Effects of neonicitinoid seed treatments on soybean aphid and its natural enemies

Abstract

Insecticidal seed treatments are increasingly being applied to soybeans in North America, and several recent studies question what they add to current pest management. Here, we examine the effects of two neonicotinoid insecticidal seed treatments on insect populations (pest and natural enemies) in SD soybeans over 2 years. Moreover, we conducted laboratory experiments to determine the duration that seed treatments remained effective against the soybean aphid (Aphis glycines, Hemiptera: Aphididae) and how thiamethoxam affected survival of one of the aphid's predators, Orius insidiosus (Hemiptera: Anthocoridae) on soybean. Soybean aphids, thrips, and grasshopper populations were unaffected by the insecticidal seed treatments in the field. The laboratory trial revealed that all bioactivity of the seed treatments against soybean aphids was gone within 46 days after planting, prior to aphid populations damaging the crop. Bean leaf beetles, a sporadic pest in our area, were reduced by the seed treatments. But, there were no yield benefits of insecticidal seed treatments over the 2 years of the study at this location. Natural enemy communities were significantly reduced by thiamethoxam seed treatments relative to the untreated control, particularly populations of Nabis americoferus (Hemiptera: Nabidae). Chrysoperla (Neuroptera: Chrysopidae) adults were reduced in the imidaclopridtreated plots. In the laboratory, rearing O. insidiosus on soybean plants treated with thiamethoxam resulted in higher mortality for both the nymphs and the adult stage. Offering the predator insect prey on the thiamethoxam-treated plants improved survival of the adult stage, but not the nymphal stage. This work confirms that insecticidal seed treatments offer little benefit to soybean producers of the Northern Great Plains and adds to the discussion by suggesting that generalist predators are adversely affected by the insecticides.

Thiamethoxam Toxicity and Effects on Consumption Behavior in Orius insidiosus (Hemiptera: Anthocoridae) on Soybean

“…Such information could allow a better characterization of the exposure levels to thiamethoxam in the field and a more accurate characterization of risk of neonicotinoids to beneficial species in soybean crops. The results on the abundance of O. insidiosus in soybean fields with neonicotinoid seed treatments are consistent with the studies by Ohnesorg et al (2009) and Seagraves and Lundgren (2012), where no significant differences in O. insidiosus abundance were observed between fields derived from neonicotinoid treated and untreated fields. Orius insidiosus is a generalist predator consuming thrips, pollen, and nectar from flowers, vegetative tissue, and aphids in soybean fields (Rutledge and O'Neil 2005).…”

“…Seed treatments with neonicotinoid insecticides have been promoted to be relatively nontoxic to natural enemies due to the lack of direct exposure to chemical residues (Seagraves and Lundgren 2012). Exposure of predatory insects can occur by ingestion of residues in prey and plant material or through contact with guttation drops or dust particles that are generated during planting (Gentz et al 2010, Pisa et al 2015.…”

“…Exposure of predatory insects can occur by ingestion of residues in prey and plant material or through contact with guttation drops or dust particles that are generated during planting (Gentz et al 2010, Pisa et al 2015. Residues of neonicotinoids in insect prey and vegetative material can affect the compatibility of these insecticides with biological control through direct mortality to natural enemies or indirectly through reduction in consumption rates of the insect pests (Gentz et al 2010, Seagraves andLundgren 2012).…”

“…Consumption of plant material can be detrimental for predatory species if soybean plant tissues or vegetation near treated areas contain lethal concentrations of systemic pesticides (Seagraves and Lundgren 2012). Neonicotinoid toxicity to zoophytophagous predators has been reported for Harmonia axyridis Pallas (Coleoptera: Coccinelidae) feeding on seed treated corn seedlings under laboratory conditions using a systemic plant bioassay (Moser and Obrycki 2009).…”

Non-target effects of chlorantraniliprole and thiamethoxam on Chrysoperla carnea when employed as sunflower seed treatments

“…Cloyd and Bethke (2011) Seagraves and Lundgren (2012) found reduced numbers of adult natural enemies, e.g., Chrysoperla sp and Nabis americoferus Carayon (Hemiptera: Nabidae), in soybean fields grown from neonicotinoid-treated seed. When applied as a soil drench, imidacloprid reduced the survival of adults of C. carnea (Rogers et al 2007) and the parasitoid Anagyrus pseudococci (Girault) (Hymenoptera: Encyrtidae) that fed on flowers of Fagopyrum esculentum (Polygonaceae) ).…”