Good Fruit Grower

May 15

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Justin Vincett, beekeeper from Ellensburg, Washington, opens a beehive. A Are these insecticides the root cause of problems with bees? by Richard Lehnert Neonicotinoids and bees 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 stud- ies 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 insecti- cides by definition) are toxic to bees, but some are more toxic than others. There are currently six neonicotinoids used in agricul- tural crops: imidacloprid (Provado and others), clothian- idin (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 8 MAY 15, 2012 GOOD FRUIT GROWER "I was surprised they published it." —Dennis vanEngelsdorp 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 pro- ducers 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 rec- ommend 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. "Syn- ergism of neonicotinoid insecticides with the sterol- inhibitor fungicides (Nova/Rally, Indar, Inspire Super) has been shown when they are tank mixed in the lab," Bid- dinger 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 (triflumi- zole) 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 formu- lated 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 contami- nated 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 sev- eral 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 photo by melissa hansen

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