Rearing Istocheta aldrichi (Diptera: Tachinidae) from field-collected Japanese beetles ( Popillia japonica ): 1. Methods to improve insect collection and parasitoid pupariation

Abstract Istocheta aldrichi (Diptera: Tachinidae), a specialist parasitoid of the invasive Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae), was released to eastern North America in the 1920s as part of a classical biological control program. Further releases are being considered in different regions of North America and Europe where P. japonica is establishing. Successful releases of the biocontrol agent depend on identifying efficient techniques for collecting parasitized hosts from the field and rearing the parasitoid through diapause to obtain I. aldrichi adults. In this study, we evaluated how the collection date, the collection method (hand-picking vs. regular traps vs. modified traps) and rearing conditions (food provision and substrate type) of parasitized hosts influence I. aldrichi pupariation and emergence. The proportion of parasitized beetles yielding I. aldrichi puparia decreased considerably as the season progressed. Rearing conditions immediately after collection influenced both puparium yield and quality: withholding food from parasitized P. japonica slightly increased puparium yield but reduced puparium weight, while the effect of food provision on subsequent overwintering survival depended on rearing substrate. Finally, simple modifications to commercial traps (larger, ventilated, containers with added food source and substrate) collected more beetles than regular traps and promoted successful development of the parasitoid to the puparium stage. Our results are used to suggest basic guidelines for collecting and rearing I. aldrichi in experimental research and applied biological control of P. japonica. Competing Interest Statement The authors have declared no competing interest. Footnotes Minor revisions to main text. Figure 3 separated in two new figures.