ABSTRACT
Egg retention and oviposition behavior of four species of mosquito vectors viz., Anopheles stephensi, Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus to a topical insect repellent diethyl-phenylacetamide (DEPA) at 0.1-1000 mg/L was investigated under laboratory conditions. Based on oviposition activity indices, DEPA demonstrated concentration dependent oviposition deterrent effect to A. stephensi (-0.18 to -0.97), A. aegypti (-0.18 to -0.91) and A. albopictus (-0.50 to -0.98) females. In contrast, positive oviposition response by C. quinquefasciatus (+0.39 and +0.70) was observed respectively at 0.1 and 1 ppm, while 10 ppm of DEPA on water received 50% lesser egg rafts than control. Gravid Culex females laid no egg rafts at 100 and 1000 ppm DEPA treated bowls effecting 100% oviposition deterrence. Test mosquito females deposited most of their eggs (>90%) in the absence of repellent odour, while DEPA odour on water surface forced them to retain huge numbers of eggs. Females of A. aegypti, A. albopictus and A. stephensi retained 49, 67 and 50% of total eggs, respectively throughout the experiment. Egg retention by Culex females due to DEPA on the water surface was ca. 65%, equivalent to 4 egg rafts. Therefore, DEPA at lower concentrations could effectively disturb the oviposition by these vectors. Application of repellents in small water bodies would help in reducing the population build up of mosquitoes near human households and could be useful in the integrated management of mosquito vectors.
ABSTRACT
Background & objectives: The sensilla and sensory mechanism play a significant role in hostseeking and oviposition behaviour of mosquitoes, which enable them to transmit various diseases to humans. Aedes albopictus (Skuse) has emerged as a major vector of Chikungunya virus in the recent epidemics in most parts of southern India. Studies on the sensory structures of dengue vector, Aedes aegypti (Linn) are comprehensive; whereas information on the sensillary systems of Asian tiger mosquito, Ae. albopictus is inadequate. Therefore, the present study has been carried out to observe various types of sensilla located on the antenna, maxillary palp, labial palp, tarsi and ovipositor of Ae. albopictus using scanning electron microscopy. Methods: The antennae, maxillary palpi, labellum, tarsi and ovipositor of 10 different female mosquito of Ae. albopictus were fixed individually in 2.5% glutaraldehyde solution, washed twice and dehydrated with ascending grades of ethanol. Samples were cleared with xylene, air-dried, mounted on stubs, gold coated in an ion-sputtering unit and the sensilla were viewed between 5 and 10 KV using FEI-Quanta 400–EDAX scanning electron microscope. ANOVA revealed significant differences in the morphometric features of various sensilla. Results: In the antenna Sensilla trichoidea are numerously distributed in all flagellar segments revealed four distinct subtypes. Two types of grooved peg sensilla were observed. Sensilla coeloconica was observed in the terminal flagellum of antenna and tarsomeres with large variation in diameter. Sensilla chaetica are distributed throughout the body and revealed greater variation in morphology and morphometric parameters. Interpretation & conclusion: The significant difference among various types of sensilla would possibly reveal their functions. The porous sensilla are olfactory and contact chemoreceptors while the aporous sensilla would play the role of mechanoreception. Sensilla coeloconica on the antenna, tarsus showed major differences with Ae. aegypti. The ovipositor sensilla revealed three types of chaetica arranged in rows but has not been reported earlier with other mosquito species.