larvae, shows that long-projection trichomes, short-projection trichomes, anchor-setae, and hind tarsal fan together function for carrying debris in their nymphs. The hind tarsal fan is able to throw sand particles and press debris to fix on the body, while trichomes and anchor-setae respectively act as mechanical attachment and mucus secretion auxiliary attachment for the debris (Kou, 2017). In comparison to the ultrastructure associated with debris-carrying behavior in assassin bugs, it is of interest to figure out which structures act with similar function in the debris-carrying larvae of green lacewings. In this study, we present a SEM observation on the green lacewing larvae with and without debris-carrying behavior. The larval specimens of five species of Chrysopidae ( Chrysopidia ( Chrysotropia ) orientalis Hölzel, 1973, Mallada flavimaculus Yang & Yang, 1991, Cunctochrysa albolineata Killington, 1935, Chrysopa formosa Brauer, 1850, Chrysoperla bellatula Yang & Yang, 1922) were observed by scanning electron microscopy (SEM). Two types of sensilla on the antennae and three types of sensilla on the mouthparts were identified and described. Besides, the specialized structures on the dorsum of larval trunk associated with debris-carrying behavior were found. The SMS (Submedian seta) with curved tip is the single structure only present in the debris-carrying larvae. The present study will serve as a morphological basis for the future exploration on evolution of the debris-carrying behavior in lacewings. 2 | Materials and methods not-yet-known not-yet-known not-yet-known unknown 2.1 | Insects A total of five specimens of green lacewing larvae were selected for SEM observation. Three larvae belong to the species with debris-carrying behavior, i.e., Cpd . orientalis, M . flavimaculus, and Cun . albolineata ; the other two belong to the naked type, i.e., Chr . formosa and Cpl . bellatula. Cpd . orientalis was collected from Ailao Mountain, Yuxi, Yunnan, China; M . flavimaculus was collected from Jinyun Mountain, Chongqing, China; Cun . albolineata was collected from Zhenxiong, Zhaotong, Yunnan, China; Chr . formosa was collected from Xiaojinggou, Hohhot, Inner Mongolia, China; and Cpl . bellatula was collected from Tong’an, Xiamen, Fujian, China. The specimens are preserved in 95% absolute ethanol. The habitus of the specimens was observed under Nikon®SMZ745/745T stereoscopic microscope. Habitus photos were taken by using Nikon® D850 digital camera with Laowa® 25 mm F/2.8 2.5–5.0X Ultra Macro lens (Figure 1). 2.2 | Identification The identification of these larvae was performed based on DNA barcoding using the standard barcoding region of COI. COI was extracted from the hind leg of each specimen using the Hipure Universal DNA Kit (Magen Inc., Guangzhou, China) mitochondrial COI was amplified using primers COI1-F (5’-ATTCAACCAATCATAAAGATATTGG-3’) and COI1-R (5’-TAAACTTCTGGATGT-CCAAAAAATCA-3’). Each 25 µl volume contained 12.5 µl 2 × EasyTaq PCR SuperMix (TransGen Biotech, Beijing, China), 9.5 µl ddH2O, 1 µl of each primer, and 1 µl DNA template. The PCR products were sequenced on ABI3730XL Genetic Analyzer by Beijing Tsingke Biotec Co., Ltd., Beijing, China. Protocols for DNA extraction, PCR amplification, sequencing, and sequence alignment follow Lai et al. (2021). Meanwhile, the sequence was compared with the NCBI database (National Center for Biotechnology Information), and the data for the five species were uploaded to NCBI. The specific information of the five species is given in Table 1. Finally, we combined the sequences with those of the same genus and species from NCBI for generating a dataset to infer Neighbor-Joining tree (Supplementary Figure 1). And the Gene ID of the species forming NJ tree is given in Supplementary Table 1 not-yet-known not-yet-known not-yet-known unknown 2.3 | Scanning Electron Microscope (SEM) For SEM observation, the specimen was first removed from the alcohol and placed in a centrifuge tube with dish soap, and the centrifuge tube was placed in a KQ5200E ultrasonic cleaner for ten minutes of washing. The dehydration process involved the specimens being sequentially subjected to the following increasing ethanol concentrations: 30, 50, 70, 80, 90, 95, and 100%. Specimens remained in each concentration of ethanol for 40 minutes during each step of the dehydration