Food resources can interact directly or indirectly through herbivores with omnivores which can influence the nature and intensity of interactions of species within communities and can alter the structures of communities. There is a need to understand the underlying mechanisms of omnivory as diet switching may not be just a random process. The top-down interactions can also change the dynamics of community assembly through various mechanisms. It is vital to fully explore these mechanisms so that the impact of the upper trophic guild members on a local community and its assembly can be predicted. Foraging behaviour of Dicyphus hesperus was evaluated in the presence of different resources (plant, shared and intra-guild prey), testing the hypothesis that the omnivores will spend more time basic resource feeding and less time searching if the basal resource types have higher values for supporting fitness. One week old, 72 h starved adult female D. hesperus were placed in arenas with varied plant and prey resources and time spent searching, number of times D. hesperus encountered prey and which prey type was encountered, time spend eating prey, and time spend plant feeding were recorded.

Results/Conclusions

Time spent plant feeding was greatest on mullein, then tomato, pepper and chrysanthemum. In the absence of prey, mullein is a higher value resource for reproduction whereas chrysanthemum is a poor resource, with tomato and pepper intermediate. In the presence of prey, all 4 plants are equally valuable resources for D. hesperus. Encounter rate for all prey was highest on pepper, then tomato, chrysanthemum and mullein whereas success ratio was highest on chrysanthemum, then pepper, tomato and mullein. Contrary to our prediction, plant feeding was higher in the presence of shared prey because of higher success ratio and after every successful encounter the omnivore would engage in plant feeding for extra oral digestion.  As predicted, encounter rate was also higher for shared prey compared to intra-guild prey because the shared prey was less mobile. As predicted, more time was spent plant feeding in the presence of either prey type at lower densities (total of 8 individuals per Petri dish) compared to higher densities of 28. At higher densities more time was spent prey feeding. Time spent by the omnivore on different activities was found to be a function of basal resource type, prey type and the density.