The desert termite Gnathamitermes tubiformans and its unique foraging tubes are a common fixture in rangelands across Arizona, New Mexico, northern Mexico, and Texas. Although it is a native species and has thrived for millions of years, recent droughts have made its activity more visible and raised questions about its impact on vegetation. Since G. tubiformans prefers grasses as food, there has been a concern about competition between livestock and termites. Monitoring of desert termite activity was conducted through two experiments focusing on foraging distances and forager population sizes. The foraging distances experiment used circular grids in 5 m x 5 m plots to map the movement of marked G. tubiformans released from the center of the grid. Analyses showed no significant correlations between distances moved and abundance or type of vegetation. Movement of marked termites did not favor any compass directions. The second experiment used a mark-recapture estimation model to predict G. tubiformans forager populations in 5 m x 5 m plots. Linear regression analyses showed a significant positive correlation between size of the forager population and amount of total vegetation. In addition, linear regression analyses showed a significant positive correlation between total estimated number of collected termites during early recruitment and amount of vegetation cover, specifically grasses. Desertification of rangelands used by G. tubiformans and livestock is a worry with few known solutions. Elucidating answers to this problem involves ferreting out the sources of the degradation. The results of this thesis shed light on the role G. tubiformans plays in its habitat, and infer that degraded habitats with low amounts of vegetation will exhibit low termite populations.

The biological control of subterranean termites (Isoptera: Rhinotermitidae; Termitidae) using entomopathogenic nematodes (Nematoda: Steinernematidae; Heterorhabditidae) (EPN) was investigated. The desert subterranean termite Heterotermes aureus Snyder was found to be very susceptible to Steinernema riobrave Cabanillas, Poinar and Raulston. In laboratory bioassays S. riobrave (355, TP, 3-8b and 7-12 strains), S. carpocapsae Weiser (Mexican 33 strain), S. feltiae Filipjev (UK76 strain), and Heterorhabditis bacteriophora Poinar (HP88 strain) were all capable of infecting and killing H. aureus, Reticulitermes flavipes Kollar, R. virginicus Banks, Coptotermes formosanus Shiraki and Gnathamitermes perplexus Banks. In sand assays, S. riobrave caused > 90% H. aureus mortality in 3 days and 100% mortality by day 5 at 22 °C. TP strain of S. riobrave caused 75% R. flavipes mortality and 90.91% C. formosanus mortality in 7 days. EPNs utilizing termites as hosts produced smaller sized offspring, with the exception of S. feltiae. Stunted females of S. feltiae were frequently found in termite cadavers, but no progeny. Small IJs of S. carpocapsae, S. riobrave and H. bacteriophora infect, reproduce and form normal size IJs after subsequent infection in Galleria mellonella L. The progeny of small IJs were as effective as the normal size IJs, with regard to subsequent induced mortality, under the conditions tested. In laboratory two-container choice experiments, H. aureus were repelled by EPN treated areas for up to 10 days at 10,000 IJs per device. The repellency threshold was found to vary among nematodes species. We hypothesis that it is the physical movement of the nematodes that repels the termites. Temperature is a key factor affecting nematode pathogenicity. Temperature tolerance of the nematodes varied between species. After a gradual heat adaptation process, S. riobrave and H. bacteriophora caused significantly higher H. aureus mortality at 32 °C compared with original laboratory cultured strains. Further work may result in the contribution of commercially available strains with enhanced heat tolerance. Preliminary field studies confirmed EPN protection of a structure, however, termites began to reinfest 4 weeks after the application. Additional tests are necessary to provide more evidence before we can conclude nematodes as useful in the field.