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 0.5 kg(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 0.5 kg(ai)/ha resulted in >80% emergence inhibition (EI) of adults for 4 weeks. At 0.1 and 0.25 kg(ai)/ha, the EI was always less than 80%. In stagnant drains, the IGR yielded >80% EI for 1-week period at 0.1 kg(ai)/ha. At 0.25 and 0.5 kg(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 0.1 kg(ai)/ha, for 11 weeks at 0.25 kg(ai)/ha and 9 weeks at 0.5 kg(ai)/ha. In disused wells treated at the dosage 0.1 kg(ai)/ha, there was >80% EI for 15 weeks and at 0.25 and 0.5 kg(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 0.1 kg(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.