Morphological Studies on Entomogenous Stem Galls of Microgramma squamulosa (Kauf.) Sota (Polypodiaceae)

Abstract

The cells, tissues and organs of many plants are subject to the effects of a series of factors which may result in pathological growth, characterized by disease and loss of function or atypical growth, which involves changes in normal patterns of development and differentiation (Bloch, 1965; Rohfritsch & Shorthouse, 1982). One of the more complex forms of atypical growth is that known as gall. Galls are structures which originate through processes of hypertrophy and hyperplasia, inhibition of growth or cytohistological modification, in response to the attacks of gall-inducing organisms (Mani, 1964). More than 15,000 types of gall are at present known; they are found on algae, fungi, lichens, bryophytes, pteridophytes, gymnosperms and angiosperms (Mani, 1964). Gall inducers are also widely varied, and include algae, lichens, fungi, bacteria, viruses, nematodes, arachnids and insects. The principal cause of gall formation is insects, and of the groups known to participate in this phenomenon, the most important in terms of frequency and importance are Coleoptera, Hemiptera, Diptera and Lepidoptera (Mani, 1964; Occhioni, 1979; Ferandes & Martins, 1985). Fossil evidence of various levels of interaction between pteridophytes and the arthropods dates back to the Devonian period, and in some cases suggests complex associations (Scott et al., 1985). Even so, entomogenous galls are not frequently found among cryptogams (Houard, 1933; Mani, 1964; Fernandes, 1987). Interactions between insects and pteridophytes have been studied by Mohan-Daniel & Chandrasekar (1986). According to Fernandes (1987), of the principal types of gall-inducing agents only insects are important for pteridophytes. Mani (1964) claims that the family Polypodiaceae, comparatively young and rich in number of species, is the best represented in terms of numbers of galls. The same author points out that none of the galls which occur in this family are known to be caused by Lepidoptera. This work is concerned with some morphological aspects of entomogenous galls found on the stems of Microgramma squamulosa, an epiphytic Brazilian fern, and with the understanding of the inter-relationship between plant and inducing agent. MATERIALS AND METHODS