Irritability and repellency of synthetic pyrethroids on an Aedes aegypti population from Thailand

The main objective of this study was to find the optimal dosage of deltamethrin, cyphenothrin, d‐tetramethrin, and tetramethrin that would elicit repellency and irritability responses of Aedes aegypti. The F1‐F3 generations of field mosquitoes collected from Pu Teuy Village, Sai‐Yok District, Kanchanaburi Province, Thailand, were tested with four pyrethroids to determine the LC₂₅, LC₅₀, and LC₉₉. These concentrations were 0.010%, 0.020%, and 0.055%, respectively, for deltamethrin; 0.113%, 0.167%, and 0.353%, respectively, for cyphenothrin; 2.091%, 2.770%, and 5.114%, respectively, for d‐tetramethrin; and 2.377%, 4.251%, and 10.715%, respectively, for tetramethrin. All dosages were tested in the excito‐repellency system. Survival analysis was used to compare each chamber of the test. It was found that cyphenothrin had a stronger repellent effect than the other pyrethroids, while the contact irritant effect was similar among compounds tested. The LC₅₀ of each pyrethroid was found to be the optimal dose for repelling Ae. aegypti. There was no significant difference in LC₉₉ values for either non‐contact or contact trials for each pyrethroid.     

Electronic mosquito repellers induce increased biting rates in Aedes aegypti mosquitoes (Diptera: Culicidae)

Studies have demonstrated that electronic mosquito repellers are useless and that some of them could even increase the attraction of mosquitoes. While testing some electronic repellers, we noted that they also promoted an increase in biting rates. The present work has evaluated three commercial devices and a computer program working on five different sound frequencies. In a test chamber, the number of Aedes aegypti L. bite attempts was computed during four cycles of 3 min each by alternately turning the devices off and on. The mosquito biting rates for five sound frequencies (ranging from 9.6 kHz to 18.2 kHz) initially demonstrated a significant increase (ranging from around 20% to 50%), which decreased from 8.3% to 25.1% when the repellers were turned off. The biting rate significantly increased at 11.8 kHz (33.7%) when the device was turned on again. The danger of using electronic repellers and the role of sound frequencies stimulating mosquito biting are discussed.     

Anti-mosquito antibodies and their effects on feeding, fecundity and mortality of Aedes aegypti

Anti-mosquito antibodies, produced in mice inoculated with mosquito homogenates or exposed to mosquito bites, reacted with a variety of mosquito antigens including muscle, gut, fat body and nervous tissue; those in anti-mosquito bite sera reacted solely with salivary glands. Mosquitoes fed on restrained immunized mice showed a significant increase in mortality correlated to both the titre and specificity of the anti-mosquito antibodies ingested. No changes in their fecundity or feeding success were noted. Mosquitoes exposed to unrestrained immunized mice or mosquito-bitten mice, however, showed a significant reduction in feeding success, possibly reflecting enhanced host grooming.     

Effects of mosquito larval feeding behavior on Bacillus sphaericus efficacy

Three species of mosquito larvae, representing three genera, were exposed from 10 min to 2 hr to the pathogen Bacillus sphaericus. Culex quinquefasciatus rapidly ingested the bacterium with resulting high mortality. Anopheles albimanus ingested it at a much lower rate initially with correspondingly low mortality. At the longest time interval they had accumulated approximately the same number of bacterial cells as C. quinquefasciatus but achieved a lower mortality. Aedes aegypti ingested and accumulated bacterium at the same rate as C. quinquefasciatus but was resistant to all time intervals. Utilizing ¹⁴C-labeled bacteria, we demonstrated that these differences were attributable to larval behavior in the case of A. albimanus but not in the case of A. aegypti.     

Permethrin-impregnated bednets: behavioural and killing effects on mosquitoes

Permethrin-treated pieces of netting and simulated bednets were evaluated against Anopheles gambiae Giles and Aedes aegypti (L.) in the laboratory. When female mosquitoes were allowed to feed on a human arm through pieces of impregnated netting fastened at the end of tubes, doses above 2 g/m2 were required to stop blood-feeding of both An. gambiae and Ae. aegypti. A much lower dose prevented Ae. aegypti from feeding on mice through impregnated netting. When mosquitoes were released in a room and a human subject sat under a permethrin-impregnated (0.2 g/m2) bednet with an arm pressed against the net (mesh 1.5 mm), mosquitoes failed to bite through the net. All the mosquitoes trying to bite through or entering the net through holes cut in it were knocked down within 30 min of release and ultimately died. Permethrin-impregnated wide-mesh (4 or 8 mm) bednets similarly prevented entry and caused high mortality-rates of An. gambiae.     

登革热的传播模式、蚊媒及防控

在自然界存在两种登革热传播模式：人－伊蚊－人循环,蚊媒是埃及伊蚊与白纹伊蚊。猴－伊蚊－猴循环,蚊媒是白纹伊蚊与白雪伊蚊群。我国学者首先于1975年从无输入性病例的我国西南边疆山林地区的白纹伊蚊体内分离到登革热病毒4型,白纹伊蚊承担两种传播模式的中介。本研究介绍了埃及伊蚊与白纹伊蚊的生态习性与全球及在中国的分布。认为在我国厦门地区迄今为止还未曾发现过埃及伊蚊的存在,也简介了沃尔巴克体新技术防控蚊媒研究的进展。     

Feeding behaviour of female Aedes aegypti: effects of diet temperature, bicarbonate and feeding technique on the response to ATP

Abstract. The effects of variation in diet temperature, mouthpart deployment and the addition of bicarbonate to a saline-ATP diet were investigated for their effects on amount ingested and diet destination in female Aedes aegypti (L.). Mouthpart deployment was achieved by having the insects feed through a membrane, or from a free-liquid surface with mouthparts intact, or with the fascicle separated from the labial groove.
Under the 'feeding through membrane' protocol, a 6-fold increase in the percentage of Aedes feeding on ATP-diets was recorded at 37C compared with 21C. Bicarbonate (9.5 or 19 mM) induced a 3-fold increase in numbers feeding at both 21C and 37C. Neither diet temperature nor bicarbonate content appeared to affect meal size. The pH of all diets was adjusted to 7.0. Diet was directed primarily to the midgut for all diets tested under this regimen, with the exception of the saline-ATP-19 mM NaHC0₃ at 37C which caused the diet to be directed primarily to the crop.
Under the 'feeding without membrane through feeding tube' protocol, females showed little control over diet destination. Female Aedes aegypti exhibited no strong response to ATP when the mouthparts were immersed in 21C diets in feeding tubes and few of these insects ingested large meals. The addition of bicarbonate to the ATP diets did not enhance feeding under these test conditions.