Pollen-starved bumblebees bite 'half-moons' into plants to make them bloom

A bumble bee (Bombus terrestris) worker damaging a plant leaf
(Image credit: Hannier Pulido, De Moraes and Mescher Laboratories)

When their pollen supply runs short, bumblebees bore tiny half-moon-shaped holes in the leaves of flowering plants, causing blooms to appear weeks ahead of schedule. 

Bee-bitten plants bear flowers about two weeks to a month sooner than untouched plants, according to a new study, published today (May 21) in the journal Science. Researchers attempted to recreate these bee-bite patterns using metal forceps and a razor, but even then, the damage inflicted by bees boosted flower production more effectively than the scientists could; bee-bitten plants bloomed eight to 25 days before the artificially damaged ones did, depending on the plant species. 

Some plant species flower early in response to drought, or in response to infections caused by certain pathogens, but few studies have explored how animal behaviors might prompt plants to bloom early, said study author Mark Mescher, a professor of environmental systems science at ETH Zürich. Mescher and his coauthor Consuelo De Moraes, a professor of biocommunication and ecology at ETH Zürich, spotted bumblebees munching on leaves during an unrelated experiment, and they wondered why.

Related: 7 amazing bug ninja skills  

"It started really with observing the behavior," Mescher said. Other researchers told the team that they'd also observed bees biting leaves, anecdotally, but no formal studies had probed why the insects did it, he said. 

In early laboratory experiments, buff-tailed bumblebees (Bombus terrestris) appeared to ramp up this biting behavior when deprived of pollen, a key food source for both bee larvae and the worker bees themselves, the authors noted. To test the hypothesis, the team deprived one group of worker bees of pollen for three days, while a different group was provided "abundant pollen resources." When released into enclosures full of flowerless tomato and black mustard plants, the deprived bees began nibbling at the leaves with gusto. The satiated group, in contrast, inflicted only minor amounts of leaf damage.

To confirm that the hungry bees weren't simply eating the leaves, or carrying bits back to their hive, the authors placed paper cones beneath the plants to catch falling debris. Leaf bits accumulated in the cones, and no leaf residue appeared back at the hive, they noted. The bee-inflicted damage resembles tiny half-moons, carved by the insects' mandibles, or pinprick holes poked out with their proboscises (tubular mouthparts), De Moraes said. "But it's quite quick," with each cut only taking a second or so to complete, she added. 

Related: Naughty by nature: The most disgusting and deadly flowers 

The team observed this biting behavior in both their laboratory bees and wild colonies that visited plants housed on rooftops at the ETH Zürich campus. In the wild bees, the team noted that biting behavior dropped off once the outdoor plants began to flower, bolstering the idea that the bees damage leaves when their available pollen supply runs low. 

While several species of wild bumblebees, including B. terrestris and B. lucorum, ravaged the flowerless foliage, honeybees and common furry bees that visited the roof would not, Mescher noted. "The honeybees just ignored the plants that didn't have any flowers," he said. "Who knows, but I'd be surprised if there were other pollinators [besides bumblebees] that were doing this." 

But why would only bumblebees beat up plants to boost their flower supply? That the scientists don't know yet, they said. Bumblebees do exhibit so-called "nectar-robbing" behaviors, where they slice into plant parts that house nectar beyond the confines of a flower, and the leaf-biting behaviors may be related to that, Mescher said. But we don't know for sure yet. 

Looking forward, the team plans to study precisely how bee-inflicted damage drives plants to bloom early, and whether the same biochemical changes occur in plants subjected to drought, pathogens or other environmental stressors. It may be that fatty acids in bumblebee saliva trigger a reaction in flowering plants, as is true of some caterpillar species, De Moraes said. Alternatively, the bees may release some unknown chemical cue, or else damage the leaves in a highly specific way that scientists cannot yet replicate, she added. 

If cues from bees can accelerate flowering, "scientists might realize a horticulturist's dream by deciphering the molecular pathways through which flowering can be accelerated by a full month," Lars Chittka, a professor of Sensory and Behavioural Ecology at the Queen Mary University of London, wrote in a letter in the journal Science accompanying the new paper.

"An encouraging interpretation of the new findings is that behavioral adaptations of flower visitors can provide pollination systems with more plasticity and resilience to cope with climate change than hitherto suspected," he wrote. In other words, as climate change alters when various plants bloom, understanding how bumblebees influence flowering could help farmers manage their crops. 

