Parasitism of Corn Earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by Tachinid Flies in Cultivated Hemp

SIMPLE SUMMARY: Hemp has become a rapidly growing industry in the United States in recent years. However, due to many decades of prohibition, there has been relatively little research on insect pests and their interactions with natural enemies in hemp production systems. Here, we provide the first quantitative assessment of corn earworm (CEW) Helicoverpa zea parasitism in a hemp system. Corn earworm larvae exhibited high parasitism rates by tachinid flies resulting in elevated mortality. Host mortality increased with the number of tachinid eggs per larva even though typically only one parasitoid successfully developed per host. Larger CEW larvae were more likely to survive parasitism, but frequently, neither parasitoid nor host larvae successfully developed. Our results suggest that tachinid flies hold promise as biological control agents for populations of this important pest attacking hemp. ABSTRACT: In a survey on hemp grown in western Kentucky we found an average of 27.8 CEW larvae per plant. We recorded 45% parasitism of CEW in these fields by two species of tachinid flies, Winthemia rufopicta and Lespesia aletiae. Most parasitized larvae were third to sixth instars at the time of collection. We found up to 22 tachinid eggs per host larva, 89% of which typically bore between 1 and 5 eggs on the thorax. 45.9% of CEW bearing eggs died. The number of tachinid eggs per host was unrelated to host body mass, but both the number of tachinid eggs and caterpillar body mass influenced CEW survival. Larger CEW often survived parasitism and the number of fly eggs was negatively related to survival rate. The emergence of adult flies was positively correlated with the number of eggs, but no influence of the host size was found. High mortality of CEW larvae and the parasitoids developing within them in this system suggests that secondary chemicals (or poor nutrition) of the hemp diet may be negatively affecting host and parasitoid development and influencing their interactions.