Field studies to investigate the effect of intercropping on the relative resistance and susceptibility of cowpea cultivars to Maruca testulalis impure stands and intercropped with maize, were conducted at the International Centre of Insect Physiology and Ecology (ICIPE). It was clearly indicated that intercropping affected the relative resistance and susceptibility of cowpea cultivars. The resistance of TVU 946 to Maruca was reduced when the cultivar was under maize. This was attributed to the phenological changes observed, i.e. when planted with maize there was a significant (P = 0.05) increase in length of the pods and peduncles and significant (P = 0.05) reduction in the number of branches. Weekly mean temperatures and relative humidities indicated that there were significant differences between cropping patterns. Similarly there was a significant reduction in the photosynthetic active radiation incident on cowpea canopy in all the intercropped plots. This suggested that both intercropping and microenvironmental differences observed, reduced resistance in cultivar TVU 946 by probably acting directly on the crop, thus rendering it more susceptible.