Ground spraying trials involving a new formulation of synthetic pyrethroid, alphamethrin (OMS 3004, WL 85 871) e.c. 10% were carried out in January 1983 against G. palpalis palpalis in the Bouaflé human trypanosomiasis focus, Ivory Coast. Four dosages were tested in five localities: 12 g of active ingredient (a.i.) per hectare; 24, 36 and 48 g (a.i.)/ha. Each dosage was applied once as a residual spray. The atomiser SOLO PORT 423 was used for spraying and the total area treated was estimated at 20 ha.

The results were evaluated with Challier-Laveissière biconical traps. The knock-down and short term effects of the insecticide were very satisfactory, 96–100% reduction in apparent density of the vector obtained with all the four dosages applied during the first 2 months after treatment.

Three to five months after spraying, more than 98% reduction in apparent density of G. palpalis palpalis was achieved even with the lowest dosage of 12 g (a.i.)/ha. The highest dosages tested did not seem to increase the persistence of the insecticide nor the mortality rate of the vector in the study area.

Due to adverse side effects on man at high dosages during and after treatment, it is recommended that in residual ground spraying, alphamethrin e.c. 10% be applied at a maximum dosage of 12 g (a.i.)/ha and at a concentration not exceeding 0.016% of active ingredient.