Controlling mosquitoes as a labor of Hercules: Timing of mortality of larvae and production of adult Aedes albopictus

Overcompensatory mortality occurs when an additional source of mortality causes an increase in population (Hydra Effect). One hypothesis that accounts for this postulates that additional mortality eases density-dependent effects on remaining individuals, allowing for greater survivorship. Added mortality occurring prior to density dependent effects is predicted by theory to have a greater chance of creating an overcompensatory response by alleviating density-dependent effects. Moreover, the earlier in the density-dependent stage of development that additional mortality occurs, the more severe the predicted overcompensatory effect.

We tested the prediction that the earlier additional mortality affects a population of Aedes albopictus larvae, the stronger the overcompensatory effect on production of adults and on rate of population increase.  Similar cohorts of 250 larvae were designated as Control (no additional mortality), or received one of 3 controlled mortality treatments (totaling 48.8% cumulative additional mortality): Early (day 2), Late (day 6), Throughout (20% mortality on each of days 2,4,6). Treatment effects on adult males, adult females, and estimated rate of increase were analyzed by ANOVA. Early cohorts produced significantly more adults and females than other treatments (overcompensation). Neither Late nor Throughout treatment cohorts differed significantly from Control cohorts in adult production (compensation).  Our results are consistent with predictions indicating that early mortality of larval Aedes albopictus could yield greater populations of adults, particularly females, which could be detrimental to mosquito control.  These results have implications for how biological, chemical, or genetic control targeting larval mosquitoes should be implemented for maximal effectiveness.