Field and post-maturation infestation of maize by stored product pests in Mexico

Abstract

An assessment of the levels of field infestation of maize by stored-product pests was carried out in El Bajio, Central Mexico. Their presence was low at the initial harvest stage with only 0.76% of fields infested with either Prostephanus truncatus (Horn) or Sitophilus zeamais Motschulsky, but after several months of drying on site in stacks, 54.4% of fields were infested with P. truncatus and 63.6% with S. zeamais, with a corresponding increase in the infestation rate within individual fields. Numbers of Ahasverus advena (Waltl) were also higher in the second sampling period and the moisture content had dropped, creating conditions more suitable for the development of stored-product pests. An initial infestation by P. truncatus was seen to increase the probability of further infestation within individual stacks over time. In Mexico, this drying stage allows easy access for stored-product pests, although subsequent farmer selection of unifested cobs at storage reduces their effect. An investigation of insect migration into artificial stores indicated that P. truncatus is more attracted to P. truncatus-infested cobs, although the initial migration and subsequent build-up was slow. Other stored-product pests showed a tendency towards attacking uninfested cobs. These results indicate that storage pests can infest the crop at any time from field maturation to the storage period. However, particularly in the case of P. truncatus, the earlier they arrive the greater the risk of loss not only from the progeny of the original colonizers but also because further adults appear to be attracted to existing infestations.