Influence of grain storage practices or kind of structure and pesticide use on insect presence in wheat bulks after a long-term storage: a multi-dimensional analysis

Abstract: A survey of stored-wheat bulks in France was carried out during two years in the spring seasons of 2010 and 2011 to improve the knowledge about the relationships between grain storage practices, preventive sanitation, grain insecticidal treatment, stored-grain temperature management, and presence of insect species in grain samples. Ninety-four wheat storage sites were surveyed each year (after 8-9 month storage). Besides the quantitative analysis of grain samples for insect presence and residue content, a questionnaire was submitted to grain-store managers to record their storage practices, the characteristics of their equipment for grain quality preservation, and the preventive and corrective means they use for insect control. The data from these two groups of variables were processed in a multidimensional statistical analysis to reveal significant correlations between grain management practices for sanitary quality maintenance and the level of presence of insects in wheat samples.A strong relation was observed between the kind of storage structure and the frequency of insect presence in wheat samples. Flat storage of large grain bulks was the most risky storage structure vs. vertical storage in metal or concrete bins. A relationship was observed between the frequency of insect presence in samples and stored grain temperature levels and also with the lack of temperature measurement equipment installed inside grain bins linked to cooling aeration systems. Preventive sanitation before the grain harvest period, i.e. systematic cleaning and insecticide spraying of unfilled bins, was related to 50% reduction of insect presence in corresponding grain samples. The preventive chemical treatment of harvested grain before long-term storage was not related to a limitation of insect presence in samples taken after 8-9-month storage period. The results of this representative survey give objective arguments for the implementation of good IPM practices and risk prevention for grain sanitary quality preservation during long-term storage periods.