Studies on the the Distribution and some Management Options of Bean bruchids, Acanthoscelides obtectus Say (Coleoptera: Bruchidae) on Faba Bean Grains (Vicia faba L.) in North Western Amhara, Ethiopia

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Addis Ababa University


Faba bean is one of the most important cultivated legume crops in the world that substitutes meat due to its high protein contents. Bruchids are damaging the grains starting from field to storage. A study was conducted in Amhara Region to assess bruchids distribution and species composition, to determine the time when bean bruchids start infesting faba beans in the field, to screen out effective botanicals against A. obtectus and to determine safe moisture (5-5.5%, 9-9.5, 11-11.5, 14-14.5, 16-16.5 and 20-20.5%) contents for faba bean grain storage. Day one old unsexed newly emerged bruchids were artificially infested on various stages of faba bean pods in the field and in laboratory experiments. Infested pods were followed to observe the sensitive stages of the pods due to A. obtectus infestation at opened matured pods, closed matured pods, bean grains reached for consumption, two weeks before harvest, first emerged pods and free matured pods with no grains. Seeds of botanical oils and various levels of moisture contents were evaluated to manage bruchids. The number of bruchid eggs, number of emerged progenies, number of perforated grains (pods), grain weight loss and developmental period of bruchids were recorded. Data were analyzed by SAS software version 9.2 and MS Excel 07. Hundred percent of the faba bean grain samples collected from various Districts were infested by bruchids. The bruchid species were Callosobruchus chinensis (86.25%), A. obtectus (76.25%) and Bruchus pisorum (33.75%). The Parent A. obtectus were laid significantly higher number of eggs on opened matured pods (20.8±4.34) and closed matured pods (16.5±1.3). All the the faba bean pods were free from bruchid eggs and no progenies emerged from first emerged pods and free matured pods with no grains. Four days after treatment application, 100% of the parent A. obtectus killed in ethiothion 5% dust and oil treated grains indicating the fast knock down effect of the treatments. Statistically lower number of eggs and bean bruchid progenies recorded from ethiothion 5% dust and oil treated grains than the acetone treated and the untreated grains. Treatments like Noug (Guizotia abyssinica L), Rape seed (Brassica napus L.) and Groundnut (Arachis hypogaea L.) were the top effective botanical oils to control A. obtectus parents and their progenies. There was no progenies emerged and egg laid at 5-5.5% grain moisture content, while 393±5.86 eggs were recorded at 20-20.5% grain moisture content. The highest faba bean grain weight loss was recorded to 18.6%±1.87 at 20-20.5% grain moisture content. About 98.3% of the grains germinated and developmental periods of the A. obtectus extended for additional 17.5 days at 9-9.5% moisture content. From the current study, it can be concluded that bruchids distributed in all study areas. Opened matured pods were the sensitive stages of A. obtectus infestation both in the field and laboratory studies. Oils inhibited emergence of A. obtectus from 71.7+2.56%-100% and grain moisture content ranging from 9% to 11.5% were safe for faba bean grain storage. Botanical oils and faba bean grain moisture adjustments can control bruchids that used as a component of IPM techniques to manage bruchids. Key words’:- Bruchids, Acanthoscelides obtectus, infestation, progenies, egg, grain, pod, oil, moisture



Bruchids, Acanthoscelides obtectus, infestation, progenies, egg, grain, pod, oil, moisture