Irradiation disinfestation of pulses and resistance of packaging films to insect penetration

Stored broad beans (Vicia faba L.) were examined and its was found that the rates of infestation varied from 10.1 to 12.0% due to Bruchus rufimanus and Bruchidius incarnatus. Beans in polyethylene (0.1 mm thick) bags were irradiated at 0.4, 0.6 and 0.8 kGy. Initially, a few insects were observed, even in the irradiated (0.6 kGy) bags. After 3 months of storage, a few insects were observed in the untreated beans, but none in the irradiated bags. Polyethylene (0.4 mm) bags measuring 12.5 cm x 17 cm and containing cowpea (Vigna sinensis Savi.) were infested with Callosobruchus maculatus and irradiated at 0.4, 0.6 and 0.8 kGy. No insects were observed in the bags during the 120 days of storage, even at a dose of 0.4 kGy, whereas high infestation was found in the untreated beans. The presence of only a few insects in the irradiated bags after 120 days of storage was due to reinfestation. Kraft papers and cellophane were not suitable materials for checking the reinfestation of stored product insects. The most insect resistant packaging material was polyester-polyethylene laminate. The thinnest polypropylene film was penetrated by Rhyzopertha dominica. Polyethylene films of different thicknesses were liable to insect penetration. The experimental results revealed that R. dominica was a strong penetrator, and B. incarnatus and Tribolium castaneum were weak penetrators. Adults of Tragoderma granarium, C. maculatus, Oryzaephilus surinamensis and the larvae of O. surinamensis were unable to penetrate any of the materials tested. 5 refs, 4 tabs