29. Intercropping and weeding: effects on some natural enemies of African bollworm, heliothis armigera (hbn.) (lep., Noctuidae), in bean fields.
J. Appl. Ent., 112, 1991, pp. 38-42
Intercropping is an age-old practice that has been used by subsistence farmers in the tropics to suppress pests and to increase crop yield. One advantage of diverse environments, such as intercropped and weedy fields, is that they result in greater natural enemy numbers because they provide shelter and alternative food sources for natural enemies.
In general, natural enemy numbers are known to be greater in diverse environments than in monocultures.
The objective of the experiment discussed here was to determine the effects of intercropping and weeding on pests and natural enemies.
The effects of strip-cropping haricot bean (Phaseolus vulgaris L.) with maize (Zea mays L.) under weedy and weed-free conditions on the abundance of tachinid parasitoids and a predatory wasp that are associated with African bollworm were studied at Awassa, southern
Ethiopia, during the 1987 and 1988 crop seasons.
Results of the experiments described above demonstrated that tachinid parasitoids and Tiphia sp. were more abundant in diverse bean plots than in bean monoculture. This may give one possible explanation for the low level of Heliothis armigera numbers and hence less pod damagae in haricot bean strip-cropped with maize in previous experiments. Increases in natural enemy numbers in diverse environments are consistent with reviews and reports by several authors. It is possible that the availability of other food sources, such as pollen and nectar, are responsible for increased numbers of natural enemies in diverse environments.
Increase in natural enemy numbers, and consequently decreases in pest numbers, brought about by the presence of weeds are not usually adequate, at least in the short-run, to offset yield losses caused by weeds, especially when more than one pest species are important in a particular crop. If properly managed, intercropping and weed management have a great long term benefit in the integrated management of Heliothis armigera and other pests in bean fields.
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