Tag Archives: entomology

Colony Collapse Disorder: Dead Bees and Sloppy Science

A flurry of recent scientific papers, and a blizzard of subsequent news hype, has led a lot of people to conclude that the mystery of colony collapse disorder (CCD), which causes beehives to die suddenly, has been solved. Indeed, a Reuters reporter recently proclaimed exactly that in an editorial published on the wire service’s site.

All of these reports have converged on a single culprit: neonicotinoid insecticides, a category that includes some of the most widely-used chemicals in agriculture. According to this story, the pesticides aren’t present in high enough levels to kill the bees right away, but low-level exposure over a period of weeks slowly poisons them.

Beehive

A beehive. Image courtesy artethgray.

Of course the pesticide industry hasn’t been taking this lying down. Agrochemical giant Bayer, for one, has been issuing testy press releases faulting the new studies. Bayer is a leading supplier of imidacloprid, a very popular neonicotinoid compound that is used in both agricultural and home pesticides.

Imidacloprid was also the focus of the most recent scientific study to pin CCD on pesticides, and in this case, at least, Bayer may have a point.

I’ve found this new study, by Chensheng Lu of the Harvard School of Public Health and two collaborators from the Worcester County Beekeepers Association, particularly interesting – and not in a good way. The press release about the paper has been the source of most of the news coverage, so I suppose it made a better impression on other science journalists than it did on me. Here’s how it starts off:

The likely culprit in sharp worldwide declines in honeybee colonies since 2006 is imidacloprid, one of the most widely used pesticides, according to a new study from Harvard School of Public Health (HSPH). The authors, led by Alex Lu, associate professor of environmental exposure biology in the Department of Environmental Health, write that the new research provides “convincing evidence” of the link between imidacloprid and the phenomenon known as Colony Collapse Disorder (CCD), in which adult bees abandon their hives.

The study will appear in the June issue of the Bulletin of Insectology.

“The significance of bees to agriculture cannot be underestimated,” says Lu. “And it apparently doesn’t take much of the pesticide to affect the bees. Our experiment included pesticide amounts below what is normally present in the environment.”

Let’s take this a little bit at a time. First, we’re being told the “likely culprit” has been found in a condition that’s baffled researchers for several years. That’s an extraordinary claim, so I’m expecting extraordinary data to back it up. Apparently the new paper will contain just that, because it’s supposed to be “convincing evidence.” Anyone setting the bar that high is either sitting on rock-solid results, or full of shit. In my experience the latter is much more common, so my skeptic senses are already tingling.

Then things really start to go pear-shape. The Bulletin of Insectology? I try to avoid being a journal snob, but come on, insectology? The name of the field is entomology, and a quick Google search confirms that “insectology” appears nowhere else in science except for the title of this journal. Their web site doesn’t exactly scream “high publication standards,” either. If you’re a fan of impact factors, the B of I scores a whopping 0.371, so apparently it’s not going to be rivaling Nature for citations anytime soon, either.

Then it gets even worse. The press release came out in early April, with no embargo, but the paper is scheduled to be published in June. Nor is this an “advanced online publication” situation – this paper really isn’t out yet in any format. This is truly science by press release. Maybe we should just move on, forget we ever saw this, and also ignore the absurdity of the author’s quote (he didn’t really say “cannot be underestimated” did he?).

The subsequent media storm was deafening, though, so I felt compelled to dig in. Emailing Dr. Lu, I got a prompt and courteous reply with an attached PDF of the paper – or at least a “corrected proof.” After confirming that it was okay to discuss it even though it wasn’t slated to be published for two more months (a question I gather he hadn’t been asked yet), I started reading.

It wasn’t as bad as I’d expected.

I realize that’s faint praise given the foregoing, but working my way through the paper a picture started to emerge. This project seems to have begun as an earnest effort to do good science. Then, somewhere along the line, someone decided to push the data out the door in a big hurry, bypassing the revisions that a competent peer reviewer would have demanded. Perhaps it was because two other publications about neonicotinoids and bees had just come out in Science (Henry et al. and Whitehorn et al.). Or perhaps the collaboration fell apart, or the team decided that some of the additional experiments they needed would take another year to do and they were sick of waiting. Whatever the reason, the final publication suffered.

Nonetheless, the experiment – there’s only one in the paper – had a lot of potential. Hypothesizing that imidacloprid sprayed on corn crops could contaminate the high-fructose corn syrup (HFCS) that’s fed to commercial beehives, the researchers decided to see what eating sub-lethal doses of the pesticide would really do to bees under field conditions.

