Biological control of the bean weevil, Acanthoscelides obtectus, by a Hymenopteran parasitoid, as part of an IPM system
Acanthoscelides obtectus (Say) (Col.: Bruchidae) and Zabrotes subfasciatus (Boheman) (Col.: Bruchidae) are the major post harvest pests of dry beans in Latin America. Breeding of resistant bean varieties has been successful against Z. subfasciatus , but these varieties remain susceptible to A. obtectus . The aim of this study was to find a biological control against A. obtectus , and to test whether this control method could be part of an IPM system, integrating resistant bean varieties and parasitoids.
1 . The longevity and the progeny production of three larval/pupal ectoparasitoids of A. obtectus were evaluated, with and without food source. Dinarmus basalis Ashmead (Hym.: Pteromalidae) produced the highest number of progeny and had the longest reproductive lifespan, making it the most promising agent for the control of A. obtectus compared to Anisopteromalus calandrae (Howard) (Hym.: Pteromalidae) and Heterospilus prosopidis (Viereck) (Hym.: Braconidae). Honey given as a food supplement to the synovigenic species D. basalis and A. calandrae increased their lifetime progeny production through an increased reproductive lifespan, while in the pro-ovigenic species H. prosopidis consumption of honey resulted in a higher number of progeny through an increased daily oviposition rather than an increased oviposition period.
2 . Over a period of three years, samples of recently harvested beans were taken from small-scale farms in Restrepo, Valle de Cauca, Colombia. The level of infestation by A. obtectus was found to be low, but consistent over this period. At harvest time 90% of the bean samples were infested by the weevil. Based on emergence data it can be concluded that oviposition by A. obtectus in the field had been restricted to a very short period before harvest. The only parasitoid which emerged was Horismenus ashmeadii (Dalla Torre) (Hym.: Eulophidae), being recorded from 21% of the samples. The samples in which the parasitoid was found carried an average of 5 parasitoids per 1000 beans, with a maximum of 12 parasitoids. During 16 weeks of storage, two weevil generations emerged causing visible damage ranging from 0.5 to 34% of the beans (average of 14%). (Abstract shortened by UMI.)