William L. Nutting

Seasonal activity and environmental control of foraging of the subterranean termite, Heterotermes aureus (Snyder), in a desert grassland

This research was conducted on a shrub-invaded desert grassland ecotone 40 km S of Tucson, Arizona. To examine the abiotic factors affecting or regulating foraging of subterranean termites a modified bait sampling method using toilet paper rolls was developed. Observations of foraging activity of Heterotermes aureus (Snyder) were made during 24-hr periods each week for one year. Pertinent environmental data were collected at each check. H. aureus foraged day and night throughout most of the year with minimal activity from December through February. Foraging intensity increased moderately in the spring and fall and was high but erratic during the summer months. The number of foragers generally increased with increasing temperature. Rainfall had little effect on foraging when daily mean soil temperatures were below 20°C (toilet paper roll-soil interface); however, even the slightest amount of rain during the hot summer months greatly increased foraging intensity. Above 33°C, even with precipitation, foraging numbers plummeted. The number of surface foragers at any instant (Y) is best explained by the equation, In Y = −0.985 − 0.0761 T + 2.928 ln T + 0.327 ln R where T is the temperature at the roll-soil interface and R is daily rainfall. It appears that foraging activity is not endogenously controlled; rather it is exogenously controlled by temperature and moisture.

The symbiotic microbial community of the sonoran desert termite: Pterotermes occidentis

Pterotermes occidentis is a large, obscure, very primitive dry wood termite limited to the Sonoran desert of North America. Its development, caste system and behavior are discussed in relation to aspects of its ecology. What appear to be single wood-digesting individual termites are in fact insect hosts which harbor extensive microbial communities estimated to contain more than 40 interacting species. All healthy, wood-eating Pterotermes contain these densely populated communities of highly motile symbionts suggesting that species diversity is necessary for termite survival. A morphological catalogue of the major hindgut microbes is presented here. From 10(7) to 10(11) bacteria and from 10(3) to 10(6) protists/ml of hindgut fluid are found in an average nymph or larva. The species of four wood-ingesting mastigotes (genera Trichonympha, Metadevescovina, Tricercomitus and Microrhopalodina) and nearly 30 morphologically distinct types of bacteria are described. The description of this morphological diversity observed with light, scanning and transmission electron microscopy is a prerequisite to functional analyses of the symbioses. Since Pterotermes is easily maintained in the laboratory and is so large it is hoped that it will provide a useful model for symbiosis research.