Resource Opportunities from the Nest of Dying Subterranean Termite (Isoptera: Rhinotermitidae) Colonies: A Laboratory Case of Ecological Succession

Abstract

Subterranean termites such as Coptotermes formosanus Shiraki inhabit underground nests consisting of a complex network of galleries resulting in a highly modified environment relative to the surrounding soils. A healthy colony can maintain homeostatic conditions within the nest, limiting opportunities for pathogens, parasites, and predators to exploit the termite colony as a resource. However, a stressed or senescent colony can display a lack of nest maintenance, leading to the colonization of the nest as an opportunistic niche by other organisms. In this study, we described the nest colonization by microbes and arthropods during the collapse of three dying C. formosanus laboratory colonies. The carton nest and the tunnel lining that are mostly made out of termite fecal material were invaded by a variety of fungi, and Acari and Collembolan populations quickly increased during the senescence phase of the termite colony, presumably scavenging on the fungal material. Finally, the carton colonized by fungal mycelia hosted numerous larvae of a sciarid fly, Bradysia sp. (Diptera). This fungus gnat used the decomposing carton material as a breeding site, and numerous adults of this fly were found hovering above the dying termite colony. Bradysia larvae also showed infestation by parasitic nematodes, suggesting the presence of multiple trophic levels in the resource utilization of the nest of a declining termite colony. We concluded that a dying subterranean colony represents a resource opportunity for scavenging organisms and that the nest structure represents an opening niche that initiates an ecological succession.

Chemical Interaction among Termite-Associated Microbes

“…4231 and T. harzianum WC13 (Genbank: KX694115) were both isolated from C. formosanus colonies, though were not found in the same colonies. T. harzianum WC13 was isolated from a dying C. formosanus colony and as the microbial community from the carton nest also collapsed, T. harzianum became the dominant saprophyte in a case of ecological succession (Chouvenc et al 2013a ). The actinobacterial strains were grown on 1/5 potato dextrose agar (DB Difco PDA) or 1/5 potato dextrose broth (DB Difco PDB) for 14 days.…”

“…All crude extracts were fractionated by reverse-phase (RP) solid phase extraction (SPE) using a stepwise gradient solvent system of decreasing polarity, starting from 75% water (H 2 O)/acetonitrile (ACN) to 100% DCM (five fractions, A-75% H 2 O/ACN, B-50% H 2 O/ACN, C-25% H 2 O/ACN, D-100% ACN, and E-100% DCM). All SPE fractions were tested for antimicrobial activity against Bacillus subtillis , a gram-positive bacterium and five soil fungi known to opportunistically be associated with termite nests (Zoberi and Grace 1990 ; Chouvenc et al 2013a ), T. harzianum , Beauveria bassiana , Penicillum sp., Aspergillus nomius , and Metarhizium anisopliae . SPE fractions that exhibited activity against any of the microbes were subsequently purified on RP HPLC using one of the following Phenomenex semi-preparative columns, Kinetex biphenyl, Luna C18(2), Phenyl-Hexyl, or Hydro-RP, resulting in the purification of 11 known secondary metabolites (Table 1 and Figs S18-S29).…”

“…4231 was combined with fresh media (2/5 PDA, 3% agar) and subsequently used to make CM plates (55 mL; 150 × 15 mm Petri dish). These plates were then inoculated with refrigerated glycerol spore stocks (in 25% glycerol) from T. harzianum WC13 (Chouvenc et al 2013a ) and incubated at 30 °C for 4 days. At this time the plates were extracted and preliminarily fractionated following the method described above.…”

“…Due to the sheer size of these nests, they can be difficult to control via conventional soil insecticide treatments (Su and Scheffrahn 1998 ) and biological control attempts failed to eliminate field colonies (Culliney and Grace 2000 ; Grace 1997 ; Lax and Osbrink 2003 ; Chouvenc et al 2011 ). The core of the termite nest is filled with ‘carton material’, a sponge-like structure composed of nutritious chewed wood particles and fecal material that promotes the growth of mutualistic and opportunistic microbes, including parasites and pathogens (Chouvenc et al 2013a ). Preventing pathogenic fungi or other microbes from proliferating in the termite colony and on the fecal nest structure requires multiple mechanisms, including mutual- and self-grooming behavior by the termites to avoid bringing spores or fungal mycelia into the nest (Yanagawa et al 2008 ; Chouvenc and Su 2010 ; Chouvenc and Su 2012 ).…”

“…Interestingly, one Streptomyces metabolite induces the production of cryptenol ( 1 ), t22-azaphilone ( 2 ), and homodimericin A ( 3 ) in Trichoderma harzianum (Fig. 1 ), an ecologically relevant soil fungus that is known to take over the carton material of collapsed termite nests (Chouvenc et al 2013a ). The induction of these metabolites led to insights into the chemical interactions that are possibly occurring among microbes within the termite nest.…”