Oviposition site choice and subsequent offspring fitness of Aedes aegypti mosquito in short- and long-term detritus accumulation treatments

MONTINI, PEDRO; FISCHER, SYLVIA

La Plata

Congreso; II Congress of the Latin American Society for Vector Ecology; 2022

Universidad Nacional de La Plata

Larval habitats of Aedes aegypti are artificial containers with water, where the larvae depend on the external contribution of plant detritus as a source of nutritional resources. Containers with longer outdoor exposure accumulate more detritus than containers with recent outdoor exposure or some sort of regular maintenance. According to optimal oviposition theory, females lay their eggs in habitats that maximize the fitness of their offspring, i.e., containers of high nutritional quality. The aim of this study was to evaluate the relationship between the selection of oviposition sites by Ae. aegypti females and the subsequent success of the larvae in habitats with different detritus accumulation times. For this, outdoor containers were used, in which detritus were added 2 weeks before starting (short-time treatment: S) and 2, 4, 6 and 8  weeks before starting (long-time treatment: L). Detritus was collected during two weeks  at different sites to represent the natural variability (i.e., each replica accumulated different quantity and quality of detritus depending on its location), then weighed and added to the container. The experiment consisted of two parts: 1) the selection of oviposition sites by females was studied in S and L containers. Here, the number of eggs and the number of eggs per gram of organic detritus were compared between treatments. 2) Larvae were reared at low densities in S and L containers to evaluate success during development. Here, a composite index of performance (λ´) was calculated for each container based on larval survival, time to adult emergence, and female size. The effect of treatments (S, L) and of the amount of organic detritus on λ´ was analyzed. The number of eggs was significantly higher in the L treatment than in the S treatment (mean: 193 and 55 respectively). However, since the L containers collected on average 4 times more organic detritus than the S containers, the number of eggs per gram of organic detritus was similar in both treatments. The performance in the containers was positively affected by the amount of organic detritus collected. No significant effect of treatment was detected, although a slightly higher developmental success in S than in L was observed. The higher number of eggs in the L treatment suggests a preference of females for laying eggs in containers with longer detritus accumulation time. However, at the low and constant densities used in this experiment, no differences in performance were detected between treatments. At larval densities related to the number of eggs actually laid, a worse performance would be expected in the most selected treatment, what should be addressed in future studies. The results of this study suggest that female selection of oviposition site may contribute to larval crowding and play a role in population regulation.