The quantity of total lipids in Culex tarsalis Coquillett (Diptera: Culicidae) under laboratory and field conditions in Manitoba
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The most characteristic feature of overwintering insects is the accumulation of a large lipid reserve prior to the overwintering period. These reserves of metabolizable energy ensure that the insect will survive prolonged periods of metabolic activity without feeding. Culex tarsalis Coquillett overwinters as an inseminated, nulliparous adult. The objective of this study was to identify the various environmental factors affecting lipid accumulation and depletion in the summer generations and in overwintering females. The total lipid content of adult Cx. tarsalis females was determined using Van Handel's (1985) colorimetric assay. The use of soybean oil as a standard to determine total lipid content provided an accurate and reliable representation of total lipids in mosquitoes. The total lipid content of newly emerged, fed and starved Cx. tarsalis females indicated that lipids increased with sucrose feeding. The baseline lipid level (ie. starved to death), representing all non-nutritional and structural lipids was 104 ug total/female. The relationship between temperature, development and lipid content was investigated to determine the duration of larval development at different constant temperatures, the upper and lower thresholds of development and the relationship between temperature and the lipid content of newly emerged females. These results indicated that the low temperature theshold for Cx. tarsalis development was 14oC and the upper threshold was 34oC or above. At low temperatures (ie. 14 and 17oC), an increase in development time and larger quantities of lipid were observed at emergence. At higher temperatures (ie. 25 to 34oC), a decrease in development time and decreased quantities of lipid were observed at emergence. Therefore, temperature significantly affected development time and total lipid content. The relationship between environmental temperature and photoperiod on total lipid content was investigated in 1986 to determine the period of the summer or fall season in which lipid accumulation occurred in natural populations. These results indicate that total lipid content in field population was not closely related to air temperature and development time. Therefore, the possible role of photoperiod was proposed...