Galls are structures that form as a result of the abnormal growth activities of plants in response to gall-inducing organisms. Most galls are caused by nematodes, insects and mites, while a very small percentage are caused by bacteria, fungi and viruses. There are thousands of species of insects in the world that induce gall formation on the roots, stems, leaves, buds, flowers and fruits of plants in a wide variety of plant families. Insect galls range in complexity from simple outgrowths to more highly differentiated structures such as those typified by many of the cynipid wasp galls. Despite the large numbers and types of insect- induced galls, very little is known regarding the underlying mechanism or mechanisms of insect gall formation. In contrast, the mechanism of crown gall formation by the bacterium Agrobacterium tumefaciens, has been well characterized. An understanding of the mechanism of crown gall formation may provide some clues to the mechanism or mechanisms of insect...
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