Jocelyn Smith

Neonicotinoid Insecticide Residues in Surface Water and Soil Associated with Commercial Maize (Corn) Fields in Southwestern Ontario

Neonicotinoid insecticides have come under scrutiny for their potential unintended effects on non-target organisms, particularly pollinators in agro-ecosystems. As part of a larger study of neonicotinoid residues associated with maize (corn) production, 76 water samples within or around the perimeter of 18 commercial maize fields and neighbouring apiaries were collected in 5 maize-producing counties of southwestern Ontario. Residues of clothianidin (mean = 2.28, max. = 43.60 ng/mL) and thiamethoxam (mean = 1.12, max. = 16.50 ng/mL) were detected in 100 and 98.7% of the water samples tested, respectively. The concentration of total neonicotinoid residues in water within maize fields increased six-fold during the first five weeks after planting, and returned to pre-plant levels seven weeks after planting. However, concentrations in water sampled from outside the fields were similar throughout the sampling period. Soil samples from the top 5 cm of the soil profile were also collected in these fields before and immediately following planting. The mean total neonicotinoid residue was 4.02 (range 0.07 to 20.30) ng/g, for samples taken before planting, and 9.94 (range 0.53 to 38.98) ng/g, for those taken immediately after planting. Two soil samples collected from within an conservation area contained detectable (0.03 and 0.11 ng/g) concentrations of clothianidin. Of three drifted snow samples taken, the drift stratum containing the most wind-scoured soil had 0.16 and 0.20 ng/mL mainly clothianidin in the melted snow. The concentration was at the limit of detection (0.02 ng/mL) taken across the entire vertical profile. With the exception of one sample, water samples tested had concentrations below those reported to have acute, chronic or sublethal effects to honey bees. Our results suggest that neonicotinoids may move off-target by wind erosion of contaminated soil. These results are informative to risk assessment models for other non-target species in maize agro-ecosytems.

Neonicotinoid insecticide residues in soil dust and associated parent soil in fields with a history of seed treatment use on crops in Southwestern Ontario

Using neonicotinoid insecticides as seed treatments is a common practice in field crop production. Exposure of nontarget organisms to neonicotinoids present in various environmental matrices is debated. In the present study, concentrations of neonicotinoid residues were measured in the top 5 cm of soil and overlying soil surface dust before planting in 25 commercial fields with a history of neonicotinoid seed treatment use in southwestern Ontario in 2013 and 2014 using liquid chromatography-electrospray ionization tandem mass spectrometry. The mean total concentrations were 3.05 ng/g and 47.84 ng/g in 2013 and 5.59 ng/g and 71.17 ng/g in 2014 for parent soil and soil surface dust, respectively. When surface and parent soil residues were compared the mean concentration in surface dust was 15.6-fold and 12.7-fold higher than that in parent soil in 2013 and 2014, respectively. Pooled over years, the surface dust to parent soil ratio was 13.7, with mean concentrations of 4.36 ng/g and 59.86 ng/g for parent soil and surface dust, respectively. The present studys results will contribute important knowledge about the role these residues may play in the overall risk assessment currently under way for the source, transport, and impact of neonicotinoid insecticide residues in a maize ecosystem.

Field-scale examination of neonicotinoid insecticide persistence in soil as a result of seed treatment use in commercial maize (corn) fields in southwestern Ontario

Neonicotinoid insecticides, especially as seed treatments, have raised concerns about environmental loading and impacts on pollinators, biodiversity, and ecosystems. The authors measured concentrations of neonicotinoid residues in the top 5 cm of soil before planting of maize (corn) in 18 commercial fields with a history of neonicotinoid seed treatment use in southwestern Ontario in 2013 and 2014 using liquid chromatography-tandem mass spectrometry with electrospray ionization. A simple calculator based on first-order kinetics, incorporating crop rotation, planting date, and seed treatment history from the subject fields, was used to estimate dissipation rate from the seed zone. The estimated half-life (the time taken for 50% of the insecticide to have dissipated by all mechanisms) based on 8 yr of crop history was 0.64 (range, 0.25-1.59) yr and 0.57 (range, 0.24-2.12) yr for 2013 and 2014, respectively. In fields where neonicotinoid residues were measured in both years, the estimated mean half-life between 2013 and 2014 was 0.4 (range, 0.27-0.6) yr. If clothianidin and thiamethoxam were used annually as a seed treatment in a typical crop rotation of maize, soybean, and winter wheat over several years, residues would plateau rather than continue to accumulate. Residues of neonicotinoid insecticides after 3 yr to 4 yr of repeated annual use tend to plateau to a mean concentration of less than 6 ng/g in agricultural soils in southwestern Ontario.

Quantifying Neonicotinoid Insecticide Residues Escaping during Maize Planting with Vacuum Planters.

