Examining sex allocation in Tamalia coweni (Hemiptera: Aphididae) in response to nutrient variability in Arctostaphylos patula. Colin Purdy and Donald Miller; Department of Biological Sciences, California State University Chico, Chico Ca.

Aphids have been shown to invest differentially in male and female offspring. Previous findings indicate the aphid foundresses of the gall-forming aphid Tamalia coweni actively manipulate offspring sex ratios, in accordance with the Trivers-Willard hypothesis of condition-dependent sex allocation. Nitrogen is a key nutrient in terrestrial systems limiting growth and reproduction in many insects. By manipulating nitrogen levels in the host-plant Arctostaphylos patula it is predicted that in response to increased nitrogen, T. coweni will preferentially invest in female offspring. Further, as larger individuals tend to be produced in favorable environmental conditions and larger females possess greater fecundity in T. coweni, broods under optimal conditions will be not only female biased but have larger individuals. It is hypothesized that increased foliar nitrogen in A. patula will result in offspring sex ratios favoring females as a result of sex allocation in T. coweni. The goal of this research is to better understand this aphid host-plant relationship and specifically to test directly the Trivers-Willard hypothesis of conditional sex allocation in T. coweni.