Sudden and Prevalent Deaths of Foraging Honey Bees in Early Spring During Sowing of Clothianidin Coated Maize Seeds Between 2013 and 2018 in Turkey

Honey bees are important for the balance of the ecosystem, contributing to the wider floral biodiversity and qualitative and quantitative characteristics of agricultural production. In addition, such honey bee products as honey, pollen, wax, propolis and royal jelly are appreciated for their importance in human consumption and the agricultural economy (Klein et al., 2007; Bacandritsos et al., 2010).

Honey bee deaths and population decline are a multifactorial issue involving such things as pesticide poisoning from agricultural activities, honey bee parasites (Varroa destructor, Acarapis woodi), pathogens (Nosema spp. and bee viruses), contaminated water, nutritional stress and their interactions (Higes et al., 2008; Naug, 2009; van Engelsdorp et al., 2009; Pistorius et al., 2009; Sharpe & Heyden, 2009).

The use of pesticides in agricultural production is often discussed as a factor influencing bee health (Johnson et al., 2010). Honey bees can be exposed to pesticides through contaminated pollen and nectar collected and stored in the hive (Chauzat et al., 2006; Chauzat & Faucon, 2007), through air contamination via the drifting of dust in coated seeds during sowing (Greatti et al., 2003; Tapparo et al., 2012), through the exudate excreted from the plants (Girolami et al., 2009), and through surface water (van Dijk, 2010). In addition to the reduction in the quality of hive products and the effects on bees’ behavior, the accumulation of insecticides in honey bee tissue can also influence honey bee health and the colony population development, as they act as stressors for the entire colony. Compared to other insects, honey bees are extremely sensitive to pesticides due to a deficiency in the number of gene encoding de­ toxification enzymes (Claudianos et al., 2006). Intraspecific genetic differences also impact the susceptibility to pesticides, e.g., imidacloprid (Suchail, Guez, & Belzunces, 2001).

Different classes of pesticides are used in agricultural activities, and the neonicotinoid class is one of the types of the insecticides used. Neonicotinoid compounds are used in more than 120 countries, with at least 140 different crop uses (Jeschke et al., 2011; Lundin et al., 2015).

Nitro-substituted neonicotinoids, such as imidacloprid, clothiani din and thiamethoxam, are more toxic to bees (Kiljanek, Niewiadomska, & Posyniak, 2016). The environmental releases of substances with recognized toxic and ecotoxic effects such as neonicotinoid insecticides have been associated with the worldwide crisis of honey bee colonies (Ratnieks & Carreck, 2010; Tapparo et al., 2012). The European Commission voted to place a moratorium on the use of three neonicotinoid insecticides: imidacloprid, thiamethoxam and clothianidin, after the European Food Safety Authority (EFSA) determined that these products put bees at a high risk to through such exposure routes (EFSA, 2013) as direct dust exposure during seed planting operations (Greatti et al., 2003; Tapparo et al., 2012) and ingestion of residues in guttation droplets (Girolami et al., 2009), nectar and pollen from treated plants (Rortais et al., 2005). Taking into account these facts the European Commission (EC) proposed to restrict the use of three neonicotinoids: clothianidin, imidacloprid and thiamethoxam, for seed treatment, soil application (granules) and foliar treatment on bee attractive plants and cereals (EC, 2013; EFSA Technical Report, 2018), and toxicity risk of clothianidin when use as seed treatments was indicated by EFSA (EFSA, 2018). Similarly, neonicotinoids including acetamiprid, clothianidin, imidacloprid, thiacloprid and thiamethoxam were also restricted by the Ministry of Agriculture and Forestry in Republic of Turkey at the end of 2018 (Official Decision, 2018).

