D3208: Epigenetic mechanisms of cross-resistance in the Colorado potato beetle (Leptinotarsa decemlineata)

The evolutionary mechanisms by which major pests such as the Colorado potato beetle, Leptinotarsa decemlineata, evolve rapid insecticide resistance remains poorly understood. Given that insect pests are regularly exposed to a wide range of pesticides, it is possible that cross-resistance can contribute to insecticide resistance. Cross-resistance occurs when sublethal exposure to a substance affects the response to another toxic substance. We tested if cross-resistance is associated with epigenetic modifications, such as histone modifications, which alter gene expression without changing the DNA sequence. Although the role of epigenetic modifications has been documented in resistance, no study has examined its role in cross-resistance. To understand alternative drivers of insecticide resistance in CPB, we hypothesize that prior sublethal exposure to the fungicide, chlorothalonil, and the insecticide, imidacloprid, will impact CPB performance and elicit epigenetic changes via histone modification. We predicted that exposure to sublethal doses of chlorothalonil and imidacloprid would decrease larval performance and survival but would increase the frequency of histone modifications compared to control beetles. We tested how prior exposure to fungicides (control vs. LC10) influenced insect survival and performance after exposure to insecticide treatments (control and LC10). We examined how the treatments influenced insect performance by examining beetle herbivory and mortality. We discuss the results in the context of cross-resistance in CPB and the role of epigenetic mechanisms in insecticide resistance.