Adaptive radiation and diversification in gall-inducing insects in the Indian subcontinent: search for a pattern

The most striking behaviour among gall-inducing insects is that a majority of them arespecialist organisms that display a high level of fidelity to their host plants. In a contextof discussing species diversity among and richness of gall-inducing insects, thispaper attempts to discuss the patterns of adaptive radiation evident in different gallinducinginsects of the Indian subcontinent, which is characterized by profound geological,vegetation, and climatic variations. As a case study, in this paper I have analyzedand discussed patterns of adaptive radiation apparent in gall-inducing Cecidomyiidaeon Indian Anacardiaceae with a particular reference to Mangifera indica. The possibleabsence of resistance-breaking genes in Indian Cecidomyiidae on different Anacardiaceaeand M. indica explains why these elements have not radiated and diversified asaggressively as the gall-inducing Eulophidae have done on different Eucalyptus taxaintroduced into India as commercial plantation crops. Alternatively, the host-plant populationsare, in high likelihood, restricting the gene flow between specific gall-midgepopulations, through their secondary chemistry because, the host-plant mediated impedimentson the breeding behaviours impact on the radiation of gall-inducing insects. Asignificant majority of Indian gall-inducing insects show features of conservative diversification,and based on available evidence their conservative diversification appears tobe strongly plant mediated.