Differences in body size and egg loads of western cherry fruit fly (Rhagoletis indifferens) from introduced sweet and native bitter cherries

Western cherry fruit fly, Rhagoletis indifferens Curran, infests fruit of introduced sweet and pie cherry, Prunus avium (L.) L. and Prunus cerasus L., respectively, and native bitter cherry, Prunus emarginata (Douglas ex Hook.) D. Dietr., in the western United States. Sweet and pie cherry fruit are larger than bitter cherry fruit and this along with other factors could affect body size, which is important because fly size and egg load or fecundity in tephritid fruit flies are correlated. In this study, we hypothesized that flies established in sweet/pie cherries are larger than those in bitter cherries and have higher egg loads. In studies of flies from multiple sites in Washington and Montana, puparia and adults reared from sweet/pie cherries were larger than those from bitter cherries. Flies caught on sticky yellow panel traps in sweet/pie cherry trees were larger than flies caught in bitter cherry trees and had higher egg loads. When offered four diets with 0 to 20% yeast extract mixed with sucrose in the laboratory, flies reared from sweet cherry on average always had higher egg loads than flies reared from bitter cherry. Puparia of flies from bitter and sweet cherry that developed from larvae in sweet cherry did not differ in size, suggesting body size differences in R. indifferens from sweet and bitter cherries are environmentally induced.