Physical response of Physalis leaves to Heliothis subflexa eggs

Plant-insect interactions include many different types of relationships, some of which are negative for the plant. Plants have evolved a number of ways to defend themselves against insects; one way in which plants protect themselves from herbivorous insects is the formation of 1) necrotic tissue or 2) undifferentiated cells forming a bump (neoplasm) under the eggs of these insect herbivores. This has been observed in plants in the genus Physalis in response to oviposition by Heliothis sublexa, a caterpillar that consumes the fruit of plants in this genus. The goal of this study was to determine if these reactions by the plant in response to the presence H. subflexa eggs affect egg viability. Reactions to eggs were characterized for two Physalis species: P. pubescens and P. angulata. Egg placement on the leaf (upper, lower, proximity to the major vein, abaxial or adaxial) did not significantly affect the likelihood of a reaction occurring, nor did the location of an egg in the plant canopy. However, plant age and species significantly affected the elicitation of a reaction to eggs: younger plants and plants of the species P. angulata were much more likely to react to eggs compared to older plants and P. pubescens. The presence of a reaction under an egg significantly decreased the probability that an egg would hatch; thus the formation of nectrotic tissue and/or neoplasms on plant tissue in contact with eggs of H. subflexa may be a defensive response of Physalis species against this herbivore.