Biological differences in reproductive strategy between the mosquito sibling species Anopheles gambiae sensu stricto and An. quadriannulatus

Females of the afrotropical mosquito species Anopheles gambiae Giles sensu stricto and An. quadriannulatus (Theobald) (Diptera: Culicidae) were studied for the effect of blood meal size and the frequency of blood feeding on reproductive development during the first gonotrophic cycle. To standardize the blood meals, meals were administered by enema in some experiments. The effects of insemination, mosquito size, and metabolic reserves at emergence on egg development were also investigated. Maximum insemination was reached after seven days, varying from 62% in An. quadriannulatus to 95% in An. gambiae and was significantly different (P<0.05) between the two species. Insemination had no effect on feeding success. Females of An. quadriannulatus were significantly larger than An. gambiae females (mean wing size 2.90 +/- 0.01 mm versus 2.82 +/- 0.01 mm), but the protein, glycogen, and lipid content of newly emerged females of the two species were not significantly different. Without a blood meal, larger females of both species were significantly more likely to develop oocytes up to Christopher's stage II. With one blood meal, 27% of An. gambiae became pre-gravid and 73% matured eggs. In contrast, all An. quadriannulatus females remained in the pre-gravid stage following ingestion of one blood meal. Vitellogenesis was significantly reduced in smaller-sized pre-gravid An. quadriannulatus compared to larger individuals. When given the opportunity to feed up to three times on three successive days, all females of An. gambiae matured eggs but only 85% of An. quadriannulatus did so. When 1 microliter of human blood was administered by enema, none of the females of either species developed eggs. With a single enema of 1.5 microliter of human blood, only An. gambiae developed eggs. A similar result was observed with 1 microliter and 1.5 microliter enemas of bovine blood although some An. gambiae also developed eggs with 1 microliter of blood. Anopheles quadriannulatus developed eggs only when given two 1 microliter enemas on successive days. However, the percentage of females developing eggs was significantly lower than that of An. gambiae. The implications of these differences in reproductive strategy are discussed in the light of behavioural traits in the field.