BIOCHEMISTRY AND PHYSIOLOGY OF OVERWINTERING IN THE MATURE LARVA OF THE SUNFLOWER STEM WEEVIL, CYLINDROCOPTURUS-ADSPERSUS (COLEOPTERA, CURCULIONIDAE) IN THE NORTHERN GREAT-PLAINS

The sunflower stem weevil, Cylindrocopturus adspersus (LeConte), overw inters as a mature larva at the base of the stalk and in the root crow n of cultivated sunflower plants. Sunflower stalks from fields known t o be infested with C. adspersus larvae were collected in southeastern North Dakota in October 1991. Larvae from stalks kept outdoor accumula ted a high whole-body concentration of trehalose (up to 69 mu g/mg wet wt) at the expense of glycogen with the onset of winter followed by a partial reconversion of trehalose to glycogen with the onset of sprin g. Larvae from stalks acclimated to 0 degrees C also accumulated a hig h level of trehalose (similar to 69 mu g/mg wet wt) with a concomitant decrease in glycogen. Those larvae from stalks kept at 20 degrees C s howed an initial sharp increase in whole-body trehalose that then stab ilized but a concentration well below that of larvae acclimated to 0 d egrees C. This indicates that there exists in the larva an underlying developmental component to trehalose accumulation which is further enh anced by low temperature (0 degrees C) exposure. The mean temperature of crystallization (T-c) of larvae exposed to outdoor conditions showe d an abrupt drop from October (-25.0+/-1.3 degrees C) to November (-28 .2+/0.6 degrees C) with a minimum in February (-29.1+/-0.3 degrees C). The level of trehalose accumulated by the sunflower stem weevil larva is to our knowledge the highest reported in an overwintering insect.