Colorado potato beetles show differential digestive compensatory responses to host plants expressing distinct sets of defense proteins

Herbivorous insects fed plants expressing proteinase inhibitors (PIs) compensate for the loss of digestive proteolytic functions by producing novel proteinases. We assessed here whether such compensatory responses represent a general, non-specific adaptation to defense-related proteins in host plant tissues, or if distinct responses occur depending on the stress exerted on the plant. As a model, growth, development, and digestive proteases of the Colorado potato beetle (Leptinotarsa decemlineata Say) were monitored after feeding larvae with plants pre-treated with either methyl jasmonate or arachidonic acid, two compounds inducing different sets of defense genes in potato. In brief, larvae fed plants treated with jasmonate or arachidonate were negatively affected compared to larvae fed non-treated plants, suggesting the potency of both molecules to induce partial resistance to potato beetles in potato. On the other hand, larvae fed treated plants partially compensated for the presence of defense-related proteins by adapting their digestive proteolytic system, both quantitatively and qualitatively. These compensatory processes varied depending on the treatment, the larvae fed arachidonate-treated plants showing the most dramatic response. Compensation to jasmonate and arachidonate was also influenced by a cysteine PI from rice expressed in the plant, pointing out the possible indirect effects of recombinant defense proteins on naturally-occurring plant-insect interactions. These observations, while showing the potential of jasmonate and arachidonate as inducers of partial resistance to the potato beetle in potato, also suggest that digestive compensation in herbivorous insects is determined, at least in part, by defense-related compounds found in the plant in response to different stress stimuli or as a result of ectopic expression in transgenic plants.