Differential water deprivation tolerances of adult Rhagoletis indifferensand Rhagoletis pomonella(Diptera: Tephritidae) as a possible factor affecting their distributional abundances in Washington State, USA

Insects that evolved in mesic regions may have difficulty establishing in xeric regions. Rhagoletis pomonella(Walsh) (Diptera: Tephritidae) was introduced into drier western North America from mesic eastern North America while Rhagoletis indifferensCurran is native to western North America. Here, we predicted that R. indifferenssurvives water deprivation longer than R. pomonella, as R. indifferensis more abundant than R. pomonellain dry central Washington (WA) State, USA. Sweet and bitter cherry-origin R. indifferensand apple- and hawthorn-origin R. pomonellafrom xeric central or mesic western WA were provided water throughout or were water-deprived at 2–4 and 14–18 d old and held at 20°C or 30/31°C and daily survival recorded. At 20°C and 30°C, western WA apple-origin R. pomonellaprovided water survived longer than sweet cherry-origin R. indifferens. When water-deprived, however, 2–4 d old R. indifferens, although smaller, survived significantly longer than western WA apple-origin R. pomonellaof the same age. This was also generally true for 14–18 d old flies, although differences were less often significant. Central WA large-thorn hawthorn-origin R. pomonellasurvived water deprivation significantly longer than western WA apple-origin R. pomonella, and as long as R. indifferens. Water-deprived flies of both species survived longer at 20°C than 30/31°C. Survival analyses suggest that low water availability rather than high temperature contributes to lower R. pomonellathan R. indifferensabundances in central WA, with R. pomonellapopulations in that region differing from western WA R. pomonellawith respect to tolerance of xeric climates.