Hypersensitivity and egg drop: A novel mechanism of host plant resistance to Colorado potato beetle (Coleoptera: Chrysomelidae)

A potato, Solanum spp. hybrid, clone was identified that responded to egg masses of the Colorado potato beetle, Leptinotarsa decemlineata (Say), with a hypersensitive necrotic zone that subsequently disintegrated around the border and detached from the leaf. This clone was a somatic fusion with a complex Solanum species background. The necrotic response was observed in every case of naturally oviposited eggs on this clone during 2 field seasons. Tests of egg masses artificially attached to the leaves demonstrated that shading reduced the necrosis and prevented the subsequent disintegration. There was no indication that the eliciting agent was a bacterium associated with insect eggs. Leaf necrosis and detachment alone did not affect egg hatch. In greenhouse studies, Colorado potato beetle larvae from eggs that were detached from the host plant and placed on soil at various distances from the plant had a high success rate of colonizing the target plant. However, when this experiment was conducted in the field, larval survival and plant colonization were reduced greatly. We speculate that this was the result of abundant ground predators in the area. Based on these results, it appears that detachment of Colorado potato beetle eggs with subsequent deposition on the ground could be considered a new mechanism of host plant resistance to insects.