A survey of dengue viral infection in Aedes aegypti and Aedes albopictus from re-epidemic areas in the north of Thailand using nucleic acid sequence based amplification assay.

Immature stages of Aedes aegypti and Ae. albopictus were collected from 17 dengue re-epidemic areas in Chiang Mai and Lampang Provinces, in the north of Thailand. They were reared to adults and tested for dengue viral RNA by a nucleic acid sequence based amplification assay (NASBA). Of a total of 9,825 Ae. aegypti and 150 Ae. albopictus examined, none of them were found positive for the virus, suggesting that transovarial transmission may be very low in the vector populations and may not play a significant role in the epidemiology of dengue infection in Thailand.

Insecticide susceptibility tests of Anopheles minimus s.l., Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus in northern Thailand.

The susceptibility of Anopheles minimus s.l., Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus to insecticide in northern Thailand was monitored by using the WHO standard susceptibility test. One- to two-day old female mosquitos, which were reared from wild caught females or immature stages, were exposed to discriminating dosages of insecticides for recommended exposure periods, and the 24-hour mortality recorded. The results revealed that, in general, An. minimus s.l. was still susceptible to DDT and permethrin, except in some areas where a slight increase in tolerance to DDT was observed. Ae. aegypti and Ae. albopictus were both highly resistant to DDT, but in some areas the former was also resistant to permethrin and deltamethrin. Cx. quinquefasciatus was resistant to DDT and etofenprox, with a slight increase in tolerance to permethrin, deltamethrin, malathion and fenitrothion. No resistance to lambda-cyhalothrin was detected in any of the species studied.

Trypsin and aminopeptidase activities in blood-fed females Anopheles dirus (Diptera: Culicidae) of differing susceptibility to Plasmodium yoelii nigeriensis.

Midgut proteolytic enzymes contribute to the success or failure of Plasmodium infection of the mosquito. The present study investigated trypsin and aminopeptidase activities in the midgut of two strains of Anopheles dirus selected for susceptibility and refractoriness to Plasmodium yoelii nigeriensis. At intervals of 6 hours following a bloodmeal, the midguts of fully engorged female mosquitos were dissected, homogenized, and assayed for enzyme activity. No differences trypsin activity (nmole/min) were observed between the two strains throughout the course of blood digestion. By contrast, the aminopeptidase activity measured at 0 to 18 hours post-feeding was the same for the two strains, but at 24, 30 and 36 hours significantly less activity was observed in the refractory females. The results suggest neither trypsin nor aminopeptidase plays a role in the limitation of parasite development.