Efficacy of three formulations of diflubenzuron, an insect growth regulator, against Culex quinquefasciatus Say, the vector of Bancroftian filariasis in India.

Background & objectives: Insect growth regulators (IGRs) offer alternatives to conventional chemical larvicides that pose problem of resistance and environmental safety. However, only a limited number of IGRs have been approved for use in mosquito control. In the present study, two new formulations of the IGR diflubenzuron, 2 per cent granular (GR) and 2 per cent tablet (DT) were tested for its efficacy against Culex quinquefasciatus, in comparison to its 25 per cent wettable powder (WP) formulation. Methods: The WP, GR and DT formulations were tested in cesspits, street drains and abandoned wells each at four dosages, 25, 50, 75 and 100 g ai/ha. Additionally, the DT formulation was tested at a higher dosage of 1 tablet/m2 (equal to 400 g ai/ha). Results: The WP and GR formulations yielded >80 per cent inhibition of adult emergence (IE) for 7-10 days in cesspits, 4-7 days in street drains and 7-21 days in abandoned wells at all dosages tested. The DT formulation was effective only at higher dosage 100 g ai/ha and or 1 tablet/m2 for 7-15 days at all habitats. Interpretation & conclusions: The trial showed that the dosage 25 g ai/ha of 25 per cent WP could be the field dosage for cesspits and wells, and 50 g ai/ha for drains, to be applied at weekly intervals. The dosages 25, 50 and 100 g ai/ha of 2 per cent GR could be the field dosages for application in cesspits at weekly intervals, in abandoned wells every three weeks and in drains at weekly intervals, respectively. Diflubenzuron 25 per cent WP and 2 per cent GR could be used for larval control of Cx. quinquefasciatus under integrated vector management programme.

Efficacy of two organophosphorus insecticides, Reldan & Dursban against the larvae of Culex quinquefasciatus.

BACKGROUND & OBJECTIVES: The resistance in vectors to conventional insecticides warrants development of newer insecticides for mosquito control besides use of other counter-measures. The present study was undertaken to test the efficacy of a new and toxicologically safe organophosphorus compound, Reldan (chlorpyrifos-methyl) and compare its efficacy with Dursban (chlorphyrifos-ethyl) against larvae of different mosquito vectors under laboratory conditions and against Culex quinquefasciatus in three larval habitats. METHODS: The susceptibility of larvae of mosquito vector species to Reldan and Dursban was determined by following the standard procedure and the LC50 in mg/l values were calculated by probit analysis. The insecticides were evaluated in the larval habitats of C. quinquefasciatus in and around Pondicherry. The percentage reduction in larval density was calculated using Mulla's formula and duration showing more than 80 per cent reduction was calculated by annotating the graph obtained by plotting percentage reduction in larval density against days of post-treatment. RESULTS: Dursban and Reldan were effective against Anopheles fluviatilis larvae at lower LC50 of 5.90 x 10(-7) and 1.07 x 10(-9) mg/l respectively compared to other species of mosquitoes. Dursban and Reldan were equally effective against Aedes aegypti, An. stephensi and An. culicifacies. Reldan was about nine times more effective than Dursban against C. quinquefasciatus with respective LC50 of 1.17 x 10(-4) and 1.34 x 10(-3) mg/l. Field evaluation of these insecticides against C. quinquefasciatus showed that Reldan and Dursban at the application rate of 500 g (ai)/ha reduced immature density by more than 80 per cent for a mean duration of 4.0 and 4.5 days and 4.6 and 3.7 days in cesspits and cement tanks respectively. In U-drains, at 500 g (ai)/ha, Reldan was effective for a period of 3.6 days whereas, Dursban was not effective. It was effective for 4.0 days only at 1000 g(ai)/ha. There was no significant increase in the residual activity of both Dursban and Reldan with increase in application rates. INTERPRETATION & CONCLUSION: In view of the lack of sustained control with the applications, it is inferred that these insecticides will be of limited use as larvicides against C. quinquefasciatus breeding in polluted habitats.

Field evaluation of Spicbiomoss, a biolarvicidal formulation of Bacillus sphaericus against immatures of Culex quinquefasciatus & Anopheles species.

Spicbiomoss, an aqueous suspension formulation of Bacillus sphaericus was evaluated for its efficacy against immatures of Culex quinquefasciatus at the application rate of 120 l/ha in cement tanks, cesspits and drains in Pondicherry and in drains in Kochi, Kerala. The formulation was also tested against anophelines (Anopheles fluviatilis and An. culicifacies) breeding in stream pools in Malkangiri district, Orissa. In cement tanks and cesspits more than 80 per cent reduction in immature density was observed for a period of 6-13 days (mean 9.8 +/- 1.25 days) and 3-8 days (mean 5.2 +/- 0.7 days) respectively. The same level of reduction was found to last for 1-4 days (mean 2.2 +/- 0.52 days) in drains in Pondicherry and 2-9 days (mean 4.8 +/- 1.17 days) in Kochi. In bunded stream pools 40-79 per cent reduction in immature density of Anopheles was obtained for an average period of 1-7 (mean 3.83 +/- 0.98) days. There was no improvement in the efficacy of the formulation against anophelines even at the higher application rate (240 l/ha). Thus, Spicbiomoss can be used against Cx. quinquefasciatus in an integrated vector management programme.