Neonicotinoid residues escaping in vacuum-planter exhaust during maize planting were measured in 25 fields in southwestern Ontario in 2013-2014 using filter bags to collect planter exhaust dust and horizontal and vertical sticky traps to collect planter operation-generated dust. Atrazine residues were used to differentiate between neonicotinoid residues originating from seed or from disturbed soil. Recovery rates of seed-applied neonicotinoids in exhaust were 0.014 and 0.365% in 2013 and 2014, respectively, calculated on the basis of neonicotinoid concentrations in preplant soil and seed application rates. Neonicotinoid exhaust emission rates were 0.0036 and 0.1104 g/ha for 2013 and 2014, respectively, with 99.9472 and 99.7820% originating from treated seed in 2013 and 2014, respectively, calculated on the basis of the atrazine marker. Rates of recovery of seed-applied neonicotinoid residues by exhaust filter bags were 0.015 and 0.437% for 2013 and 2014, respectively. Neonicotinoid residues captured on horizontal and vertical traps were 1.10 ng/cm2 (0.1104 g/ha) and 1.45 ng/cm2 (0.0029 g/ha), respectively, with 92.31 and 93.03% originating from treated seed, respectively, representing 0.3896% of the original active ingredient applied to the seed planted. Exposure to pollinators can be best reduced by strategies to keep active ingredient on the seed, below the soil surface, and in the field where applied.

Impact of the Bt Corn Proteins Cry34/35Ab1 and Cry3Bb1, Alone or Pyramided, on Western Corn Rootworm (Coleoptera: Chrysomelidae) Beetle Emergence in the Field

ABSTRACT Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a major pest of corn, Zea mays L. The effect of the Bt proteins Cry34/35Ab1 and Cry3Bb1, alone or pyramided in corn hybrids on D. v. virgifera adult emergence was evaluated in field experiments for 3 yr. Experiments were infested artificially with 2,500 viable D. v. virgifera eggs per row meter of corn. The reduction in beetle emergence compared with non-Bt controls, from Cry34/35Ab1, Cry3Bb1, and the pyramided hybrids ranged from 64.3 to 97.4%, 91.1 to 95.2%, and 98.1 to 99.6%, respectively. The sex ratio of emerged beetles was usually female-biased from the Cry3Bb1 and pyramided treatments, but not from Cry34/35Ab1 treatment alone. Emergence from all Bt hybrids was delayed compared with the control, with the delay longest from the pyramided hybrid. In 2013, three egg infestation levels were tested, with densitydependent mortality observed at 1,250 viable eggs per row meter. The effect of Bt proteins on the emergence timing and sex ratio of D. v. virgifera may impact the suitability of resistance management plans, specifically the effectiveness of the refuge strategy. Susceptible males emerging from refuge might not be synchronized to mate with potentially resistant females emerging later from Bt corn hybrids.

Evidence for Field-Evolved Resistance of Striacosta albicosta (Lepidoptera: Noctuidae) to Cry1F Bacillus thuringiensis Protein and Transgenic Corn Hybrids in Ontario, Canada

Abstract Western bean cutworm, Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), is a pest of corn (Zea mays L.) that has recently expanded its range into Ontario, Canada. Control of S. albicosta damage to corn hybrids containing event TC1507-expressing Cry1F Bacillus thuringiensis protein alone or pyramided with event MON 89034 expressing Cry1A.105 and Cry2Ab2 Bt proteins was tested in 2011–2015 in Ontario in small- and large-scale field plots with natural infestation. In 2011, significantly lower incidence and severity of kernel damage was sustained by Cry1F × Cry1A.105 + Cry2Ab2 corn compared with a non-Bt near-isogenic hybrid. However, from 2012 to 2015, there was no difference in incidence or severity of damage comparing non-Bt hybrids with Cry1F hybrids alone or pyramided with Cry1A.105 and Cry2Ab2 planted as a pure stand or with an integrated refuge (95% Bt: 5% non-Bt seeds). In 2015, neonate larvae derived from Ontario field-collections were tested in concentration-response diet-overlay bioassays with lyophilized Cry1F protein at concentrations up to 75 µg cm–2. The concentrations at which mortality of 50% (LC50) of the collections occurred ranged from approximately 10 µg cm–2 (F0) to >28 µg cm–2 (F1) in a 7-d bioassay, indicating relative insensitivity to Cry1F. Results from field experiments, laboratory bioassays, and the history of exposure to Cry1F in corn show that S. albicosta in Ontario are not controlled by Cry1F-expressing corn hybrids and provide evidence for the conclusion that the evolution of resistance to Cry1F has occurred.

Factors associated with winged forms of soybean aphid and an examination of North American spatial dynamics of this species in the context of migratory behaviour

Soybean aphid is a severe invasive pest of soybeans in North America. From 2005 onward, a network of 47 suction traps in North America, each approximately 7 m in height, has monitored aerial populations of this species. Suction trap captures of alate viviparous Aphis glycines in summer, and gynoparae and males in the autumn, were subjected to negative binomial regressions with environmental parameters. Models were ranked by using information‐theoretic methods to determine which parameters best explained aerial density of aphids. Multiparameter models incorporating the best parameters were constructed. Best‐fit models were used to compute peak values of each parameter, where a quadratic relationship between captures and that parameter occurred. Data were subjected to non‐metric multidimensional scaling and analysis of similarity to observe patterns in the geographical and temporal distribution of captures. Summer flight activity A. glycines was explained best by the level of aphid infestation in fields local to the trapping site, although the autumn female flight activity peak and male activity was best explained by photoperiod. Seven‐metre tall suction traps are useful for determining when flight activity of A. glycines occurs within a region.

