There are inherent
advantages in agroforestry from an insect-pest management point of view. In order to get the most out of these practices, the features of an agroforestry system that influence insect pests should be suitably manipulated. A properly
designed agroforestry system with the right choice of components can create conditions that are favourable for natural enemies of the insect pests and unfavourable for the latter. The establishment of an environment-friendly
agroforestry system requires that the following factors be taken into account.3.1 Choice of species
To introduce selective diversity in an agroforestry system, the plants chosen should be taxonomically far
apart, have a narrow pest complex and have resistant strains. The mix of species in the assemblage should be altered until the right combination of plants is obtained as indicated by a reduced number of pests and an increased
number of predators. Such a system would be stable from the insect-pest point of view.
3.2 Microclimate
When introduced into a land unit, trees create a microclimate in the area that is different from that of
the surrounding areas. Depending on the tree species chosen (whether erect, spreading, with a thick or thin canopy cover, etc.) and the crops underneath, a microclimate of the desired type can be created for the agroforestry
system. The choice of tree species is determined by the requirements of the crops concerned. Systems with multistrata vegetation are expected to favour the development of food webs, thus creating a stable pest–parasite equilibrium.
3.3 Field configuration and design
The arrangement of crops and woody perennials in an agroforestry system affects the activity of insect pests and their natural enemies. By planting trees in line with the
direction of the sun's path, the shading effect can be minimized, while planting perpendicularly to the sun's rays will give maximum shading. Where the trees are planted will depend on whether the crops require shade or sunlight.
Plants aligned in the direction of the wind will let insects pass through the field, while those aligned across the wind direction will shield the field.
3.4 Introduction of barriers
Large trees act
as barriers to the movement of wind and insects in a field. The non-host plants may also act as a barrier to pests. These may be planted in broad strips along with the host plants. Thick hedges around the field define the
boundaries for the movement of natural enemies of the pests. Preferably hedges should be of flower-bearing plants to provide food for the natural enemies.
3.5 Odoriferous plants
Introduction of a variety of
odour-emitting plants in an agroforestry system may help to divert the major pests if they are guided by odours. The system can be planned to include plants that would repel the pests of companion crops.
3.6 Trap plants
In the case of some pests, the main crop or woody plant may be protected from attack by insect pests by growing a more palatable plant with it. Such 'trap' plants may or may not be component plants of the system but
serve to divert the pests from settling on the main crops.
3.7 Management practices
The practices for management of an agroforestry system need to be developed or modified with a view to minimizing insect-pest
incidence and injury. Depending on the habits of the major insect pests in the system, agronomic practices may be tailored to discourage the pests and to favour the predators and parasites.
There are several ways in
which pest populations may be kept down in an agroforestry system, though it is difficult to test all of them in the field. The practitioner can develop an effective package after trying different practices
