Induced Resistance in Ipomoea Purpurea

Abstract

A series of experiments indicate that induced changes occur in the foliage of the annual morning glory Ipomopea purpurea when subjected to prior damage. These changes reduce the growth rate, consumption rate, growth efficiency of larvae of the generalist lepidopteran Spodoptera eridania. They also alter the pattern of damage caused by specialist flea beetles, Chaetocnema confinis, and by generalist insect herbivores in the field. No effects of induction were detected on specialist tortoise beetles, Deloyala guttata and Metriona bicolor. Although total damage by both flea beetles and generalist insects did not differ between induced and noninduced plants, this result does not necessarily imply that the effects on these insects were nonadaptive. The observed effects of induced response are consistent with both "diffuse" and "pairwise" views of the selection imposed by herbivores on plant resistance. Finally, the existence of induced responses suggests that previous conclusions by Simms and Rausher that resistance to flea beetles and generalist insects is not costly in I. purpurea may be premature.