2016-17 Rapid Ag: The Role of Insecticidal Seed Treatments in Limiting Biological Control of Soybean Aphid
Department of Entomology
- 2016 Fiscal Year: $85,400
- 2017 Fiscal Year: $85,400
The soybean aphid, Aphis glycines, remains a critical pest in Minnesota and the region. Since the aphid’s invasion from Asia in 2000, soybeans in the North Central United States have experienced massive increases in insecticide use comprised of both foliar applications and more recently neonicotinoid seed treatments (Ragsdale et al. 2011; Douglas & Tooker 2015). Some of the insecticides used against the soybean aphid are toxic to beneficial insects as well as vertebrate animals and humans. A recent analysis shows that the manufacture and application of foliar insecticides against soybean aphid leads to the emission of substantial amounts of greenhouse gases (Heimpel et al., 2013). For all of these reasons, finding alternatives to insecticides is a critical issue for soybean production in Minnesota and beyond. Soybean host plant resistance is a further strategy, but soybean aphid biotypes able to tolerate resistance traits in newly-developed soybean cultivars have been observed and this may limit the long-term effectiveness of host plant resistance (Crossley & Hogg 2015).
Since 2006 a new insecticide application method has entered the market in the form of insecticidal seed treatments. By 2014, 60 to 75% of the soybean acreage in North Central states was treated with systemic neonicotinoid insecticides including imidacloprid and thiametheoxam nationwide (C. Krupte, unpublished). Producers in the North Central Region spend approximately $316 million a year on neonicotinoid seed treatments for insect management in soybean (NCSRP report 2015). Systemic neonicotinoids are delivered with each seed, providing a focused application method, but the insecticide within plants is found in effective quantities only until the V2 stage (two trifoliate leaves). This is not a part of the season when insecticides are generally necessary, and yet the effect on early-season aphid colonists may be substantial (Bahlai et al. 2014).
One of the most promising strategies to control soybean aphid permanently and sustainably is importation biological control – the introduction of one or more natural enemies from the native range of the aphid (Asia). Parasitoid biological control shows promise on the basis of studies showing that soybean aphid is well-controlled by insect predators and parasitoids in Asia and also the discovery of numerous parasitoid species in Asia that are not present in North America (Heimpel et al. 2004; Ragsdale et al. 2011). We have been investigating biological control of soybean aphid by Asian parasitoids over the past 14 years and are now at a critical juncture for this research as there is one established parasitoid (Aphelinus certus) and another that we are in the process of releasing (A. glycinis) (Fig. 1). Apelinus certus is already an important player in the soybean aphid system and widespread in Minnesota (J. Kaser & G.E. Heimpel unpublished) (Fig. 2). However, this species is mainly found in August, long after soybean aphid populations have established (J. Kaser & G.E. Heimpel unpublished). We suspect that something is limiting its effectiveness in the early season, and one possibility is the use of nicotinoid seed treatments.
In a study by a different research group, both thiamethoxam and imidicloprid seed treatments reduced parasitism of A. certus by 80% in a laboratory setting (Frewin et al., 2014). Thus, these seed treatments may be greatly limiting the effectiveness of this parasitoid as a natural enemy of soybean aphid. Similarly, it may limit our ability to establish a different species, Aphelinus glycinis, which is more specialized on soybean aphids than A. certus is and therefore could be impacted even more than A. certus by seed treatment use on soybean.
In this proposal we develop an experiment and on-farm observations aimed at determining whether neonicotinoid seed treatments have the capability to substantially limit the effect of parasitoids attacking soybean aphid in Minnesota.
- Field evaluation of the effect of seed treatments on soybean aphid parasitism.
- On-farm evaluation of parasitism from fields with known seed treatment status.