Laboratory & field evaluation of controlled release formulation of the insect repellents N,N-diethyl-m-toluamide (DEET) & N,N-diethyl phenylacetamide (DEPA) against mosquito vectors.

BACKGROUND & OBJECTIVES: Repellents can play a useful role in reducing the man-vector contact and help in interrupting disease transmission. Newer formulations are necessary to improve the efficacy of the repellent on the treated sites for enhanced protection. METHODS: To determine the comparative efficacy, 20 per cent liposphere lotion formulation and 20 per cent alcohol solution of two insect repellents DEET and DEPA were evaluated for the extent of protection on rabbits against Aedes aegypti during the day in the laboratory and on human volunteers during the night against Culex quinquefasciatus in the urban areas of Pondicherry, India. RESULTS: In the laboratory, the lotion formulations of DEPA and DEET were found to enhance the repellency by 1.5 (4.00 to 6.00 h) and 1.25 (4.00 to 5.00 h) times respectively compared to the alcohol solution of the repellents against Ae. aegypti at the application rate of 0.5 mg/cm2. In the field, the lotion formulation of DEPA at 0.3 mg/cm2 could increase the protection time from 6.30 to 8.36 h (1.3 times) whereas the lotion formulation of DEET at 0.3 mg/cm2 could increase the protection time from 6.54 to 8.42 h (1.2 times). INTERPRETATION & CONCLUSION: In laboratory and field tests, the lotion formulations of both repellents were found to give a higher protection compared to alcohol solution. The lotion formulations of DEET and DEPA were found to be equally effective.

Effects of a juvenoid, DPE-28, on biology and behaviour of Culex quinquefasciatus, the human filariasis vector.

Studies on the effect of a juvenoid, DPE-28 (2,4-dinitrophenyl-2',6'-di-tertiarybutyl phenyl ether) on biology and behaviour of Cx. quinquefasciatus showed that the developmental duration, sex ratio, mating success and blood feeding were considerably affected by the exposure of larvae and pupae to the compound. Exposure of fourth instar larvae to 0.007 (EI90) and 0.0019 (EI50) ppm of DPE-28 prolonged the duration of pupation by 58.6 and 52.4 hr and delayed the adult emergence by 35.4 and 17.7 hr in males and 36.8 and 21.1 hr in females respectively. Exposure of freshly ecdysed pupae to 10 and 5 ppm delayed the adult emergence with respect to the control by 54.3 and 32.4 hr in males and 55.2 and 33.2 hr in females respectively. The sex ratio of the adults emerged from treated larvae and pupae was also affected. The female mosquitoes that survived from the exposed fourth instar larvae and pupae exhibited a low blood engorgement ratio. This depression in blood feeding was more pronounced in adults emerged from treated pupae than that of treated fourth instar larvae. A significant proportion of adults emerged from treated larvae and pupae were able to feed only partially. Mating success of the treated populations declined considerably when crosses were made between the males and females emerged from treated fourth instar larvae and pupae. The adults emerged from treated larvae and pupae showed a significant reduction in the oviposition.