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Study Shows Fungus Attacks Honeybee Digestive Tract


Pollinators, like honeybees, face a barrage of obstacles every day while just trying to do their jobs - pollenating Earth’s plants and perpetuating their colonies. Keeping the queen bee happy, the hive clean, and the young fed while dodging stressors like pesticides and parasites is no easy task.

Holly Holt is a graduate student in the Entomology Department at Penn State. Holt says the numbers of pollinators, like honeybees, are declining world-wide. She says stressors including pesticides, aggressive agricultural practices, parasites, and pathogens are constant threats that can cause habitat fragmentation in pollinator populations here in South Dakota and across the globe.

Holt says she is studying two honeybee stressors in particular - microsporidian fungal pathogens - and the effects they have on the bee’s behavior, physiology, and gene expression.

Nosema apis and nosema ceranae are two species of microsporidia that attack honey bees. Microsporidia employ a dual-life-stage strategy – they persist in the environment as these really hard durable spores and they wait to be eaten by honeybees. So when honeybees eat nosema spores from contaminated food supplies those spores travel to the digestive tract of the bee until they reach a portion of the tract called the mid-gut,” says Holt.

Once in the mid-gut, Holt says the spores invade the bee’s digestive cells - inhibiting its ability to absorb nutrients from food. Holt says infected bees can quickly become energetically stressed and have shorter life spans. She also says bees infected with the fungus can pass it along to the rest of the colony.

Holt says the study also includes looking at the bees on a molecular level.

“We looked at differences in gene expression between infected bees and healthy bees. What we found is that there are a number of genes that are involved in nutritional pathways and hormonal pathways that were affected by nosema infections,” says Holt.

Holt says much still remains unknown about the effects of the nosema fungus on individual honeybees and their colonies.

But, she says people can help bolster healthy bee populations by providing a water source and planting a pollinator garden – a diverse mix of native plants that helps ensure bees are getting a well-balanced diet.

“It’s really important to have a healthy pollinator populations for both food security and just the stability of our ecosystems. The agricultural industry relies on pollinators to produce fruits, nuts, and vegetables. But also in natural ecosystems, eighty-percent of flowering plant species rely on animal-pollenated services, the other twenty- percent relying on wind or water pollination,” says Holt.

Holt says she plans to continue her study on honeybees and is focusing her attention on drones – the male bees - and how they deal with stressors in comparison to female bees.