Preliminary field testing of a long-lasting insecticide-treated hammock against Anopheles gambiae and Mansonia spp. (Diptera: Culicidae) in West Africa.

The efficacy of an experimental long-lasting insecticide-treated hammock (LLIH) with a long-lasting treated net used as a blanket and made of the same fabric (polyethylene) was tested in a concrete block experimental hut, against the malaria vector Anopheles gambiae s.l. and the arbovirus vectors and nuisance mosquitoes Mansonia africana (Theobald) and Mansonia uniformis (Theobald). The LLIH was treated with the pyrethroid insecticide permethrin. It was evaluated concurrently with ignited mosquito coils over 20 successive weeks. In total, 2,227 mosquitoes (130 An. gambiae and 2,097 Mansonia spp.) corresponding to 27.8 mosquitoes per trap-night were collected in the untreated hut (control). The repellent effect of both coils and LLIH significantly reduced the number of mosquitoes entering the huts (35- 60%). There was no significant difference between LLIH and mosquito coils in blood-feeding inhibition (93-97%) or in mortality (88-98%). The LLIH is more cost-effective and user-friendly than mosquito coils, which need to be replaced nightly to protect people sleeping indoors from mosquito bites. The effects of LLIH on exophagic vectors also need to be investigated because most people that sleep in hammocks are outdoors.

A biological test to quantify pyrethroid in impregnated nets.

First instar larvae of Aedes aegypti (L.) (Diptera: Culicidae) are very susceptible to deltamethrin, which kills all larvae at a very low dose (0.1 microg/l). Thus the sensitivity of this insect to detect that pyrethroid is in parts per billion, as obtained with most common chromatographic methods of analysis. Here we describe a biological test (BT) to quantify deltamethrin in long-lasting insecticidal nets (LLINs) by exposing first instar larvae of Ae. aegypti to serial extracted insecticide solutions from net samples. The deltamethrin concentration in the net was calculated at the doses killing 50% of larva, from the LC(50) of deltamethrin (6.5 x 10(-5) mg/l) and the dilution factor (DF(50)) of the extracted net solution. The pyrethroid quantification in LLINs after 0-25 washes with this BT was correlated with those obtained by direct chromatographic analysis (r(2) = 0.84). This BT did not require sophisticated equipment and could be extended to other molecules and materials. It appeared accurate, robust, cheap and well adapted to the national malaria programmes as the eggs of Ae. aegypti might be used for some months. This method was adapted to provide an easy to use kit test for the quality control of LLINs in the field.