MITOCHONDRIAL-ENZYMES DURING OVERWINTERING IN 2 SPECIES OF COLD-HARDYGALL INSECTS

Larvae of two cold-hardy insects, a freeze tolerant Eurosta solidagini s and a freeze avoiding Epiblema scudderiana species, were sampled at different times over a winter season and the activities of three mitoc hondrial enzymes were measured. Citrate synthase (CS), glutamate dehyd rogenase (GDH), and NAD-isocitrate dehydrogenase (NAD-IDH) activities all decreased by 50% over the mid-winter compared with autumn values. In Eurosta solidaginis all activities returned to initial values by mi d-April, but decreased again in late April when the larvae pupated. In Epiblema scudderiana, activities of GDH and NAD-IDH increased in the spring, but CS activity remained relatively unchanged from mid-winter on. To determine the influence of temperature alone on enzyme activiti es, mid-October larvae acclimated to -4 or 15 degrees C were compared; results showed greater activity of NAD-IDH at 15 degrees C than at -4 degrees C in Eurosta solidaginis (P < 0.05 by the Student's t-test), but a lower activity of GDH in Epiblema scudderiana at 15 degrees C (P < 0.05). Other enzyme activities were unchanged by acclimation. Reduc ed activities of mitochondrial enzymes in mid-winter are consistent wi th winter dormancy of these species, and could reflect lower mitochond rial numbers at this time. The regulation of these seasonal changes ap pears to be largely a response to cues other than short-term temperatu re acclimation,