A method for measuring rate of grass-harvesting by Trinervitermes geminatus (Wasmann) (Isoptera, Nasutitermitinae) and observation on its foraging behaviour in southern Guinea savanna, Nigeria.
Abstract
Trinervitermes geminatus (Wasm.), one of the most abundant grass-eating termites in Nigeria, harvests standing grass by cutting it into pieces and carrying it back, via foraging holes at the soil surface and subterranean galleries, to the nest, a low domed mound. Field observations were made near Mokwa on the foraging behaviour in southern Guinea savana in order to develop a method for quantifying the rate at which grass is harvested by the termite. The dominant grass species was Andropogon gayanus var. bisquamulatus. Observations during February-March indicated that there was daily variation in the number of foraging holes open (155-1332/ha) and the mean activity curve (expressed as the number of pieces of grass harvested per unit time). The time of the onset of foraging was relatively constant, all holes being opened between 06.00 and 06.30 h, but the length of the foraging period varied from 90 to 210 min. Different holes were used on successive days. Harvesting rates (expressed as a mean for the entire foraging period) varied from 10.6 to 46.3 pieces per hole in a 5-min. period. Harvesting began at a slow rate and gradually built up to a maximum (the highest recording being 170 pieces/5 min.) before declining rapidly. The shape of the mean activity curve was constant for different holes on the same day (although the amplitude varied because of differences in harvesting rates at different holes) but differed from day to day, largely due to the time at which foraging ceased. A method developed for calculating the total daily harvesting rate showed that from 11.4 pieces (weighing 0.011 g) to 89.3 pieces (0.083 g) were collected per m2.