Biochemistry and physiology of overwintering in the mature larva of the pine needle gall midge, Thecodiplosis japonensis (Diptera : Cecidomyiidae) in Korea

Abstract

The pine needle gall midge, Thecodiplosis japonensis, overwinters in the soil as a third instar mature larva. The metabolic and physiological compensations and adjustments during its overwintering and acclimation were studied. Field-sampled larvae in 1997/98 winter showed a significant increase in whole-body trehalose by January (5.71 ± 0.09 vs. 9.41 ± 0.42 mg/g wet weight) along with a more significant decrease in whole-body glycogen (16.25 ± 0.18 vs. 5.65 ± 0.45 mg/g wet weight). Afterwards, there was a partial reconversion of trehalose to glycogen. Moreover, trace amounts of glycerol and steady content of glucose as potential cryoprotectants were found during the overwintering period. Temperature acclimation of field-sampled larvae affects interconversion between trehalose and glycogen. Trehalose accumulation does not affect the larval supercooling capacity. The mean supercooling point of the larvae remained nearly constant at about -20°C over the winter and was unchanged after temperature acclimation. Low temperature survival experiment suggested that the larvae adopt a freeze-avoiding strategy for overwintering.