PS 27-78 - Investigating the behavior of an insect herbivore: do behavioral types affect plant damage?

Background/Question/Methods

Increasing evidence suggests that consistent individual differences in behavior (“behavioral types”) and correlations among behavioral types (“behavioral syndromes”) exist in species of insect herbivores. However, the influence of insect herbivore behavior on interspecific interactions, such as those with host plants, is not well understood. We used lab behavioral bioassays to determine whether adults (n= 25) of the specialist herbivore, Leptinotarsa juncta (Chrysomelidae), showed consistent levels of boldness and exploration. Behavioral bioassays were repeated five times per individual over two weeks to assess consistency. To test for a behavioral syndrome, we evaluated whether boldness and exploration were correlated. We determined whether the behavioral type, sex, or body size of an adult (n = 23) influenced the amount of plant damage by placing individuals in mesh enclosures with a host plant, Solanum carolinense (Solanacae). Plant damage was calculated as the difference between total leaf area before and after exposure to an L. juncta for seven days. Boldness was measured as the time to leaving a darkened 8.5-cm long tube (“dark-light test”), and the time spent feigning death (thanatosis) following a gentle pinch. We measured exploration by quantifying the time individuals spent moving in a small arena.

Results/Conclusions

The level of boldness measured for each individual was consistent. Individual’s exploration levels were not consistent over time. We found no evidence of a behavioral syndrome; there was no correlation between the exploration and boldness level obtained using the dark-light test or the thanatosis reaction test. We found that neither measure of boldness (from the dark-light test and thanatosis reaction test) nor body size was correlated with host plant damage. Plant damage was greater on plants with female L. juncta. Our results suggest that adult L. juncta have at least one consistent behavior (boldness), but this behavior type had no effect on herbivory. Our finding that females inflicted greater damage, even when accounting for body size, suggests that L. juncta traits do influence plant damage. Behaviors of L. juncta may be influenced by biotic factors, such as predators, that were not accounted for in our laboratory study. We suggest that future work should explore the relationship between behavioral types of herbivores and herbivory in the field, as well as in the lab, to account for the influence of biotic factors that are normally present.