“They are small insects, but the combination of their sociality
with their ability to efficiently digest lignocellulose led to a tremendous evolutionary success.”
Brune 2014
Termites
Termites are a highly socialised, polyphagous form of cockroach (Eggleton 2011) (Image 1). There are up to 1 X 1018 termites on earth and they can comprise 10% of tropical animal biomass and 95% of the biomass of soil insects (Bignell 2006). Of 2700 described termite species about 270 are considered agricultural pests (Rouland-Lefevre 2011) and 26 are invasive pests of wood (Evans 2011). They are generally divided into lower termites (28% of species - generally wood feeders with more similarity to cockroaches) and higher termites (more advanced social system and broader dietary range) (Sun and Zhou 2011).
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Termites are a keystone species in many semi-arid ecosystems (Black and Okwakol 1997). Their ability to build nests of constant temperature and humidity gives them the ability to remain active in hot, dry conditions (Jouquet et al 2011). In hot areas, they and ants undertake many of the soil development activities that earthworms provide in cooler, wetter areas (Evans et al. 2011). As the world warms and some areas (including Australia) receive less rainfall, both termites and ants will play an increasingly important role in improving soil structure, water-holding capacity and fertility.
As eusocial insects, no single termite can perform all the functions needed for survival and the colony exists as a superorganism (Eggleton 2011). There are three castes (Image 2) with specific roles: reproductives that disperse (as alates) and reproduce (usually one queen and king per colony); soldiers that defend and fight; and, workers that feed themselves and others. Eusociality, nest-building and ability to utilise abundant supplies of near-indigestible plant material, has assisted their spread to, and survival in, many areas of the world.
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Termite Digestion
Termites can feed upon soil, humus, carbon, wood (decomposing, dead and living), woody litter, vegetation (decomposing, dead and fresh), dung, fungi and lichen (Black and Okwakol 1997). Due to their broad-ranging diet, termites have a relatively complex digestive system that serves at least 2 or 3 of the following functions (Rouland-Lefevre and Bignell 2001, Bignell 2006 and Bignell 2011):-
1. breaking down and transforming plant-sourced materials into short chain fatty acids to provide energy both to the termite and its intestinal microbiota;
2. providing a microaerobic or anaerobic environment to facilitate fermentation of carbohydrates and amino acids to provide short chain fatty acids;
3. transforming nitrogen into higher-quality, more usable forms;
4. conserving energy through actegoenesis or methanogenesis;
5. facultative N2 fixation;
6. lignin degradation; and,
7. humification.
1. breaking down and transforming plant-sourced materials into short chain fatty acids to provide energy both to the termite and its intestinal microbiota;
2. providing a microaerobic or anaerobic environment to facilitate fermentation of carbohydrates and amino acids to provide short chain fatty acids;
3. transforming nitrogen into higher-quality, more usable forms;
4. conserving energy through actegoenesis or methanogenesis;
5. facultative N2 fixation;
6. lignin degradation; and,
7. humification.
Termites have three mouthparts: the labium, the maxillae and the mandibles. The labium and maxillae are used to sense and handle food. Reproductives have simple mandibles and soldiers have enlarged defensive mandibles (Image 1). Worker mandibles are either heavily ridged for grinding plant material or work together like a mortar and pestle for pounding soil or humus (Donovan et al. 2001 cited in Eggleton 2011). Termites also have a first apical tooth that is short and close to the first marginal tooth to tear wood fibres or long and relatively far from the first marginal tooth to scoop soil or humus (Eggleton 2011) (Image 3). |
The basic termite gut is divided into three main parts (Image 4):-
1. The foregut includes the crop, proventriculus and salivary glands; 2. a midgut with caeca; and, 3. a hindgut that contains the paunch, rectum and anus. In higher termites the paunch contains |
Malpighian tubules, long thin tubes that filter wastes and maintain osmoregulation, are located beteen the midgut and the hindgut. An enteric value sits between the first (P1) and third (P3) sections of the hindgut. Whilst all termites have a similar body-plan there are some differences in their digestive system due to different diets. They can vary in: Malpighian tubules number; degree of enteric valve sclerotisation; size of mandibular molar plate ridges; degree of intestinal coiling; presence of a 'mixed segment'; and, paunch (P3) size and compartmentalisation (Bignell 2011, Eggleton 2011). One litter-feeding termite (Syntermes wheeleri) from Brazil had bacteria, archaea and even fungi in their gut (Santana et al. 2015).