Wild Bee Exposure to Pesticides in Conservation Grasslands Increases along an Agricultural Gradient: A Tale of Two Sample Types

Abstract

Conservation efforts have been implemented in agroecosystems to enhance pollinator diversity by creating grassland habitat, but little is known about the exposure of bees to pesticides while foraging in these grassland fields. Pesticide exposure was assessed in 24 conservation grassland fields along an agricultural gradient at two time points (July and August) using silicone band passive samplers (nonlethal) and bee tissues (lethal). Overall, 46 pesticides were detected including 9 herbicides, 19 insecticides, 17 fungicides, and a plant growth regulator. For the bands, there were more frequent/higher concentrations of herbicides in July (maximum: 1600 ng/band in July; 570 ng/band in August), while insecticides and fungicides had more frequent/higher concentrations in August (maximum: 110 and 65 ng/band in July; 1500 and 1700 ng/band in August). Pesticide concentrations in bands increased 16% with every 10% increase in cultivated crops. The bee tissues showed no difference in detection frequency, and concentrations were similar among months; maximum concentrations of herbicides, insecticides, and fungicides in July and August were 17, 27, and 180 and 19, 120, and 170 ng/g, respectively. Pesticide residues in bands and bee tissues did not always show the same patterns; of the 20 compounds observed in both media, six (primarily fungicides) showed a detection-concentration relationship between the two media. Together, the band and bee residue data can provide a more complete understanding of pesticide exposure and accumulation in conserved grasslands.

Conserved grasslands support similar pollinator diversity as pollinator-specific practice regardless of proximal cropland and pesticide exposure

“…arable land) has been linked to both declines in flying insects and increased insect exposures to pesticides [5,15,16]. A study conducted concurrently with the present study found that concentrations and number of pesticides detected with above-ground passive samplers within conservation grasslands increased with proportion of cropland proximal to those grasslands (radius 1 km), although it found no relationship between proportion of proximal cropland and pesticide residues (number or concentration) in bee tissues at these sites [17]. In addition, the number of pesticides detected in the tissues of flying insects collected in nature conservation areas in Germany was related to the proportion of agricultural production area in a 2 km radius around the reserves [15].…”

“…We previously showed that there was a positive relationship between proportion of agriculture proximal to conserved grassland fields and pesticide concentrations accumulated on silicone bands at a site (a.k.a., ‘pesticide exposure') [17]. Pesticide exposure did not differ between CRP-other and CP42 fields [17]. Summed (total) pesticide concentration and summed insecticide concentration at a site were not significantly correlated due to the relatively low concentrations of insecticides compared with other compounds such as herbicides (see §2.6).…”

“…Fields selected in our study were at least 1 km apart to increase independence of pollinator responses among sites, were enrolled in the CRP for at least 3 years ( planted before 2016) and were a minimum of 1 ha (0.01 km 2 ). The 24 fields were a mix of CRP grasslands specifically planted with diverse (greater than nine species) pollinator-friendly forbs that bloom throughout the growing season (CP42, n = 13) and other CRP grassland fields (n = 11, practices included CP1, CP2, CP4D, CP10, CP25 and CP38) [27]. These other CRP grassland practices meet a variety of conservation needs and include some forb planting (from zero to a minimum of five species depending on the practice) but do not specifically target the needs of pollinators.…”

“…These other CRP grassland practices meet a variety of conservation needs and include some forb planting (from zero to a minimum of five species depending on the practice) but do not specifically target the needs of pollinators. The proportion of cropland agriculture (mainly maize and soya bean) proximal to the fields in a 1 km radius ranged from 6 to 85% [17,27]. Within each field, an approximately 1 ha plot (0.7-1.1 ha) was delineated near the centre of the field.…”

“…To assess pollinator exposure to pesticides, silicone wristbands were deployed around the perimeter of each conserved grassland field for approximately 30 days prior to each pollinator sampling (see Hladik et al [17] for more details). The bands were analysed for 180 pesticides and pesticide transformation products, and total pesticide and insecticide concentrations were calculated [17,27]. Pesticide concentrations as reported here are the summed concentrations of all agricultural pesticides (insecticides, fungicides and herbicides) detected per band per field.…”