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 (S ay), with a hypersensitive necrotic zone that subsequently disintegrat ed around the border and detached from the leaf. This clone was a soma tic fusion with a complex Solanum species background. The necrotic res ponse was observed in every case of naturally oviposited eggs on this clone during 2 field seasons. Tests of egg masses artificially attache d to the leaves demonstrated that shading reduced the necrosis and pre vented the subsequent disintegration. There was no indication that the eliciting agent was a bacterium associated with insect eggs. Leaf nec rosis and detachment alone did not affect egg hatch. In greenhouse stu dies, 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 resu lt of abundant ground predators in the area. Based on these results, i t appears that detachment of Colorado potato beetle eggs with subseque nt deposition on the ground could be considered a new mechanism of hos t plant resistance to insects.