Neonicotinoid Seed Treatments (Douglas & Tooker 2015)

Figure 1. US neonicotinoid sales (Douglas & Tooker 2015).

I just read this cool paper by Douglas and Tooker (2015) Environmental Science and Technology in which they synthesized data on neonicotinoid insecticidal seed treatments in the US. This is nice because we all know that seed treatments are super common, but getting a good estimate on the prevalence is not so easy.

They used publically available data spanning 2003-2011 (*see below for data sources). Among a number of interesting findings, they report that 34-44% of soybeans and 79-100% of corn grown in the U.S had neonicotinoid seed treatments in 2011. The authors admit that the high estimate in corn of 100% is clearly too large, but we can be confident that the true percentage is quite high.

Almost all of the neonic seed treatment usage is in crops (see Fig 1, from Douglas & Tooker 2015). While this is unsurprising, it contrasts with much of the public debate over neonicotinoids, which has often emphasized urban use – for example, the controversy in Oregon after a large bumble bee die-off in a Target parking lot.  More interesting to me is the rapid increase in use, particularly in soy and corn. Things have really spiked since the early 2000s.

Soybeans have seen a dramatic increase in foliar insecticide use, as well, as a result of the soybean aphid which was first reported in N. America in 2000 (see Fig 2, from Heimpel et al. 2013). As Douglas and Tooker point out, seed treatments are not particularly great for soybean aphid infestations, due to the timing of pest outbreak relative to planting.

Why then such high use of seed treatment in soybeans? If it’s not for soybean aphid, then what?

Figure 2. Foliar application of insecticides in US soybeans (Heimpel et al. 2013).

Douglas and Tooker’s paper draws attention to some important problems regarding risk assessment in pest management. Prophylactic insecticide use may increase risk of the evolution of resistance in pest populations, while potentially causing adverse effects on beneficial insects like biological control agents.

*Data sources used by Douglas and Tooker (2015): 1) Pesticide National Synthesis Project of the US Geological Survey; 2) the USDA Agricultural Chemical Use Survey (conducted through NASS & EDS); 3) a report by Pioneer submitted to APHIS; 4) surveys conducted at North Dakota State University; and 5) information gathered by the Minnesota Department of Agriculture.

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