Honey bee life spans are 50% shorter today than they were 50 years ago

A new study by University of Maryland entomologists shows that the lifespan for individual honey bees kept in a controlled, laboratory environment is 50% shorter than it was in the 1970s. When scientists modeled the effect of today's shorter lifespans, the results corresponded with the increased colony loss and reduced honey production trends seen by U.S. beekeepers in recent decades.

Colony turnover is an accepted factor in the beekeeping business, as bee colonies naturally age and die off. But over the past decade, U.S. beekeepers have reported high loss rates, which has meant having to replace more colonies to keep operations viable. In an effort to understand why, researchers have focused on environmental stressors, diseases, parasites, pesticide exposure and nutrition.

This is the first study to show an overall decline in honey bee lifespan potentially independent of environmental stressors, hinting that genetics may be influencing the broader trends seen in the beekeeping industry. The study was published November 14, 2022, in the journal Scientific Reports.

"We're isolating bees from the colony life just before they emerge as adults, so whatever is reducing their lifespan is happening before that point," said Anthony Nearman, a Ph.D. student in the Department of Entomology and lead author of the study. "This introduces the idea of a genetic component. If this hypothesis is right, it also points to a possible solution. If we can isolate some genetic factors, then maybe we can breed for longer-lived honey bees."

Nearman first noticed the decline in lifespan while conducting a study with entomology associate professor Dennis van Engelsdorp on standardized protocols for rearing adult bees in the laboratory. Replicating earlier studies, the researchers collected bee pupae from honey bee hives when the pupae were within 24 hours of emerging from the wax cells they are reared in. The collected bees finished growing in an incubator and were then kept as adults in special cages.

Nearman was evaluating the effect of supplementing the caged bees' sugar water diet with plain water to better mimic natural conditions when he noticed that, regardless of diet, the median lifespan of his caged bees was half that of caged bees in similar experiments in the 1970s. (17.7 days today versus 34.3 days in the 1970s.) This prompted a deeper review of published laboratory studies over the past 50 years.

"When I plotted the lifespans over time, I realized, wow, there's actually this huge time effect going on," Nearman said. "Standardized protocols for rearing honey bees in the lab weren't really formalized until the 2000s, so you would think that lifespans would be longer or unchanged, because we're getting better at this, right? Instead, we saw a doubling of mortality rate."

Although a laboratory environment is very different from a colony, historical records of lab-kept bees suggest a similar lifespan to colony bees, and scientists generally assume that isolated factors that reduce lifespan in one environment will also reduce it in another. Previous studies had also shown that in the real world, shorter honey bee lifespans corresponded to less foraging time and lower honey production. This is the first study to connect those factors to colony turnover rates.

When the team modeled the effect of a 50% reduction in lifespan on a beekeeping operation, where lost colonies are replaced annually, the resulting loss rates were around 33%. This is very similar to the average overwinter and annual loss rates of 30% and 40% reported by beekeepers over the past 14 years.

Nearman and vanEngelsdorp noted that their lab-kept bees could be experiencing some sort of low-level viral contamination or pesticide exposure during their larval stage, when they're brooding in the hive and worker bees are feeding them. But the bees have not shown overt symptoms of those exposures and a genetic component to longevity has been shown in other insects such as fruit flies.

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Studying mosquito immune cells could improve understanding of disease transmission

A new study that details mosquito immune cells could shed light on the insect immune system and how mosquitoes transmit parasites that cause malaria.

A new study, published recently in the peer-reviewed scientific journal eLife, identifies several new forms of mosquito immune cells, providing new clarity into the mosquito immune system. Immune cells play a central role in the immune response of mosquitoes toward malaria parasites and viruses after these pathogens are taken up upon feeding on an infected person. It's a field of study that has remained poorly understood due to the lack of genetic tools, said Ryan Smith, an associate professor of entomology at Iowa State University and lead author of the study.

"These experiments lay the foundation for a better understanding of how these immune cells function that could lead to a future when humans are able to make mosquitoes unable to transmit disease," Smith said.

The new study utilized single-cell RNA sequencing, a relatively new technique that allows researchers to examine the cellular messages within individual cells, to characterize mosquito immune cells, known as hemocytes. The study found mosquito hemocytes show greater complexity than previously thought, evidence of cell differentiation, and that some cells may even undergo a maturation process. The authors also provided comparative analysis to single-cell studies in other insect systems, highlighting important similarities and differences between mosquitoes and other insects. The new study is an important first step for future exploration of the mosquito immune system, which could be important for gaining better understanding of how mosquitoes transmit pathogens, such as malaria parasites, to humans through their bite.

