Laboratory studies on dispersion behaviour of adult beetles in grain. II.—The saw-toothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera, Silvanidae)

Abstract

Dispersion behaviour in adults of the saw-toothed grain beetle, Oryzaephilus surinamensis (L.), was studied under controlled laboratory conditions. The effect of density, temperature and moisture content on surface dispersion was studied using groups of insects in jars of 500 g. grain and vertical dispersion by using groups of insects in thin vertical plates of wheat held between two sheets of glass. The ethological basis of group behaviour was investigated by using isolated individuals.Over the range of conditions used, 1–10 per cent, of the individuals comprising the groups studied appeared on the surface of the grain. In grain at 14 per cent, moisture content, at 25°C., 3·4 per cent, of the group appeared on the surface. A greater proportion was found on the surface of grain at 9 per cent, moisture content than at higher moisture contents at all temperatures tested (15–35°C.). At all moisture contents, surface numbers were relatively high at 15°C.In grain at 14 per cent, moisture content and 25°C., individuals moved vertically and laterally at random but were more active in the evening than in the morning. In grain at 9 per cent, moisture, there was marked irritability, and at 15°C. and 14 per cent, moisture, there was continual but slow movement without any detectable diurnal pattern of activity. Activity was reduced at 30°C., and at 25°C. it was reduced in grain of 17 per cent, moisture content.The significance of these results is discussed in relation to the detection of populations, group formation and the initiation of foci of heating in patches of damp grain.

Laboratory studies on dispersion behaviour of adult beetles in grain. VI.—Three-dimensional analysis of dispersion of five species in a uniform bulk

“…The only homogeneous pattern of vertical dispersion found under the conditions of these experiments was in 0. surinamensis. This was to be expected from earlier studies suggesting that individual vertical movement is random and intragroup disturbance insufficient to elicit negative geotaxis (Surtees, 19636). A positive response to container boundaries was found, and lateral spread was demonstrated, the greatest number of recoveries being made from the corner units.…”

“…Dispersion was denned as the spatial structure of a population as opposed to the more dynamic processes of dispersal which may be involved (Surtees, 1963a). The patterns of dispersion obtained were considered to be spatial expressions of individual and group response to physical stimuli within the limits of the experimental set-up (Surtees, 19636) and indicative of the type of behaviour to be expected in the presence of physical gradients or localised grain conditions. I t was also found that locomotory activity became minimal in certain conditions, peculiar for each species, and it was postulated that if such physical conditions were encountered in grain bulks, there would be a local increase in density.…”

The effect of aeration on the vertical distribution of grain beetles (Coleoptera) in wheat

“…Use of a very high airflow at 10°C may have the same effect. Surtees (1963) recorded increased activity of this species at sub-optimum temperatures, which may explain its reaction to cooling.…”

Emigration activity of the saw-toothed grain beetle Oryza Philus Surinamensis L. (Coleoptera: Silvanidae) in various environmental temperatures

“…The laboratory studies on the effects of insect population density as well as the temperature and humidity of grain on the formation of groupings and on the dispersion of various species of storage beetles, were carried out by Surtees (1963). One of the species studied was the sawtoothed grain beetle.…”