Effect of Infestation bySitotroga cerealella(Lepidoptera: Gelechiidae) andSitophilus oryzae(Coleoptera: Curculionidae) on the Deterioration of Bagged Wheat

Abstract

The quantitative and qualitative losses of simulated bagged wheat ( Triticum aestivum L.) infested by Sitotroga cerealella (Olivier), Sitophtlus oryzae (L.), or both species were studied at 28°C and 60% RH for 22 weeks. Ventilated bottles with 130 g of wheat of 11.5% moisture content were placed inside 44-kg bags of wheat for evaluation of four treatments to simulate the environment inside a grain bag, the most popular method of storing grain in the tropics and subtropics. The treatments consisted of wheat with no insects, with S. cerealella by itself, with S. oryzae by itself, and with a mixture of S. cerealella and S. oryzae. The variables measured were insect numbers, temperature, CO 2 concentration, moisture content of wheat, microflora, seed germination, 100-kernel weight, dust weight, and fat acidity value (FAV). The numbers of live S. cerealella increased rapidly until week 15 and then decreased in both single- and mixed-species treatments. The rapid growth of S. cerealella in single- and mixed-species treatments resulted in increases in temperature, CO 2 concentration, moisture content, bacterial infection, dust weight, and FAV and decreases in germinability and 100-kernel weight. The infection level of fungi of the Aspergillus glaucus group in wheat increased during 10–15 weeks but then decreased after severe deterioration had occurred. The numbers of S. oryzae increased slowlyin single- and mixedspecies treatments but did not appreciably affect other variables during 22 weeks.