"There's a big body of evidence that suggests that immune cells of mosquitoes are really critical to their ability to transmit disease," Smith said. "From that perspective, we haven't really known a great deal about the molecular aspect of what those immune cells look like."

Previous evidence suggests immune cells mediate disease pathways in mosquitoes, and play vital roles in killing malaria parasites at multiple stages in the mosquito host. The new study sets the stage for future research aimed at answering those questions, he said.

Smith even envisions a future, though it's still years away, when this line of research could lead to the production of mosquitoes genetically modified to overexpress certain immune cell populations that reduce the ability of a mosquito to transmit pathogens that cause mosquito-borne disease. These resistant mosquitoes could then be introduced into wild mosquito populations to breed and spread these genetic traits. The result could be mosquito populations that are less likely to spread disease to humans, though Smith cautions it's all purely theoretical at this point.

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Unsure how to help reverse insect declines? Scientists suggest simple ways

 Entomologist Akito Kawahara's message is straightforward: We can't live without insects. They're in trouble. And there's something all of us can do to help.

Kawahara's research has primarily focused on answering fundamental questions about moth and butterfly evolution. But he's increasingly haunted by studies that sound the alarm about plummeting insect numbers and diversity.

Kawahara has witnessed the loss himself. As a child, he collected insects with his father every weekend, often traveling to a famous oak outside Tokyo whose dripping sap drew thousands of insects. It was there he first saw the national butterfly of Japan, the great purple emperor, Sasakia charonda. When he returned a few years ago, the oak had been replaced by a housing development. S. charonda numbers are in steep decline nationwide.

While scientists differ on the severity of the problem, many findings point to a general downward trend, with one study estimating 40% of insect species are vulnerable to extinction. In response, Kawahara has turned his attention to boosting people's appreciation for some of the world's most misunderstood animals.

"Insects provide so much to humankind," said Kawahara, associate curator at the Florida Museum of Natural History's McGuire Center for Lepidoptera and Biodiversity. "In the U.S. alone, wild insects contribute an estimated $70 billion to the economy every year through free services such as pollination and waste disposal. That's incredible, and most people have no idea."

Insects sustain flowering plants, the lynchpins of most land-based ecosystems, and provide food sources for birds, bats, freshwater fish and other animals. But they face a barrage of threats, including habitat loss, pesticides, pollution, invasive species and climate change. If human activities are driving the decline, Kawahara reasons, then people can also be a part of the solution.

In an opinion piece published in a special edition of the Proceedings of the National Academies of Sciences, Kawahara and his collaborators outline easy ways everyone can contribute to insect conservation.

Mow less

If you have a lawn, mowing less can give insect populations a boost. Kawahara suggests reserving 10% of a landscape for insects, either actively replacing a monoculture of grass with native plants or simply leaving the space unmown. These miniature nature preserves provide crucial habitat and food reservoirs for insects, he said, particularly if they remain free of chemical pesticides and herbicides. Benefits for lawn-maintainers include less yardwork and lower expenses.

"Even a tiny patch could be hugely important for insects as a place to nest and get resources," Kawahara said. "It's a stepping stone they can use to get from one place to another. If every home, school and local park in the U.S. converted 10% of lawn into natural habitat, this would give insects an extra 4 million acres of habitat."

If you don't have a lawn, you can still help by cultivating native plants in pots in window boxes or on balconies and patios.

Dim the lights

Nighttime light pollution has spiked since the 1990s, doubling in some of the world's most biodiverse places. Artificial lights are powerful attractants to nocturnal insects, which can exhaust themselves to death by circling bulbs or fall prey to predators that spot an easy target.

You can give insects a hand -- and reduce your electric bill -- by turning off unnecessary lights after dark and using amber or red bulbs, which are less attractive to insects.

Use insect-friendly soaps and sealants

Chemical pollutants in soaps for washing cars and building exteriors and in coal-tar-based driveway sealants can harm a variety of insect life. Kawahara recommends swapping these out for biodegradable soaps and soy-based sealants. In winter, trading rock salt for salt-free formulations is safer for both insects and pets.

Become an insect ambassador

In the U.S., insects have historically been depicted as devourers of crops, disease vectors and hallmarks of poor sanitation, even though the vast majority do not harm humans. Kawahara said rethinking your own stereotypes of insects and gaining a better understanding of their beauty, diversity and roles is a first step in helping others appreciate them, too.

He recalled leading schoolchildren on an insect-collecting trip during which a student found an elephant stag beetle, an enormous insect with massive jaws -- "one of the coolest, most amazing bugs," Kawahara said.

The student wanted to step on the beetle, thinking it was a cockroach.

"Other students were grossed out, too," Kawahara said. "When I saw that, I was dumbfounded. If this was Japan, kids would be clamoring to be the first to get it and keep it as a pet. The juxtaposition of those cultural reactions was striking."