They placed five newly constructed and stocked honey bee hives on each of four field sites, for a total of twenty hives. The field sites were more than 12km apart, so the bees from different sites would forage on independent territories. Following conventional apicultural practices for commercial hives, the team fed HFCS to all of the bees to supplement their honey stores during the winter. Four hives on each site ate HFCS spiked with various doses of imidacloprid, while the fifth hive was a control, receiving unadulterated HFCS. At the end of the winter, fifteen of the sixteen imidacloprid-fed hives – and one of the four control hives – had died.

The authors claim that the hives’ deaths resembled CCD, but that may be a bit of a stretch. For one thing, they report seeing dead bees on the ground near the hive entrances, which isn’t typical of colony collapse. They also didn’t see any of the pathogens that often correlate with CCD, such as varroa mites, iridoviruses, and the unicellular parasite Nosema ceranae. In addition, these experiments all took place in Worcester County, MA, just east of where I live, during 2010 and 2011. That was an absolutely horrific winter, breaking all kinds of records for snowfall, ice accumulation, and cold. It was hardly representative of the way traveling commercial hives spend their winters (they go to Florida). Of course the usual numerical objection also comes up; this was a very small experiment that clearly lacked the statistical power to extrapolate to an entire industry.

The biggest problem, though, is that the work is full of provocative but completely unsupported speculation. The authors discuss imidacloprid use on corn in some depth, and outline a plausible route by which it could end up in HFCS – but that’s entirely theoretical. Nowhere do we see data or a reference showing that the pesticide was ever actually in the sweetener that commercial bees ate, or measuring its levels.

Even if we assume, without a shred of evidence, that imidacloprid routinely contaminates HFCS, that would raise a whole new problem. Control bees also got HFCS. That means the controls also would have been eating some unknown amount of the chemical, and the experimental bees would have gotten a double dose, rendering the result meaningless. To do the experiment right, one would have to test the HFCS for the pesticide to confirm the levels, and also find some source for uncontaminated HFCS for the controls. If I were reviewing this paper for publication, I’d demand those data, and would also insist that claims of “convincing evidence” be edited to more cautious language – which, I suppose, might drive the authors to send the paper elsewhere.

We should see whether low levels of imidacloprid are contributing to CCD. It’s an entirely plausible hypothesis. Unfortunately, it remains untested.

Lu, C., Warchol, K., Callahan, R. (2012). In situ replication of honey bee colony collapse disorder, Bulletin of Insectology (in press).

Henry, M., Beguin, M., Requier, F., Rollin, O., Odoux, J., Aupinel, P., Aptel, J., Tchamitchian, S., & Decourtye, A. (2012). A Common Pesticide Decreases Foraging Success and Survival in Honey Bees Science DOI: 10.1126/science.1215039

Whitehorn, P., O’Connor, S., Wackers, F., & Goulson, D. (2012). Neonicotinoid Pesticide Reduces Bumble Bee Colony Growth and Queen Production Science DOI: 10.1126/science.1215025

The Other Superbugs: Pesticide Resistant Insects

In 1955, the World Health Organization launched an ambitious campaign to eradicate malaria. The effort relied on new, synthetic antimalarial drugs such as chloroquine and a miraculous new insecticide called DDT. Initially, it went pretty well: several countries’ malaria rates plummeted. Then it fell apart. The malaria parasites became resistant to the new drugs, and the mosquitoes which transmit the disease became resistant to DDT. After two decades of work and a massive expenditure of money and effort, the WHO gave up. Once again, Plasmodium and Anopheles had kicked Homo‘s butt.

Quick Henry, The Flit!

Quick Henry, The Flit!

By the 1990s, a new generation of public health officials was ready to take another run at the problem. Armed with a wider spectrum of antimalarial compounds, campaigns such as Roll Back Malaria seemed well prepared to deal with the problem of drug resistance by the parasite. Insecticide resistance was a different story. As before, the WHO-sponsored effort would rely heavily on a single chemical class to combat mosquitoes. This time, the effort favored pyrethroids.

The WHO’s enthusiasm for pyrethroids was understandable. As insecticides go, they’re pretty spectacular. These compounds are either mixtures or derivatives of a natural plant product called pyrethrum. Pyrethrum is only modestly effective by itself, but in the late 1940s chemists discovered that mixing it with another compound, piperonyl butoxide, boosts its killing power dramatically. Since then, researchers have synthesized several variants of pyrethrum, such as permethrin and deltamethrin, that are even more effective. What really makes these pesticides blockbusters, though, is that they’re highly specific for arthropods; their human and environmental toxicities are extremely low.

