Population estimates of insect pests of stored products on farms on the Darling Downs, Queensland

Abstract

Three surveys were undertaken to obtain estimates of the numbers of insects in stored products on farms on the Darling Downs, Queensland. In one survey, 57 farms were sampled once during 1977-1 978. In another, samples were taken at four-weekly intervals from three farms throughout 1977 and in the third, 16 of the first 57 farms were revisited in 1979. Samples were taken from grain stored for farm use, or grain spills and residues. Live adult insects were removed by mechanical sieving, counted and identified. The mean amounts of grain per farm, estimated visually, were 950 kg of bulk and bagged stocks of feed and seed grain, 270 kg of grain spills, 65 kg in auger boots, 100 kg in trucks and in headers, and 75 kg in other residues. Modal amounts were less, being in the range of 0-100 kg per farm for bagged and bulk grain, and spills on earthen floors, and 0-50 kg for other residues. Sitophiius oryzae (L.) (the rice weevil), Rhyzopertha dominica (F.) (the lesser grain borer), the Cryptolestes spp, group (flat grain beetles), and Trifolium castaneum (Herbst.) (rust-red flour beetle) were the most common pests, being 46.5%, 20.9%, 10.8% and 7.3% of the 52 330 insects found in the first two surveys. These four pests were found on 89.3%, 87.5%, 62.5% and 91.1% of the 57 farms in the first survey. The mean farm populations of these four pests combined was estimated at 360 000 adults (with a modal population per farm in the range of 0-50 000) of which approximately 88% were in bulk and bagged stocks of grain. However, this mean was inflated by a small number of farms having very large populations. An estimated 54% of farms had less than 50 000 adult pests. The second survey showed that insect populations peaked in late autumn, and reached a minimum in early summer.