Insect Science (2010) 00, 1–6, DOI 10.1111/j.1744-7917.2010.01344.x
ORIGINAL ARTICLE Estimation of food composition of Hodotermes mossambicus (Isoptera: Hodotermitidae) based on observations and stable carbon isotope ratios
Craig T. Symes1 and Stephan Woodborne1,2 1School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits, 2Natural Resources and the Environment, CSIR, Pretoria, South Africa
Abstract The diet of the harvester termite Hodotermes mossambicus was investigated 13 at two sites with distinct dietary components: C4 grasses (δ C isotope values, −13.8 13 to −14.0)andC3 plants (δ C isotope values, −25.6 to −27.1). By comparing observations of food items carried into the colony by the termites and carbon isotope ratios of whole termites (that determined assimilated carbon), the relative proportion of the C3 and C4 plant food components of the termite diet was estimated. There was agreement between the observational data and stable carbon isotopic data, with grass representing approximately 93% of the diet of H. mossambicus at two study sites (urban and rural) on the South African highveld. However, when correcting for mass of food items, that is, C3 and C4, carried by termites, the proportion of grass (C4) in the diet may be underestimated. Key words carbon assimilation, colony, harvester termite, Suikerbosrand
Introduction 1990). Colonies consume considerable quantities of plant material, particularly during the dry winter months, and Termites are important soil organisms that play a signif- are capable of removing a large proportion of standing icant role in soil-forming processes (LaFage & Nutting, crop, as well as litter (Nel & Hewitt, 1969; Duncan & He- 1978; Hewitt et al., 1990). By decomposing and recy- witt, 1989; Duncan et al., 1990; Hewitt et al., 1990; Dun- cling plant material, they contribute to soil fertility and can, 1997). Most studies of H. mossambicus have focused the global cycling of carbon, nitrogen and other elements on the major dietary item of grass (C4), and less so on (LaFage & Nutting, 1978; Hewitt et al., 1990; Tayasu, the importance and/or contribution of detrital shrub (C3) 1998). The harvester termite Hodotermes mossambicus material (Duncan & Hewitt, 1989; Hewitt et al., 1990). (Hagen) (Isoptera: Hodotermitidae) has a widespread In addition, no studies that we know of have considered distribution from the semi-arid areas of southern South stable isotope analysis to investigate diet. Africa, through central and east Africa to Ethiopia, wher- Diet determination of termites has traditionally been ever the average annual rainfall is < 750 mm (Coaton & from observations, but more recently dietary studies have Sheasby, 1972, 1975). Its diet consists primarily of ripe used stable isotopes (e.g., Spain & Reddell, 1996; Tayasu and/or frost- or drought-killed grass but it also consumes et al., 2002; Bourguignon et al., 2009). Because the sta- tree and shrub material (Nel & Hewitt, 1969; Hewitt et al., ble isotope ratio of a consumer’s tissue reflects that of the food, stable carbon isotopes offer the opportunity to quan- tify assimilated carbon from C3 and C4 sources in termite Correspondence: Craig T. Symes, School of Animal, Plant colonies, rather than ingested or collected material alone and Environmental Sciences, University of the Witwatersrand, (Peterson & Fry, 1987; Tayasu et al., 1997; Kelly, 2000; Private Bag 3, Wits 2050, South Africa. Tel: +27 11 717 6423; Bourguignon et al., 2009). C3 and C4 plants fix carbon fax: +27 11 717 6494; email: [email protected] isotopes (12C and 13C) in different ratios as determined