Originally published on Live Science. 

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Nicoletta Lanese
Channel Editor, Health

Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers' work.

  • adam
    Amazing .... shows how bees are better than artificial methods.... and how bees have natural abilities to manage plants

    Washington Post article below suggests that bees have some serious enemies.....

    Was a USDA scientist muzzled because of his bee research?

    For years, his body of research was either neutral or favorable to farming policy and the chemical industry. But , he started cautioning against the overuse of pesticides.

    Lundgren believes his problem began in 2012, when he published findings in the Journal of Pest Science suggesting that a popular class of pesticides called neonicotinoids don’t improve soybean yields.

    He also served as a peer reviewer for a Center for Food Safety report on the dangers of neonics.

    The next year, he published a paper suggesting that a new genetic pest treatment, dubbed RNAi pesticides, required a new means of risk assessment.

    “We’re using all of these pesticides because we’ve created a pest problem,” Lundgren says, “and bee health is a symptom of this underlying cause.”

    He says the solution is to diversify American farming. “Any other course is unsustainable,” he says. “Pesticides, herbicides, fungicides should be something we resort to, not a first option.”

    U.S. corporate agriculture tends toward monoculture farming — in the simplest terms, one giant farm specializing in one crop. The two key monoculture crops are corn and soybeans. Corn alone takes up 30 percent of the country’s crop space, an area almost the size of California.

    Soybean acreage is nearly as vast. The corn rootworm, the Colorado potato beetle and soybean aphids all thrive best on the crops that give them their names. And so monocultures have allowed, even caused, says Lundgren, pest populations to explode.

    Most of the attention has focused on neonicotinoids. Entering broad use here in the late ’90s, neonics’ global share of the pesticide marketplace ballooned by 2008 to roughly 25 percent and $2.5 billion. Neonics can be implanted directly on the seed and are classified as a “systemic” insecticide because they are fully incorporated into the plant’s tissue, remaining present in pollen and nectar.

    Two key studies have found that feeding neonics to bees, even in amounts so low they couldn’t be detected afterward, render them more susceptible to infection. The co-author of one of those studies, Jeffrey Pettis, is joining Lundgren in speaking out.

    Pettis is a highly respected entomologist and led the USDA’s bee laboratory in Beltsville for nine years, through April 2014, when he testified before the House Agriculture Committee.

    Pettis had developed what he describes as a “significant” line of research showing that neonics compromise bee immunity. But in his opening remarks before Congress, he focused on the threat posed by the varroa mite, often put forward by chemical company representatives as the main culprit behind bee deaths.

    Only under questioning by subcommittee Chairman Austin Scott (R-Ga.) did Pettis shift. Even if varroa were eliminated tomorrow, he told Scott, “we’d still have a problem.” Neonics raise pesticide concerns for bees “to a new level,” he said.

    About two months later, Pettis was demoted, losing all management responsibilities for the Beltsville lab.

    Dave Hackenberg, a central Pennsylvania beekeeper and longtime friend of Pettis’s, says Pettis confided in him that the official reason given for his demotion — poor performance as an administrator — wasn’t the real one. The real reason was his congressional testimony.

    Pettis, 61, has never provided a full public account of his side of the story. But with Hackenberg talking he decided to respond. “Dave and I talk a lot,” he said, “and I cannot be sure what I might have said to him around the time of my demotion.”

    But, Pettis said, the USDA’s congressional liaison told him that the Agriculture Committee wanted him to restrict his testimony to the varroa mite. “In my naivete,” he said, “I thought there were going to be other people addressing different parts of the pie. I felt used by the whole process, used by Congress.”

    The hearing was “heavily weighted toward industry,” he said, “and they tried to use me as a scientist, as a way of saying, ‘See, it’s the varroa mite,’ when that’s not how I see it.”

    As for his demotion, Pettis called himself a “bad administrator.” But did he think the hearing played a role?

    Pettis delivers an elliptical answer. He said he walked up to Scott afterward, to make small talk, and the congressman “said something about how I hadn’t ‘followed the script.’ ”

    A spokeswoman for Scott said the congressman no longer chairs the same House agriculture subcommittee and referred questions to the committee’s professional staff. A spokesperson there declined to make anyone available for an interview.

