Behavioral responses of malaria vectors, Anopheles minimus complex, to three classes of agrochemicals in Thailand.

Behavioral responses of two wild-caught populations of Anopheles minimus complex, species A and C, exposed to operational field doses of three commonly used agricultural insecticides, carbaryl (carbamate), malathion (organophosphate) and cypermethrin (pyrethroid), were characterized using an excito-repellency test system. Test populations were collected from different localities in Kanchanaburi Province, western Thailand. Both populations showed strong irritancy by quickly escaping test chambers after direct contact with individual surfaces treated with each insecticide compared with match-paired untreated controls. Noncontact repellency response to cypermethrin and carbaryl was significantly pronounced in both A and C populations, but comparatively weak when exposed to malathion. Noncontact repellency produced much weaker escape response in both populations, but in some species-chemical combinations, it remained significant compared with controls. We conclude that contact irritancy is a major behavioral response of both A and C when exposed directly to any of the three compounds, whereas only cypermethrin produced a significant repellency response in species A.

Susceptibility and avoidance behavior by Culex quinquefasciatus Say to three classes of residual insecticides.

The behavioral responses ofthree colonized strains of Culex quinquefasciatus, two from recent field collections in Thailand (Nonthaburi and Mae Sot) and one from a long-established colony from the National Institute of Health (NIH), Ministry of Public Health, Thailand, were compared during and after exposure to deltamethrin (0.02 g/m2), propoxur (0.2 g/m2), and fenitrothion (0.2 g/m2) using an excito-repellency escape chamber system. We observed striking differences in behavioral response and excito-repellency between mosquito strains and test compounds. Greater escape responses were observed in the NIH strain during direct contact with deltamethrin and fenitrothion compared with the two field populations. Deltamethrin was the most irritant, followed by fenitrothion. Escape responses with propoxur were significantly delayed but increased slightly towards the end of the 30-min exposure period, more notably in the Nonthaburi strain (P < 0.05). Non-contact repellent responses were generally much weaker than irritancy, with the greatest escape response seen with NIH and Nonthaburi. Deltamethrin showed the weakest repellent response overall (< 10% escape), while propoxur again demonstrated a delayed effect (NIH and Mae Sot) before escape occurred. We conclude that irritant and repellent behavioral responses by Cx. quinquefasciatus are important components for assessing the impact of residual spraying in mosquito control programs. A better understanding of chemical properties that elicit behavioral responses in mosquitoes should be considered in formulating control strategies designed to control mosquitoes or mitigate disease transmission risk.

Ten species of Culicoides Latreille (Diptera: Ceratopogonidae) newly recorded from Thailand.

A survey of biting midges in animal sheds, mangroves and beaches along the Andaman coastal region in southern Thailand between April 2012 and May 2013 collected 10 species of Culicoides which were not previously known from Thailand. These new records are C. arenicola, C. flavipunctatus, C. hui, C. kinari, C. kusaiensis, C. parabubalus, C. quatei, C. spiculae, C. pseudocordiger and C. tamada. An updated checklist of species of Culicoides reported from Thailand is provided.