PARENT SESSION
Symposium #21: Effects of inbreeding and loss of genetic diversity on interactions with natural enemies.

Organized by: CT Ivey, DE Carr, and MD Eubanks
Wednesday, August 7. 1:00 PM to 4:30 PM. Crystal Ballroom, TCC.

Inbreeding affects the intensity of herbivory by diabroticite beetles in wild gourds.

Stephenson, Andrew^*,1, Breault, Steven¹, Hayes, Nelson¹, ¹ The Pennsylvania State University, University Park, PA

ABSTRACT- Our previous studies had shown that inbreeding depression in Cucurbita pepo ssp. texana (a wild gourd) increases with the intensity of inbreeding (the coefficient of inbreeding, F) under field conditions. In order to determine if there is an interaction between inbreeding and herbivory by diabroticite beetles, we grew 240 plants representing five families and six coefficients of inbreeding (F=0 to F = 0.94) per family in an experimental garden. Half of the plants in each family and in each coefficient of inbreeding were sprayed at weekly intervals with an approved commercially available insecticide to control for the beetles. The other half of the plants were unsprayed and served as the control treatment. Throughout the growing season we monitored survivorship and reproductive output through both the male and female function. We found that inbreeding depression not only increases with the coefficient of inbreeding but we also found that the inbred plants suffer significantly higher levels of beetle damage and that there is a significant interaction between inbreeding and the insecticide treatment, especially for early vegetative traits and traits related to the female function. Interestingly, we also found that inbred plants not only suffer from higher levels of beetle damage but they are also more likely to suffer from a bacterial wilt disease whose pathogen (Erwinia tracheiphila) is transmitted by the beetles. These findings indicate that the mating pattern of plants can indirectly affect other trophic levels in the community. Currently, we are attempting to determine a) if the increase in the wilt disease is due solely to an increase in the rate of infection or whether it is also due to a decrease in the resistance of the inbred plants to the bacterial pathogen and b) if inbred plants serve as epicenters for the spread of diseases within the population.

KEY WORDS: herbivory, inbreeding depression, mating systems, trophic interactions