    “In my gut,” said Pettis, “I feel I pissed someone off with my testimony. Beyond that I have not felt or seen the big hand of industry saying, ‘We’re going to make you pay for this.’ I have seen more direct evidence that Congress was influenced by industry than I ever felt with regard to the USDA.”

    Bees are vital to U.S. agriculture, pollinating foods that make up roughly a third, and the most nutritious portion, of our diet, such as fruits and leafy greens. But commercial beekeepers continue to report escalating losses of 42 percent or more, jeopardizing $30 billion in annual revenue and our health.

    A couple of years ago, the now 40-year-old Lundgren — running a government lab, winning awards from both his agency and President Obama — occupied the right position to aid in this crisis. He says he was doing just that when the trouble started: a pair of suspensions — one for conduct unbecoming a federal employee and another for violating travel regulations.

    In October, Lundgren filed a whistleblower suit alleging that he was disciplined to suppress his science. The government says the suspensions had nothing to do with his research. Today, he is the most outspoken of several scientists who say they feel muzzled by the government.
    What happens when a whistleblower returns to work after a decade’s fight]The lawyers who filed Lundgren’s suit allege that nine additional USDA scientists have been ordered to retract studies and water-down findings, or have faced discipline in retaliation for their work. They further allege that three of those scientists, beyond Lundgren, were also working on pollinator-related research. The USDA’s inspector general just announced an audit, to take place later this year, in response to the “significant volume” of complaints they’ve had on their office’s hotline, alleging scientific censorship on pesticides and other issues.

    As a USDA-ARS employee, Lundgren has run his own lab and staff for 11 years, wrote a well-regarded book on predator insects, published nearly 100 scientific papers and acted as a peer reviewer for dozens of publications.

    The dispute hit a new low for Lundgren in July, when he finished a draft of a new paper on RNAi pesticides.

    RNAi pesticides work by attaching a molecule to the target pest’s DNA, keeping specific, vital gene sequences from functioning.

    Lundgren and postdoc Chrissy Mogren used computer software to mimic the action of 21 such pesticides to determine if any threaten honeybees. What they discovered is that each pesticide might bind with some section of the honeybee’s DNA. Lundgren himself describes this result as not so dramatic as it sounds. The honeybee genome is vast, and any overlap between the pesticide and the bee’s genome might prove innocuous and unrelated to survival.

    Still, Lundgren thought of this research as a step to encourage further study. He also knew the data would likely spark more trouble with his bosses, so he sent the paper to seven colleagues for informal peer reviews. Five suggested relatively minor revisions, checking one of two boxes indicating the paper as “acceptable” for submission. Neil Hoffman and John Turner, both managers for the USDA’s Animal and Plant Health Inspection Service, referred to the paper as “trivial” and didn’t check a box.

    Hoffman and Turner said the paper offered no evidence of “meaningful” interactions between the pesticides and the honeybee genome. Lundgren’s supervisors made the same argument and refused him permission to submit the paper to an outside journal.

    “The whole process seemed tainted to me by then,” says Lundgren. “They were suppressing science. This was a ‘proof of concept’ paper” — a pointer to areas scientists might research further — “a standard part of science.”

    Greg Heck, Monsanto’s weed control platform lead, with an expertise in RNAi technologies, believes Lundgren is too alarmist about the new technology and says Monsanto is conducting tests to make sure the pesticides are harmless to bees. But, hearing what the paper contains, he said he believes submitting it for publication was appropriate. “I haven’t seen the study, but I am a firm believer in getting research out there,” he said, “because then we can discuss the results and say, ‘Hey, is any of this truly meaningful?’ ”

    At this point, Lundgren started planning a lab outside USDA, with some of the people he calls his “professional family,” including a pair who worked with him when he was suspended for unbecoming conduct.

    Bee declines, says Lundgren, are not difficult to understand. “Yes, the bees are in crisis, and we need to help them,” he says. “But what we have is not a bee problem. What we have is a biodiversity problem.”

    U.S. corporate agriculture tends toward monoculture farming — in the simplest terms, one giant farm specializing in one crop. The two key monoculture crops are corn and soybeans. Corn alone takes up 30 percent of the country’s crop space, an area almost the size of California.

    Soybean acreage is nearly as vast. The corn rootworm, the Colorado potato beetle and soybean aphids all thrive best on the crops that give them their names. And so monocultures have allowed, even caused, says Lundgren, pest populations to explode.

