A schedule of insecticide spray combining two insecticides: Decis®(deltamethrin) and Systoate® (dimethoate) with four times of spray: 35, 45, 55 and 65 days after planting (DAP) was investigated in order to search for the most effective treatment against Maruca testulalis (Geyer) population on cowpea (Vigna unguiculata (L.) Walp). The local cowpea cultivar “Kpodjiguegue” was used to study the onset and fluctuation of M. testulalis larvae infestation on cowpea terminal shoots, flowers and pods. The trial was carried out during the 1985 early cropping season at Abomey-Cala vi. The treatments' effect on M. testulalis in the terminal shoots was not significant at the 5% level of probability because of the very low infestation of this part of the plant. In the flowers and pods, Decis® was better than Systoate® which failed in controlling this borer satisfactorily. In the unsprayed plots (i.e. control), the peak of the natural infestation occurred in the flowers towards 50 DAP and 65% of the flowers were injured. In the pods, up to 89% of infestation by M. testulalis larvae were observed 60 DAP. The lowest yield was recorded from the unprotected plots (322 kg/ha) whereas the treatment 0-Decis®Systoate®Decis® provided the highest yield (1367 kg/ha) and the highest returns.