process. Finally, the specimen was subjected to critical point drying using an HCP-2 critical point dryer (Hitachi Corp., Tokyo, Japan), attached to double-stick tape on aluminum stubs in the correct orientation, coated with gold in an E-1010 ion sputter (Hitachi Corp., Tokyo, Japan), the dorsum of trunk and mouthpart are observed using a HITACHI UHR FE-SEM SU8010 (Hitachi Corp., Tokyo, Japan) at 15.0 kV at the Microscopy Core Facility, Biological Technology Centre, Beijing Forestry University (Beijing, China) (Wang et al., 2014). Scanning electron microscopy of larval antennae was performed using a HITACHI UHR FE-SEM SU8000 (Hitachi Corp., Tokyo, Japan), at 3.0 kV at the Institute of Microbiology, Chinese Academy of Sciences, not-yet-known not-yet-known not-yet-known unknown 2.4 | Terminology The morphological terminology of sensilla follows Nowińska & Brożek (2017), while the terminology of the larval morphology follows Tauber & Teresa De León (2001). TABLE 1 | Sampling of five green lacewing species for DNA barcoding. not-yet-known not-yet-known not-yet-known unknown Cpd. orientalis L41 Yunnan 24.05°N, 101.58°E PV533825 M. flavimaculus L42 Chongqing 29.79°N, 106.35°E PV533989 Cun. albolineata L45 Yunnan 27.43°N, 104.87°E PV533836 Chr. formosa L38 Inner Mongolia 40.98°N, 111.07°E PV498541 Cpl. bellatula L8 Fujian 24.88°N, 118.13°E PV534788 Note: The data have been unloaded to NCBI, and publish time is Oct 15, 2025. FIGURE | 1 Habitus of green lacewing larvae in dorsal view. (A) Cpd . orientalis ; (B) M . flavimaculus ; (C) Cun. albolineata ; (D) Chr . formosa ; (E) Cpl . bellatula . 3 | Results 3.1 | Sensilla of antenna There are two types of sensilla: Sensilla Trichoidea 4 (ST4) and Sensilla chaetica 2 (SCh2). Sensilla Trichoidea 4 (ST4) is located aside the joint between antennomeres. Number of ST4 ranges 2-3. It is tapering from base toward tip, with smooth surface and a terminal pore (Figure 2). The length ranges from 5.455-9.845 μm. There is no significant difference among species (Table 2). Sensilla chaetica 2 (SCh2) is located at the tip of the antenna. Number of SCh2 is 1. The length is 9.420 μm. It is tapering from base toward tip, with ribbed surface. SCh2 was found only in Cpl . bellatula , and the tip of the antennae of other four specimens were broken (Figure 3). TABLE 2 | Morphological comparison of sensilla trichoidea 4 (ST4) in green lacewing larvae. Cpd . orientalis 5.663 2 Yes Tapering from base toward tip, with smooth surface and a terminal pore M . flavimaculus 9.845 3 Yes Same as above Chr . formosa 6.727 2 Yes Same as above Cpl . bellatula 5.455 3 Yes Same as above Cun . albolineata - 2 - - Note: The number of sensilla in this study is limited to five species, and thus may not be broadly representative. FIGURE | 2 Sensilla trichoidea 4 (ST4) on the antenna of green lacewing larvae. (A) The head of Cpd . orientalis ; (B) The fine structure of ST4 on the antenna in Cpd . orientalis ; (C) The head of Cpl . bellatula ; (D) The fine structure of ST4 on the antenna in Cpl . bellatula ; (E) The head of M . flavimaculus ; (F) The fine structure of ST4 on the antenna in M . flavimaculus ; (G) The head of Chr . formosa ; (H) The fine structure of ST4 on the antenna in Chr . formosa ; (I) The head of Cun . albolineata ; (J) The fine structure of ST4 on the antenna in Cun . albolineata . FIGURE | 3 (A) The head of Cpl. bellatula. (B) The fine structure of SCh2 on the antenna 3.2 | Sensilla of mouthparts Sensilla trichoidea 1 (ST1) is located at the both sides of the tip of mandible. Number of ST1 ranges 3-5. It is tapering from base toward tip, with smooth surface and different degree of curvature in different species (Figure 4). The length ranges from 10.801-34.914 μm, and the length varies in the same individual (Table 3). The ST1 of M . flavimaculus and Cpl . bellatula is more curved than that of the other three species (Figure 4B, E). Besides, there is no significant difference among five species. Sensilla basiconica 3 (SB3) is located on both sides of the mandible and maxillae. Number of SB3 ranges 5-9. It is tapering from base toward tip, straight and short, with curved tip. The length ranges from 2.723-6.422 μm (Table 3). There is no significant difference among five species (Figure 5). Sensilla chaetica 3 (SCh3) is located at the tip of the mandible. Number of SCh3 ranges 3-11. It is tapering from base toward tip, with ribbed surface, and the tip of SCh3 is forked and slightly curved. The length ranges from 1.595-3.413 μm (Table 3), and there is no significant difference of SCh3 among five species (Figure 6). TABLE 3 | Morphological comparison of sensilla on mouthparts in green lacewing larvae. Cpd . orientalis 11.475-34.914 μm, 4 ST1, slightly curved, smooth surface, tapering from base to tip. 3.076-6.422 μm, 9 SB3, short, extremely curved, tapering from base to tip, with smooth surface. 