A high density of bee colonies is located in the Adana, Mersin, Osmaniye and Hatay provinces of southern Turkey’s Çukurova Region (Fig. 1), due to the mild climate that promotes a rapid development of colonies in late winter (February) and early spring. This region is important for Turkey due to its having a fertile and large plain area for agricultural activities. For this reason, a high number of bee-attractive crops, such as fruit trees (plum, apricot, peach, nectarine and citrus fruits) and vegetables (cucumber, tomato, pepper and pumpkin), allow for the rapid development of colonies and good beekeeping conditions in early spring. Migratory beekeeping is also prevalent in this region.

Fig. 1

Because bee death incidents have been observed on a large scale and are related temporally and spatially with the sowing of clothianidin-coated maize seeds, pesticides has been suspected of poisoning honey bees in the Çukurova Region. Maize seeds have recently been treated with clothianidin (Poncho^® FS 600) in this region for the eradication of the western corn rootworm (Diabrotica virgifera virgifera). Even though these sudden and prevalent deaths of honey bees with clinical symptoms were shown to be a poisoning case, bee pathogens had also been considered for differential diagnosis. Thus, the objective of this study was to investigate reasons for the sudden and prevalent honey bee deaths in early spring from 2013 to 2018 in the Çukurova Region.

The highest number of bee deaths was recorded in 2017 during the maize sowing period in the region, especially in Adana. Ten areas had sudden and extensive bee deaths in 530 apiaries in Adana, and 117556 colonies (83%) out of 141606 colonies were damaged; 102669 (87%) of the damaged colonies (117556) had honey bee losses over 30%, and 14887 (13%) of the damaged colonies had losses below 30% (ADFAL Report, 2017). Sudden and extensive honey bee deaths with losses up to approximately 80% in some apiaries were observed from the beginning of February to the middle of March between 2013 and 2018. Clinical findings in dying bees were cramping, disoriented behavior, aggressiveness, abnormal wing movements and incapability to enter the hive, and there was sudden and high number of deaths of foraging bees in front of bee hives (Fig. 2).

Fig. 2

Bee deaths have been observed on a large scale and are related temporally and spatially with the sowing of clothianidin-coated maize seeds in the Çukurova Region. When the wind blew from the plains to the hives during maize-seed sowing on the plains and when the apiary locations were as far as 15–25 km from the plains, honey bees were affected and died. When the weather was rainy in the region, bee deaths decreased or stopped. The results of the analyzed pesticides except neonicotinoids and determined bee pathogens are shown in Tab. 1 (ADFAL Report, 2017). Clothianidin and acetamiprid residues were detected in five and two of five dead bee samples, respectively, and the results of clothianidin, imidacloprid, acetamprid and thiamethoxam analysis are presented in Tab. 2.

Researchers who searched bee deaths verified and claimed in clinical findings that there was a correlation between the acute pesticide poisoning and the sudden and high number of deaths of foraging bees in front of bee hives and that in dying bees there were cramping, disoriented behavior, aggressiveness, abnormal wing movements and incapability to enter the hive (Bortolotti et al., 2009; Pistorius et al., 2015; Kiljanek, Niewiadomska, & Posyniak, 2016; FAO, 2018). These were also harmonized with observed clinical findings in dying and death bees in this case related to acute pesticide poisoning (Fig. 2).

The results of the pesticides analysis (Tab. 1) did not support bee poisoning with the determined pesticides until 2018 because these pesticides were from different classes and were not harmonized from year to year between 2013 and 2017. In addition, such pesticides as carbendazim, epoxiconazole, tebuconazole, cyprodinil and coumaphos generally low or moderately toxic for honey bees. Although some pesticides, such as carbofuran and pyridaben, are highly toxic for honey bees, only one each was found in the dead bee samples in 2013 and 2017, respectively (Tab. 1). Therefore, a correlation was not observed between the determined pesticides and sudden and prevalent foraging bee deaths according to the Tab. 1 results.