Because they’re so effective and nontoxic, pyrethroids are now the dominant over-the-counter insecticides worldwide. If you walk into the hardware store to buy some bug spray, you’ll see what appears to be a huge variety of products, but a close reading of the ingredient lists reveals that they’re almost all the same. Raid Ant Killer, Ortho Garden Insecticide, generic wasp killer, and most of the other colorful containers are just different package designs. What you’re really looking at is shelf upon shelf of pyrethroids.

We should know better. Bacteria, viruses, fungi, and protozoans have repeatedly taught us the same fundamental lesson about adaptation: if you keep throwing one chemical at a class of organisms long enough, they’ll eventually get used to it. Inevitably, the same has now happened with insects and pyrethroids.

In the tropics, particularly Africa, pyrethroid resistance has become a major public health problem. Because malaria control in poor, hot countries relies so heavily on pyrethroid-treated bed nets, resistant mosquitoes can now bypass the only real barrier between them and their victims.

Using these compounds willy-nilly has also spawned other problems. The treated bed nets, plus indoor spraying, have placed heavy selective pressure on all of the other insects that live in close association with people. Bedbugs, for example.

Indeed, bedbug populations have become highly resistant to pyrethroids, which is why homeowners’ DIY efforts to control them seldom work out. There’s been some debate about where that resistance came from, but recent results on US bedbug populations suggest that this resurgent pest is an import. It’s possible – even likely – that widespread pyrethroid use to combat mosquito-borne diseases in developing countries has spawned these new populations of superbugs.

Switching to other pesticides may help, at least sometimes with some insects. A study in Benin found that bendiocarb-treated bed nets were very effective against pyrethroid-resistant mosquitoes. Unfortunately, bendiocarb is highly toxic to birds and fish, and acutely toxic to humans in high doses. Treating a bed net with it is probably okay, but it’s not the kind of thing that should be sprayed around the house by amateur exterminators.

Nor is chemical-switching a panacea. Turning back to bedbugs, it appears their pyrethroid-resistance mechanisms are many and varied. Deep sequencing analysis revealed that the pesticide-resistant strains in a US infestation carry multiple changes in multiple genes, including increased expression of general detoxifying enzymes that could be useful against a broad spectrum of chemicals.

The solution, if there is one, will have to be twofold. First, we need a sustained research effort to understand the basic mechanisms of insecticide resistance and find new compounds that can overcome it. Second, both pesticide makers and public health officials need to take more responsibility for how these products are actually being used in the field, with a special focus on the problem of resistance. Our approach to distributing these powerful and important chemicals needs a thorough debugging.

Akogbeto, M., Padonou, G., Bankole, H., Gazard, D., & Gbedjissi, G. (2011). Dramatic Decrease in Malaria Transmission after Large-Scale Indoor Residual Spraying with Bendiocarb in Benin, an Area of High Resistance of Anopheles gambiae to Pyrethroids American Journal of Tropical Medicine and Hygiene, 85 (4), 586-593 DOI: 10.4269/ajtmh.2011.10-0668

Adelman, Z., Kilcullen, K., Koganemaru, R., Anderson, M., Anderson, T., & Miller, D. (2011). Deep Sequencing of Pyrethroid-Resistant Bed Bugs Reveals Multiple Mechanisms of Resistance within a Single Population PLoS ONE, 6 (10) DOI: 10.1371/journal.pone.0026228

Genetically Modified Mosquitoes: Available Now, Apparently

Count me among those surprised by this:

About a year ago, genetically modified (GM) mosquitoes were released into the wild—and they have been flying under the world’s radar screen until last week. On 11 November, British company Oxitec announced that it carried out the world’s first small outdoor trial with transgenic Aedes aegypti mosquitoes in the Caribbean island of Grand Cayman in the fall of 2009, followed by a larger study there last summer.

The trials were designed to test whether such designer mosquitoes could be successfully used to fight wild mosquitoes that transmit diseases like dengue fever. The announcement, made at a press briefing in London, has taken aback opponents of GM mosquitoes and surprised many researchers in the field of genetic control of insect vectors.

Some are questioning why the company stayed mum for so long, calling it a strategic mistake that provides critics of genetic modification with fresh ammunition. “I don’t think they did themselves a favor,” says Bart Knols, a medical entomologist at the University of Amsterdam. “This could well trigger a backlash.”

Knols is absolutely right. The company claims it publicized the trial among island residents (but see the comments after the Science piece for a different take on that). Even if they did have a good local information campaign, they clearly failed to tell the wider world about an experiment that they should have known would be highly controversial. I personally think the benefits of their strategy far outweigh the risks, but doing something like this without a full-blown global PR campaign ahead of time is just asking for trouble.

