Biological control of the bean weevil, Acanthoscelides obtectus (Say) (Col.: Bruchidae), by the native parasitoid Dinarmus basalis (Rondani) (Hym.: Pteromalidae) on small-scale farms in Colombia

Abstract

The potential of the parasitoid Dinarmus basalis to control natural infestation by Acanthoscelides obtectus was evaluated on seven farms. All samples taken at harvest already contained some level of immature weevil stages inside the bean seeds. If left untreated, weevils caused visible damage of up to 40% of the beans during a 16-week storage period. In this study, we distinguished between farms with low and high levels of infestation at the time of harvest. A single introduction of the parasitoid D. basalis (five males and five females per kg bean seeds) in the first week following harvest resulted in weevil eradication on four farms with a low level of initial infestation. Suppression of the weevil population on the three farms with a high level of initial infestation depended on the developmental stage of the weevil population at harvest time. When weevil larvae were present as early instars, parasitoids reduced weevil populations by 88–97%. Control was ineffective in beans containing later weevil instars at time of harvest. The results show that biological control of the bean weevil by its natural enemy D. basalis under on-farm conditions can be quite successful. The effectiveness can be further improved by harvesting beans as early as possible. [KEYWORDS: Biological control ; On-farm ; Storage ; Parasitoids ; Bean weevil ; Natural infestation ; Phaseolus vulgaris]