Lower development threshold temperatures and thermal constants for four species of Asphondylia (Diptera: Cecidomyiidae) in Japan and their larval developmental delay caused by heat stress

Abstract

Lower development threshold temperatures (LDT) of gall midges (Diptera: Cecidomyiidae) were directly determined by comparing developmental stages before and after incubation of galls for a definite period under a range of temperatures sufficient to cover the borders of the linear response. The LDT was determined to be 15 and 17 °C, respectively, for the soybean-pod gall midge, Asphondylia yushimai Yukawa and Uechi, and the ampelopsis fruit-gall midge, A. baca Monzen. They are host-alternating multivoltine species, but their LDT did not differ between generations on winter–spring and summer–autumn hosts, supporting the hypothesis that the value of LDT is stable and species specific. Based on the LDT and the 50 % emergence dates (ET50) of an overwintered generation, we estimated the thermal constants from first instars to adults to be 47.4 day-degrees for A. yushimai and 164.9 day-degrees for A. baca. The estimated thermal constant enables A. yushimai to repeat many generations annually, which may support the possibility that the gall-midge infestation range expands every summer and autumn from southern to northern Honshu, where winter–spring hosts have never been detected. The larval development of A. yushimai and A. baca, as well as those of two other univoltine congeners, A. aucubae Yukawa and Ohsaki and A. sphaera Monzen, was delayed at temperatures of 26, 28, or 29 °C. Global warming, when it becomes more prominent, will reduce the number of generations and the survival rate of multivoltine gall midges that spend summer without diapause.