title: Delayed egg hatching of Anopheles gambiae (Diptera: Culicidae) pending water agitation.
abstract: Mosquito eggs laid on water surfaces typically hatch spontaneously soon after the embryos within them become fully formed first-instar larvae. However, we have found that Anopheles gambiae Giles, an important vector of malaria in Africa, exhibits delayed hatching until the water surface is agitated, a feature overlooked in most laboratory colonies. Agitation within 24 h postoviposition, before embryonation was complete, failed to stimulate delayed postembryonic hatching of isolated eggs on the following day (day 2), when < 1% had hatched spontaneously. However, 5 min of water agitation of these dormant pharate first-instar larvae on day 2 resulted in an almost immediate hatch of 63.3 versus 0% of nonagitated controls, plus another 3.9 versus 0.3%, respectively, during the following 24 h. With daily agitation, installment hatching occurred mainly during 2-6 d postoviposition. The mean cumulative hatch after 7 d of daily agitation was 83.1 versus 1.1% of nonagitated eggs. Experiments with eggs in groups demonstrated that egg density and activity of already-hatched larvae had no stimulatory effect. Eggs stored 1-4 wk at 25.5 or at 15.5 degrees C, and then agitated daily for 6 d at 25.5 degrees C, showed a gradual decline in viability. Viability was sustained longer at the lower temperature. Implications of agitation-induced egg hatching for rainy-season and dry-season ecology of An. gambiae are discussed. Suspended hatching and cool storage already are proving convenient for efficient mass rearing and accurate modeling of weather-based population dynamics.
authors.forename: Babak
authors.initials: B
authors.lastname: Ebrahimi
authors.forename: Sanam
authors.initials: S
authors.lastname: Shakibi
authors.forename: Woodbridge A
authors.initials: WA
authors.lastname: Foster
mesh_terms: D000818:Animals; D000852:Anopheles / Q000254:growth & development / Q000502:physiology*; D007814:Larva / Q000254:growth & development / Q000502:physiology; D009032:Mosquito Control / Q000379:methods; D010063:Ovum / Q000254:growth & development / Q000502:physiology; D012621:Seasons; D013997:Time Factors; D014872:Water Movements