COS 68-4
The concurrent effects of a plant-based resource and herbivory-induced plant volatiles on the colonization and predation behaviors of an omnivorous predator insect
Many plants emit a blend of volatile organic compounds following herbivory. These blends sometimes attract omnivorous predator insects in search of herbivorous insect prey. Many types of plant tissue and exudates are consumed by and may also attract omnivorous insects. Therefore, herbivory-induced plant volatiles and plant-based resources are both capable of facilitating antagonistic interactions between omnivorous and herbivorous insects through the attraction of the former. However, because volatiles represent information while plant-based resources are actual food items, each may be perceived and utilized differently by omnivores. We hypothesized that 1) plant-based resources may interact with herbivory-induced volatiles to increase the attraction of omnivores to damaged plants but 2) also reduce subsequent predation against herbivores by the same omnivores due to their consumption of plant-based resources. We performed a series of field experiments over two consecutive years coupling an omnivore–herbivore-host plant natural tritrophic system with a locally co-occurring resource plant. We simultaneously manipulated the presence of 1) herbivory-induced volatiles and 2) plant-based resources, and subsequently measured the effects of these manipulations on 1) the rate of predation against the herbivore and 2) the local density of the omnivorous predator insect. Data were analyzed using ANOVA and ANCOVA models.
Results/Conclusions
Both the presence of herbivory-induced volatiles and their positive effect on the omnivore predation were transient over the course of the study (P < .0001 and P < 0.0003, respectively). In contrast, plant-based resources had a more sustained negative effect on predation behaviors in the omnivore (P = 0.0005). Local density of the omnivorous predator insect on the other hand was enhanced both by volatiles (P = 0.0389) and plant-based resources (P < 0.0001). Per our hypothesis on predation, we found that volatiles increased predation (while present), whereas plant-based resources reduced it, resulting in an overall conflicting effect on the predation behavior of the omnivore. We also found that both volatiles and plant-based resources increased local density of the omnivores as we predicted. These findings indicate that plant-based resources can positively augment or conflict with the potential effects of co-occurring induced volatiles on individual aspects of omnivorous insect behavior. Research into how different plant cues are perceived and utilized by omnivorous insects, especially when encountered in unison, can provide valuable information regarding the indirect interactions between plants and predatory insects as well as the manipulation and implementation of these insects as biocontrol agents in agricultural systems.