Prey consumption and effects on performance in the specialist frugivore Heliothis subflexa

Omnivory has recently been discovered to be both stabilizing to food webs and widespread. This mixed diet feeding strategy has been found to be especially prevalent among insect and is thought to have evolved as a way to overcome the low nutrient intake that an herbivorous or predaceous diet may have. However, some insects engage in omnivory less frequently than others. The Heliothis subflexa is a specialist moth whose larvae feed only on plants in the Physalis genus. Although thought to be a frugivore, H. subflexa also feed on fruit that has been infected with the smaller larva, Symmetrischema lavernaella.
The goal of this study was to observe whether H. subflexa has a preference for infected fruit and to find out how consuming fruit with S. lavernaella affects the performance of the moth. A dual choice experiment on infected and uninfected fruits will be used to determine preference. To evaluate the effects on performance, the change in larval body mass will be divided by total fruit consumed and the assimilation efficiency will be compared in larvae fed diets of infected or uninfected fruits. I found that H. subflexa in their fifth instar prefer to feed on fruit that showed signs of infection and would consume the whole fruit, including S. lavernaella. However, performance of larvae fed infected fruit diets were significantly lower than those given multiple uninfected fruits. This suggests that the preference for infected fruit is a response to S. lavernaella changing the chemical composition and making the fruit more palatable rather than the fruit being more nutritious. I also found that smaller H. subflexa would frequently leave S. lavernaella uneaten when fed infected fruits thus not recovering nutrition that has already been lost to the smaller larvae. As a result, competition between the two caterpillar for the fruit may be affecting the performance of H. subflexa but having a broader host plant range than S. lavernaella may be keeping this poorer performance from having any detrimental effects on the population as a whole.
This will be the first study to address omnivorous behavior in the Heliothis subflexa. Also, this study will provide further evidence on specialist being omnivorous and how the ingestion of prey affects the performance of larvae in herbivorous insects.