Improved bruchid management through favorable host plant traits and natural enemies

Abstract

The combination of favorable host plant traits and biological control by the parasitoid Dinarmus basalis (Rondani) has been suggested to contribute significantly to the protection of stored beans ( Phaseolus vulgaris L.) from attack by Acanthoscelides obtectus (Say) and other bruchids. Physical seed parameters have previously been reported to impede penetration by neonate bruchid larvae into dry beans. However, those parameters could also affect parasitoid performance. In addition, other plant traits such as chemical seed parameters have the potential to contribute to bruchid suppression but may influence food processing. We characterized 22 bean lines in regard to physical attributes, such as seed coat thickness and cotyledon strength, and tested 10 selected lines for potential correlated effects on bruchid survival and parasitoid efficiency. Bean lines expressing the natural seed storage protein arcelin and arcelin-free cultivars were compared regarding their hydration kinetics. Bioassay results showed that increasing seed coat thickness and cotyledon strength did not reduce bruchid penetration into the seeds, indicating that the survival of neonate bruchid larvae does not depend on their individual capability to pierce a seed. Introduction of parasitoids yielded only few parasitoid offspring, but resulted in increased post-penetration mortality of bruchids in samples with arcelin containing bean lines. This finding is discussed in the context of host feeding. Comparisons of hydration kinetics of arcelin containing and arcelin-free beans yielded no significant differences in water absorption rate and hydration capacity. The present work corroborates earlier evidence that the natural storage protein arcelin is a promising component for integrated storage systems and demonstrates that it does not detectably alter the cooking quality of dry beans.