Laboratory studies on dispersion behaviour of adult beetles in grain. X. Reaction of saw-toothed grain beetle, Oryzaephilus surinamensis (L.), to isolated pockets of damp and mouldy wheat.
Abstract
The following is almost entirely the author's summary of this part of a series [cf. R.A.E., A 53 580, etc.]. The effect of pockets of damp wheat on the dispersion (spatial structure) of experimental populations of adults of Oryzaephilus surinamensis (L.) was investigated. By means of a method described elsewhere [52 135], pockets of mouldy or non-mouldy wheat with a moisture content of 18 per cent. (85 per cent. relative humidity) were each placed in a larger bulk with a moisture content of 14 per cent. (70 per cent. relative humidity) at 25°C. [77°F.], and adults of O. surinamensis were released on the top. The entire bulk of 25 kg. could be broken down for inspection in approximately three minutes in order to record the relative positions of individuals. Adults bred at 70 per cent. relative humidity accumulated in the pocket of damp wheat, and this pattern of behaviour was intensified among insects previously kept at 85 per cent. relative humidity for 14 days. The response was found to be hygrokinetic. The mechanism of response was klinokinetic in adults bred and maintained at 70 per cent. relative humidity but orthokinetic in those previously kept at 85 per cent. Adults did not accumulate in damp pockets containing sporulating moulds but were dispersed along the surrounding humidity gradients. Behavioural mechanisms responsible for dispersion of populations of grain-infesting beetles are discussed, particularly in relation to damp grain, storage conditions and detection of sparse populations.