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 formulations of the bioinsecticide spinosad against Culex quinquefasciatus in India.

Spinosad 12% suspension concentrate (SC) and 0.5% granular (G) formulations were tested against Culex quinquefasciatus immatures at 3 dosages--50, 100, and 150 mg active ingredient (AI)/m2--in cesspits, street drains, and disused wells in comparison with temephos 1% G at 1 part per million. The 2 formulations reduced the density of pupae of Cx. quinquefasciatus by 80-100% for 7-14 days in cesspits, 7-18 days in drains, and 33-69 days in disused wells at the 3 dosages tested. The 12% SC and 0.5% G formulations were equally effective in suppressing the larval and pupal populations of Cx. quinquefasciatus in all the habitats treated. At 100 mg AI/m2 in drains and cesspits, the efficacy of spinosad 0.5% G was greater than that of temephos (1% G) and that of spinosad 12% SC was comparable to that of temephos (1% G) applied to the 2 habitats. In disused wells, both the formulations lasted longer than temephos. Based on the small-scale trial, the rate of 150 mg AI/m2 of spinosad was selected for field application to cesspits and drains and 50 mg AI/m2 for application to disused wells. The efficacy observed in medium-scale trials was in agreement with that of small-scale trials. The trial showed that the 2 formulations of spinosad can be used for larval control of Cx. quinquefasciatus, at 50 mg AI/m2, applied at weekly intervals to cesspits and street drains and at monthly intervals to disused wells. At the higher dose of 150 mg AI/m2, the 2 formulations were effective in suppressing the pupal population for 2 wk in cesspits and street drains and for 2 months in disused wells.

Field evaluation of an insect growth regulator, pyriproxyfen 0.5% GR against Culex quinquefasciatus, the vector of Bancroftian filariasis in Pondicherry, India.

Pyriproxyfen, 0.5% granular formulation (GR), an insect growth regulator (IGR) was tested against Culex quinquefasciatus larvae and pupae in disused wells, cesspits and drains at the dosages of 0.1, 0.25, and 0.5kg(ai)/ha to determine the most appropriate field dosage. The IGR was found to be effective against C. quinquefasciatus larvae and pupae in all the larval habitats tested. In drains with slow moving water, application of pyriproxyfen 0.5% GR at 0.5kg(ai)/ha resulted in >80% emergence inhibition (EI) of adults for 4 weeks. At 0.1 and 0.25kg(ai)/ha, the EI was always less than 80%. In stagnant drains, the IGR yielded >80% EI for 1-week period at 0.1kg(ai)/ha. At 0.25 and 0.5kg(ai)/ha, the efficacy was 5-10 times higher. In cesspits, the EI was >80% for 6 weeks when pyriproxyfen 0.5% GR was applied at 0.1kg(ai)/ha, for 11 weeks at 0.25kg(ai)/ha and 9 weeks at 0.5kg(ai)/ha. In disused wells treated at the dosage 0.1kg(ai)/ha, there was >80% EI for 15 weeks and at 0.25 and 0.5kg(ai)/ha, the effective duration was about 1.6-1.8 times longer (24-28 weeks). Considering the quantum of IGR required and the cost and also for safety reasons, the low dosage 0.1kg(ai)/ha is recommended as the field dosage to be applied at weekly interval in stagnant drains, 6 weeks interval in cesspits and 15 weeks interval in disused wells. Since pyriproxyfen 0.5% GR has a relatively longer residual effect than the other IGRs the operational cost could be minimized. Pyriproxyfen 0.5% GR could be one of the choices in the chemical control strategy in Integrated Vector Control Programmes.

Laboratory and field evaluation of Teknar HP-D, a biolarvicidal formulation of Bacillus thuringiensis ssp. israelensis, against mosquito vectors.

Larvicidal efficacy of Teknar HP-D, an improved biolarvicidal formulation of Bacillus thuringiensis ssp. israelensis (Bti), against Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti was determined in the laboratory, and in field the efficacy of the formulation was tested against Cx. quinquefasciatus breeding in cesspits, unused wells and drains. The toxicity of the formulation to Gambusia affinis (larvivorous fish), Notonecta sp. and Diplonychus indicus (water bugs) was also evaluated in the laboratory. Teknar HP-D was field tested at three recommended dosages, 1, 1.5 and 2l/ha, selecting five habitats for each dosage. Another five habitats were kept untreated as controls. Ae. aegypti showed greatest susceptibility to the Bti toxin in the laboratory. In cesspits, all the three dosages caused >80% reduction of pupal recruitment up to day 6 post-treatment, indicating that a weekly application at the lowest would be necessary for sustained control. The residual activity of the formulation was longer in unused wells, causing >80% reduction of pupal recruitment for 17 days from the day of treatment. In controlling pupal recruitment the three dosages produced equal effect. Application of Teknar HP-D at 1 l/ha once in three weeks is therefore recommended to control Cx. quinquefasciatus in unused wells. However, in drains, >80% reduction of pupal recruitment was observed for only 3 days and hence, application of Teknar HP-D at 2 l/ha that caused significantly higher level of reduction twice in a week at 3-day interval is necessary. At dosages from 0.032 to 3.2 mg/l (ppm), Teknar HP-D was non-toxic to Gambusia fish. The two predatory water bugs, Notonecta sp. and Diplonychus indicus that fed on the surviving larvae of Cx. quinquefasciatus exposed to the sub-lethal doses (LC(50) and LC(80)) of Teknar HP-D were safe with out having any mortality.

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.

Efficacy of aqueous suspension and granular formulations of Bacillus thuringiensis (Vectobac) against mosquito vectors.

The efficacy of aqueous suspension (AS) and granular (G) formulation of Bacillus thuringiensis var. israelensis (Vectobac) was tested against the immatures of mosquito vectors in the laboratory and under field conditions. Laboratory tests showed that the aqueous suspension was relatively more effective against Culex quinquefasciatus than Aedes aegypti and Anopheles stephensi, the respective LC(50) values being 0.046, 0.060 and 0.190 mg/l. In stream pools, with the application of Vectobac AS at 1.2 l/ha, more than 80% reduction in immature density of Anopheles larvae (Anopheles fluviatilis and Anopheles culicifacies) was observed for 2-8 days, and at 2.4 l/ha for 3.5-9.0 days. At the dosage of 7.0 kg/ha of the granular formulation, a reduction in immature density by more than 80% was observed for 2-9 days. In polluted habitats such as cesspits, U-drains and cement tanks, the effectiveness of Vectobac AS lasted for 1-4 days when applied at 1.2 and 2.4 l/ha, and Vectobac G was effective for 1-3 days at application rates of 7. 0 and 14.0 kg/ha against C. quinquefasciatus. There was no significant difference in the effectiveness between the two formulations and the two application rates.

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.