Distribution of insect pests and their natural enemies in a barley pile

Abstract

The distribution and abundance of stored product pests and their natural enemies infesting the upper layer of a barley pile was assessed in this study. Sampling was carried out on a monthly basis from February to December 2009. Insects were sampled with a grain trier and pitfall traps. Yellow sticky traps were also used to capture flying insects. Most abundantly captured species were, in order of abundance: Rhyzopertha dominica, Sitophilus granarius, and Latheticus oryzae. Fewer individuals of other species were occasionally captured, such as Cryptolestes ferrugineus, Oryzaephilus surinamensis, Lasioderma serricorne and Stegobium paniceum. Concerning Hymenoptera, the species Anisopteromalus calandrae and Cephalonomia waterstoni were abundantly captured with yellow and pitfall traps, while lower numbers were captured with the grain trier trap. Comparing pitfall and grain trier captures, in the former one, natural enemies were abundantly captured, whilst captures with the grain trier were punctual. The predator Withius piger (Pseudoscorpionida: Withiidae) was captured both with grain trier and pitfall traps. Its captures peaked in August-September. The abundance of coleopteran pests varied among the different depths sampled and the time of the year. The highest captures of pests occurred in March and May; the natural enemy A. calandrae peaked in April, and C. waterstoni was scarcely captured. The three species of natural enemies were occasionally found in the deepest samples, thus, they were able to penetrate around 80-cm deep in the grain searching for their hosts.

Keywords: Grain, Sampling, Biological control, Host finding.