Currently, more than 360 spray adjuvants are registered in Germany (September 2021). Unlike plant protection products (PPPs), adjuvants are not subjected to regulatory risk assessment. In practice, numerous combinations of PPPs and adjuvants are therefore possible. Thus, tank mixtures containing insecticides that are classified as non-hazardous to bees up to the highest approved application rate or concentration may raise pollinator safety concerns when mixed with efficacy increasing adjuvants and applied in bee-attractive crops. This study analyzes whether selected “PPP–adjuvant” combinations result in increased contact mortality and pose an elevated risk to honey bees. To answer this question, we chose six common spray adjuvants of different classes for laboratory screening. These were then tested in a total of 30 tank mixtures, each with a neonicotinoid (acetamiprid), pyrethroid (lambda-cyhalothrin), diamide (chlorantraniliprole), carbamate (pirimicarb), and butenolide (flupyradifurone) formulation. We adapted an acute contact test (OECD Test Guideline 214) to our needs, e.g., by using a professional spray chamber for more realistic exposures. Our results showed that, in total, 50% of all combinations significantly increased the mortality of caged honey bees in comparison with individual application of insecticides. In contrast, none of the adjuvants alone affected bee mortality (Cox proportional hazard model, p > 0.05). With four of the five insecticide formulations, the organosilicone surfactant Break-Thru® S 301 significantly increased bee mortality within 72 h (for all insecticides except chlorantraniliprole). Furthermore, acetamiprid yielded the highest and second highest mortality increases from a tank mixture with the crop oil surfactant LI 700® (hazard ratio = 28.84, p < 0.05) and the organosilicone Break-Thru® S 301 (hazard ratio = 14.66, p < 0.05), respectively. To assess risk in a more field-realistic setting, field trials should be performed to provide a more realistic exposure scenario under colony conditions.

The ongoing debate about glyphosate-based herbicides (GBH) and their implications for beneficial arthropods gives rise to controversy. This research was carried out to cover possible sublethal GBH effects on the brood and colony development, adult survival, and overwintering success of honey bees (Apis mellifera L.) under field conditions. Residues in bee relevant matrices, such as nectar, pollen, and plants, were additionally measured. To address these questions, we adopted four independent study approaches. For brood effects and survival, we orally exposed mini-hives housed in the “Kieler mating-nuc” system to sublethal concentrations of 4.8 mg glyphosate/kg (T1, low) and 137.6 mg glyphosate/kg (T2, high) over a period of one brood cycle (21 days). Brood development and colony conditions were assessed after a modified OECD method (No. 75). For adult survival, we weighed and labeled freshly emerged workers from control and exposed colonies and introduced them into non-contaminated mini-hives to monitor their life span for 25 consecutive days. The results from these experiments showed a trivial effect of GBH on colony conditions and the survival of individual workers, even though the hatching weight was reduced in T2. The brood termination rate (BTR) in the T2 treatment, however, was more than doubled (49.84%) when compared to the control (22.11%) or T1 (20.69%). This was surprising as T2 colonies gained similar weight and similar numbers of bees per colony compared to the control, indicating an equal performance. Obviously, the brood development in T2 was not “terminated” as expected by the OECD method terminology, but rather “slowed down” for an unknown period of time. In light of these findings, we suggest that chronic high GBH exposure is capable of significantly delaying worker brood development, while no further detrimental effects seem to appear at the colony level. Against this background, we discuss additional results and possible consequences of GBH for honey bee health.

