Defensive strategies in the ecology of neotropical termites

Coles, Helen R (1980) Defensive strategies in the ecology of neotropical termites. University of Southampton, Doctoral Thesis.

Abstract

The termite species present in each of six major subdivisions of the cerrado (savanna) vegetation of the Distrito Federal, Brazil, were studied. Information on the relative abundance, nest biology, feeding habits and soldier defensive behaviour of 60 species is presented, together with a key to the soldier caste of 29 termite genera. Field observations on the major vertebrate and invertebrate termite predators are included. The morphological and chemical specialisations of the soldier casteare discussed for termites in general. Detailed studies on the morphological specialisations of the soldiers in eight species of the family Termitidae (Grigiotermes metoecus; Armitermes euamignathus,, Procornitermes, arauioi, Cornitermes sp.n.A., Svntermea rus, Nasutitermes sp.n.D., Cortaritermes silvestri and Velocitermes Paucipilis) are described, together with information on the chemical composition of their defensive secretions. Seven monoterpenes and two straight chain hydrocarbons, found in defence secretions, were tested for toxic effects on topical application to ants in petri dishes. Toxic effects varied with the compound used, its concentration and the ant species tested. Three of the monoterpenes were shown to be feeding deterrents to a captive giant ant-eater (Nyrmecophaaa tridactvla).The defensive behaviour of three species from the Neotropical genus Svntermes,was also studied. The soldier to worker ratio in foraging parties, and the behaviour of soldiers during mound breaching, were found to be related to the chemical composition of the defence secretions. The monoterpene cis-p -ocimene forms 95% of the volatile component of 9. dirus and S. molestus secretions. S. grandis does not produce this compound. The difference in the defensive behaviour of the two former species is attributed to the different amounts of secretion present per unit of soldier biomass. The correlation between defensive adaptations of the soldier caste and defence of the whole colony was studied in the eight termite species named above. In general, two defensive strategies were evident. Species with nasute soldiers produce compounds that are toxic to ants and act as feeding deterrents to ant-eaters. These species were selected less often in food-selection experiments with giant ant-eaters and their mounds had a low incidence of armadillo attacks. They build soft-walled mounds which workers reconstruct slowly and which rarely have other inquiline termite species. The corollary of this is found in species with soldiers specialised principally in mandibular defence, which produce no volatiles, have hard mounds, which workers reconstruct quickly, and which have many inquiline termite species. The defensive strategy of the termites of the Distrito Federal is related to their ability to exploit certain food resources. The importance of defence as an ecological factor governing the survival and success of a termite species in a given ecosystem is discussed for the Distrito Federal and other regions.

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