2.228-3.413μm, 11 SCh3, short, ribbed surface, slightly curved at tip, tapering from base to tip, with forked tip. M . flavimaculus 11.291-28.660 μm, 4 ST1, strongly curved, smooth surfaces, tapering from base to tip. 3.910-4.600 μm, 8 SB3, short, extremely curved, tapering from base to tip, with smooth surface 2.380-3.132 μm, 4 SCh3, short, ribbed surface, slightly curved at tip, tapering from base to tip, with forked tip. Cun . albolineata 11.327-34.581 μm, 3 ST1, slightly curved, smooth surfaces, tapering from base to tip. 2.986-4.534 μm, 9 SB3, short, extremely curved, tapering from base to tip, with smooth surface 2.430-3.125 μm, 9 SCh3, short, ribbed surface, slightly curved at tip, tapering from base to tip, with forked tip. Chr . formosa 10.801-35.535 μm, 5 ST1, slightly curved, smooth surfaces, tapering from base to tip. 3.977-5.682 μm, 5 SB3, short, extremely curved, tapering from base to tip, with smooth surface 1.595-2.099 μm, 3 SCh3 short, ribbed surface, slightly curved at tip, tapering from base to tip, with forked tip. Cpl . bellatula 13.248-21.828 μm, 3 ST1, extremely curved, smooth surface, tapering from base to tip. 2.723-4.374 μm, 5 SB3, short, extremely curved, tapering from base to tip, with smooth surface - Note: The number of sensilla in this study is limited to five species, and thus may not be broadly representative. Original Article FIGURE | 4 Sensilla trichoidea 1 (ST1) on the mouthparts of the green lacewing larvae. (A) Chr . formosa ; (B) Cpl . bellatula ; (C) Cpd . orientalis ; (D) Cun . albolineata ; (E) M . flavimaculus . FIGURE | 5 Sensilla basiconica 3 (SB3) on the mouthparts of the green lacewing larvae. (A) Chr . formosa ; (B) Cpd . orientalis ; (C) M . flavimaculus ; (D) Cpl . bellatula ; (E) The fine structure of SB3 on the mouthparts in Cpl . bellatula ; (F) Cun . albolineata . not-yet-known not-yet-known not-yet-known unknown FIGURE | 6 Sensilla chaetica 3 (SCh3) on the mouthparts of the green lacewing larvae. (A)The mouthpart of Cpd . orientalis ; (B) The fine structure of SCh3 in Cpd . orientalis ; (C) The mouthpart of M . flavimaculus ; (D) The fine structure of SCh3 in M . flavimaculus ; (E) The mouthpart of Chr . formosa ; (F) The fine structure of SCh3 in Chr . formosa ; (G) The mouthpart of Cun . albolineata ; (H) The fine structure of SCh3 in Cun . albolineata ; (I) The finer structure of SCh3 in Cun . albolineata . 3.3 | Structure associated with debris-carrying behavior on the dorsum of trunk Submedian seta (SMS) was found in debris-carrying larvae and naked larvae. The SMS in debris-carrying larvae is long, numerous, with a curved tip, while the shape of SMS is long, thick, with a straight tip in naked larvae. The number of SMS in two naked larvae is different, in Chr . formosa is numerous, in Cpl . bellatula is few. And there is different degree of curvature of the SMS in Cpd . orientalis, Cun . albolineata, and M . flavimaculus, especially Cpd. orientalis, where tips of SMS are extremely curved (Figure 7B, D, F); SMS tips of Chr . formosa and Cpl . bellatula are straight and thick (Figure 7H, J). The scale-like seta and slender hair-like seta were found in the body wall of dorsal trunk of debris-carrying larvae and naked larvae. The scale-like seta is dense, with a terminal constriction, the slender hair-like seta is relatively scattered, curved, and tapering from base to tip. The scale-like seta was found at the dorsum of trunk of Cpd . orientalis, Cun . albolineata, M . flavimaculus, and Chr . formosa (Figure 8B, D, F, H), the slender hair-like was only found in Cpl . bellatula (Figure 8J). FIGURE | 7 Submedian setae (SMS) on the dorsum of body in the green lacewing larvae. (A) The dorsum of body of Cpd . orientalis ; (B) Curved tip SMS in Cpd . orientalis ; (C) The dorsum of body of Cun . albolineata ; (D) Curved tip SMS in Cun . albolineata ; (E) The dorsum of body of M . flavimaculus ; (F) Curved tip SMS in M . flavimaculus ; (G) The dorsum of body of Chr . formosa ; (H) Straight tip SMS in Chr . formosa ; (I) The dorsum of body of Cpl . bellatula ; (J) Straight tip SMS in Cpl . bellatula . FIGURE | 8 Structure on the body wall of dorsal trunk in the green lacewing larvae. (A) The dorsum of body of Cpd . orientalis ; (B) Scale-like seta on the body wall in Cpd . orientalis ; (C) The dorsum of body of Cun . albolineata ; (D) Scale-like seta on the body wall in Cun . albolineata ; (E) The dorsum of body of M . flavimaculus ; (F) Scale-like seta on the body wall in M . flavimaculus ; (G) The dorsum of body of Chr . formosa ; (H) Scale-like seta on the body wall in Chr . formosa ; (I) The dorsum of body of Cpl . bellatula ; (J) Slender hair-like seta on the body wall in Cpl . bellatula . \papertype Original Article 4 | Discussion 4.1 | Sensilla on the antennae of larvae We found two types of sensilla, i.e., ST4 and SCh2, on the antennae of green lacewing larvae. There is no significant morphological difference of ST4 between debris-carrying larvae and naked larvae, suggesting that this type of sensilla may not be directly related to debris-carrying behavior. Among four types of sensilla trichoidea (ST) in insects, ST4 on antenna may function as a chemosensilla, while that on mouthparts may act as a mechanoreceptor (Abouzied, 2008; Nowińska & Brożek, 2017). Thus, the ST4 on the antenna of green lacewing larvae may be a chemosensilla. Due to damage of the antennal tips in the observed specimens, the comparison of SCh2 between the two types of larvae remains unavailable. So far, the function of SCh2 is still unknown. Nevertheless, a similar sensillum named SCh1 was reported to function for sensing mechanical stimulation during feeding in insects (Payne et al., 1973; Shi, 2021), suggesting similar function as a proprioceptor between SCh1 and SCh2. Thus, the SCh2 in green lacewing larvae may also function during feeding, and whether it is associated with debris-carrying behavior remains unknown. 4.2 | Sensilla on the mouthparts We found three types of sensilla, i.e., SB3, SCh3, and ST1 on the mouthpart of green lacewing larvae. There is no difference in Sensilla basiconica 3 (SB3) between debris-carrying larvae and naked larvae (Figure 5), suggesting that SB3 may not play a functional role in debris-carrying behavior. Pérez‐González and Zaballos (2013) suggested that SB3 is responsible for recognizing smell of prey as an olfactory receptor in antennae of hemipteran insects. Therefore, the SB3 of the mouthpart may function as olfactory receptor. There is no significant difference between debris-carrying larvae and naked larvae through the comparison regarding the morphology and location of SCh3 (Figure 6), while the number of SCh3 is different. The number of SCh3 in the two debris-carrying larvae ( Cpd . orientalis , Cun . albolineata ) is more than that in the naked larvae ( Chr . formosa ). Thus, SCh3 may have function associated with debris-carrying behavior. Previous research showed that SCh3 in hemipteran insects function as a mechanoreceptor, including sensing environment, recognition of prey through mechanical touching, or reflection of gravity as a proprioceptor (Rani & Madhavendra, 2005; Nowińska & Brożek, 2017; Bin, 1981; Chen et al., 2024; Schneider, 1964). During the camouflage process, green lacewing larvae grasp fragments with their mouthparts and may sense the weight of the debris through the sensilla located on their mouthparts. If the weight is appropriate, the larvae will place the fragment on its back. Conversely, if the weight is unsuitable, the larvae will abandon it. This behavior suggests that these sensilla may function as mechanoreceptors to detect changes in weight of debris. Besides, SCh3 may also serve in recognizing prey by mechanical touching. There is no significant difference in ST1 between debris-carrying larvae and naked larvae (Figure 4), suggesting that ST1 may not play a role in debris-carrying behavior. Previous study suggested that ST1 on the mouthparts function as a detector of mechanical stimulation, while that on the antennae as a proprioceptor (Shi, 2021; Moeck, 1968). Therefore, the ST1 on the mouthpart may function as a detector to sense mechanical stimuli. 