Resistance categories to Acanthoscelides obtectus (Coleoptera: Bruchidae) in tepary bean (Phaseolus acutifolius), new sources of resistance for dry bean (Phaseolus vulgaris) breeding

Acanthoscelides obtectus (Coleoptera: Bruchidae) is one of the most important post-harvest pests of dry bean Phaseolus vulgaris L. Tepary bean (Phaseolus acutifolius) could be a novel source of resistance against A. obtectus to improve dry bean. We studied the resistance of tepary bean varieties to A. obtectus. We focused on three categories of defense: antixenosis, antibiosis, and tolerance. Tepary pinto amarillo (T-amarillo) and Tepary pinto negro (T-negro) beans show high antixenosis to adults, increased numbers paralyzed per hour and per day, and increased duration of development in winter; reduced oviposition, number of emerged adults and adult weight. Due to the small number of emerged adults, there was very little grain weight loss. Volatile compounds were discarded as the cause of paralysis in adults. Adults in T-amarillo and T-negro were paralyzed until day 10 and 14 and then, they die at an exponentially increasing rate. In addition T-negro and T-amarillo produced the highest mortality in larvae before entering the seeds. T-amarillo and T-negro showed antixenoxis, resistance and tolerance to A. obtectus infestation and they can be used as sources of resistance for P. vulgaris breeding. The compound that causes the antixenosis and paralysis in adults is in the testa of the resistant varieties and is not likely to be a volatile compound, whereas the mortality and antixenosis in larvae is caused more probably by a volatile compound present in the testa.