Varroa Mites, Virus Make Honey Bees Susceptible to Insecticides, Study Says

Controlling for Varroa mites, the parasitic mites that feed on honey bees and serve as vectors for viral diseases such deformed wing virus, can help with improving honeybee populations and make bees less susceptible to harmful insecticides, according to a recent study published in Environmental Pollution

Foraging honey bees may be directly exposed to toxic insecticide sprays in the field or exposure may come from honeybees collecting and bringing pesticide-contaminated pollen and nectar back to their hives to feed lar vae and young bees The presence of insecticides, along with other environmental stressors in agricultural areas, can be a factor leading to issues like colony loss – something beekeepers from around the world are trying to overcome

“Previous research has shown how chemicals like pesticides make bees more susceptible to mites,” said Yu-Cheng Zhu, a research entomologist at Agricultural Research Service’s Pollinator Health in Southern Crop Ecosystems Research Unit in

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Continued from PAGE 1 the few places they are still regularly found is around the Minneapolis-St Paul area of Minnesota and in Wisconsin

“With the amount of detailed information that we and other researchers now have access to in this newly sequenced genome, we have an opportunity to find a whole different approach to strengthening rusty patched bumble bee populations,” said research entomologist Jonathan B Uhaud Koch with the ARS Pollinating Insect-Biology, Management, Systematics Research Unit in Logan, Utah

Koch explained that some of the factors contributing to the decline of rusty

Stoneville, Miss “In our study, we wanted to see if mites and viral infestations make bees more susceptible to insecticides ”

In a study, researchers with the U S Department of Agriculture’s ARS applied the miticide amitraz Apivar, a product commonly used for treating Varroa mites, offlabel to four bee hives and left the other four hives untreated They monitored the mite population density monthly and DWV density in early, middle and late season

Researchers collected bees from miticide-treated and untreated hives, and quantified gene expressions of four immune genes and two physiology-related genes They also tested bees’ sensitivity to five representative insecticides In addition, bees’ natural mortalities were recorded during three seasons

“Miticide treatment led to minor or undetectable mite and DWV infestations during the whole bee season, while untreated colonies had substantially higher mite and DWV infestations,” said Zhu

The data analyses showed that Varroa patched bumble bees are already known: loss of habitat, reduced variety of nectar sources, climate change, exposure to pesticides and more pathogens and pests

While scientists have known the widespread presence of the fungal pathogen Varimorpha bombi (formerly called Nosema bombi) has a detrimental impact on many rusty patched bumble bee populations, Koch said he was a bit surprised by how much Varimorpha genetic material he found in the bumble bee sample that was used to develop the genome map

“We used a small piece of abdominal tissue from a single male collected from a nest in Minnesota, which, given the endangered status of the rusty patched bumble bee, seemed like a ver y good idea,” Koch said “It’s only with the most cutting- mite population irregularly fluctuated over the bee season and mite population density was not dynamically or closely correlated with the seasonal shift of honey bee natural mortality Unlike mites, DWV density in untreated colonies progressively increased over the bee season The density was highly correlated with the seasonal increase in honey bee natural mortality

“In the untreated hives, the increased DWV infestations resulted in decreased physiological and immunity-related functions in late-season honey bees, making the bees more susceptible to insecticides and increasing natural mortality rates during the season, ” said Zhu Varroa mites, also known as Varroa destructor, can reduce fat body and body fluids that contain important detoxification enzymes and immune proteins in honey bees,” Zhu said As a result, bees have impaired immune, detoxification/defense systems and other essential processes Coupling those impairments with exposure to insecticides can be detrimental to edge equipment that you could resolve an entire genome of 15,252 genes and 18 chromosomes from a tiny bit of one bumble bee ”

It turns out about 4 5 percent of the DNA the researchers sequenced came from Microsporidia, the fungal group that includes Varimorpha bombi

“That’s a massive amount of genetic information from the bee tissue sample to be associated with Varimorpha bombi It demonstrates how pervasive the pathogen is,” Koch said

“Having this high-quality genome will support the identification of genetic differences between rusty patched bumble bee populations that appear to be doing well versus where they are in decline,” Koch said “This may give us a handle on identi-

Bee Populations

“Having impaired immunity, especially later in the season with fewer food sources, can be challenging for honey bees,” said Zhu Zhu, whose work focuses on the toxicological impact of pesticides on beneficial insects in the Mississippi Delta Area, said that the study’s results indicated the importance of studying the bottom-up effects of mite infestations on the overall health of honey bees in real-world contexts

“Chemical control is still a major method in preventing crop loss and controlling insect pest populations,” said Zhu “It is important to study the effects of chemical control in honey bee populations so we can find best practices for protecting the health of bees ”

The Agricultural Research Service is the USDA’s chief scientific in-house research agency ARS focuses on solutions to agricultural problems affecting America Each dollar invested in U S agricultural research results in $20 of economic impact GN fying the genes that give the more capable population its flexibility to deal with its environment We may also gain a better understanding of the genetic basis of bumble bee behavior, physiology and adaptation to changing environmental conditions ”

Once the more successful genes for a particular type of local condition are identified, researchers will be able to give a population a boost in the right direction when it comes to restoring the rusty patched bumble bee to an area through captive breeding programs

This research was funded by ARS and USFWS The research was published in the journal G3: Genes | Genomes | Genetics and the genome is available on the National Center for Biotechnology Information website GN