Effect of European Chafer Larvae (Coleoptera: Scarabaeidae) on Winter Wheat and Role of Neonicotinoid Seed Treatments in Their Management

ABSTRACT A critical density of four third-instar larvae per 900 cm2 for European chafer, Rhizotrogus (Amphimallon) majalis (Razoumowsky), in winter wheat, Triticum aestivum L., was derived from smallplot greenhouse and field experiments conducted under favorable crop growing conditions at several Ontario and Michigan locations from 2001–2003. On average, plant weight was decreased by 14% and plant stand by 11% between zero and four larvae per 900 cm2. In a commercial field under moisture stress, a yield loss of 35% occurred at a density of two third-instars per 900 cm2. In short-term greenhouse experiments, density-dependent mortality was evident, whereas low larval recovery in field experiments indicates a high level of overwintering mortality, regardless of larval density. Winter wheat seed treatments of neonicotinoid insecticides, clothianidin, imidacloprid, and thiamethoxam provided protection from damage by larvae, but the level of protection was inconsistent between greenhouse and field small plots, and there was no apparent difference in protection amongst active ingredients or between application rates. There was little evidence of larval mortality owing to seed treatment, which supports the suggestion that neonicotinoid insecticides protect seedlings from loss by a nonlethal mechanism. Overall, we estimate that a low rate of neonicotinoid insecticide used at larval densities just less than the critical density will mitigate winter wheat losses by 85%.

Establishment of Striacosta albicosta (Lepidoptera: Noctuidae) as a Primary Pest of Corn in the Great Lakes Region

Abstract Western bean cutworm, Striacosta albicosta Smith (Lepidoptera: Noctuidae), is a pest of corn, Zea maize L., and dry edible beans, Phaseolus sp. L., native to the western United States. Following the range expansion into the U.S. Corn Belt, pheromone trap monitoring began in the Great Lakes region in 2006.The first S. albicosta was captured in Michigan in 2006 and in Ontario, Canada in 2008. Pheromone traps were used to document spread and increasing captures of S. albicosta across Michigan and Ontario until 2012. Trapping confirmed the univoltine life cycle of S. albicosta in this region and identified peak flight, typically occurring in late July. Overwintering of S. albicosta in this region was confirmed by emergence from infested fields and overwintering experiments. Multiple soil textures were infested with prepupae, and recovery was assessed throughout the winter. Overwintering success was not affected by soil texture; however, prepupae were found at greater depths in coarse-textured soils. Soil temperatures at overwintering depths did not reach the supercooling point. Injury to corn by S. albicosta increased in incidence, severity and geographic range from 2010 to 2014 in field plots. Decreasing control of injury by Cry1F corn hybrids was observed over time.These findings show that S. albicosta has established as a perennial corn pest in the Great Lakes region due to observations of overwintering success and unmanaged injury. We recommend S. albicosta obtain primary pest status in this region within regulatory framework and a resistance management plan be required for traits targeting this pest.

Fusarium graminearum Mycotoxins in Maize Associated With Striacosta albicosta (Lepidoptera: Noctuidae) Injury

Abstract Western bean cutworm, Striacosta albicosta (Smith; Lepidoptera: Noctuidae) has become a key pest of maize, Zea mays (L.), in Ontario, Canada which is challenging to control due to its lack of susceptibility to most Bt-maize events. Injury by S. albicosta may exacerbate Fusarium graminearum (Schwabe; Hypocreales: Nectriaceae) infection through provision of entry points on the ear. The objectives of this study were to: investigate the relationship between injury by S. albicosta and deoxynivalenol (DON) accumulation; evaluate non-Bt and Bt-maize hybrids, with and without insecticide and fungicide application; and determine optimal insecticide-fungicide application timing for reducing S. albicosta injury and DON accumulation. The incidence of injury by S. albicosta and ear rot severity were found to increase DON concentrations under favorable environmental conditions for F. graminearum infection. Incidence of S. albicosta injury was more important than severity of injury for DON accumulation which may be due to larval consumption of infected kernels. The Vip3A × Cry1Ab event provided superior protection from the incidence and severity of S. albicosta injury compared to non-Bt or Cry1F hybrids. Insecticide application to a Vip3A × Cry1Ab hybrid did not reduce injury further; however, lower severity of injury was observed for non-Bt and Cry1F hybrids when pyrethroids or diamides were applied at early VT or R1 stages. DON concentrations were reduced with application of prothioconazole fungicide tank-mixed with insecticide at late VT (before silk browning) or when insecticide was applied at early VT followed by prothioconazole at R1. The application of an insecticide/fungicide tank-mix is the most efficient approach for maize hybrids lacking high-dose insecticidal proteins against S. albicosta and F. graminearum tolerance. Results demonstrate that reducing the risk of DON accumulation requires a strategic approach to manage complex associations among S. albicosta, F. graminearum and the environment.