Mortality Sources of Eurosta solidaginis (Diptera: Tephritidae) Inhabiting Single versus Double-Galled Stems of Goldenrod

Abstract

-We compared survivorship and mortality of overwintering Eurosta solidaginis (Diptera: Tephritidae) larvae inhabiting singleversus double-galled stems of goldenrod (Solidago canadensis) in fields around Hamilton, New York, in 1990. Top galls of double-galled stems were significantly smaller in diameter than bottom galls and single galls. Consequently, top-gall larvae suffered a greater rate of parasitism by the chalcid wasp Eurytoma gigantea, but a lower rate of predation by birds, than either bottom-gall or single-gall larvae. However, overall survivorship, both before and after bird predation, did not differ among larvae of the three gall types, suggesting no overall cost or benefit to female flies injecting eggs into previously oviposited stems. Our findings are consistent with the belief that ovipositing female gallflies neither recognize nor avoid nonvirgin goldenrod stems.