Oviposition of potato tuber moth,Phthorimaea operculella Zell. (Lepidoptera: Gelechiidae); identification of host-plant factors influencing oviposition response

Abstract

A series of laboratory experiments was conducted to investigate the nature of the factors which determine acceptance or rejection of plants for oviposition by potato tuber moth. Bare leaves of only two plant species (potato and egg-plant) were accepted for oviposition, but when covered with a layer of muslin, leaves of all plants examined—including several known non-host plants—were rendered acceptable. Thus, volatile repellent factors are not possessed by unacceptable plants; rather, they must be rejected either because of chemical deterrents detectable only on contact or because of unsuitably textured surfaces. Plant juices expressed on to a covering layer of muslin increased the acceptance of potato and egg-plant, had no effect with tobacco, and decreased acceptance of all known non-host plants and of tomato. Brushing the leaf surface without releasing plant juices induced a detectable deterrent effect with some plant species. There was no stimulation or deterrence when the oviposition surface was separated from expressed plant juices by about 2 mm. Tomato reacted like known non-host plants in all tests. Potato and egg-plant stimulated greater total egg deposition in most experiments, but strongly deterrent treatments did not reduce the total egg lay. Antennectomy reduced but did not eliminate the stimulatory effect of potato and the deterrent effect of bean plant juices. Virgin moths were not stimulated to oviposit by potato peel. It is concluded that selection of plants for oviposition is determined both by the physical nature of their surfaces and by chemical factors which are detected only on contact. The effects of stimulative chemical factors in host plants and deterrent factors in non-host plants reinforce each other in the plant selection process.