Pests and Pollinators

Are We Spraying the Bees Away?


Blueberry growers are faced with the consistent challenge of balancing pest and pollinator management. Fruit production is highly reliant upon insect pollinators. This requires growers to deploy managed pollinators and consider the effects of farm management on pollination. Unfortunately, pollinators are not the only insects that growers must consider. Several damaging insect pests such as thrips, gall midge, and spotted wing drosophila lead to frequent prophylactic treatments of insecticides, some of which occur during the pollination window. Recent research has shown that insecticide applications can have significant non-target effects on pollinators that result in death, reduced foraging rates, changes in bee behavior, and reduced reproductive ability. Many of these studies have assessed season-long impacts of pesticides including several applications. Although this is valuable information, growers also need to know the immediate impacts of a single insecticide application on pollination, including potentially repelling pollinators from flowers. We assessed pollinator activity and pollinator health impacts of a single application of three commonly used insecticide products, Sivanto Prime, Delegate WG, and Assail 70 WP along with an untreated control. 

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Research activities 

In the Spring of 2021, we carried out an experiment to examine the effects of single insecticide applications on pollinator behavior and health. The experiment took place at a large-scale commercial blueberry farm located in Hawthorne, FL. Sixteen large field cages were used with each cage containing one bumble bee (Bombus impatiens)research hive, like those commonly used by growers, and 50 one-gallon Chickadee blueberry plants. In each cage, we observed bumble bee visits to blueberry flowers for at least three days prior to insecticide application and seven days following application. All insecticides were applied at recommended label rates targeting thrips on small blueberry plants. Additionally, all four treatments including the control were sprayed with the surfactant DyneAmic to ensure effective coverage and to replicate farmer practices. After the estimated 10 days of observation, bumble bee colonies were removed from cages and allowed to forage freely until the end of the blueberry pollination period, at which point they were taken back to the lab for dissection.


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Research findings

Bumble bee visits to blueberry flowers were not significantly affected by any of the three single applications of insecticides applied. Immediately following insecticide applications, bumble bee activity increased across all treatments, likely because of the warmer weather later in bloom (Figure 1). However, visitation increased most in the unsprayed control and least in the Assail 70 WG showing a slight negative effect of Assail on pollinator activity (Figure 1). Thus, growers can utilize any of these three insecticides in line with label recommendations and are unlikely to experience significant reductions in pollinator activity but may have small reductions with the use of Assail 70 WG as compared to other products or unsprayed areas. 



We also found significantly higher bumble bee death in colonies exposed to Delegate compared to our other three treatments (Figure 2). This is a surprising result as Delegate is currently considered a pollinator-safe insecticide and is commonly recommended for treating pests during the bloom period. However, some studies have found that Delegate is only safe to pollinators on contact but is highly lethal when ingested. Bumble bees may be ingesting lethal quantities of Delegate when it is applied to blueberry plants in bloom despite following label guidelines to reduce pollinator contact.



Conclusions and management recommendations 


Our results indicate that blueberry growers can utilize single applications of any of the three insecticides (Assail, Delegate, Sivanto) without significantly reducing pollinator flower visits, though all insecticides showed slight reductions in activity as compared to the unsprayed control and Assail had the greatest negative effect on pollinator activity. Based upon results from previous research, repeated or combined use of these insecticides within the bloom period may lead to reductions in pollinator visitation and pollination efficacy that could affect yields. It remains crucial that blueberry growers use IPM practices such as scouting for pests and only apply insecticides when established economic thresholds are met. Reducing prophylactic applications by utilizing IPM practices will allow for fewer applications during the bloom period and reduce the chance of impacting pollinator visitation rates. 


Despite being commonly recommended for use during the bloom period, it seems that Delegate needs to be assessed further for its lethal effects on bumble bees and other pollinators. Our results indicate that bumble bees encountered toxic concentrations of Delegate even when mitigation strategies such as evening applications were utilized. It is unclear if these lethal effects would also occur in honey bees and wild native bees, but the consequences of a similar effect could lead to reduced pollination. Based on this result, growers should consider alternative insecticides if application is necessary during the bloom period.

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