He pointed to media characterizations of Asian giant hornets -- which he grew up seeing drink sap from the oak tree outside of Tokyo -- as "murder hornets" as another example of how framing insects as dangerous or disgusting has the power to evoke strong reactions from the public.

As antidotes to unfounded fears, walk outdoors to look for local insect life or adopt pet insects, a simple, inexpensive way to introduce children to science, Kawahara said. Documenting what you see on platforms such as iNaturalist not only helps you learn more about your finds, but also provides data for scientific research.

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A tasty Florida butterfly turns sour

A spider feeding on a viceroy butterfly.

The viceroy butterfly is a mimic, modeling its orange-and-black colors after the queen butterfly, a bug that tastes so disgusting predators have learned not to eat it or anything that looks like it, including viceroys. The apparent dependence of mimics on their models made biologists wonder if the fates of the two species are forever intertwined. If so, then what happens when the mimic and the model part ways?

A study recently published in Communications Biology and led by Katy Prudic, an assistant professor in the College of Agriculture and Life Sciences at the University of Arizona, has found an interesting answer. Viceroy butterflies living in northern Florida, far away from the southern-dwelling queen butterflies, are not only more abundant than their southern kin, but they have also developed their own foul flavor.

"In classical mimicry theory, we wouldn't predict that the viceroy butterfly would be able to stay or be in northern Florida. It should be limited to southern Florida, where the queens live," Prudic said.

The classical theory, called Batesian mimicry, posits that one animal, known as the mimic, looks like another animal -- the model that predators recognize as "unpalatable." An unpleasant experience trying to munch on the model species convinces predators to avoid both species, since they cannot reliably tell the difference between the two.

If the butterflies followed Batesian mimicry, populations of viceroys living in regions where predators had never met the unpalatable queens would not recognize the orange color of the butterfly as something awful; it would look like a delicious, easy-to-find snack, and predators would pick off the viceroy.

Yet Prudic's study found that the viceroy thrives where the queen is not found, because it has evolved the ability to taste bad.

"Have you ever chewed aspirin?" Prudic said. "It will not kill you, but you may want to die because it will be really, really unpleasant."

Prudic's study began more than 15 years ago, as part of her doctoral dissertation. Prudic and her co-author, UA data science specialist Jeff Oliver, counted viceroy and queen butterflies and their host plants at eight sites across Florida.

All over Florida, the viceroy caterpillar feeds on the same kind of plant: the Carolina willow. The tree arms itself against pests with phenolic glycosides, chemical relatives of aspirin.

To pests, the aspirin-related toxins may be deadly, but caterpillars have evolved ways to avoid being poisoned by the plants. By possibly storing them in fatty bodies, viceroy caterpillars keep the chemicals out of their metabolic processes, and they live unharmed.

When the viceroy lives alongside its model species, it likely discards the toxins when it metamorphoses from caterpillar to butterfly. But Prudic and her team found that when the mimic lives independently from the queen butterfly, it keeps the toxins, making the viceroy unpalatable to predators.

In a pharmacology lab, UA Regents' Professor Barbara Timmerman helped Prudic investigate how much of the aspirin-related chemical could be found in the viceroy butterflies. These results were then compared to the abundance of queens at the capture sites.

The second experiment was to test the viceroys' chemical defenses against predators. The butterflies were fed to praying mantids that had been hand-reared in the lab, and Prudic studied how they reacted to the butterflies. The mantids had a much stronger response to viceroys originating from those places where there were not any queens.

"They learned to avoid these viceroys faster, and remembered to avoid them for longer," Prudic said.

Years of rigorous statistical analysis followed, so that Prudic and her team could be certain about the relationship between the unpalatability of viceroy butterflies and the abundance of queen butterflies.

A mimicry continuum

This discovery changes the way biologists must think about mimicry.

The relationship between viceroy and queen butterflies once fell into the Batesian mimicry category, but when one of Prudic's co-authors, David Ritland, first discovered that viceroys had the ability to be nasty, the butterflies' relationship was recategorized as "Mullerian." There are no models in this mimicry theory, only "co-mimics:" two different animals that look the same and are both unpalatable.

But Prudic's study proves that the viceroy butterfly does not fit neatly into either mimicry category.

"Both these categories that we thought about in mimicry are now coming together, and we are thinking more about a continuum between Batesian and Mullerian," Prudic said.

She expects that such a continuum is not limited to just the viceroy-queen system; however, studies that deeply investigate mimicry relationships are unusual because they are time-consuming, labor-intensive and difficult to execute.

Aside from proving that mimicry in the animal world cannot be sorted into a simple binary, this study may be helpful for conservation and management of species in the changing world.

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