4.3 | Structures on dorsum of trunk in debris-carrying behavior Three types of structures were found, i.e., SMS (Submedian seta), scale-like seta, and slender hair-like seta on the dorsum of trunk of green lacewing larvae. SMS is located at the abdominal segment (Tauber & Garland, 2014; Tauber et al., 2013; Penny et al., 2000), with two types: apically curved and straight. The former is present in the debris-carrying larvae ( Cpd. orientalis , Cun . albolineata, and M . flavimaculus ), while the latter is present in the naked larvae ( Chr . formosa and Cpl . bellatula ). Similar difference in the terminal curve of SMS, but named as “hooked hair” was also recorded by Canard (1984), Tauber et al. (2014), and Hayashi et al. (2014). Therefore, the SMS with terminal curve is confirmed to be related to debris-carrying behavior. Notably, The SMS tip differs among species, being thin and nearly straight (180°) in Cpd . orientalis , thick and curved (>180°) in Cun . albolineata , and intermediately thick with a 90-180° angle in M . flavimaculus . Previous study found that there is significant difference in debris among the larvae of different species. For example, the larvae of Ceraeochrysa cincta Schneider, 1851 specifically carry fungal spores (Melo et al., 2024), the larvae of Leucochrysa ( Leucochrysa ) insularis Walker, 1853 specifically carry snail shell (Tauber et al., 2013), and the larvae of Leucochrysa pavida Hagen, 1861 specifically carry lichen (Wilson & Methven, 1997). Thus, the morphological differentiation in the SMS could be associated with the types of debris, which, however, needs future test. Scale-like seta occurs in the debris-carrying larvae, while slender hair-like seta occurs in the naked larvae. Notably, the scale-like seta is also found in Chr . formosa , a species whose larvae were recorded as “naked” in our research, with SMS apically straight. However, Chr . formosa seems more similar to debris-carrying larvae in having dense and long SMS, and cylindrical and digitiform lateral tubercles on thorax. Previous studies found that although the larvae of most Chrysopa species are naked, some are ”occasional debris-carriers”. In such species, the debris-carrying behavior is usually present in the first-instar larvae, e.g., Chrysopa quadripunctata Burmeister, 1939, which carry scattered fragments of material (Tauber & Tauber, 1987; Tauber et al., 2014; Tsukaguchi, 1978). Thus, we cannot exclude the possibility of the debris-carrying behavior in Chr . formosa , and its morphology may represent the intermediate type between the typical debris-carrying and naked larvae. 5 | Conclusion The present SEM observation provides new data for understanding the morphological adaptation related to the debris-carrying behavior in the green lacewing larvae. The SMS with terminal curve and scale-like seta on the dorsum of trunk are found having important function in debris-carrying behavior. However, we still need to describe the ultrastructure in the larvae of more species for comprehensive comparison. In particular, the correlation between the category of debris and corresponding morphological modifications on SMS and scale-like seta is of high interest to be explored. In addition, the fine structure and debris-carrying behavior of putative “occasional debris-carriers” in some green lacewing species should also be investigated. References Abouzied, E. M. (2008). 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Keywords debris-carrying behavior green lacewing larvae scanning electron microscopy sensilla seta Authors Affiliations Jun Lu 0009-0009-4122-6093 China Agricultural University College of Plant Protection View all articles by this author Hongyu Li China Agricultural University College of Plant Protection View all articles by this author Xingyue Liu [email protected] China Agricultural University College of Plant Protection View all articles by this author Metrics & Citations Metrics Article Usage 338 views 149 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Jun Lu, Hongyu Li, Xingyue Liu. Ultrastructure on head and trunk of green lacewing larvae associated with debris-carrying behavior. Authorea . 29 April 2025. DOI: https://doi.org/10.22541/au.174590650.03598161/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. 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