Pest Biological Control
The term “biological control” refers to the control of insect pests by natural enemies. It is generally taken to mean the use of parasites, predators and pathogens to sup-press populations of insect pests. Biological control takes several forms and these arecategorised as classical, natural (conservation.) and inundative biological controls.
All pests have natural enemies. For example, no less than 188 species of natural enemies (parasites, predators and pathos-gens) have been recorded from the brown plant hopper, Nilaparrata lugens (Stal), an important pest of rice. The actions of these natural enemies are probably the main read-sons that N. lugens was not a serious pesto rice in the past. This is probably true of many insect pests.
Despite effective natural enemies, out-breaks occur occasionally. While adverse weather and migration of insects have been responsible for the development of some outbreaks, the most common cause of out-breaks of native pests in. Studies using insecticide check and exclusion cage tech-inquest have provided proofs of the importance of natural biological control in keep-in native pests under control. In a studying the early 1960s, oil palms sprayed regularly with organ chlorine insecticides were found to have higher populations of bag-worms than palms kept free of insecticides. The results have encouraged oil palm growers to avoid prophylactic use of insecticides. In rice, it was observed that farmers who used more insecticides had more insect pest problems. In cage trials, populations of the brown plant hopper in field cages without natural enemies were found to be50 times higher than those where natural enemies were present. Follow-up studies showed that regular use of insecticides re-moved natural enemies, resulting in higher pest populations. The results of these studies emphasize the need to conserve effective natural enemies of pests to prevent outbreaks.
In cases where a pest is exotic and no effective natural enemies exist, introduction and establishment of new natural en-emu species should be considered. The importation of biological control agents is popularly known as classical biological control. The approach involves search, selection and introduction of natural enemies from the area of origin of the pest. Classical biological control has been used against the diamond back moth, Plutellaxylostella (Linnaeus), an exotic pets and the most important one of cabbages in Cameron Highlands. Of these, 2 species, Diadegma semiclausum Hellen and Diadromus collaris Gravenhorst established well and inrecent years have kept the diamond back moth populations in the Cameron Highlands low. When effective natural enemies are found and established, they provide long term control with little intervention from farmers. A highly successful classical biological control programmed is the importation of Gyranusoidea tebygi Noyesfrom India to Togo to control the mango mealy bug Rastrococcus invaders Williams.
Sometimes, natural enemies can be pro-diced in large numbers and released repeatedly on the crop where the pest exists. Such an approach is referred to asinundative biological control. This approach is often expensive and should be pursued only if conservation and importation are not effective or feasible.
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