Runway Building and Food Exploration Strategy of Pseudacanthotermes militaris (Insecta: Isoptera)
1974; Wiley; Volume: 6; Issue: 3 Linguagem: Inglês
10.2307/2989647
ISSN1744-7429
Autores Tópico(s)Ecology and Vegetation Dynamics Studies
ResumoPseudacanthotermes militaris explores and attacks timber in the vicinity of cracks. Maximum stimulation of the termite was observed when the crack width approximated both the modal height of the runways and the height to which a minor worker could lift a soil particle. OBSERVATIONS ON THE DAMAGE to telegraph poles (Usher and Barnacle 1974) and fencing material in Ghana indicated that termites sometimes preferentially attacked wood in the vicinity of cracks or checks. Such observations posed the question of whether the presence of cracks could act as a termite attractant, the answer to which would influence two aspects of termite research. First, if man's wooden structures (e.g. poles and building timbers) are to be protected from attack, then a smooth continuous surface may be more resistant to attack than one with cracks or badly fitted joints. Secondly, an attractant property could be used as a bait (Fougerousse 1969; Lund 1969) when designing tests on the resistance of materials or treatments to termite attack, or as a lure (Gray 1969) in survey work. In some areas of Kumasi, Ghana, the most frequent wood-destroying termite is Pseudacanthotermej militaris (Hagen), Termitidae: Macrotermitinae. The chewed wood (or other material) is taken underground to the nest, where it is used in the construction of a fungus comb, having passed once through the gut of the worker termite. This species forages on the soil surface at night or when the weather is cool and moist, and when a food resource has been located it is covered by a soil structure and the path leading to it is completely enclosed by a soil tube, referred to as a runway. In section these runways are approximately semi-elliptical, with the substrate forming the shorter diameter of the ellipse. If a runway or food location is examined, four castes of P. militaris will usually be found, major and minor soldiers and major and minor workers. Observational evidence by Sands (1972), Williams (1973), and myself suggests that minor workers are usually associated with the building of the runways while major workers are the means of transport of the food to the fungus comb. STIMULUS TO EXPLORE To test the response of P. militaris to cracks, 18 strips of wawa or obeche (Triplochiton scleroxylon K. Schum.) 70 x 30 x 15 mm were used between two sheets of glass. The blocks were glued side by side to the glass leaving spaces of 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, and 6 mm. These spaces were randomly arranged, and were repeated once on each side of a plate (a similar plate is shown in figure 1). Each crack was therefore 30 mm high and 70 mm long. Four such plates were made, set level with the ground surface, and covered with roofing felt supported on hollow bricks. Each day the plates were uncovered and the amount of termite penetratioln, as indicated by runway construction, recorded by observation through the glass. Two plates were explored by termites on the first day of exposure, one on the seventh, and one on the nineteenth day. An index of exploration was determined by scoring 3 if the whole crack had been explored, 2 if more than 10 mm of the depth had been explored, 1 if less than 10 mm had been explored, and 0 if there was no exploration. The indices for the first and third days after exploration of the plate had commenced, averaged over all plates, are shown in figure 2. From this graph it is apparent that small cracks do not stimulate termite exploration, probably because they are too narrow for all castes of P. militaris to enter. One question which remained unanswered was whether the smaller index for 6 mm cracks was a real reduction of exploration with crack size. Thus a second experiment was set up, again using 4 plates, but with crack widths of 3, 4, 5, 6, 7, 8, 10, 12, and 15 mm (fig. 1). The crack height, depth, and the scoring system for the index of exploration were the same as before. The plates were exposed in December 1971, which is during the dry, sunny season in Kumasi (Gibbs and Leston 1970), and it was apparent that the level of ground surface activity in P. nzilitaris was reduced at this 1 Present address: Department of Biology, University of York, York YO1 5DD, United Kingdom. 154 BIOTROPICA 6(3): 154-157 1974 This content downloaded from 207.46.13.28 on Tue, 30 Aug 2016 04:57:32 UTC All use subject to http://about.jstor.org/terms time of year. Exploration of the plates began on the first, second, third, and thirty-sixth days of exposure. The data, shown in figure 2, also demonstrate a decrease in the index of exploration at larger crack sizes. With cracks of 12 and 15 mm width it was frequent for P. militaris not to occupy the whole crack width, but to build a runway on the side of one of the wawa blocks. RUNWAY AND WORKER SIZE Runways of P. militaris from the same habitat were collected and measured. Histograms of the maximum height and of the basal width are shown in figure 2. ... * ..... ..** .* .... * * . . .. FIGURE 1. The layout of a plate in the second crackwidths experiment. The outline of the glass sheet is shown, and stippling indicates obeche strips. On each side of the plate the crack widths are arranged randomly. From this data it was found that the mean height is 3.95 mm (S.E. 0.097) with a mode of about 4.75 mm. The mean width is 6.99 mm (S.E.0.216), and the mode is 7 mm. The distribution of heights is strongly skewed to the left, with no runways being greater than 5.5 mm high. The distribution of widths is more nearly normal, though only one runway was found with a width of less than 4.5 mm. Fifteen minor workers have been measured from a collection made on the test site and preserved in ethanol. Experimentation with models yielded two possible mechanisms whereby the minor workers, carrying soil particles in their mouths, could push the particles upward into position. Figure 3 shows the two models, one where the termite is bipedal and one where it is quadripedal. Taking first the bipedal model, the height to which the termite could raise a soil particle is approximately the sum of the lengths of tibia III, femur III, coxa III, the thoracic segments, and the majority of the head capsule. The mean lengths together with their standard errors are recorded in table 1. In interpreting these measurements, it should be noted that the maximum height can only be TABLE 1. Measurements (in mm) of fifteen minor wokers of P. militaris. Quadripedal model Bipedal model Structure Mean S.E. Mean S.E. Tibia (II or III) 0.94 0.014 1.18 0.014 Femur (II or II) 0.79 0.016 1.05 0.018 Coxa (II or III) 0.57 0.013 0.57 0.014 Thoracic segments (I-II or I-III) 0.75 0.030 1.09 0.034 Part of head and mandible 1.22 0.020 1.22 0.020 Total 4.27 0.062 5.11 0.067 realized if the termite is able to bring all five sections measured into a straight line. This practice is certainly possible for the legs, but the forward prolongation dorsally of the first thoracic segment probably prevents the head being raised to more than 300 from the vertical. Assuming 300, then the head and mandibles height will be reduced to a mean of 1.22 cos 30? 1.06 mm, giving a mean total height of 4.95 mm. The maximum total height of the 15 minor workers measured would be reduced from 5.68 to 5.50 mm. Bipedality in these insects is probably less common than quadripedality. Figure 3 illustrates a model Runway Building and Food Exploration in Termites 155 This content downloaded from 207.46.13.28 on Tue, 30 Aug 2016 04:57:32 UTC All use subject to http://about.jstor.org/terms 0 30 0~~~~~~~~~~~~~~/0
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