A Comparison of Attractants for Sampling Stomoxys calcitrans (Diptera: Muscidae) on Dairy Farms in Saraburi Province, Thailand.

The efficacy of different stable fly attractants was evaluated at four dairy cattle farms in Muak Lek district, Saraburi province, Thailand. Dry ice, octenol, a mixture of cow dung and urine, a combination of dry ice plus octenol, and no attractants (control) were tested with Vavoua traps. In total, 7,000 individuals of Stomoxys species were collected between July 2013 to September 2014, of which 1,058, 867, 1,274, and 3,801 were trapped on farms 1­4, respectively. Four species of Stomoxys were identified: Stomoxys bengalensis Picard, 1908, Stomoxys calcitrans (L., 1758), Stomoxys indicus Picard, 1908, and Stomoxys sitiens Rondani, 1873. S. calcitrans was the predominant species, comprising 99% of all the samples collected. The number of male and female S. calcitrans collected differed significantly by attractant type. Significantly more S. calcitrans were attracted to dry ice or a combination of dry ice plus octenol-baited traps than to unbaited or octenol-baited traps. The Vavoua traps baited with dry ice alone or a combination of dry ice plus octenol were effective attractants for S. calcitrans.

Insecticide-induced behavioral responses of Anopheles minimus, a malaria vector in Thailand.

This study was designed to determine the behavioral responses of 2 test populations of Anopheles minimus females to DDT at 2 g/m2, deltamethrin at 0.0625 g/m2, and lambdacyhalothrin at 0.0369 g/m2 using an improved excito-repellency escape chamber. One test population was colonized in 1993 and referred to as a young colony. The 2nd field test population was collected from Ta-Soa County, Tri-Yok District, Kanchanaburi Province. in western Thailand and referred to as a wild population. Results showed that females of both young and wild test populations rapidly escaped from direct contact with DDT, deltamethrin, and lambdacyhalothrin. Lambdacyhalothrin exhibited the strongest irritant effect on female mosquitoes, followed by DDT and deltamethrin. Fewer females escaped from test chambers without direct contact with treated surfaces but the response was significantly different from that of the controls (P < 0.05). The noncontact response is indicative of a noncontact repellent action. Both contact irritancy and noncontact repellency are involved in An. minimus escape responses. Experimental hut studies that include monitoring of house-entering populations of An. minimus are needed for a meaningful assessment of noncontact repellent actions.

Effects of nutritional and physiological status on behavioral avoidance of Anopheles minimus (Diptera: Culicidae) to DDT, deltamethrin and lambdacyhalothrin.

The monitoring of behavioral responses of mosquitoes to insecticides are critical to the understanding of how chemicals function in the control of disease transmission. The excito-repellency avoidance responses of laboratory-reared Anopheles minimus females exposed to diagnostic concentrations of DDT (2 g/m2), deltamethrin (0.0625 g/m2), and lambdacyhalothrin (0.0369 g/m2) were observed using an excito-repellency escape chamber. Insecticide contact (measuring irritancy) and non-contact (measuring repellency) behavioral assays were conducted on non-blood-fed (unfed), sugar-fed, early blood-fed (recently engorged) and late blood-fed mosquitoes. Rates of escape from the contact and non-contact chambers, regardless of chemical compounds, were most dramatic in unfed mosquitoes compared to other nutritional states (P < 0.05). In general, across all 3 chemicals, slower escape response was observed in sugar-fed and early blood-fed specimens, whereas late blood-fed showed an intermediate response. Relative suppression of escape flight response in comparison to matched non-insecticide treated controls and the unfed condition is likely the result of normal reduced flight activity among recent blood and sugar-engorged mosquitoes. We conclude that nutritional states and physiological conditions of mosquitoes as a result of blood feeding can dramatically influence excito-repellency test results. Therefore, for interpretive purposes, studies on chemical irritancy and repellency must account and control for the inherent variability of avoidance responses to insecticides influenced by nutritional and physiological conditions of the mosquitoes at the time of test.