Relationship of cold tolerance to developmental determination in the Indian meal moth, Plodia interpunctella (Lepidoptera : Phycitidae)

Abstract

Diapause and non-diapause larvae of Plodia interpunctella from two selected lines, fast development (FDL) and slow development (SDL), reared at 20°C and 25°C were tested for low temperature tolerance, supercooling ability and accumulation of cryoprotective compounds. Exposure to -20°C was fatal for both diapause and non-diapause larvae. Diapause larvae, particularly those reared at 20°C, were more tolerant to -10°C than non-diapause larvae. Their higher survival under increased exposure periods indicates that the chilling tolerance in P. interpunctella is associated with diapause. Rearing temperatures did not affect the supercooling capacity of the larvae, since the supercooling points (SCPs) of the diapause and non-diapause larvae reared at 20°C and 25°C did not differ ; mean SCPs ranged from -12°C to -15°C. Trehalose was the major cryoprotective compound synthesized by the larvae. Photoperiod and temperature affected the accumulation of trehalose as diapause larvae reared at 20°C (LD 12 : 12) had significantly higher concentrations of trehalose than non-diapause larvae at 20°C and diapause and non-diapause larvae at 25°C. Low temperature (5°C) exposure for 30 days enhanced the supercooling ability of diapause larvae reared at 20°C by decreasing the SCP to ca. -22°C. The results suggest that diapause larvae can overwinter successfully in a supercooled state. Acclimation did not increase trehalose concentration. This leads to the conclusion that the regulation of supercooling in P. interpunctella is independent of trehalose concentration. Diapause and non-diapause larvae from the two selection lines did not differ in SCP, concentration of cryoprotectants, or rate of survival at low temperature.