A verandah-trap hut for studying the house-frequenting habits of mosquitos and for assessing insecticides. II.—The effect of dichlorvos (DDVP) on egress and mortality of Anopheles gambiae Giles and Mansonia uniformis (Theo.) entering naturally

Abstract

A verandah-trap hut, designed to enable assessment to be made of the numbers of mosquitos that leave an experimental hut through the open eaves, together with studies on the egress from it of Anopheles gambiae Giles and Mansonia uniformis (Theo.) have been described by Smith (1965). It was found that, in the Umbugwe area of Tanzania, A. gambiae rarely left an untreated hut by the open eaves when window traps were available for egress. M. uniformis, on the other hand, left largely by the eaves and was caught in the verandah traps. MethodsA dichlorvos (DDVP) dispenser was suspended in the middle of one hut, half-way between the ridge and the eaves, in order to study the effects of the insecticide both on the egress and on the mortality of A. gambiae and M. uniformis entering naturally. A second (untreated) hut was used as a control. The same methods of counting and collection were used as described in Part I, with additional observations to determine mortalities. Dead mosquitos were collected on the floor indoors and in the verandah and window traps. Delayed mortalities over a period of 24 hours were determined for mosquitos caught alive in the window and verandah traps. Experimental-hut assessments of kill inflicted by dichlorvos were complicated by the mode of action of the insecticide; it is brought into contact with the mosquito as a vapour that diffuses from a dispenser, and thus mosquitos confined in window traps are subjected to the fumigant action of the insecticide diffusing through the funnels of cotton netting. Additional studies were therefore made to assess the fumigant effect of dichlorvos in the window traps and in the verandah trapsThe results are based on daily counts and. collections, from 2nd March to 30th April 1964, from the hut treated with dichlorvos and from the untreated control hut. The dichlorvos was dispensed from a Ciba XI type dispenser opened on 2nd March.

Behavioral Responses of Mosquitoes to Insecticides

“…This modular system is substantially reduced in size compared to the previous excito-repellency box and minimizes the treated surface area and therefore the amount of chemical required for testing. In field observations, numerous attempts have been made to determine behavioal responses of mosquitoes using specially constructed experimental huts (Smith, 1965;Roberts et al, 1984Roberts et al, , 1987Roberts & Alecrim, 1991;Rozendaal et al, 1989;Bangs, 1999;Grieco et al, 2000;Grieco et al, 2007;Polsomboon et al, 2008;Malaithong et al, 2010). Most experimental hut studies have been conducted to observe the behavior of Anopheles mosquitoes with far fewer studies on other genera.…”

“…So-called hut studies provide valuable information that can facilitate vector control operations by helping select the most appropraite and effective tool in combating disease vectors. Since the 1940s, most attention has been directed to the study of Anopheles mosquitoes, yet few investigations have been carried out to describe the innate behaviors of mosquitoes entering, resting, biting (blood feeding) and exiting human dwellings (Gahan & Lindquist, 1945;Giglioli, 1948;Smith, 1965;Roberts et al, 1984;Bangs, 1999;Grieco et al, 2000;Pates & Curtis, 2005;. Another important vector species, Ae.…”

The effects of smoke from mosquito coils on Anopheles gambiae Giles and Mansonia uniformis (Theo.) in verandah-trap huts at Magugu, Tanzania

“…Overall mortalities (Table IV).-The overall mortalities have been calculated according to the formula given by Smith (19656). Mortalities of A. gambiae never exceeded 22% and those of M. uniformis never exceeded 12%, either in treated or in control huts.…”

Abbreviations and acronyms

“…To better approximate insect behaviour in natural field settings, numerous experiments have been made over many decades using specially constructed experimental huts (Smith, 1965;Rozendaal et al, 1989;Roberts and Alecrim, 1991;Bangs, 1999;Grieco et al, 2000Grieco et al, , 2007Polsomboon et al, 2008;Malaithong et al, 2010). Most experimental hut studies have been conducted to observe the behaviour of Anopheles mosquitoes; however, Grieco et al (2007) successfully demonstrated that chemical actions could be observed in experimental huts using Ae.…”