Can attractive toxic sugar baits harm nontarget species? Scientists test a new ingredient to find out

Mosquito control may well be one of the most debated topics among IPM professionals. Pesticide sprays such as DDT and malathion have been decried by groups concerned about their effect on the environment, while groups concerned about the health risks posed by mosquitoes argue that the chemicals save lives. In some situations, attractive toxic sugar baits (ATSBs) have been used as an alternative to broadcast sprays, with effective results.

Although the baits are designed to target mosquitoes, some groups have concerns about their impact on nontarget species. Baits can contain any variety of insecticide; the group proposed testing dinotefuran, a toxin that at the time was considered to be low-risk for nontarget organisms but effective in killing certain species of mosquitoes. A group of scientists from Israel and Florida collaborated on a project to test the effects of dinotefuran sugar baits on Culex quinquefasciatus and Aedes aegypti L. Their results were published in the October 2013 issue of Environmental Entomology.

Attractive toxic sugar baits can be enclosed or sprayed or painted on vegetation or dunked in water in chemical form. Typically they are used in areas where malaria is prevalent; most US citizens would not necessarily use them in their yard to control mosquitoes. They are typically made from a low risk insecticide—usually boric acid—and a sugar solution to attract the insect. They are “targeted” for mosquitoes because mosquitoes are guided by scent when sugar feeding, whereas pollinators are typically attracted to color.

I need to note that the experiments took place well before the large Oregon bee killing in June of this year. In that incident, a pesticide containing dinotefuran was sprayed on flowering linden trees, and the bees ingested the toxin after pollinating the flowers.

Scientists tested the following situations:

  • whether or not the dinotefuran would effectively kill the mosquitoes,
  • whether mosquitoes and/or nontarget species would be attracted to bait applied to leafy vegetation,
  • whether mosquitoes and/or nontarget species would be attracted to bait applied to flowering vegetation
  • whether mosquitoes and/or nontarget species would be attracted to bait applied to objects like cisterns
  • whether predators of mosquitoes would die when they ate treated mosquitoes.

To test the effectiveness of the dinotefuran, mosquitoes were placed in plastic cups containing the toxin and then watched to note the time of death. Field studies consisted of a treatment and control site in two ditches, and dye was added to each solution to determine whether the mosquito ingested the solution in either case. To see the rate of ingestion, scientists dissected the guts to see the amount of staining.

For the experiment with nontarget species (which included pollinators), early experiments that included the toxin yielded confused insects that were hard to collect, so instead of spraying insecticide, scientists sprayed only a nontoxic, dyed sugar solution. Scientists sprayed the solution on the foliage of non-flowering plants and the blooms of flowering plants. After they collected the insects, they dissected them to see how much stain was in the gut.

All mosquitoes ingested the sugar solution, and nearly every dose resulted in mosquito mortality, with lower doses resulting in death later than higher doses. In the mosquito field experiment, the treated field resulted in a 70 percent reduction of mosquitoes, while the control field saw an increase in population.

Nontarget experiments yielded more varied results. None of the predators (spiders and beetles) that fed on treated mosquitoes died as a result. Staining of the gut proved that mosquitoes had ingested the toxin.

From the nontarget field experiments, scientists discovered that pollinators did not ingest the solution sprayed on foliage but did ingest the solution sprayed on flowers. The concluded that as long as ASTB solutions were applied to nonflowering vegetation, they would have few adverse effects on pollinators.

Overall, the study showed that dinotefuran could be used in ASTB applications to control mosquitoes, and if applied to nonflowering plants would have little impact on nontarget species.

Source: Khallaayoune, K., Qualls, W., Revay, E., Allan, S., Arheart, K.L., Kravchenko, V.D., Xue, R., Schlein, Y, Beier, J.C., and Muller, G.C. (October 2013). Attractive toxic sugar baits: Control of mosquitoes with the low-risk active ingredient dinotefuran and potential impacts on nontarget organisms in Morocco. Environmental Entomology, 42(5): 1040-1045. http://www.bioone.org/doi/full/10.1603/EN13119

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