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Subterranean termites forage through a network of tunnels. The topology of the networks can be characterized in terms of branch angles and branching rate. When termites encounter depressions in the walls of tunnels, they may excavate the soil from the depression, which could result in the formation of new branches, or they may deposit previously excavated soil from elsewhere, which could fill in the depression. Thus, the likelihood of a branch forming is determined by the balance between soil arriving and filling the void and soil being excavated to enlarge it. We examined the tunneling behaviour of Coptotermes formosanus Shiraki in experimental arenas and found that excavation and deposition do not take place evenly across the face of tunnel wall depressions: excavation (by unloaded termites moving towards the digging face at the tunnel tip) is more likely at the proximal face (relative to the tunnel tip), while deposition (by loaded termites returning from the tunnel tip) is more likely at the distal face. This differential focus of labour within depressions facilitated branch formation by reducing localized competition between loaded and unloaded termites. Once a branch was established, biased excavation and deposition led to a shift in branch heading from about 90° relative to the main tunnel to about 50–60°, close to the theoretical optimum for the efficient flow of termites through tunnels. The basic elements of the excavation/deposition system and feedback between the two may be selected in evolution to optimize the tunnel network and thus the cost/benefit balance of feeding. [Copyright &y& Elsevier]

Bacteria and fungi in shared environments compete with one another for common substrates, and this competition typically involves microbially-produced small molecules. An investigation of one shared environmental niche, the carton material of the Formosan subterranean termite Coptotermes formosanus, identified the participants on one of these molecular exchanges. Molecular characterization of several termite-associated actinobacteria strains identified eleven known antimicrobial metabolites that may aid in protecting the C. formosanus colony from pathogenic fungal infections. One particular actinobacterial-derived small molecule, bafilomycin C1, elicited a strong chemical response from Trichoderma harzianum, a common soil saprophyte. Upon purification and structure elucidation, three major fungal metabolites were identified, t22-azaphilone, cryptenol, and homodimericin A. Both t22-azaphilone and homodimericin A are strongly upregulated, 123- and 38-fold, respectively, when exposed to bafilomycin C1, suggesting each play a role in defending T. harzianum from the toxic effect of bafilomycin C1. [ABSTRACT FROM AUTHOR]