Effect of a Fungal Biopesticide on the Honey Bee

Riley Shultz

doi:10.7273/000003772

Honey bee health has been declining; annual hive loss rates have exceeded 35% in recent years. While there are many factors that are contributing to poor honey bee health, including pathogens, poor nutrition and pesticides, the ectoparasitic mite Varroa destructor is the most commonly reported cause of hive deaths. Washington State University’s Entomology and Plant Pathology programs have worked to develop a new strain of entomopathogenic fungus in the genus Metarhizium that kills mites. Previous research suggests treatment with fungal spores that are nonpathogenic to bees results in an increase expression of immune function genes in honey bees. Although Metarhizium shows promise in relation to boosting bee immune function, it has yet to be completely characterized. An experiment was conducted to test whether Metarhizium brunneum has significant effect on V. destructor mortality rates, as well as increased longevity and immune function of Apis mellifera. Caged bees were treated with varying doses of Metarhizium (control, low, medium, or high) and incubated at 32°C. Varroa and honey bee mortality was tracked for 20 days. It was found that treatment did not significantly increase mite mortality in relation to control; however, bees treated with a high dose lived significantly longer than control bees (t-test p=0.05 set a-priori). RNA was extracted from the honey bees and gene expression of immune related genes was analyzed using quantitative Polymerase Chain Reaction (qPCR). Some immune regulation genes, such as Apidaecin and Dorsal 2 had statistically significant immune regulation trends. While not all data had significant differences, there were promising trends that could be further confirmed with larger sample sizes. Subsequent trials with stronger doses of Metarhizium should be performed to find significant data across each immune regulator.

Effect of a Fungal Biopesticide on the Honey Bee

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