Disinfestation of wheat seed from Sitophilus granarius (L.), S. oryzae (L.), and Rhyzopertha dominica (F.) by packing under vacuum in high-barrier multi-layered plastic bags

Abstract

Conditioning under low-oxygen modified atmosphere in sealed enclosures, containers or bags is widely used for the disinfestation of grain from insect pest species. The effect of hermetic vacuum storage on the survival of primary insect pests of cereals still lacks relevant documentation. To enhance knowledge on this topic, a pilot scale experiment was undertaken. Prior to the study, batches of wheat seeds were infested by some of the most harmful insects of stored cereals, Sitophilus oryzae, S. granarius, and Rhyzopertha dominica, in order to obtain infested seed samples by all development stages. Then, 5-kg sound wheat seed lots were placed inside multilayer aluminium-plastic flexible bags and 200 g of previously infested seeds were included before vacuum packing the bags at depression levels: 30, 50 or 70 kPa. In addition to storage at an average temperature of 25.8 °C, survival rate and progeny production of insects were checked at regular time intervals after opening a series of bags. After adult recovery by sieving, the 200 g-samples were incubated for 42 d at 25.8 °C for hidden stages recovery. The exposure time for 99% reduction of survival rate and progeny production (LT99) by S. oryzae and S. granarius, at 70 kPa depression level, was observed after 37.5 and 31 d exposure, respectively. For R. dominica, LT99 was assessed at 63.5, 75.6 and 88.5 d at 70, 50 and 30 kPa depression level, respectively. Rhyzopertha dominica was observed much more tolerant than the two weevil species, especially when depression level was more than 50 kPa. This species was able to produce progeny under vacuum. The origin of the differences in susceptibility between the weevils and the lesser grain borer in relation to storage under vacuum inside flexible high-barrier multilayer aluminium-plastic bags are discussed.