BIOCHEMISTRY AND PHYSIOLOGY OF OVERWINTERING IN THE MATURE LARVA OF THE RED SUNFLOWER SEED WEEVIL, SMICRONYX-FULVUS LECONTE (COLEOPTERA, CURCULIONIDAE)

The red sunflower seed weevil, Smicronyx fulvus LeConte, overwinters in the soil as a mature fifth-instar larva. A strong correlation exists between minimum daily soil temperatures and trehalose accumulation. Larvae buried in the field in September 1988 showed a two-fold increase in whole-body trehalose levels by January (21.0 +/- 0.6 vs 40.1 +/- 0.6-mu-g/mg wet wt). During this period of trehalose accumulation, glycogen levels fell from 17.9 +/- 1.4 to 2.7 +/- 0.6-mu-g/mg wet wt. There is a partial reconversion of trehalose to glycogen with the onset of spring; trehalose levels dropped while glycogen levels increased. Trehalose accumulation does not affect the supercooling capacity of the larvae. The mean temperature of crystallization of the larvae remained constant at about -24-degrees-C from September to June and was also unchanged with temperature acclimation. Respiratory rates fell from 0.65-mu-l/h/mg in September to 0.29-mu-l/h/mg in January. Larvae collected in September 1989 and acclimated to 0-degrees-C for 7 days also had increased trehalose levels with a concomitant reduction in glycogen. Early autumn larvae subjected to -5-degrees-C for 7 days had a survival of 96%. However, only 28% of the larvae collected from containers buried in the field in November survived 1 day at -15-degrees-C and none survived 1 day at -20-degrees-C. Under the conditions tested the larvae do not appear to be freeze-tolerant.