Ecological significance and practical implications of behaviour patterns determining the spatial structure of insect populations in stored grain

Abstract

The influence of population density, temperature, humidity and other environmental factors on the individual behaviour, aggregation in restricted parts of the habitat (accumulation) and spatial structure of the population (dispersion) of five species of beetles found in stored grain in Britain was the subject of laboratory studies by the author in 1959–65. In this paper, the results of these studies are drawn together, compared with field observations, and discussed in relation to behavioural mechanisms, ecology and control. The five species comprised Oryzaephilus surinamensis (L.), Tribolium castaneum (Hbst.).Cryptolestes ferrugineus (Steph.), Rhyzopertha dominica (F.) and Sitophilus granarius (L.). A basic plan of behaviour is considered to underlie the observed dispersion of these pests in grain, which may be summarised as follows: random movement of individuals causes disturbance within the population and leads to dispersal; accumulation occurs where individual movement is most restricted in response to environmental factors and where disturbance is consequently at a minimum.The dispersion of O. surinamensis is almost entirely determined by kinesis mechanisms, and accumulation takes place in the warmest and dampest parts of a grain bulk. The dispersion of T. castaneum is determined to a lesser extent by kinesis mechanisms; accumulations take place in the drier parts of a bulk and at places where the temperature is about 25°C., but also in regions of damp grain if this is mouldy. The dispersion of C. jerrugineus is mainly determined by behaviour relating to the requirements of oviposition and feeding, which is superimposed on the basic plan. R. dominica accumulates in the driest parts of a grain bulk. The dispersion of S. granarius is largely determined by individual thigmotactic behaviour, so that accumulations are typically at the periphery of the grain bulk.The ways in which a knowledge of the underlying causes of dispersion and accumulation aid in the detection and control of the pests and point to the optimum storage conditions are described.