In agricultural crops, honey bees may be exposed to multiple pesticides. However, in field realistic conditions mixtures of products classified as harmless to bees can lead to a synergistic increase of toxicity on honey bees, as known for ergosterol biosynthesis-inhibiting (EBI) fungicides combined with pyrethroids or neonicotinoids. For substances like fertilizers, usually no information on potential side effects on bees is available. Initially, effects from tank mixes containing insecticides, fungicides and fertilizers were investigated under laboratory conditions by use of a spray chamber contact test. For selected combinations, higher tier studies were carried out. Mixtures containing thiacloprid, boscalid and dimoxystrobin with boron fertilizers showed no increase of mortality. In contrast, tank mixes of thiacloprid formulations and EBIfungicides resulted within 24 h in synergistic mortality increase in laboratory, semi-field and field. Actually, a short time interval of 24 h between individually applied potentially synergistic products like pyrethroid insecticides and EBI fungicides led to an increase of mortality up to 100% under laboratory conditions, indicating that the detoxification was still ongoing, resulting in an increased susceptibility for other stressors during the metabolization process. In conclusion, tank mixtures do not always lead to an increase of honey bee toxicity. However, former published findings about synergistic impacts between neonicotinoides and EBI-fungicides could be confirmed. The findings of our and other higher tier studies finally prompted the competent regulatory authority (BVL) to regulate these mixtures by restriction NB6613 since September 2018. Nevertheless, the investigation of potential interactions between mixing partners and their additive or synergistic effects are the basis for a better understanding and a logical risk assessment to ensure protection of honey bees.Keywords Honey bees Á Tank mixtures Á Synergistic impacts Á Contact exposure Á EBI-fungicides

The ongoing debate about glyphosate-based herbicides (GBH) and their implications for beneficial arthropods give rise to controversy. This research was carried out to cover possible sublethal GBH effects on brood and colony development, adult survival, and overwintering success of honey bees (Apis mellifera L.) under field conditions. Residues in bee relevant matrices such as nectar, pollen and plants were measured in addition. To address these questions, we adopted four independent study approaches. For brood effects and survival, we orally exposed mini-hives housed in the "Kieler mating-nuc" system to sublethal concentrations of 4.8 mg glyphosate/kg (T1, low) and 137.6 mg glyphosate/kg (T2, high) over the period of one brood cycle (21 days). Brood development and colony conditions were assessed after a modified OECD method (No. 75). For adult survival, we weighed and labeled freshly emerged workers from exposed colonies and introduced them into non-contaminated mini-hives to monitor life span for 25 consecutive days. Results from these experiments showed a trivial effect of GBH on colony conditions and survival of individual workers, even though hatching weight was reduced in T2. The brood termination rate (BTR) in the T2 treatment, however, was more than doubled (49.84%) when compared to the control (22.11%) or T1 (20.69%). This was surprising as T2 colonies gained similar weight and similar numbers of bees per colony compared to the control, indicating equal performance. Obviously, the brood development in T2 was not "terminated" as expected by the OECD method terminology but rather "slowed down" for an unknown period of time. In light of these findings, we suggest that chronic high GBH exposure is capable of delaying worker brood development to a significant extent while no further detrimental effects seem to appear at the colony level. Against this background, we discuss additional results and possible consequences of GBH for honey bee health.

Currently, more than 350 spray adjuvants are registered in Germany (January 2021). Unlike plant protection products (PPPs), adjuvants are not subjected to regulatory risk assessment. In practice, numerous combinations of PPPs and adjuvants are therefore possible. Thus, tank mixtures containing insecticides that are classified as nonhazardous to bees and approved for use in bee attractive crops may raise pollinator safety concerns when mixed with efficacy increasing adjuvants. This study analyzes whether selected “PPP-adjuvant” combinations result in increased mortality and pose an elevated risk to honey bees. To answer this question, we chose six common spray adjuvants of different classes for laboratory screening. These were then tested in a total of 30 tank mixtures, each with a neonicotinoid (acetamiprid), pyrethroid (lambda-cyhalothrin), diamide (chlorantraniliprole), carbamate (pirimicarb), and butenolide (flupyradifurone) formulation. We followed OECD test guideline 214 (acute contact test) but adopted the use of a professional spray chamber for more realistic exposures. Our results showed that, in total, 50% of all combinations significantly reduced the lifespan of caged honey bees in comparison to individual application of insecticides. In contrast, none of the adjuvants alone affected bee mortality (Cox proportional hazard model, p > 0.05). With four of the five insecticide formulations, the organosilicone surfactant Break-Thru® S 301 significantly increased bee mortality within 72 h (for all insecticides except chlorantraniliprole). Furthermore, acetamiprid yielded the highest and second-highest mortality increases from a tank mixture with the crop oil surfactants LI-700 (hazard ratio = 28.84, p < 0.05) and Break-Thru® S 301 (hazard ratio = 14.66, p < 0.05), respectively. In the next step, field trials should be performed to provide a more realistic exposure scenario under colony conditions to verify these findings.