The Science of Tequila Shots

When I was in graduate school, some colleagues once served a round of drinks in 50mL conical centrifuge tubes. If only someone had dipped a pipet into one of those shots, we might have beaten these guys to publication:

Researchers from [the University of Guelph's] Biodiversity Institute of Ontario (BIO) have discovered that mescal itself contains the DNA of the agave butterfly caterpillar — the famously tasty “worm” that many avoid consuming. Their findings will appear in the March issue of BioTechniques, which is available online now.

Tequila with worm

Tequila with worm

Grossed out yet? Well, they followed the party trick with a practical application, as described in their open-access article in BioTechniques:

We then successfully amplified and sequenced DNA from the 95% ethanol preservative of 70 freshly collected specimens and 7 archival specimens 7–10 years old. These results suggest that DNA extraction is a superfluous step in many protocols and that preservative ethanol can be used as a source of genetic material for non-invasive sampling or when no tissue specimen is left for further DNA analyses.

Instead of doing a tedious, time-consuming DNA extraction on an alcohol-preserved specimen, one can simply pull out some of the alcohol. Combined with new molecular identification techniques, that could save a lot of time and money in entomology labs. It might turn a few people off tequila, though.

You’re Grounded, Girl

In a new twist on the elegant sterile insect technique, researchers have now made a strain of Aedes aegypti mosquitoes where the females can’t fly. As the accompanying press release explains:

UCI researchers and colleagues from Oxitec Ltd. and the University of Oxford created the new breed. Flightless females are expected to die quickly in the wild, curtailing the number of mosquitoes and reducing – or even eliminating – dengue transmission. Males of the strain can fly but do not bite or convey disease.

When genetically altered male mosquitoes mate with wild females and pass on their genes, females of the next generation are unable to fly. Scientists estimate that if released, the new breed could sustainably suppress the native mosquito population in six to nine months. The approach offers a safe, efficient alternative to harmful insecticides.

Mosquito on a mirror. Image by Schristia.

Mosquito on a mirror. Image by Schristia.

Because the flightless phenotype only affects females, and the males remain fertile, the selective pressure against it should be pretty mild. These bugs should also be a lot easier to breed than strains with inducible sterility; as long as they’re in captivity getting free blood meals and protection from predators, the females should be able to mate and reproduce just fine.

Aedes aegypti is a major vector for Dengue fever, a nasty virus which infects upwards of 50 million people a year, so if this strategy works in the field, it could be a huge boon to public health. It could be even bigger news if they do the same thing with Anopheles, which transmits the ninth leading cause of death worldwide.

The original paper is open access, for those who want the details.

Another Reason to Hate Flies

Flies are wonderful for genetics research, but it’s hard to say whether their scientific contributions as a model system can ever outweigh the Dipteran order’s crimes against humanity. Here’s another reason to hate them:

Researchers at the Johns Hopkins Bloomberg School of Public Health found evidence that houseflies collected near broiler poultry operations may contribute to the dispersion of drug-resistant bacteria and thus increase the potential for human exposure to drug-resistant bacteria. The findings demonstrate another potential link between industrial food animal production and exposures to antibiotic resistant pathogens. Previous studies have linked antibiotic use in poultry production to antibiotic resistant bacteria in farm workers, consumer poultry products and the environment surrounding confined poultry operations, as well as releases from poultry transport.

“Flies are well-known vectors of disease and have been implicated in the spread of various viral and bacterial infections affecting humans, including enteric fever, cholera, salmonellosis, campylobacteriosis and shigellosis,” said lead author Jay Graham, PhD, who conducted the study as a research fellow with Bloomberg School’s Center for a Livable Future. Our study found similarities in the antibiotic-resistant bacteria in both the flies and poultry litter we sampled. The evidence is another example of the risks associated with the inadequate treatment of animal wastes.”

“Although we did not directly quantify the contribution of flies to human exposure, our results suggest that flies in intensive production areas could efficiently spread resistant organisms over large distances,” said Ellen Silbergeld, PhD, senior author of the study and professor in the Bloomberg School of Public Health’s Department of Environmental Health Sciences.

Housefly. Image courtesy yimhafiz

Housefly. Image courtesy yimhafiz.

Some of this is still conjecture, as the researchers have not connected the contaminated flies with specific epidemiological outcomes. This study was just traditional environmental microbiology:

Graham and his colleagues collected flies and samples of poultry litter from poultry houses along the Delmarva Peninsula—a coastal region shared by Maryland, Delaware and Virginia, which has one of the highest densities of broiler chickens per acre in the United States. The analysis by the research team isolated antibiotic-resistant enterococci and staphylococci bacteria from both flies and litter. The bacteria isolated from flies had very similar resistance characteristics and resistance genes to bacteria found in the poultry litter.

