by Scott McArt Pre-bloom pesticide sprays in apple orchards — safe for bees? s I write this, it’s peak apple in the fall and prior to bloom to con- and colleagues and published in En- bloom here in New York. All trol pests and diseases. Since many vironmental Pollution [114589 (2020)]. Athe big orchards in our Big of those pesticides are systemic (i.e., For their study, Heller and col- Apple state are filled with pallets of they’re taken up into plant tissues), leagues actually conducted two differ- hives and the bees are busily doing they can potentially accumulate in ent studies. First, the authors applied their thing. Since apples are worth pollen and nectar during bloom and one of six systemic insecticide or fun- ~$320 million/year in New York, and expose bees to harmful chemicals. gicide products to groups of 20-year- apple is also ~90% reliant on insect So, are fall and pre-bloom pesti- old apple trees: Assail 30SG (active in- pollination to produce fruit, those cide sprays safe for bees? Given the gredient acetamiprid), Calypso 480SC bees are currently delivering ~$288 economic importance of apple pol- (thiacloprid), Actara 25WP (thiameth- million in pollination services. lination, any beekeeper, grower or oxam), Provado 1.6EC (imidacloprid), At the same time, apple growers consumer of apples or apple products Closer 240SC (sulfoxaflor), or Nova are protecting their crop from poten- should want to know. This is the topic 40W (myclobutanil). The pesticides tially devastating insect pests such as for our thirty-first “Notes from the were applied once (5-7 days before the European apple sawfly and rosy Lab,” where we highlight “Pollinator bloom) at commercially-recommend- apple aphid, or diseases such as ap- exposure to systemic insecticides and ed rates via a standard airblast spray- ple scab and fire blight. Most growers fungicides applied in the previous er. Provado 1.6EC (imidacloprid) is apply a variety of insecticides, fungi- fall and pre-bloom period in apple not labeled for pre-bloom application cides and bactericides to their trees orchards,” written by Sarah Heller but was included as a positive control since it’s a commonly-used systemic insecticide outside of the pre-bloom and bloom periods. Second, the authors conducted a fall pesticide treatment on different trees. For this experiment, Heller and col- leagues applied one of five systemic insecticide products: Endigo ZC (ac- tive ingredients thiamethoxam and lambda-cyhalothrin), Leverage (imi- dacloprid and beta-cyfluthrin), Scor- pion 35SL (dinotefuran), Belay 2.13SC (clothianidin), and Closer 240SC (sulfoxaflor). Each pesticide product was applied 1-4 times via an airblast sprayer in August and/or September according to management guidelines for the brown marmorated stink bug. For both studies, whole flowers, pollen and nectar were collected at peak bloom for each group of plants A typical apple orchard during peak bloom. Photo Scott McArt and analyzed for concentrations of July 2020 787 dosed honey bee colonies with dur- ing the queen-rearing period, observ- ing that new queens were 34% less likely to survive four weeks after emergence and, of the queens that did survive, 38% less likely to lay eggs compared to queens reared in control colonies. Compared to sulfoxaflor, a lot more is known about sublethal effects of thiamethoxam on bees. In fact, a new paper from our lab (in re- view) shows there have been 19 pub- lished scientific studies that have ob- served sublethal effects on honey bee reproduction, behavior or physiology from exposure to less than 50 ppb thi- amethoxam. Furthermore, from a re- Fig. 1 Pesticide concentrations found in apple blossoms following pre-bloom application cent survey of 30 New York apple or- chards, we know that bee bread from each systemic insecticide or fungi- bees. While the pesticides in nectar honey bee colonies conducting apple cide. Pesticide analyses occurred and pollen were not at concentra- pollination contains thiamethoxam at via liquid chromatography-mass tions that would acutely kill bees concentrations up to 48 ppb (McArt et spectrometry (LC-MS) and limits of (i.e., death within 24-48 hours), some al. 2017). This study found that apple quantification were 50 ppb for all of the pesticides were at levels that pollen was not always the dominant pesticides in flower samples and 5-22 could cause sublethal harm to bees. pollen consumed by bees during ppb for pesticides in nectar and pol- For example, the average concen- apple bloom, though risk from pesti- len. Any detections below the limit of tration of sulfoxaflor was ~80 ppb in cides was still over regulatory agency quantification were set to 0. In other pollen (Figure 1). That’s 20x higher levels of concern at 22 of 30 orchards. words, the results summarized below than the 5 ppb sulfoxaflor that Siviter Finally, it’s also worth noting that (and shown in Figure 1) are conser- et