Insect pests in agroforestry

Insect-pest regulation in agroforestry is a function of interactions among the components of the system. The interactions are more intricate in complex agroforestry systems than in simple ones. Diversity of plant material in polycultural systems often leads to lower pest intensities. Taxonomically related plant species have a tendency to share common pests. The host range of phytophagous insects has a bearing on the extent of infestation on different plants in the assemblage. Polyphagous pests inflict greater injury to plants in a mixed vegetation system compared with monophagous insect pests. Changes in microclimate in a land unit on which trees and crops are co-cultivated influence insect activity within the system. The modified configuration of a field resulting from integration of trees with crops, or vice versa, may affect colonization of the plants by insect pests. The masking effect of odours released by different plant species in polycultural systems such as those of agroforestry interfere with insects' orientation abilities. Trees raised with crops in agroforestry fields act as physical barriers to the movement of insects to, from and within the field. A barrier effect can also result from the presence of non-host plants among the host plants. Agroforestry practices favour the establishment of natural enemies of insect pests. Caution is recommended when introducing exotic plants into agroforestry systems.Little information is available about insect pests in different agroforestry systems. The effect of interactions among components on the insect pests needs to be studied. The insect-pest situation in agroforestry is reviewed. Insects associated with selected multipurpose trees and shrubs (MPTS) are listed. Studies on insect pests in ongoing agroforestry trials in Africa are discussed and future directions for research suggested

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