Low Temperature Duration and Adult Rearing Regimes Affect Eclosion of Rhagoletis indifferens (Tephritidae: Diptera).

Western cherry fruit fly, Rhagoletis indifferens Curran, is a quarantine pest of sweet cherries in the Pacific Northwest of the United States that overwinters as diapausing pupae. Eclosion responses of R. indifferens puparia to different low temperature durations and postdiapause conditions affect the pest status of the fly. Here, we determined the effects of holding R. indifferens puparia at 3°C for 0, 1, 2, 5, 10, 15, and 20 wk on adult eclosion times and rates at two simulated temperate and two simulated tropical climate treatments over 40 wk. When puparia were chilled 0, 1, or 2 wk, adult eclosion across the four climate treatments displayed a bimodal distribution with low eclosion at 3 wk and high eclosion at 23-35 wk. When puparia were chilled ≤ 10 wk, there was a weaker bimodal distribution. However, when puparia were chilled 15-30 wk, eclosion was more synchronous and occurred at 5-7 wk across the four postchill climate treatments. Eclosion was greater at a postdiapause temperature of 26°C than 23°C. Timing to 50% eclosion was faster at longer photoperiod (16:8 L:D) than shorter (12:12 L:D). The bimodality of eclosion in respect to the duration of low temperature exposure may be indicative of univoltine insect species with obligate diapause that may span over two seasons.