Effects of cyromazin and methoprene on the developmental stages of Anopheles dirus, Aedes aegypti and Culex quinquefasciatus (Diptera : Culicidae).

The effects of two chemical compounds, cyromazin and methoprene, on the developmental stages of Anopheles dirus, Aedes aegypti and Culex quinquefasciatus were investigated under laboratory conditions, with the mean temperature of 24 degrees +/- 1 degree C and the relative humidity at 65-75%. Both compounds were tested against the second, third and fourth instar larvae. The concentrations of cyromazin used for An. dirus and Cx. quinquefasciatus ranged from 0.0008 to 0.5 mg/l; and for Ae. aegypti from 0.004 to 2.5 mg/l. The concentrations of methoprene used for An. dirus, Ae. aegypti and Cx. quinquefasciatus ranged from 0.00016 to 0.1 mg/l. The mortality rates were found to be relatively high in larval and pupal stages when treated with cyromazin and methoprene. The primary toxic effects of cyromazin were on the second stage larvae. The LC50 values for cyromazin on the second, third and fourth stage larvae were, respectively, 0.0027, 0.0042 and 0.0114 mg/l for An. dirus, and 0.1662, 0.2307 and 0.3005 mg/l for Ae. aegypti. Cx. quinquefasciatus was the most sensitive species to cyromazin with LC50 values for second, third and fourth stage larvae of 0.0015, 0.0068 and 0.0130 mg/l, respectively. The primary toxic effects of methoprene were in the fourth stage larvae. The LC50 values for methoprene on the second, third and fourth stage larvae were, respectively, 0.0110, 0.0041 and 0.0022 mg/l for An. dirus, and 0.0077, 0.0034 and 0.0025 mg/l for Ae. aegypti. Cx. quinquefasciatus was the most sensitive species to methoprene, with LC50 values for second, third and fourth stage larvae of 0.0013, 0.0008 and 0.0006 mg/l, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Field studies on the bionomics of Bithynia siamensis siamensis and the transmission of Opisthorchis viverrini in Bangna, Bangkok, Thailand.

A field study on the bionomics of Bithynia siamensis siamensis and the transmission patterns of Opisthorchis viverrini was carried out in Bangna, Bangkok, Thailand, from May 1975 to April 1976. Snail populations were found to fluctuate according to rainfall. During the high rainfall period where snail habitats were deep, snail populations recovered at the water surface were higher than those recovered on the mud bottom; during the low rainfall perod where snail habitats were shallow, snails were both found copiously at the water surface and on the mud bottom. Snails infected with O. viverrini occurred almost all year round, with an overall infection rate of 1.6% (46/2800).