Forced egg retention induced by diethyl-phenylacetamide diminishes the fecundity and longevity of dengue vectors.

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.

Behavioral and electrophysiological responses of Culex quinquefasciatus to certain fatty acid esters.

Oviposition response of gravid Culex quinquefasciatus females to a series of synthetic fatty acid esters was evaluated at 10ppm under laboratory conditions. Octyl tridecanoate and propyl octadecanoate elicited 85% and 73% increased ovipositional responses respectively, compared to control, among the 16 esters tested. Other 14 esters showed highly significant repellency (67-96%) to gravid females. Standard 3-methyl indole received 69% increased egg deposition compared to control. In the Y-tube olfactometer, gravid C. quinquefasciatus females exhibited 78, 64% and 58% orientation respectively to octyl tridecanoate, propyl octadecanoate and 3-methyl indole. Gravid females exhibited 19-41% reduced orientation toward treatment odors of other esters significantly different from respective control. Electroantennogram studies revealed 4-18-fold increased antennal response, in which 3-methyl indole, octyl tridecanoate and propyl octadecanoate elicited 8-, 18- and 15-fold EAG response respectively, compared to control. Relative EAG response of octyl tridecanoate compared to standard 3-methyl indole was significantly different. Reduced EAG responses were elicited by FAE-06, -08, -13, -14 and -15, while the relative EAG responses of other esters were at par with the standard stimulus. These, esters could be utilized potentially as oviposition attractants and repellents against C. quinquefasciatus females to reduce the breeding in polluted water along with existing integrated vector control methods.

Electroantennogram, flight orientation and oviposition responses of Anopheles stephensi and Aedes aegypti to a fatty acid ester-propyl octadecanoate.

Studies were carried out to evaluate the role of a C(21)-fatty acid ester; propyl octadecanoate (PO) for olfaction-mediated behavioral responses of urban malaria vector, Anopheles stephensi and dengue vector, Aedes aegypti mosquitoes using electroantennogram (EAG), flight orientation and oviposition experiments. Dose dependent electrophysiological responses were recorded for PO from the antenna of both mosquito species in which 10(-5) g elicited significant EAG response. An. stephensi exhibited 2.4, 4.2 and 5.5 fold increased EAG response compared to control, while Ae. aegypti showed 1.9, 4.6 and 5.8 fold EAG responses respectively at 10(-7) g, 10(-6) g and 10(-5) g doses. In the Y-tube olfactometer, 77-80% gravid females of An. stephensi, and 64-77% of Ae. aegypti were caught in the chambers releasing 10(-6) g and 10(-5) g plume of PO. The synthetic fatty acid ester loaded onto an effervescent tablet at 0.1 mg/L, 1 mg/L and 10 mg/L elicited increased ovipositional responses from gravid mosquitoes compared to control. The oviposition activity indices (OAI) of An. stephensi females were +0.40, +0.51 and +0.58, whereas the OAI for Ae. aegypti females were +0.05, +0.36 and +0.57 respectively in 0.1, 1, 10 mg/L of PO; indicated concentration dependent increased egg deposition. Similarly, in the residual activity studies, oviposition substrates treated with PO on effervescent tablet at 1mg/L and 10mg/L received significantly increased egg deposition by gravid females of both mosquito species for up to 1 week compared to control substrates. PO can potentially be used in ovitraps to monitor An. stephensi and Ae. aegypti populations in the vector surveillance programs.