Directed evolution of Metarhizium fungus improves its biocontrol efficacy against Varroa mites in honey bee colonies

Abstract

Entomopathogenic fungi show great promise as pesticides in terms of their relatively high target specificity, low non-target toxicity, and low residual effects in agricultural fields and the environment. However, they also frequently have characteristics that limit their use, especially concerning tolerances to temperature, ultraviolet radiation, or other abiotic factors. The devastating ectoparasite of honey bees, Varroa destructor, is susceptible to entomopathogenic fungi, but the relatively warm temperatures inside honey bee hives have prevented these fungi from becoming effective control measures. Using a combination of traditional selection and directed evolution techniques developed for this system, new strains of Metarhizium brunneum were created that survived, germinated, and grew better at bee hive temperatures (35 °C). Field tests with full-sized honey bee colonies confirmed that the new strain JH1078 is more virulent against Varroa mites and controls the pest comparable to current treatments. These results indicate that entomopathogenic fungi are evolutionarily labile and capable of playing a larger role in modern pest management practices.

Entomopathogenic Fungi for Pests and Predators Control in Beekeeping

“…In subsequent years, the entomopathogenic fungus Clonostachys rosae was tested in a laboratory test with unsatisfactory results [78]. Afterwards, Sinia and Guzman-Novoa [104] tested the acaricidal efficacy of entomopathogenic fungi in combination with thymol. Mortality of mites was close to 82%, but this value was not significantly different from thymol treatment alone used as a control [104].…”

“…Afterwards, Sinia and Guzman-Novoa [104] tested the acaricidal efficacy of entomopathogenic fungi in combination with thymol. Mortality of mites was close to 82%, but this value was not significantly different from thymol treatment alone used as a control [104]. Lastly, two valuable studies carried out in more recent years are worthy of mention.…”

“…In any case, none of the above-mentioned in vivo studies resulted in a significant difference in the density of phoretic mites between the treated hives and the control groups. Positive exceptions to this rule are the work of Kanga et al [91,101], in which colonies were treated in the absence of brood and this may have contributed to the success of the treatment, and the treatments in combination with thymol performed by Sinia and Guzman-Novoa [104]. In the latter case, the overall effectiveness is due to the synergy of the action.…”

Varroa destructor from the Laboratory to the Field: Control, Biocontrol and IPM Perspectives—A Review

“…Besides, V. destructor infested-brood inoculated with the fungi showed a recovery in the expression of hymenoptaecin gene, involved in immunity, thus correcting the immunosuppression induced by the mite [ 227 ]. To date it is not crystal clear whereas M. anisopliae is safe for honeybees if applied intra hive even considering the improved results showed by Hans et al [ 228 ] with a modified strain. Further experiments are still needed.…”

In Vitro Thermal Requirements of Some Beauveria sp. Isolates Under Constant Conditions

“…Biocontrol strategies, which are based on the use of entomopathogens, dependent not only on the interaction between the pathogen and the host, but also on the environmental conditions to which they might interfere (Mishra et al, 2015). Many abiotic factors are known to have an influence on mycelial growth of entomopathogenic fungi, while also producing fundamental changes in the process of conidia production (Hu et al, 2021) and certain characteristics could restrain their use, in particular, temperature sensitivity, ultraviolet radiation or different abiotic factors (Han et al, 2021). Identification of the thermal profile of entomopathogenic fungi has a major importance in their selection as future candidates in the development of a mico-insecticide.…”