The action of lecithin monolayers on mosquitoes

Abstract

The feasibility of using monolayers of lecithin to control the larvae and pupae of anopheline mosquitoes was investigated in irrigated rice fields in Kenya.

Solutions of soya lecithin in kerosene spread rapidly over the breeding sites but full surface pressure (measured with a Wilhelmy balance) was attained only slowly. Tests with larvae confirmed that patches of low surface pressure persisted for many hours. The lecithin monolayer was disrupted by light breeze (5–10 km per hour) and disappeared more rapidly by day than at night. Dissolved oxygen levels were only low enough for larvicidal action for about ten hours of the night. Five litres of 50% lecithin solution per hectare persisted at full pressure for 38–45 hours and gave about 70% and 90% reduction of Anopheles gambiae s.l. larvae and pupae respectively. At lower dosages the treatment was much less effective. Analysis of covariance confirmed that the lecithin was active against larvae for about two days. Calculation of the k exponent of the negative binomial distribution indicated that the degree of aggregation of larvae was increased by the treatment. This is probably because surviving larvae congregate in patches of low surface pressure. Most non-target organisms survived the treatment.

It is concluded that in certain circumstances lecithin might be useful for the control of anopheline mosquitoes if applied in relatively large quantities.