As primary producers, plants are a source of
food for a large number of animals. Insects are a predominant group of herbivores and they have developed a variety of associations with plants over millions of years of co-evolution. The spectrum of insects associated with a plant
species in one locality may be quite different from that in another place. Only a few of the many insect species associated with plants cause damage on an economic scale and are therefore considered pests.The output
of a production system can be enhanced either by an increase in production level or by a reduction in the losses from it. In agroforestry systems, attempts to increase production without heavy inputs can affect the sustainability
of the systems. The potential increase in output is the difference between the current level of production and the capacity of the system. Prevention of loss will lead to a higher output from an agroforestry system without
affecting its sustainability.
Insect pests are the most important group of organisms causing injury to plants in agroforestry systems. Therefore, the management of insect pests in these systems is crucial to sustained production,
and even farmers have recognized this as a priority issue for agroforestry research (Prinsley 1991). Pest management figures prominently in ICRAF's strategy for research in the nineties (ICRAF 1990).
ICRAF recognized
the need, as a first step, to collate information on the current status of research on insect pests in agroforestry through a literature review and field observations before any major research on insect-pest management could begin.
Consequently, ICRAF constituted a one-year fellowship with assistance from GTZ to undertake the task. The objectives were (1) to review current knowledge on how mixed plant and tree communities affect insect pests and the
pest–parasite complex, (2) to identify insect pests occurring in the on-going experiments in ICRAF's Agroforestry Research Networks for Africa (AFRENAs), and (3) to suggest future lines of research in the field of insect-pest
management in agroforestry. However, because of the limitation of time and funds the second objective could not be accomplished satisfactorily. Only a few sites were visited and those visits, too, only once, which is not enough to
identify all potential pests and establish their relative importance.
1.1 Sources of information
The literature search was carried out utilizing the library resources and documentation centres at
the International Centre for Research in Agroforestry, the International Centre for Insect Physiology and Ecology, and the Kenya Forestry Research Institute. The resource materials included periodicals (journals, newsletters,
magazines), books, conference proceedings, booklets, working papers, tour reports and technical reports. The principal sources of information were electronic databases. The bulk of the information was drawn from the three volumes
of CABI Abstracts (vol. 1, 2, 3: 1984–1990). Other databases scanned were AGRICOLA (1970 to October 1991) and AGRIS (1986 to April 1991). The review articles and other publications listed were also made use of but without checking
the primary sources.
To complement the literature review, a questionnaire was designed and dispatched to about 40 agroforestry researchers asking for information about insect pests in the systems with which they work.
It was also sent to 30 different national and international organizations and networks in Africa, Asia and Latin America. The response to the questionnaire was poor, probably because there have been few experiments conducted on the
entomological factors in agroforestry trials. Visits were made to the AFRENA experimental sites: Maseno in Kenya; Mashitshi and Karuzi in Burundi; Butare, Gakuta, Rubona and Rwerere in Rwanda; and Minkomeyos and Abondo in Cameroon.
During these visits observations were mainly focused on the insects associated with multipurpose trees and shrubs (MPTS) as some information on insect pests of crops is already available. Frequent visits were made to the ICRAF
field station at Machakos in Kenya.
