Background & objectives: Oviposition is an important event in the life cycle of mosquito which is a decisive factor for the fate of its progeny. If oviposition is prevented, the life cycle of mosquito is disrupted and the population growth can be reduced. Diethyl-phenylacetamide (DEPA) is an effective topical repellent against various haematophagous insects. The study reports the egg retention effect and subsequent lethal effect of DEPA on the gravid females of Aedes aegypti and Ae. albopictus mosquitoes.
Methods: DEPA was applied at 1000 mg/l onto water surface in oviposition bowls under no-choice condition. Experiments had three replicates with three control and treated cages separately, containing 100 gravid females of each test mosquito species. Every day freshly treated oviposition bowls were provided to the gravid mosquitoes till the last surviving female of the cohort was dead. On completion of one experimental day (24 h) the number of eggs laid in control and treatment bowls were counted manually to assess the oviposition response and longevity of test mosquito species.
Results: DEPA at 1000 mg/l concentration reduced the egg deposition and affected the longevity of gravid females. In the DEPA treated cages >1100 eggs were retained by both the species. In the treated cages, about 50% of Ae. albopictus and 41% of Ae. aegypti females died, retaining eggs in their abdomen. The average life span of Ae. aegypti and Ae. albopictus females in control cages were 43 and 50 days respectively, while the females of both the species exposed to DEPA in treated cages survived for 16-22 days.
Interpretation & conclusion: Presence of DEPA odor on water surface forced the gravid Aedes females to retain their eggs, affecting their fecundity and longevity. This indigenously developed topical repellent DEPA may be applied to container's water that act as breeding grounds for dengue vectors to deter gravid females from oviposition in the vicinity of a household.