Changes of respiration rate and fatty acid composition in cell membranes of pupae of the large cabbage white, Pieris brassicae (Lepidoptera: Pieridae) during winter

Cell membranes are very sensitive to low temperatures and undergo changes and adaptations to prevent this damage. One of the most common changes is the increase in unsaturated to saturated fatty acids ratio of phospholipids, which leads to increase the fluidity of membranes at low temperatures. In this study, overwintering pupae of the large cabbage white, Pieris brassicae were collected during November 2014 to April 2015. To investigate the metabolic quiescent, changes in respiratory gases (O2 and CO2) and respiration rate (‍CO2/O2) were measured using GC. After extracting the whole body lipids, phospholipids were separated from other lipids by solid phase extraction (SPE) and then fatty acids and their changes were investigated using the GC. Respiration rate decreased about 30% from 0.9 in November to 0.6 in February and March, indicating that metabolism has reached to its lowest level during these period and insect has been in deep pupal diapause. Two 16-carbon and four 18-carbon fatty acids were identified in cell membranes. During winter, the highest decrease was observed in two saturated fatty acids C16: 0 and C18: 0 and the highest increase occurred in C16: 1. In general, unsaturated /saturated fatty acids ratio increased about 40 percent during the winter months. The results indicated that in spite of decreasing metabolism level in the whole body, in order to enhance the cold-hardiness, dynamic changes occurred in cell membranes, allowing insect to adapt successfully to winter hard conditions.