Yeast Extract: Sucrose Ratio Effects on Egg Load, Survival, and Mortality Caused by Gf-120 in Western Cherry Fruit Fly (Diptera: Tephritidae)

Abstract

It is unclear which ratios of yeast extract to sucrose result in maximum egg production and survival in many tephritid fruit flies. Objectives here were to determine yeast extract:sucrose ratios that maximize egg loads without compromising survival in western cherry fruit fly, Rhagoletis indifferens Curran, and their effects on mortality caused by spinosad bait (GF-120). Yeast extract:sucrose ratios of 20:80 and 30:70 maximized egg loads without reducing survival in most cases. In 1 experiment, mortality of flies with low to high egg loads exposed to fresh GF-120 for 1 or 2 h in the absence of food did not differ. In a separate experiment, egg loads were lowest in flies fed 0:100 and 1:99 diets and highest in flies fed 20:80, 30:70, and 50:50 diets. When these flies were exposed to dried GF-120 for 6 h in presence of yeast extract and sucrose, percent mortality was lower in flies fed 20:80 and 30:70 (40%) than 0:100 (69%) and 1:99 (63%) diets. In another experiment, egg loads were lowest in flies fed 0:100 and 1:99 diet and highest in flies fed 20:80 diet. When these flies were exposed to dried GF-120 for 6 h in the presence of sucrose only, percent mortality was lower in flies fed 20:80 (39%) than 0:100 (72%) and 1:99 (62%) diets. High yeast extract:sucrose ratios result in high egg loads in R. indifferens and may reduce the fly's feeding responses to GF-120, although not to the extent that the bait is rendered completely ineffective.