Abstract
The purpose of this study was to elucidate the mechanism by which the Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) invaded paper cups containing peanut cream or blueberry jam sealed in heat-shrunk packaging. An industrial fold wrapping machine was used to wrap the cup samples (lid diameter 8 cm, depth 6.3 cm, bottom diameter 6 cm) with 13.5 μm-thick OPP film. Each paper cup was individually packed in a closed plastic container (15 cm in diameter, 9 cm deep) together with 10 last-instar P. interpunctella larvae. The plastic container was kept at 30°C, 70% r.h. and 24 h constant light conditions. The number of larvae that had infiltrated between the film and the paper cup was recorded after one, four and seven days. These experiments revealed that the larvae were able to invade the paper cup. The frequency of invasion was 70%. However, few entry holes made by the larvae were found on the outer covering film: most larvae invaded via the hole acting as an air vent in the heat-shrunk packaging by gnawing around and enlarging the air vent hole. There was no difference in invasion frequency between the blueberry jam and the peanut cream by larval choice in the experiments over three days. The larvae also invaded a paper cup containing water sealed in heat-shrunk packaging. To prevent larval invasion, the position of the air vent holes on the film was changed from the lid to the bottom of the paper cup. This method of heat-shrunk packaging resulted in a decrease of frequency of invasion from 70% to 5%.
