The Late Immature Development of Toxoneuron nigriceps, a Koinobiont Endoparasitoid, and Steps Toward an In Vitro Rearing System
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Toxoneuron nigriceps is a koinobiont larval endoparasitoid of the tobacco budworm, Heliothis virescens. No koinobiont parasitoid (which develop in active, growing hosts) has been reared completely in vitro. However, T. nigriceps has been partially reared in vitro, from egg stage through 2nd larval instar and from 2nd to 3rd larval instar. Despite reaching its final larval instar, T. nigriceps failed to develop past the larval stage. In the following study, two aspects of T. nigriceps development, post-egression tissue feeding and cocoon formation through pupation, were examined to determine why T. nigriceps failed to develop in vitro beyond the larval stage and how in vitro rearing might be improved to rear T. nigriceps to adulthood. The importance of post-egression feeding and the possibility of developing an artificial post-egression diet were examined by manipulating the post-egression feeding behavior of T. nigriceps. The tissues of pre- and post-tissue feeding T. nigriceps larvae were analyzed to investigate the macronutritional benefit of post-egression feeding. A preliminary artificial post-egression diet was tested, and the putative quality of T. nigriceps reared to adulthood using this diet was examined. The formation of subterranean pupation chambers by healthy and parasitized H. virescens larvae was examined to investigate potential behavioral manipulation by T. nigriceps during this process. Finally, the potential use of artificial pupation chambers by T. nigriceps was investigated. Post-egression feeding was determined to be a vital part of T. nigriceps development, contributing to both parasitoid size and survival to adulthood. A preliminary artificial post-egression diet was developed, which facilitated rearing of T. nigriceps from 3rd larval instar to adulthood. The dimensions and burial depth of chambers formed by parasitized H. virescens were significantly different from those of chambers formed by healthy H. virescens, suggesting that T. nigriceps manipulated host behavior during excavation. Toxoneuron nigriceps was able to use a number of common laboratory items as substitute pupation chambers during cocoon formation, and the merits of several artificial chambers were discussed. With provision of an adequate post-egression and artificial pupation chamber, in vitro rearing of T. nigriceps from the larval stage to adulthood may be possible.
Henderson, Ruth 1982- (2012). The Late Immature Development of Toxoneuron nigriceps, a Koinobiont Endoparasitoid, and Steps Toward an In Vitro Rearing System. Doctoral dissertation, Texas A&M University. Available electronically from