In the course of a study on mosquito movement at a zoo in Manhattan, Kansas, researchers discovered that local colonies of honey bees had foraged on a sugar bait for the mosquitoes that had been applied to foliage near the zoo. The bait had been dyed for the purpose of tracking mosquitoes that had fed on it, but the dye also showed up in much of the bees’ honey. Here, a frame from one of the zoo’s bee hives shows honey dyed red (black arrow). The bait in this case was nontoxic, but the discovery indicates a need for further study on attractive toxic sugar baits’ impacts on bees and other nontarget insects. (Image originally published in Kapaldo et al 2018, Journal of Insect Science)

By Meredith Swett Walker

Honey bees are hard-working foragers who get most of the carbohydrates they need from floral nectar, but they won’t pass up a sweet snack just because it doesn’t come from a flower. They’ll occasionally forage on honey dew produced by other insects and sugary food left out by humans. The honey bee’s flexibility in foraging from nonfloral sources is handy for beekeepers who can supplement their hives with sugar water when flowers are scarce. But searching for sweetness in the wrong places has the potential to expose bees to danger.

Meredith Swett Walker

In a new study published this week in the Journal of Insect Science, Nathaniel Kapaldo and James Carpenter, Ph.D., from Kansas State University and Lee Cohnstaedt, Ph.D., from the U.S. Department of Agriculture’s Center for Grain and Animal Health Research in Manhattan, Kansas, describe significant foraging by honey bee colonies on dyed sugar baits similar to those used in attractive toxic sugar bait (ATSB) systems to control insects such as mosquitoes. While prior studies have shown limited impact of ATSBs on nontarget insects, results of this study suggest that honey bees may have higher exposure to these baits than previously estimated.

ATSBs consist of a sugar source, an oral toxin, and sometimes a chemical attractant. They are gaining popularity as a mosquito-control technique because they are easy to use, reasonably effective, and can be relatively environmentally friendly. Both male and female mosquitoes feed on sugary plant juices, including nectar. Female mosquitoes also require protein-rich blood in order to produce eggs, but both sexes are attracted to and can be killed using sugar baits. Because mosquitoes ingest the bait, the toxin does not have to kill on contact, and so moderate toxins can be used including pyrethroids, borates, and botanicals. To reduce effects on nontarget insects, ATSBs are typically sprayed on foliage, not flowers.

The researchers in Kansas did not set out to study honey bee foraging on sugar baits; they were interested in mosquito movements. They deployed dyed, nontoxic sugar baits to mark mosquitoes in the Sunset Zoo in Manhattan, Kansas, to help determine where they were coming from. Sugar baits consisted of an approximately 1-to-4 ratio of sugar to water and standard food coloring (red, blue, or green) from a grocery store. The sugar bait was sprayed on foliage (not flowers) of plants at three locations in the zoo, and mosquitoes were then sampled to determine if they had dyed foreguts.

But, about one month following the experiment with the dyed sugar baits, the apiculturist maintaining the zoo’s bee hives reported some oddly colored honey. Four of the zoo’s six hives contained red honey—of the 133 kilograms (kg) of honey the apiculturist harvested, about 57 kg of it was dyed bright red.

The dyed honey demonstrates significant foraging by the bees on the sugar baits, which in this instance were not toxic. But, had this been a toxic bait, the effect on the bees could have been significant, depending on the toxin used. Cohnstaedt emphasizes that, based on the amount of honey that contained dye, future studies of the effect of ATSB on honey bee colonies should examine whole-hive health, rather than just the effects on individual bees as has been done in the past. The authors also recommend measuring sublethal effects of toxins used in ATSBs—a toxin may not kill the bees, but it could affect a colony’s ability to forage, produce honey, and reproduce.

To prevent contact with bees and other nontarget insects, a toxic sugar bait station can be deployed with a screen, such as this one used to control biting midges and sand flies on an organic farm in Greece. (Photo credit: Lee Cohnstaedt, Ph.D.)

To study mosquito movement near a zoo in Manhattan, Kansas, researchers sprayed a dyed sugar bait on foliage in forested and riverine areas of the zoo. Along the way, however, they discovered that local colonies of honey bees had foraged on the bait when much of their honey appeared red from the dye used in the bait. (Image originally published in Kapaldo et al 2018, Journal of Insect Science)

If future studies do show that ATSBs are bad news for bees, does that spell the end for this promising vector-management technique? Not necessarily, says Cohnstaedt: “Bait stations versus broadcast spraying would reduce contact with nontarget species and environmental contamination.” Bait stations can be fitted with a screen that prevent bees and other nontarget insects from accessing the toxic sugar bait. ATSB stations could also be used to control mosquitoes and other biting insects indoors.

In science, things don’t always go as planned, and sometimes that’s when you learn the most. According to Cohnstaedt, this study “is a case of turning a disaster into a positive. We really thought we had ruined a lot of honey at the zoo, however it turned out fine as it was a food-grade dye, and we learned a lot about the foraging of bees and sugar baits.”

Meredith Swett Walker is a former avian endocrinologist and wannabe entomologist. She now studies the development and behavior of two juvenile humans in the high desert of western Colorado. When she is not handling her research subjects, she writes about science and nature. Find a sampling of her work at www.magpiescicomm.com.