Analysis and simulation modelling of population dynamics and bioenergetics ofCryptolestes ferrugineus (Coleoptera: Cucujidae) in stored wheat

The consequences of infestation of stored wheat by the rusty grain beetle, Cryptolestes ferrugineus (Stephens) was determined for 222 d at 30°C in 70-1 drums containing wheat at 13.5% moisture content. Temperature, grain moisture, seed damage, germination and weight, dust weight, fat acidity values (FAV), published data on growth, reproduction, survival and cannibalism rates and energy budget were used to develop a computer simulation model to simulate the population dynamics of C. ferrugineus at 30°C. In the insect-free control system, the fungi, Alternaria alternata decreased, Aspergillus glaucus group and Penicillium spp. increased, probably causing a rise in FAV of the grain. In the insect-infested system, C. ferrugineus could only eat the wheat germ of kernels that had a broken bran layer; 35.7% of the wheat germ or 914.6 J per 100 kernels was consumed. Within two generations after initial introduction, C. ferrugineus reached a peak in numbers and biomass polluting the ecosystem with excreta and remains, and accelerating the deteriorative process observed in the insect-free control system by increasing respiration temperature, FAV and reducing grain germination. After 87 d, the insect population declined to low levels. The simulation model provided a close match between the observed and predicted numbers of insect life stages and bioenergetic variables during the insect population growth phase. Simulation trials suggested that cannibalism of larger compared with smaller immature stages would be more wasteful of developmental time and energy, reducing the number of individuals reaching reproductive age, and that density-dependent fecundity was probably not an important regulatory mechanism of C. ferrugineus population dynamics in this study.