Manipulating canopy structure in cassava intercropped with cowpea and its effects on cowpea insect population densities

Pest populations on cowpea intercropped with cassava were studied in relation to changes in the canopy structure of the cassava crop canopy. Flower thrips (Megalurothrips sjostedti Tryb.), the legume pod borer, (Maruca vitrata Fabricius), and pod sucking bug complex were the pests of interest in this investigation. Four month old cassava was pruned during the second crop season of 1987 and 1988 as follows: (i) no pruning; (ii) two-thirds debranching; (iii) total defoliation; and (iv) cut-back to 60 cm above ground. There were significant differences between the pest density on cowpea in the pruned cassava treatments and that of sole cowpea. In 1987, seasonal means of 408, 387, and 298 flower thrips per 20 flowers were recorded in the cut-back, the two-thirds debranched, and the defoliated cassava, respectively, compared to 1080 flower thrips per 20 flowers in the sole cowpea. The same trend was observed in 1988. The micro-environment created by the intercrops reduced the populations of flower thrips but increased those of the pod borer. Seasonal means of 22, 17.5, 21.4, and 16.7 pod borers per 20 flowers were recorded in the intercrops compared to 15.8 in the sole crops. Pod-sucking bugs followed the same trend as that of flower thrips. Overall, intercropping cassava with cowpea can be manipulated such that it contributes to the management of cowpea pests.