SEVERAL FACTORS AND THEIR ROLE IN CONTROL OF LEPIDOPTERA POPULATIONS

A number of factors influence Lepidoptera populations. The larvae are at the mercy of their environment, susceptible to the effects of poor food quality, and highly vulnerable to predation. In this thesis I present three manuscripts dealing with a small snapshot of what dynamics are at play in the control of Lepidoptera numbers. Host quality is a cornerstone of developmental success, with host suitability to the herbivore in question being affected by the plant’s nutritional profile and its defenses against herbivory. Plant genotype influences plant suitability to herbivores; domesticated plants selected for properties such as high fruit yield are demonstrably vulnerable to herbivory. I conducted an experiment assessing the suitability of five Vaccinium corymbosum cultivars to the specialist notodontid Datana drexelii. In-situ weekly surveys of a managed blueberry patch for naturally occurring D. drexelii larval clusters complemented this work. Larval survival and pupal weight did indeed differ by cultivar. Larval occurrence on the managed blueberries also differed by cultivar. One especially important result was that the cultivar ‘Jersey’ yielded few naturally-occurring larvae and resulted in very high larval mortality and low pupal weight. The low D. drexelii preference for and performance on this cultivar suggest that this variety may be appropriate for areas where this pest is common. Cultivar-level variation in herbivore vulnerability highlights how understanding plant-pest interactions can help manage agricultural-state planning policy. Natural enemies, in contrast to food plants, exert a top-down force on the populations of lepidopterans. Due to the high mortality caused by these enemies, the introduction of new enemies can have catastrophic effects on existing populations of lepidopterans. This is exemplified with the non-native generalist parasitoid Compsilura concinnata (Diptera: Tachinidae). This fly has been linked to the decline of Hyalophora cecropia and Callosamia promethea. Work done in the 1990s on these two saturniid species found that C. concinnata parasitized 81% of deployed H. cecropia and 68% of deployed C. promethea. In 2017 and 2018, we repeated this field experiment. In 2017, C. concinnata parasitized only 19% of H. cecropia larvae and 1% of C. promethea larvae; in 2018, parasitism rates were 3% and 0%, respectively. This suggests a shift in the role of this parasitoid in the population dynamics of these saturniid moths. Finally, I deal with the mere risk of predation, which has demonstrable effects on the development and behavior of prey species. While prey responses to predators reduce the threat of consumption, the physiological costs of these responses can be considerable. Actias luna is a large saturniid native to Eastern North America with multiple natural enemies. Actias luna larvae were housed with the predator Vespula maculifrons, which were rendered non-lethal but able to move freely, as well as in a control (wasp-free) treatment. To rule out generic disturbance by an obnoxious insect, a third group of larvae were housed with a similarly-sized but harmless scavenging fly. Larvae in the wasp treatment died at a higher rate than those in the control treatments; and survival in the fly and control treatments did not differ. Larvae that died in the fly and wasp treatments gained virtually no weight between the start of the experiment and their death, suggesting that they may have succumbed to starvation