Preference and performance in an herbivorous coccinellid beetle: a comparative study of host plant defensive traits, insect preference, and survival

Herbivorous insects assess and choose their potential host plants based on traits that may correlate with host suitability or quality. These traits may operate as cues for better resources, noxious chemicals, or fewer competitors and enemies. Interactions between insects and their host plants may also be modulated by the nutritional value of the plant, by plant chemical stimuli, or by physical traits such as trichomes. Differences in chemical or physical cues among plants may convey information about diet suitability. Several studies have addressed the topic of differences in plant traits between host and non-host plants; fewer have addressed these differences among potential host plants. We have studied the effect of chemical and physical plant traits on the feeding and oviposition preferences of the oligophagous herbivore Epilachna paenulata (Coleoptera: Coccinellidae) and two of its host plants, Cucurbita maxima and Cucurbita moschata (Cucurbitaceae). We first typified the volatile and non-volatile chemical profiles and the trichome distribution of the plants. Then, using behavioral assays, we evaluated feeding and oviposition preferences of E. paenulata. Further, to assess a correlation between oviposition preferences and offspring survival, we measured larval performance as indicated by survival, mass, and time to complete each instar. Female longevity in both Cucurbita host plants was also evaluated. Our results show that the congeneric plants bear differences in their chemical profiles, including volatile organic compounds, leaf waxes, and leaf parenchyma metabolites. Trichome abundance was also different, with C. maxima presenting fewer hairs. Epilachna paenulata females laid significantly more eggs in C. maxima, regardless of the plant they were raised as larvae. Female longevity on C. maxima was higher, but larval performance showed no difference between both plants. The proximate causes mediating female oviposition preferences may then involve trichome abundance, oviposition deterrents, toxic substances, or a combination of these factors.