Still, it’s more than enough justification to swat the little buggers whenever you see them.

Genetically Engineered Pests – Coming To a Field Near You?

Entomologically-minded readers of the Federal Register (you know who you are) might have noticed an interesting item shortly before Christmas: in the 19 December issue, the Department of Agriculture posted this note asking for the public’s thoughts about genetically modifying insect pests. Specifically, they’re working on inserting some choice genes into fruit flies and pink bollworms, then releasing the re-engineered critters into the environment. I’m sure the usual naysayers will soon be screaming about Frankenflies (which, by the way, would be a good name for a band), but this project could actually be a tremendous boon to the environment.

Pink bollworm life cycle illustration
Pink bollworm life cycle, image courtesy USDA

The focus of the effort is actually a decades-old insect control strategy called the Sterile Insect Technique, or SIT. Unlike most pest control approaches, SIT has the potential to eradicate an insect species completely, without any harm to non-target species. Somewhat counterintuitively, the first thing you do in SIT is to build a hatchery and start rearing thousands of the insects you want to wipe out. Then you kill the females, and expose the males to some chemical or physical insult that sterilizes (but doesn’t kill) them. Finally, you release the sterile males into the wild, where they mate with females, who then lay clutches of eggs that will never hatch.

Because many insect species mate only once in a season, each sterile male that competes successfully for a mate wipes out one female’s entire reproductive output for the year. The next season’s crop of wild flies will be that much smaller, but you release the same number of sterile males, giving them an even better chance of bedding an otherwise fertile female. After several generations of this, the wild population will go extinct, and you can fold up the hatchery and go home.

It’s a stunningly elegant strategy, and even more impressively, it works. Edward Knipling, the entomologist who invented SIT, proved that 25 years ago, with Cochliomyia hominivorax, the screw worm fly. Screw worm (another good name for a band) gets its common name from a habit of laying its eggs on live animals, letting the maggots burrow into the flesh (like a screw) to feed on blood and develop. After pupating, the adult hatches out of the now-festering wound and flies away. It’s very gross, and very costly; historically, screw worm infestations were an enormous problem for livestock farmers in the Americas, especially cattle ranchers. Using SIT, Knipling and his colleagues eradicated the fly from this country by 1982. It’s since been extirpated from several other countries the same way.

Now the Department of Agriculture is trying make SIT more efficient. Using current technology, SIT programs are damnably expensive, mainly because of the challenges of separating the sexes of tiny insects (can you tell girl bollworms from boy bollworms? ten thousand times a day?), and making sure that the sterilization works just right. Too much radiation or chemical treatment, and you get dead males. Too little, and you get fertile males. Neither is useful for SIT.

Genetic engineering could address both problems. Inserting an inducible gene regulation system that selectively kills females in the larval stage, and another that sterilizes males, would make the breeding program a snap: just induce the genes, grow up the flies, and release whatever survives pupation. One could also get more sophisticated. How about building a paternally-inherited, female-lethal gene expression system into the flies rather than sterilizing them? Males coming out of the hatchery would mate with wild females, who would then lay eggs that would only produce more males – males that would carry the same trait to the next generation. This sort of genetic pesticide, if it worked, could wipe out all of the females in a few generations, and the whole species right after that.

Beyond a few interesting laboratory findings, all of this is theoretical right now, which is exactly why it’s good to see the Department of Agriculture asking for comments on it. Maybe there will be an informed public debate about the risks and potential of this approach. Or maybe there will be a lot of screeching and shouting from various corners, followed by a permanent stalemate that keeps this promising technique on ice.

Malaria Control: Spraying You-Know-What

The US Agency for International Development just awarded a $150 million grant to open a new front in the Bush administration’s anti-malaria effort. The press release, however, has a rather obvious omission. Here’s how it starts:


The U.S. Government, through the U.S. Agency for International Development (USAID), announced the awarding of a $150 million Indoor Residual Spraying (IRS) contract to a consortium headed by Research Triangle Institute (RTI). Indoor Residual Spraying (IRS) is the application of safe insecticides to the indoor walls and ceilings of a home or structure in order to interrupt the spread of malaria by killing mosquitoes that carry the malaria parasite. Malaria is the number one killer in Africa.

And exactly what “safe insecticides” are they referring to? DDT, of course. As I pointed out in an earlier post, DDT can indeed be quite safe in this application, but its revival poses some thorny problems that the Administration might not be prepared to handle. In any case, it’s unfortunate that they felt the need to censor the press release like this. Is this the start of a pattern of obfuscation in this new effort?