Inability of Diapausing Culex Pipiens (Diptera: Culicidae) to Use Blood for Producing Lipid Reserves for Overwinter Survival

Diapausing Culex pipiens L. females fed 10% sucrose for 7 d following eclosion contained significantly more lipids (P less than 0.05) than nondiapausing females reared and maintained at the same temperature (22 degrees C) but at a longer photophase (14:10 [L:D] instead of 9:15). Diapausing females with limited lipid reserves failed to increase their reserves after blood feeding. The average lipid content of 56 females tested decreased significantly (P less than 0.05) by day 6 after feeding and there was no correlation (r = -0.06) between lipid content at this time and original bloodmeal volumes of individual females. These results refute the contention that blood meals taken by diapausing Cx. pipiens result in fat body development when females are incubated at 18 degrees C during bloodmeal digestion. Diapausing Cx. pipiens with limited lipid reserves were unable to obtain sufficient energy from a single blood meal to survive extended hibernation. Although none became gravid, only 50% remained alive after 20 d in hibernation. In contrast, nonblood-fed females fed only 10% sucrose for 7 to 10 d before being placed in hibernation on a water diet survived for 6 mo with only 50% mortality. There was no evidence for gonotrophic dissociation. Failure of blood-fed, diapausing females to initiate vitellogenesis was correlated with the significantly smaller blood meals taken by most diapausing females and not with hypertrophy of the fat body or temperature during digestion.