The Role of Moisture Content on the Preservation of Hermetically-Stored Dry Bean Infested with the Mexican Bean Weevil Zabrotes subfasciatus (Boh.)

Abstract

The aim of this work was to determine the effect of moisture content on dry common bean (Phaseolus vulgaris L., Fabaceae) during the insect disinfestation by oxygen depletion and carbon dioxide increment for elimination of all stages of the Mexican bean weevil Zabrotes subfasciatus (Boheman) (Coleoptera: Bruchidae) and avoidance of physical damage of dry bean occasioned by insect development. Experimental units with 150 g of dry bean with 10, 12, and 15% of moisture content infested with 20 adult insects sexing 1:1 were stored 27 d under hermetic and non-hermetic conditions. Oxygen and carbon dioxide levels, moisture content, and insect mortality of initial infestation were evaluated every 3 d. To quantify emergence of the insects from the offspring (F1) and percentage of damage to dry bean, the dry bean of the experimental units free of adult insects was kept 50 d in a rearing room. Non-hermetically stored grain presented with insect emergence up to 475 insects and 53.7% physical damage. However, in the hermetic storage system, after 21 and 27 d, there was no insect emergence and no dry bean was damaged with moisture contents of 10 and 12%, respectively. Oxygen levels which did not allow the development (F1) of Z. subfasciatus and the subsequent damage to the dry bean were between 3.6-6.0% and for carbon dioxide were 7.70-10.27%. These results show the importance of moisture content in dry bean to inhibit insect development of Z. subfasciatus in short time under hermetic storage conditions of low oxygen and high carbon dioxide levels.