Several have quoted the EPA Fact Sheet which says
>Although spirotetramat can be classified as practically non-toxic to honey
bees based on acute oral and contact studies, results of brood feeding studies
and tunnel tests suggest the potential for effects to broods following
spirotetramat applications at rates lower than the maximum proposed label
rates; significant brood effects including increased mortality in adults and
pupae, massive perturbation of brood development, early brood termination,
and decreased larval abundance were detected. Spirotetramat also had a
wide range in magnitude of acute effects on other various non-target
terrestrial arthropods.<
The EPA Fact sheet doesn't provide adequate context. Spirotetramat is basically an insect larvicide so yes it has the potential to affect larval honey bees. The key quesitons are "at what concentration or dose level does this happen and will bees be exposed to such levels under conditions of practical use?
There was a clear effect in a screening studies in which small colonies were fed syrup containing 144 ppm spirotetramat, which is much higher than possible exposures in the field. These were the only studies that showed "massive perturbation of brood development" or adult mortality.
Some preliminary tunnel studies showed a milder effect on brood development, but follow up definitive tunnel studies (i.e., conducted under GLP) didn't. There were limited field study results at the time of the EPA review in 2008, but these had also indicated no effects. A fair summary of the weight of the evidence at this time would be to say there was an open question about safety to bee brood that required more study. This is why the decision was made to not allow application to bee-attractive crops during bloom until more further research could be conducted. Nobody's bees have been at risk while this research was being conducted.
We now have additional research that shows no effects on brood development (or any other endpoint) under actual use conditions (i.e., real field sites) when sprayed during bloom on phacelia, canola, melons and citrus. Equally important, we have a much better understanding of what concentrations bees will be exposed to in the field and what the threshold level for effects is. Some of this research has been submitted to EPA and is under review. Some of it hasn't been yet.
Bayer discussed all of the above very openly with members of the National Honey Bee Advisory Board last March in a meeting in Davis, CA and asked for assistance in conducting a field trial to evaluate the safety of spirotetramat when sprayed during bloom in citrus. Dave Hackenberg and Dave Mendes stepped forward to cooperate. Mendes supplied the bees, and Hackenberg found suitable study sites near his winter headquarters in Florida and provided additional equipment and logistical support. With lobbying assistance of the NHBAB, we obtained experimental use permits from EPA and the Florida Department of Agriculture and Consumer Services to apply the product during bloom, which is currently not permitted by the label. Obtaining state and federal EUPs usually takes at least several months of bureaucratic review. With the NHBAB's help, we got them in 5 days. The study was designed during a teleconference with the NHBAB members, Jeff Pettis (USDA), Eric Mussen (UC Davis), Jerry Bromenshenk (U Montana), and Tom Steeger (EPA). Dick Rogers (Wildwood Labs) and Geoff Williams (Acadia Univ) conducted the field work. Dick will be presenting the results of the study this Friday afternoon at the American Bee Research Conference.
Best regards to all,
Dave Fischer
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