Poisoning of honey bee larvae

The March issue of Environmental Toxicology & Chemistry* has an article about the sublethal effects of two pyrethroids—bifenthrin and deltamethrin—on the growth and development of honey bee larvae. What the researchers found is scary and beekeepers should be aware of it. First I’ll back up. In case all this seems like a foreign language I’ll try to make it as simple as possible.

The honey bees they studied were Apis mellifera ligustica, which to most beekeepers means “Italians.” The Italian sub-species of honey bee is probably the most common in the United States and is known for its yellowish coloration and good honey production.

The pyrethroids are just man-made forms of pyrethrin. Pyrethrin is the natural pesticide found in some of the chrysanthemum species. These pesticides are found in many common products, such as Raid.

Sublethal doses are doses that will not kill an adult bee in a specified amount of time. Usually if a certain amount of pesticide doesn’t kill an adult bee in the specified amount of time—say an hour or a day—then that pesticide is considered “safe” for honey bees. Crops are often sprayed at these levels.

But lately more attention has been given to sublethal doses because, although they might not kill an adult bee outright, they can have serious consequences to the survival of young bees and to the future of the whole colony. Imagine a human who is poisoned enough to have brain damage but not enough to die. That would be a “sublethal” effect.

The researchers found that in honey bee colonies exposed to sublethal amounts of these pyrethroids, the queens didn’t lay as many eggs, the number of eggs that hatched was far fewer, and the number of hatchlings that made it to adulthood was even fewer. Since the honey bee life cycle—from egg to adult worker—is just 21 days, you could go from a very strong hive to a very weak one in less than a month.

Numerous reports from California last month indicated that about 30% of healthy hives trucked in to pollinate almonds this year were dead within two to three weeks. Although I don’t know which chemicals were used on the almonds, the length of time it took for the hives to die is suspiciously close to one honey bee life cycle.

It is time we stopped testing pesticides on adult bees and started testing them on developing larvae.  Our system of pesticide regulation is simply not serving the public or the planet. It must be changed before it’s too late.


*Ping-Li Dai et al. 2010. Effects of sublethal concentrations of bifenthrin and deltamethrin on fecundity, growth, and development of the honeybee Apis mellifera ligustica. Environ. Toxicol. Chem. 2010: 644-649.

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  • Well, I used to work in a lab where we ran pesticide trials on different groups of insects, including social Hymentoptera (Ants,Bees,Wasps), and was impressed by the resiliency of Hymenoptera to “bounce back” after pesticide applications. So, based on my experience, it’s my opinion (and it’s just that, an opinion), that insecticides aren’t a significant player in CCD, indeed, it’s likely a pathogen complex taking advantage of genetic susceptibility in non-resistant population segments.

    A friend of mine, working on her PhD, ran trials with arial mosquito treatments of adulticides, including Deltamethrin in rice fields. She placed hive boxes directly in the center of the sprayed plots, and placed control hive boxes far away from the treatments. The arial ULV applications were applied only at night, when mosquitoes are active and bees are largely in the hive boxes. Hive boxes were monitored, weighed, and pollen samples analyzed. Interestingly, the treated colonies actually fared better in population numbers, weights, etc. than the controls. I don’t think it was a significant number though. Food for thought if nothing else.

    Of course, we don’t need to apply pesticides willy-nilly either, and it’s heartening to see the industry producing pro-insecticides to replace pyrethroids and persistent compounds.

  • I’m just finishing my master’s thesis on the effects of pesticide-contaminated pollen on larval development of the honey bee. There’s a lot of recent science that suggests that pesticides that show no effect on adult bees may show developmental effects on larvae. I’m not saying that pesticides are the cause of CCD–that would be an unjustified leap. But I think there is enough evidence to support testing on larval stages as well as adult stages as part of the EPA registration process.

    I’m thinking of posting my thesis on this site after it’s done. I found a lot of interesting trials, especially from Europe and Canada. I know most people wouldn’t be interested in wading through it, but there may be some.