Aedes albopictus larvae obtained from different types of agricultural and non-agricultural localities in Peninsular Malaysia were subjected to several larvicides at World Health Organization (WHO) recommended dosages. Upon 24 h of WHO larval bioassay using two organochlorines and six organophosphates, high resistance against dichlorodiphenyltrichloroethane (DDT), temephos, chlorpyrifos and bromophos were demonstrated among all larval populations. Aedes albopictus larvae from both paddy growing areas (92.33% mortality) and rubber estates (97.00% mortality) were moderately resistant to dieldrin while only Ae. albopictus larvae from dengue prone residential areas (89.00% mortality) showed high resistance against dieldrin. All Ae. albopictus larval populations also developed either incipient or high resistance to both malathion (33.67%-95.33% mortality) and fenitrothion (73.00%-92.67% mortality). Only Ae. albopictus larvae from fogging-free residential areas that were tolerant to fenthion (97.33% mortality), whereas Ae. albopictus larvae from dengue prone residential areas were highly resistant to the same organophosphate (88.33% mortality). Cross resistance between intraclass and interclass larvicides of organochlorines and organophosphates were also exhibited in this study. The present study provided baseline data on various susceptibility levels of Ae. albopictus larval populations from different types of agricultural and non-agricultural localities against organochlorines and organophosphates at WHO recommended dosages. Nevertheless, further susceptibility investigations are suggested using revised doses of larvicides established from the local reference strain of Ae. albopictus to prevent the underestimation or overestimation of insecticide resistance level among Ae. albopictus field strains of larvae.
The resistant level of the houseflies to six kinds of insecticides, DDT, Resmethrin, DDVP, Baytex, Sumithion and Diazinon, was examined on the seven strains collected in Malaysia. It was found that their susceptibility is rather higher than that of the Takatsuki strain which is a standard strain in Japan. However, their susceptibility to Sumithion was the same or slightly lower than that of the Takatsuki strain. The resistant level to five of six kinds of insecticides was the highest in the strain of Cameron Highland. The values were close to Singh's data in 1973, and this means that the resistance of the houseflies to the insecticides is increasing in Malaysia.
Insecticides Abate, DDT, Dowco-214, Dursban, fenitrothion, fenthion, gamma-HCH, and malathion were tested against the field collected fourth instars larvae of Mansonia from Penang Island, Malaysia. The larvae appeared to be highly susceptible to Dursban and Abate with LC50 values of 1.54 and 1.92 parts per billion respectively. Other chemicals, in decreasing degree of effectiveness, were gamma-HCH, fenthion, P,P'-DDT, Dowco-214, fenithrothion and malathion. The potential use of these chemicals in Mansonia control was discussed. A simple method for collecting and testing Mansonia larvae was also described.
Five pesticides were evaluated against laboratory colonies of Leptotrombidium fletcheri (Womersly and Heaslip) by the Pasteur pipet technique. The pesticides were dieldrin (LC50 = 3.6 ppm, LC99 = 18.2 ppm), bromopropylate (LC50 = 9.2 ppm, LC99 = 239.6 ppm), dicofol (LC50 = 27.8 ppm, LC99 = 118.1 ppm), fenthion (LC50 = 15.4 ppm, LC99 = 29.7 ppm), and malathion (LC50 = 84.7 ppm, LC99 = 313.9 ppm). Dieldrin was the most toxic. Dicofol was recommended for further evaluation in field trials.