Evaluation of Beauveria Bassiana Isolates Against Varroa Destructor of Apis Mellifera Under Laboratory Condition
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Date
2024-04
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Addis Ababa University
Abstract
Varroa, Varroa destructor (Acari: Varroidae), is an ectoparasitic mite of honeybees, Apis mellifera. This parasite poses a substantial threat to the health, welfare and production of A. mellifera globally, including Ethiopia. Without chemical treatment, colony losses worldwide are common. However, resistance to synthetic chemicals in beekeeping is increasingly concerning. Entomopathogenic organisms provide an eco-friendly alternative to pesticides and can prevent resistance development. Therefore, isolates of Beauveria bassiana were tested for their pathogenicity against V. destructor and their negative effect on the brood and adult stages of the central highland honeybees of Ethiopia, A. mellifera. Varroa mites were immersed in 5 millilitres of a conidial suspension containing 1 x 108 conidia/mL of three different fungal isolates (APPRC-44BC, APPRC-27, and S#10H), as well as control solutions (0.05% Tween 80 and distilled water). The inoculated mites were placed on honeybee brood inside capped cells. Then, the infected brood combs were kept in an incubator at 33 ℃ and 60% relative humidity for ten days. The fungal isolates and control treatments were also applied to young adult workers and healthy brood to observe the effects of the treatments. Fungal isolate APPRC-44BC displayed the highest (73%) potential for killing varroa mite. All three isolates (APPRC-44BC, APPRC-27, and S#10H) were found to be highly efficient between the sixth and eighth days post-application, accounting for 96.8% to 100% of the fungal-induced deaths. Interestingly, treatment with B. bassiana isolates did not show a significant effect on brood emergence and the weight of newly merged adults. However, the treatments had significant effect on adult honeybee survival. It is clearly observed from these results that isolates of B. bassiana are potential bio-control agents against V. destructor. However, further studies are needed to evaluate the efficacy of this promising fungal isolate (APPRC-44BC) in honeybee colonies under field conditions, as well as to develop application methods that have minimal impact on adult honeybee survival.
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Keywords
Apis Mellifera, Beauveria Bassiana, Biocontrol, Honeybees, Varroa Destructor