Selection drives speciation but adaptive radiation triggers that selection by developing 'new' behaviours in organisms, which get established in their genetic constructs over time; consequently, a new species eventuates. Within the broad context of insect phytophagy, the capability to induce galls is a highly specialized and sophisticated behaviour evident only in particular taxa within specific groups of the Insecta. The most striking behaviour among gall-inducing insects is that a majority of them are specialists displaying a high level of fidelity to their host plants. Adaptive radiation among gall-inducing insects through host shifts resulting in speciation is directed to a large extent through host-plant traits and competitive interactions of the gall inducer in selecting the 'best' host resources, and to a lesser extent through windows of escape from natural enemies. Gall-inducing insects demonstrate a high degree of orientation to specific trophic niches. Close to 90% of them are host specific, displaying a high level of fidelity to particular species of plants. More importantly, gall-inducing insects are specific to particular plant organs, i.e., a leaf-gall inducing insect will induce galls only on leaves. In this article, this concept has been discussed within the overall context of patterns of adaptive radiation and biodiversification among gall-inducing insects of the world, and the apparent patterns in the gall-inducing insects of the Indian subcontinent, with a specific case analysis of the Cecidomyiidae that infest species of Indian Anacardiaceae. The case in point, viz., the Anacardiaceae-infesting Indian Cecidomyiidae, show weak patterns of adaptive radiation. The possible absence of resistance-breaking genes in Indian Cecidomyiidae explains why these organisms have not radiated and diversified as aggressively as the gall-inducing Eulophidae (Hymenoptera) have on different taxa of Eucalyptus introduced for purposes of commercialplantations into several exotic localities, from the Middle-east to India. Alternatively, the host-plant populations are restricting the gene flow between specific gall-midge populations, through their secondary chemistry because, the host-plant mediated impediments on the breeding behaviours impact on the radiation of gall-inducing insects. In conclusion, a majority of gall-inducing insects of the Indian subcontinent are implicated to show features of conservative diversification; the little known, established examples among the Indian gall-inducing taxa indicate that radiation is strongly mediated by the radiation and diversification that occur in their host plants.
|Title of host publication||Insect biodiversity|
|Subtitle of host publication||functional dynamics and ecological perspectives|
|Place of Publication||Jodhpur, India|
|Publisher||Scientific Publishers (India)|
|Number of pages||26|
|Publication status||Published - 2010|