Acanthocelides obtectus (Say)
Common name: Bean weevil.
Taxonomic placing: Insecta, Holometabola, Coleoptera, Chrysomelidae.
Geographical distribution: Cosmopolitan. Distribution Maps of Plant Pests # 625, 2002.
Host plants: Legumes, such as beans, vetch, alfalfa, soybean and lentils.
Morphology: The adult body is 2-5 mm in length, light to dark brown to black in color. The elytra, which do not completely cover the abdomen, are with longitudinal spots, a golden pubescence, and a red posterior border. The head is bent forward. The larvae are white with a brown head, setae and three pairs of reduced legs.
Life history: This pest is a warm-climate species, with optimal temperatures around 22-27°C. A female lays about 200 eggs, sticking them on bean seeds inside the drying pods in the field or on beans in storage. The emergent larva invades the seed and feeds therein, pupates and then gnaws a roundish emergence hole; several larvae may develop in the same seed. The adults do not feed, are strong fliers, live for about 3 weeks and usually complete 6 annual generations.
Economic importance: A significant pest of legumes, especially beans, in some parts of the world, attacking crops in the field and in warehouses. It may reduce yields by 60%. Due to feeding inside seeds, it may not be noticed until much of the crop is infested. Partially damaged seeds lose their germinating ability and taste quality.
Management
Monitoring: As the feeding larvae cannot be seen inside the seeds, monitoring is conducted by maintaining potentially-infested seeds in a closed container and counting the emergence holes.
Horticultural methods: Strict hygiene in stores, which should be well-closed, and the removal of infested residues from last season’s harvest. Frequent aeration of the storage container may reduce infestation. Susceptible crops are to be planted at some distance from stores and legume fields.
Mechanical methods: The pest may be killed by exposing it to subzero temperatures, or to modified atmospheres. Maintaining seeds in storage within hermetic packaging will reduce infestations.
Plant resistance: Wild bean varieties and accessions are partially resistant to the pest due to small seed size, pods with a stronger wall and indigestible seed components. Some common Bulgarian bean varieties are also partially resistant to the pest.
Chemical control: Organophosphates and pyrethroids were formerly applied against the pest and in some cases are still being applied, but the emergence of pesticide resistance has curtailed their use. Nowadays essential oils and plant extracts are in common use. The extracts and vapors of several plants, including Lavandula hybrids, Rosmarinus officinalis Linnaeus, Urtica dioica Linnaeus and Taraxacum officinale Linnaeus have strong insecticidal activities, killing the pest and/or reducing its fecundity, egg hatchability and offspring emergence.
Biological control: The pteromalid Dinarmus basalis (Rondani) almost completely suppressed weevil populations in Colombia when early pest instars were present; elder weevil larvae were less affected.
References
Applebaum, S.W. and Guez, M. 1972. Comparative resistance of Phaseolus vulgaris beans to Callosobruchus chinensis and Acanthoscelides obtectus (Coleoptera: Bruchidae): the differential digestion of heteropolysaccharides. Entomologia Experimentalis et Applicata 15: 203-207.
Apostolova, E., Palagacheva, N., Svetleva, D. and Mateeva, A. 2013. Investigation on the resistance of some Bulgarian common bean genotypes towards bean weevil (Acanthoscelides obtectus Say). Journal of Central European Agriculture 14: 1530-1540.
Dupuis, A.S., Fuzeau, B. and Fleurat-Lessard, F. 2006. Feasibility of French beans disinfestation based on freezing intolerance of post-embryonic stages of Acanthoscelides obtectus (Say) (Col.: Bruchidae). Proceedings 9th International Working Conference on Stored Product Protection, pp. 956-965.
Jovanović, Z., Kostić, M. and Popović, Z. 2007. Grain-protective properties of herbal extracts against the bean weevil Acanthoscelides obtectus Say. Industrial Crops and Products 26: 100–104.
Karabörklü, S., Ayvaz, A. and Yilmaz, S. 2010. Bioactivities of different essential oils against the adults of two stored product insects. Pakistan Journal of Zoology 42: 679-686.
Navarro, S. and Donahaye, E. 1990. Generation and application of modified atmospheres and fumigants for the control of storage insects. In: Champ, B. R., Highley, E. and Banks, H. J. (eds). Proceedings of an International Conference on Fumigation and Controlled Atmosphere Storage of Grain, pp. 152-165.
Papachristos, D.P. and Stamopoulos D.C. 2002. Repellent, toxic and reproduction inhibitory effects of essential oil vapours on Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae). Journal of Stored Products Research 38: 117–128.
Porca, M., Oltean, I. and Dobrin, I., 2003. Chemical control of bean weevil, Acanthoscelides obtectus Say in storage condition. Journal of Central European Agriculture 4: 209-216.
Schmale, I., Wäckers, F.L., Cardona, C. and Dorn, S. 2002. Field Infestation of Phaseolus vulgaris by Acanthoscelides obtectus (Coleoptera: Bruchidae), parasitoid abundance, and consequences for storage pest control. Environmental Entomology 31: 859-863.
Schmale, I., Wäckers, F.L., Cardona, C. and Dorn, S. 2006. 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. Journal of Stored Products Research 42: 31-41.
Schoonhoven, A.v., Cardona, C. and Valor, J. 1983. Resistance to the bean weevil and the Mexican bean weevil (Coleoptera: Bruchidae) in noncultivated common bean accessions. Journal of Economic Entomology 76: 1255-1259.
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