Tumbling controls bean weevils
Simply turning bags of beans upside down twice a day is the easiest way to stop the larvae of the common bean weevil causing damage. With regular disturbance the larvae soon die of exhaustion. The larvae of the common bean weevil (Acanthoscelides obtectus) is responsible for causing large losses of beans in storage. Effective control by small-holder farmers in the Tropics has been difficult. Each adult is able to lay many eggs and, once they hatch, the larvae soon bore into the beans. A recent study has shown that the larvae had to wedge themselves between two beans in order to get enough leverage to start boring. It takes a larva between 24 and 48 hours of continuous scraping to get inside a bean. Researchers from Michigan State University argued that if the larvae were repeatedly dislodged they would be unable to bore effectively into the stored beans and might even die of exhaustion. Beans were put in various containers with adult weevils. The containers were turned regularly for two weeks, and at the end of that time damage was found to have been reduced by 97%. Some of the mortality was due to exhaustion, as predicted but some larvae were also crushed as the beans moved. The researchers therefore recommend that bags of beans are turned upside down in the morning and again in the evening. It is possible that the technique might work with other pests of stored beans and grain if those pests need leverage in order to bore successfully. Department of Entomology and Pesticide Research Centre Michigan State University East Lansing, Michigan 48824, USA
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Technical Centre for Agricultural and Rural Cooperation
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