Could host plant response to eggs of its specialized herbivore select for oviposition on non-hosts?

The moth, Heliothis subflexa, is a specialist on plants in the genus Physalis, but lays approximately 20% of its eggs on nearby non-host plants. We observed that the leaves of Physalis plants respond physically to the eggs of Heliothis sublexa, while co-occurring non-host plants do not. In this study we tested the hypothesis that this plant response could have selected for non-host oviposition. We found that leaves of P. angulata and P. pubescens respond to eggs by the formation of 1) necrotic tissue, 2) undifferentiated cells that form a bump (neoplasm) under the eggs of this herbivore, or 3) both types of responses. Greenhouse experiments showed that 64% of eggs laid on P. angulata elicited a response, and that a response to an egg decreased the probability of hatching. Further experiments in the field with P. angulata showed that mean percent response to eggs by plants was 31%, and that the probability of an egg eliciting a response increased as temperature increased. Field experiments also confirmed that a plant response to an egg decreased the probability of hatching and increased the probability of removal from the plant by physical dislodgement or predation. Eggs that elicited a response had a 25% lower probability of hatching and a 28% lower probability of remaining on the plant, resulting in an average fitness cost of 22% for H. subflexa. This is the first empirical experiment indicating that insect oviposition behavior could evolve to avoid the impact of plant defenses on egg mortality.