A field study Examining container breeding mosquitoes’ oviposition choice: Do females become less “choosy” when laying eggs entering diapause?

Background/Question/Methods

Natural selection should favor female insects ovipositing in habitats that maximize the likelihood of their offspring reaching adulthood and reproducing.  Laboratory studies of female container breeding mosquitoes have found that oviposition choice is based on habitat quality and/or future productivity (i.e. presence of conspecifics).  Few field studies have examined seasonal variation in these choices.   The present field study examined the effect of habitat quality, presence of conspecifics, and seasonality on oviposition choice in the female treehole mosquito, Aedes triseriatus.  Using a random block design, females were given the choice of laying eggs in one of 4 containers: HC – high water volume, conspecific larvae present, HN – high water volume, no larvae present, LC – low water volume, conspecific larvae present, and LN – low water volume, no larvae present. Eggs were collected weekly from July 18^th through August 23^rd and counted.   It was predicted that early in the season, when assessment of habitat quality is important for hatching success and female survivorship is high, females will preferentially choose HC containers.  Later in the season, when deposited eggs enter diapause and female survivorship is low, females will reduce their assessment of containers and therefore show no preference between containers. 

Results/Conclusions

A. triseriatus lay eggs that enter diapause beginning the first week of August for this study site’s latitude.  Therefore, egg counts made prior to August 1^st (first 3 weeks) were grouped as pre-diapause and egg counts made after August 1^st (last 3 weeks) were grouped as diapause.  A non-parametric Friedman test was performed to examine the effect of the 4 treatments on egg counts for both pre-diapause and diapause groups.  For the pre-diapause group, there was a significant treatment effect (p<0.001) where females preferred laying eggs in containers where conspecific larvae were present.  Water volume had no effect on oviposition preference (p>0.05).  For the diapause group, there was no treatment effect on egg counts (p>0.05).  This data supports the prediction that females become less “choosy” late in the season.  Early in the season, when adult female mortality is low and immediate assessment of habitat quality is important, females likely assess different containers before preferentially choosing containers with conspecific larvae.  However, late in the season when adult female mortality is high, females likely reduce their risk of dying prior to oviposition by minimizing their assessment between containers and lay eggs in the first container encountered.