Effects of successful or unsuccessful parasitism by the solitary endoparasitoid wasp Cotesia vestalis (Hymenoptera: Braconidae) on the testis development in several host moth species

Parasitism by a parasitoid wasp alters the physiology and behavior of its host insects. This study investigated the effects of successful and unsuccessful parasitization on individual host development and testis growth in several moth species. Although the solitary koinobiont endoparasitoid wasp, Cotesia vestalis (Hymenoptera: Braconidae), primarily parasitizes the diamondback moth (Plutella xylostella, Lepidoptera: Plutellidae), its host range is relatively broad. Previous research confirmed successful parasitization of P. xylostella, Mythimna separata (Noctuidae), and Helicoverpa armigera armigera (Noctuidae), whereas attempts to parasitize Spodoptera exigua (Noctuidae), Palpita nigropunctalis (Piralidae), Aedia leucomelas (Nocuidae), and Mamestra brasiccae (Noctuidae) were unsuccessful. In this study, testis development in all parasitized hosts, except for A. leucomelas. was suppressed or reduced compared to the unparasitized controls. Notably, testes in parasitized hosts exhibited some degree of growth after parasitization—varying by species and occurring independently of ecdysis—except in final instar larvae of P. xylostella. These finding suggest that parasitism suppresses or reduce testis development regardless of whether parrasistization is successful. The potential mechanisms underlying a reduction of testis development in unsuccessful parasitization are discussed in the context of ecdysteroid signaling and the parasitic process.