al. (2018) dosed bumble bee colo- average myclobutanil concentrations vative estimates of the true residue nies with for 14 days and found that were ~60 ppb (Figure 1). While my- results since several low-level detec- fewer reproductive offspring were clobutanil is a fungicide and therefore tions may have been set to 0 due to produced over the colonies’ lifetime. much less toxic to bees compared to limitations of the LC-MS. Unfortunately, very little is known insecticides such as sulfoxaflor and So, what did they find? Did pre- about sublethal effects of sulfoxaflor thiamethoxam, myclobutanil can bloom sprays show up in the flow- beyond the study by Siviter et al. synergize with insecticides and in- ers, nectar or pollen during bloom? (2018). However, given their results, crease their toxicity. For example, a Yes. Every pesticide that was applied it seems reasonable to assume that ex- recent study from our lab found that pre-bloom was found in the flowers, posure to 80 ppb during apple bloom when bees are exposed to myclobuta- nectar and pollen during bloom with is likely to result in detrimental effects nil, thiamethoxam becomes 2.5 times the exception of sulfoxaflor, which to bees. Thankfully, to our knowledge, more toxic to those bees (Iverson et was not found in nectar (see Figure 1). few apple growers are currently using al. 2019). Are bees simultaneously What about the levels of pesti- sulfoxaflor as a pre-bloom spray. exposed to myclobutanil and thia- cides? Were they at concentrations Similarly, average thiamethoxam methoxam during apple bloom? Yes. that could harm bees? To address concentrations were ~50 ppb in pol- Another recent study from our lab this question, it’s best to evaluate the len (Figure 1). That’s about 10x higher found that whenever thiamethoxam contaminated pollen and nectar, since than the 5.1 ppb thiamethoxam/clo- was found in pollen collected by those are the resources consumed by thianidin that Williams et al. (2015) honey bees during apple pollination, myclobutanil was also found in that pollen (McArt et al. 2017). Well this doesn’t seem good. What about the pesticides applied in the fall, did those result in exposures to bees? No. And this is an important result. None of the systemic insecti- cides applied via foliar sprays in the fall showed up in the flowers, pollen or nectar during bloom. This indi- cates that applying these insecticides in the fall is safe for bees the follow- ing spring (though the authors note that bark sprays, trunk injections and especially soil drenches are known to carry over from fall applications and Co-author Neelendra Joshi sampling nectar from apple flowers via a microcapillary be present at substantial levels during tube. Photo Neelendra Joshi bloom the following spring). 788 American Bee Journal average thiamethoxam concentrations McArt, S. H., A. A. Fersch, N. J. Milano, L. of ~50 ppb in pollen. Furthermore, we L. Truitt and K. Böröczky. 2017. High pes- know from the peer-reviewed litera- ticide risk to honey bees despite low focal ture that, to date, 19 studies have ob- crop pollen collection during pollination of a mass blooming crop. Scientific Re- served significant sublethal effects on ports 7:46554. https://www.nature.com/ honey bee reproduction, behavior or articles/srep46554 physiology from exposure to less than Siviter, H., M. J. F. Brown and E. Lead- 50 ppb thiamethoxam. One of these beater. 2018. Sulfoxaflor exposure reduces studies found significant impacts on bumblebee reproductive success. Na- queen reproduction at an exposure ture 561:109-112. https://doi.org/10.1038/ level of only 5.1 ppb, almost 10x less s41586-018-0430-6 Van Dyke, M., E. Mullen, D. Wixted and than the levels found in pollen by S. H. McArt. 2018. A Pesticide Decision- Heller and colleagues. Making Guide to Protect Pollinators in So, does this mean applying a pre- Tree Fruit Orchards. Available for free down- bloom spray of Actara is safe for bees? load at: https://pollinator.cals.cornell.edu/ According to the EPA, the current an- resources/grower-resources/ Williams, G. R., A. Troxler, G. Retschnig, K. Sampling pollen from apple flowers via swer is “yes.” What do you think? Until next time, bee well and do Roth, O. Yañez, D. Shutler, P. Neumann a high-tech eyebrow brush from Wal- and L. Gauthier. 2015. Neonicotinoid pes- greens. Photo Scott McArt good work. And share our pesticide ticides severely affect honey bee queens. decision-making guide to protect pol- Scientific Reports 5:14621. https://www. So what’s the take-home here? linators in tree fruit orchards (Van nature.com/articles/srep14621 Applying pre-bloom pesticide Dyke et al. 2018)! sprays is risky for bees but spraying Scott McArt Scott McArt, an As- in the fall isn’t risky? A major result sistant Professor of Pollinator Health, from Heller and colleagues’ study is REFERENCES: helps run the Dyce that systemic insecticides via foliar Heller, S., N.