A spate of new studies came out this spring, all of them seeking to link neonicotinoid insecticides to mortality in honeybees, bumblebees, and several kinds of native bees, and all of the studies getting wide publicity.
Reaction among agricultural entomologists varied. Some criticized the studies as being scientifically flawed. None thought the studies showed a definitive causation between the insecticides and colony collapse disorder, although other studies have shown that neonicotinoids may make honeybees more susceptible to parasites and pathogens that have been implicated as possible causes. Everybody agrees that neonicotinoids (like most insecticides by definition) are toxic to bees, but some are more toxic than others.
There are currently six neonicotinoids used in agricultural crops: imidacloprid (Provado and others), clothianidin (Clutch and others), dinotefuran (Venom, Scorpion), thiamethoxam (Actara, Platinum, others), acetamiprid (Assail, Tristar), and thiacloprid (Calypso). They can be applied as foliar sprays, seed coatings, soil drenches, or granules, by direct trunk injection, and by chemigation. Several have been formulated for turf, ornamental, and residential uses.
Dennis vanEngelsdorp, who heads the new Bee Informed Partnership at the University of Maryland, said the study that attributed colony collapse disorder to neonicotinoid insecticide poisoning was “really badly done,” was not replicated, and contained no statistics. “I was surprised they published it,” he said of the online journal where the study appeared.
But another study that showed 85 percent suppression of queen production in bumblebees was “really quite new” and deserves a closer look and more research, vanEngelsdorp said. “Honeybees have large colonies with many workers, and they can take a lot of abuse,” he said. “But the solitary bees, like bumblebees, are much more fragile.” Bumblebees depend upon production of new queens, not worker bees, for their survival and increase.
Perhaps the publication most instructive to fruit producers is a white paper published in March by the Xerces Society for Invertebrate Conservation and coauthored by Dr. David Biddinger at Pennsylvania State University, who offers the following advice to fruit growers:
—Never use Clutch or Actara prebloom, or postbloom until all blossoms are gone. “Eighty percent petal fall means 20 percent bloom, and for growers relying on wild bees (many of which have a single generation each year), this can really wipe them out. Prebloom, I would only recommend Assail or Calypso at early pink. Be careful in blocks with multiple varieties with differing bloom times to avoid late applications in one variety.”
—Never use Assail at bloom, even though it is legal.
—Be careful when tank mixing with fungicides. “Synergism of neonicotinoid insecticides with the sterol-inhibitor fungicides (Nova/Rally, Indar, Inspire Super) has been shown when they are tank mixed in the lab,” Biddinger said. “The cause is thought to be that the fungicide inhibits the enzymatic mechanism in bees that help them to break down pesticides.”
One lab study showed more than a 1,000-fold level of synergism of Calypso when mixed with Procure (triflumizole) and more than 550-fold when mixed with Orbit/Tilt (propiconazole). Synergism of Assail was also shown in the same study, but at 105-fold and 244-fold, respectively, with the same fungicides, he said.
Several scientists at Penn State recently completed a lab study, which they hope to publish soon, using formulated product of Assail and the sterol-inhibitor fungicide Indar (fenbuconazole). They found only a sixfold level of synergism. Laboratory studies using technical pesticide dissolved in acetone to apply to insects usually greatly overestimate field impacts of water-soluble formulations of pesticides that are used in orchards, he said.
Other, nonsterol-inhibitor fungicides do not appear to synergize, he said, although mancozeb and captan can be somewhat toxic to wild bee larvae that feed on contaminated pollen.
—Imidacloprid can only be used postbloom. “But that means when all petals are off, not just when the honeybee hives have been moved out,” he said.
—Pesticide tests on honeybees (required for pesticide registration) are not necessarily good indicators of their impacts on solitary bees and bumblebees, Biddinger said. “We conducted a trial using formulated product of several insecticides used in apple on both Osmia (mason bee) and the honeybee and found in the case of Provado, Osmia was almost 26-fold less susceptible than the honeybee. Osmia, however, was more than 12-fold more susceptible to Assail than the honeybee.”
Biddinger summarized his 48-page white paper in a page published on the Internet April 6 by Penn State Extension as part of its Fruit News. Biddinger’s comments were also published that week in the weekly newsletter Scaffolds put out by Dr. Art Agnello, entomologist at Cornell University, New York.
Some of the neonicotinoids are highly toxic to honeybees, but there are several of them and they are not all equally toxic, Biddinger said. The major concern is that they are systemic, meaning they are taken up by the plants and circulate within the plants. While that provides a lethal deterrence to chewing and sucking pests, it can also be present in pollen and nectar, which makes them a problem for pollinators beyond their direct contact toxicity, he said.
One of the studies this spring, by University of Maryland entomologist Dr. Galen Dively, reported negative effects on bees visiting pumpkin flowers where soil had been treated with a neonicotinoid insecticide. This can be a serious problem, vanEngelsdorp said, since pumpkins and some other vegetables, like squash and cucumbers, bloom over a long period, unlike fruit crops.
Neonicotinoids can persist in soil for months or even years after a single application, Biddinger reported in his white paper. Measurable amounts of residues were found in woody plants up to six years after application, but, so far, these have only appeared in plants where nonfoliar applications were made at much higher rates then normally used in orchards.
Biddinger expressed concern about neonicotinoid products approved for homeowner use in gardens, lawns, and on ornamental trees. Recommended rates there can be 120 times those used in agricultural crops, he said.
One of the studies this spring focused on their use as seed protectants and the resulting contamination of nearby flowering plants exposed to the talcum powder dust used to carry the insecticide in the seed boxes. Millions of acres of corn are planted using neonicotinoid-treated seed.
Biddinger notes that the neonicotinoids, unlike other insecticides, seem more toxic to bees by ingestion than by contact. Dinotefuran, imidacloprid, clothianidin, and thiamethoxam are rated as highly toxic to bees, acetamiprid and thiacloprid as moderately toxic.
In addition to death, bees can suffer sublethal effects that impair foraging and feeding behaviors, learning, navigation, and mobility. It is very difficult to study the interactions and understand what happens in a farm setting, Biddinger said.
He also reminded everyone to not the throw the baby out with the bath water. Neonicotinoids came into wide use because they have great benefits in IPM programs, are very kind to predatory mites, are effective at very low rates, and are less toxic to people.
Biddinger’s full report can be found online at www.xerces.org/wp-content/ uploads/2012/03/Are-Neonicotinoids-Killing-Bees_Xerces-Society1.pdf.
The same week that the Xerces report on neonicotinoids was released, another publication was released from the Northeast IPM Center specifically on wild pollinators for eastern tree fruit growers. A joint publication by Cornell University, Penn State University, and the Xerces Society, this 18-page color brochure is available online at www.northeastipm. org/park2012 and offers conservation advice to fruit growers relying on native pollinators. It identifies with photos most of the important types of bees found in New York and Pennsylvania apple orchards, and contains a bee toxicity rating table of the most commonly used insecticides, fungicides, and fruit thinners.