Environmental Regulation of Dormancy in the Alfalfa Blotch Leafminer, Agromyza frontella (Diptera: Agromyzidae)

Abstract

Agromyza frontella (Rondani) enter diapause during early autumn in central New York as partially developed pupae in the soil. Diapause is maintained throughout autumn and early winter (September to January), mainly by low temperatures and partly by short daylengths. As autumn progresses, response to these factors diminishes, and by the end of January the thermal maintenance of diapause has ceased. A. frontella continue to respond weakly to photoperiod until late March. After diapause ends, heat accumulation begins when soil temperatures rise above 3.9°C, the theoretical threshold for postdiapause development. Adults emerge in the laboratory when 259 degree-days above 3.9°C have accumulated, and this value predicts closely the emergence of field populations in central New York. These results have important implications for pest management: A. frontella phenology can be predicted reliably by monitoring soil temperatures in both autumn and spring, and temperature can be manipulated either for continuously rearing blotch leafminers or for rapid reactivation of pupae stored in the cold. The strong thermal influence on diapause indicates that A. frontella populations could extend their North American range southward without requiring selection for photoperiodic adaptation.