The influence of temperature and photoperiod on the reproductive diapause and cold tolerance of spotted-wing drosophila, Drosophila suzukii

Knowledge regarding the reproductive status of spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is of critical importance in predicting potential infestations of this invasive pest, as eggs are laid in ripe or ripening fruit of several commercially important small-fruit crops. Token environmental stimuli for the induction of reproductive diapause and improved cold tolerance were identified for D.suzukii. Diapause induction was evaluated by assessing, via dissection, the number of mature eggs carried by field-captured D.suzukii and laboratory-reared D.suzukii held under various temperature and photoperiod regimes. Egg load decreased over time in females trapped from July to December at sites in Benton County, OR, and Ontario County, NY, both USA, and reached zero eggs by December at all sites. Photoperiods below 14h of day length led to reduced egg maturation in laboratory-reared flies held at moderate temperatures (15 or 20 degrees C). Whereas very few mature eggs were found in females held at 10 degrees C under short- or long-day photoperiods for several weeks after eclosion, a spontaneous return to ovarian maturity was observed in short-day-entrained females after 7weeks. Diapause termination was investigated by evaluatingfecundity in diapausing females returned to optimal environmental conditions. Whereas long-day-entrained flies began producing offspring immediately upon return to optimal conditions, short-day-entrained flies returned after 1 and 6weeks at 10 degrees C were slower to produce offspring than colony flies or short-day-entrained flies returned after 7weeks. Cold tolerance was evaluated by observing chill coma recovery rates after 24h exposure to -1 degrees C. Cold-acclimated (diapausing) females recovered from chill coma faster than cold-hardened or unacclimated females.