    “We’re using all of these pesticides because we’ve created a pest problem,” Lundgren says, “and bee health is a symptom of this underlying cause.”

    He says the solution is to diversify American farming. “Any other course is unsustainable,” he says. “Pesticides, herbicides, fungicides should be something we resort to, not a first option.”

  • Hayseed
    admin said:
    Scientists don't yet know when or how the behavior evolved.

    Pollen-starved bumblebees bite 'half-moons' into plants to make them bloom : Read more

    This is neat. Really neat and worthwhile. So many implications. And completely out of the blue. Another valuable switch to investigate. And take advantage of.

    GMO by bumblebee. I love it.
  • adam
    Yes this is good reversible GMO type activity with no dangers of introducing risky or dangerous organisms, toxins, bacteria or viruses etc into plant or animal DNA

    GMO can be good

    However Regulatory approval and the long term risks of introducing organisms, toxins, bacteria or viruses etc into plant or animal DNA need to be independently studied by a Regulator who has no connection to the Food, Pharma or Chemical Toxin Industry and certainly is not paid for however indirectly by these same parties

    The current Regulatory system is totally compromised

    See the poison papers which set out over 20,000 Federal and other documents which showing that fake tests submitted and paid for by Industry and how Regulators knew what was going on and did nothing


    The regulatory agency sources of these documents include: the EPA, the US Forest Service, the FDA, the Veterans Administration, and the Department of Defense. Chemical manufacturers referenced in the documents include: Dow, Monsanto, DuPont, and Union Carbide, as well as many smaller manufacturers and the commercial testing companies who worked for them.

    The Poison Papers are a project of the Bioscience Resource Project and the Center for Media and Democracy. The Poison Papers were largely collected by author and activist Carol Van Strum.

    The Poison Papers catalogue both the secret concerns of industry and regulators over the hazards of pesticides and other chemicals and their efforts to conceal those concerns.

    Corporate concealment is not a new story. What is novel in the Poison Papers is abundant evidence that EPA and other regulators were, often, knowing participants or even primary instigators of these cover-ups. These regulators failed to inform the public of the hazards of dioxins and other chemicals; of evidence of fraudulent independent testing; even of one instance of widespread human exposure. The papers thus reveal, in the often-incriminating words of the participants themselves, an elaborate universe of deception and deceit surrounding many pesticides and synthetic chemicals.

    The chemicals most often discussed in the documents include herbicides and pesticides (such as 2,4-D, Dicamba, Permethrin, Atrazine, and Agent Orange), dioxins, and PCBs. Some of these chemicals are among the most toxic and persistent ever manufactured.

    Except for PCBs, almost every chemical discussed in the Poison Papers is still manufactured and sold today, either as products or as product contaminants. Recent research from Australia, shows that many newly-synthesized chlorinated chemical products, including the herbicide 2,4-D, remain contaminated with dioxins. Notably, 2,4-D has just been authorized by EPA for use on Dow’s new GMO 2,4-D-tolerant soybeans.

    Some of the 20,000+ documents in this repository have surfaced over the years. Many have never been either read or publicly written about. The Poison Papers therefore offer a unique opportunity for researchers, the public and the media to discover much more about what was known about chemical toxicity, when, and by whom.

    ...........it was knownthat more than 800 safety studies performed by IBT on 140 chemicals produced by 38 chemical manufacturers were nonexistent, fraudulent, or invalid. The Poison Papers, however, show that EPA and its Canadian counterpart, the Health Protection Branch (HPB), colluded with pesticide manufacturers, to keep invalidly registered products on the market and covered up problems with many IBT tests.

    Cover-up— The papers also show that EPA staff had evidence that this IBT scandal involved more independent testing companies and more products than ever officially acknowledged.

    Concealment— The papers show that EPA concealed and falsely discredited its own studies finding high levels of dioxin — 2,3,7,8-TCDD — in environmental samples and human breast milk following routine use of 2,4-D and 2,4,5-T (Agent Orange) by the federal Forest Service and Bureau of Land Management.

    Intent— They show Monsanto chief medical officer George Roush admitted under oath to knowing that Monsanto studies into the health effects of dioxins on workers were written up untruthfully for the scientific literature such as to obscure health effects. These fraudulent studies were heavily relied upon by EPA to avoid regulating dioxin. They also were relied upon to defend manufacturers in lawsuits brought by veterans claiming damages from exposure to Agent Orange.