Maize is cultivated in Turkey and in the Adana Province in the Çukurova Region varied from 89849.2 to 96737.0 hectares between 2013 and 2018. The sowing period of maize in the Çukurova Region lasts from the beginning of February to the middle of March, a period of time that coincides with the sudden and large number of bee deaths in the region. Sudden deaths in the Çukurova Region were also coincident when in Europe maize sowing from the middle of March to May was accompanied by a rapid disappearance and die-off of foraging bees in Germany (Pistorius et al., 2009), Italy (Bortolotti et al., 2009), France (Chauzat et al., 2010) and in Slovenia (van der Geest, 2012) due to neonicotinoid pesticide poisonings from pesticides imidacloprid, thiamethoxam, and especially clothianidin.

The field research related to the sowing period of maize in spring and neonicotinoids, supported the hypothesis that solid particles emitted by drilling machines, which contained a high insecticide concentration, produced a direct powdering of foraging bees that were in free flight accidentally crossing the sowing fields (Marzaro et al., 2011; Girolami et al., 2012a; Girolami et al., 2012b; Tapparo et al., 2012). In the Çukurova Region, flying foraging bees may be acutely exposed to lethal doses f in spring when maize is sown. Maize seeds have been recently treated with clothianidin (Poncho^® FS 600) in this region for eradication of the western corn rootworm. Neonicotinoids, including clothianidin, imidacloprid, acetamiprid and thiamethoxam, were not analyzed due to the lack of some laboratory conditions in Turkey for dead bees until 2018. However, clothianidin is an active substance from neonicotinoids and was detected in all five bee samples collected from the Çukurova Region in 2018 (Tab. 2). As compared in Tab. 2 and 3, detected amounts of clothianidin were between 6 and 13 μg/kg in dead honey bees (Tab. 2) and was accordance with the results of previous studies (Tab. 3) in Germany (Pistorius et al., 2009), Slovenia (Public report, 2011; van der Geest, 2012), and Italy (Bortolotti et al., 2009). Although acetamprid was detected in two samples, its quantities were very low (1 and 2 μg/kg). On the other hand its toxicity is known not to be as high as clothianidin. In addition, maize seeds were coated with clothianidin (Poncho^® FS 600) in this region. Therefore, our results have shown that colony mortality was associated with the presence of clothianidin residues detected in honey bees, and the sudden and extensive deaths of foraging bees in the region coincided with the maize sowing period.

When the wind came from the direction of the plain to the hives during the sowing of maize seeds on the plains and when the apiary locations were as far as 15–25 km from the plain, some honey bees were affected and died. The air contained high levels the dust of such insecticides as neonicotinoids from the sowed maize fields (Marzaro et al., 2011; Girolami et al., 2012a; Girolami et al., 2012b; Tapparo et al., 2012). Thus, high concentration of insecticides could reach distant hives by wind. When the region experienced rainy weather in bee deaths decreased or stopped because neonicotinoids are water-soluble (Wood & Goulson, 2017) and neonicotinoid dust in the air can easily be washed off by rain. The main reason for the highest numbers of bee deaths in 2017 was a lack of rain rain during the maize sowing period.

Sudden and prevalent bee deaths between 2013 and 2018, especially in 2017, caused high economical, moral and motivational damage for beekeepers located in this region. The honey bee deaths in 2018 were much fewer than those in 2017 because beekeepers located in the region had been warned of sudden honey bee deaths before the maize sowing period and accordingly did not generally localize to the region during the 2018 maize sowing period in. In addition, there was regular rainfall in the region during this period.

Symptomatic adult honey bees tested positive for Varroa destructor, Nosema spp., BQCV, DWV, KBV, CBPV and AFB. The sudden and prevalent bee deaths in the springtime occurring from the beginning of February to the middle of March are chronologically distinguishable from bee deaths caused by Varroa destructor and other bee pathogens. However, a close relationship was observed between the bee deaths and the use of pneumatic drilling machines for the sowing of corn seeds coated with clothianidin in the Çukurova Region. In conclusion, the field studies in affected apiaries, on-site inspection and chemical analyses confirmed that clothianidin poisoning during the maize sowing period was related to the sudden and prevalent bee deaths in the Çukurova Region between 2013 and 2018.