Striving for sustainable pest management in no-till, field-crop systems: Understanding the role of insecticidal seed treatments
The aim of this study is to examine whether common insecticidal seed treatments pose non-target risks to natural enemies in no-till corn and soybeans. In particular, we are exploring the potential for these seed treatments to travel up food chains from plants to slugs to natural enemies, potentially disrupting biological control. In laboratory experiments with soybeans this fall, slugs were not adversely affected by neonicotinoid seed treatments, but slugs fed on neonicotinoid-infused seedlings were toxic to the common ground beetle, Chlaenius tricolor. These results suggest that slugs may be an important conduit of neonicotinoid insecticides to natural enemies. We will explore this phenomenon further in 2012 through additional laboratory and field experiments. For the outreach component of this project, we have started obtaining video footage of ground beetles and their behavior under the influence of contaminated prey. These videos and initial laboratory results have been shared with agricultural researchers at Penn State and at the Entomological Society of America’s annual meeting.
Objective 1: Determine whether insecticidal seed treatments can be transferred from crop plants to natural enemies via slugs.
Objective 2: Determine how insecticidal seed treatments influence pest communities and predation of multiple pest guilds in corn and soybeans under field conditions.
Objective 3: Educate farmers about neonicotinoid seed treatments and alternative practices through extension materials, videos, and presentations.
In the fall of 2011, laboratory experiments were conducted to investigate whether neonicotinoid seed treatments can travel up the food chain from soybean seedlings to slugs to their insect natural enemies. These experiments used the beetle Chlaenius tricolor rather than Pterostichus melanarius (as originally proposed) because preliminary experiments revealed C. tricolor to be a more reliable slug predator and easier to work with in the lab. Both beetle species are common on farms in the Northeast. Fungicide seed treatments were also included in the experiment because most soybean seeds are treated with fungicide in our region. Including the fungicide will make the results more relevant to farmer practice.
In the first phase of the experiment, soybean seedlings were enclosed with a single gray garden slug over 7 days to test whether the seed treatments (untreated, fungicide-only, fungicide + low rate thiamethoxam, fungicide + high rate thiamethoxam) influenced slug feeding behavior. In the second phase, single slugs that had fed on the various seed treatments were introduced to individual ground beetles (Chlaenius tricolor). Ground beetle behavior and mortality were recorded following exposure to slugs.
Seed treatments did not protect soybean seedlings from slug damage (Fig. 1), nor did they influence slug feeding behavior as reflected by weight gain (Fig. 2). However, slugs that fed on neonicotinoid-treated seedlings were toxic to the ground beetle Chlaenius tricolor. Over 50% of C. tricolor that ate a single slug from low or high thiamethoxam treatments were found on their backs, unable to right themselves, 12 hours after slugs were introduced. Other symptoms of beetle poisoning included twitching, slow or uncoordinated movement, and paralyzed hind legs. Some impaired beetles recovered, while others died (Fig. 3). Surprisingly, the rate of insecticidal seed treatment (low vs. high) did not appear to influence eventual beetle response.
In 2012, we will conduct similar laboratory experiments using corn as the focal plant.
This objective will be addressed largely through field experiments in the spring/summer of 2012. This fall we began working with the farm manager at Penn State’s research farm to identify fields for these experiments. In October, we monitored shelter traps in those fields to verify that slug populations are present. We have identified suitable fields and will continue preparing for those experiments this spring by ordering seeds and other supplies.
This objective will be addressed largely in 2012. However, we did begin to take video footage of beetles affected by contaminated prey. We have also started to conduct literature research that will form the basis of new fact sheets on early season pest management in corn and soybeans. This includes literature on both the efficacy of seed treatments and alternative IPM approaches for early-season pest management. This research will be used to create two farmer-friendly publications on sustainable early-season pest management in corn and soybeans.
- Slug weight gain as a function of seed treatment (U = untreated, F = fungicide-only, F + L = fungicide plus low rate insecticide, F + H = fungicide plus high rate insecticide)
- Fate of beetles fed on a single slug from different soybean treatments (U = untreated, F = fungicide, F + L = fungicide plus low insecticide, F + H = fungicide plus high insecticide)
- Slug damage to soybean as a function of seed treatment (U = untreated, F = fungicide-only, F + L = fungicide plus low rate insecticide, F + H = fungicide + high rate insecticide)
Impacts and Contributions/Outcomes
While this project is still in its early stages, the preliminary results suggest that seed treatments may have hidden costs for natural enemies via transfer of neonicotinoids up food chains in no-till systems. Our further field experiments should clarify whether this phenomenon is significant under field conditions. We have begun sharing our laboratory findings with agricultural scientists and extension professionals. In November, the results from the soybean laboratory experiments were presented at the annual meeting of the Entomological Society of America, where the talk was well-attended by biocontrol researchers. Also in November, we shared these results with the team of Penn State researchers involved in NE SARE’s Sustainable Dairy Cropping Systems Project. This group includes agricultural researchers across a range of disciplines as well as several extension specialists. As the work progresses, we will continue to share results as broadly as possible.
Pennsylvania State University, Dept. of Entomology
101 Merkle Building
University Park, PA 16802
Office Phone: 2026079328