The soybean aphid, Aphis glycines Matsumura, has become the single most important arthropod pest of soybeans in North America. Native to Asia, this invasive species was first discovered in North America in July 2000 and has rapidly spread throughout the northcentral United States, much of southeastern Canada, and the northeastern United States. In response, important elements of the ecology of the soybean aphid in North America have been elucidated, with economic thresholds, sampling plans, and chemical control recommendations widely adopted. Aphid-resistant soybean varieties were available to growers in 2010. The preexisting community of aphid natural enemies has been highly effective in suppressing aphid populations in many situations, and classical biological control efforts have focused on the addition of parasitoids of Asian origin. The keys to sustainable management of this pest include understanding linkages between the soybean aphid and other introduced and native species in a landscape context al...

Ecology and Management of the Soybean Aphid in North America

We consider the possibility of an extensive invasional meltdown occurring in central North America involving eleven Eurasian species. The scenario begins with the potential co-facilitation between the European earthworm Lumbricus terrestris and European buckthorn, Rhamnus cathartica. Once introduced, European buckthorn has served as the overwintering host for two important invasive crop pests, oat crown rust, Puccinea coronata and the soybean aphid, Aphis glycines. The spread of R. cathartica itself may have been aided by seed dispersal by the European starling, Sturnus vulgaris, and the presence of L. terrestris has likely facilitated the invasion of Bipalium adventitium, an Asian predatory flatworm that specializes on earthworms. Beyond this, the soybean aphid is consumed by a number of introduced species, including the lady beetle Harmonia axyridis, the ground beetle Agonum muelleri and the parasitoid Aphelinus certus. We hypothesize that the presence of soybean aphid increases regional abundances of these species. We discuss both the evidence for this multi-species invasional meltdown scenario and potential implications of meltdown dynamics for invasive species management. The particular management issues that we discuss are: (1) opportunities for managing multiple invasive species simultaneously by targeting facilitator species, and (2) implications of meltdown dynamics for biological control introductions against the soybean aphid.

European buckthorn and Asian soybean aphid as components of an extensive invasional meltdown in North America

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a significant insect pest of soybean in the north-central region of the United States and southern Canada, and if left untreated can reduce yield value by $2.4 billion annually. The soybean aphid is native to eastern Asia, where soybean was first domesticated, and was first detected in the United States in 2000. It quickly spread within 4 years of its discovery across 22 states and three provinces of Canada. Heavy infestations can result in a covering of sooty mold, yellow and wrinkled leaves, stunted plants, and aborted pods leading to significant yield loss of 40% or more. It can also transmit plant viruses such as Soybean mosaic virus and Alfalfa mosaic virus. The soybean aphid has a complex life cycle that involves different physical forms, sexual stages, and two host plant species-soybean and buckthorn (the overwintering host). Plant nutrition, natural enemies, climate, and weather all affect population growth rate, but the typical population doubling time is ≈6-7 days. Though at present management is primarily through broad-spectrum insecticides, biological control has a significant impact on soybean aphid population growth, and aphid-resistant soybean varieties are becoming increasingly available.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1017&context=ent_pubs

Biology of the Soybean Aphid, Aphis glycines (Hemiptera: Aphididae) in the United States

The role of natural enemy guilds in Aphis glycines suppression

Aphis glycines Matsumura, the soybean aphid, first arrived in North America in 2000 and has since become the most important insect pest of domestic soybean, causing significant yield loss and increasing production costs annually in many parts of the USA soybean belt. Research to identify sources of resistance to the pest began shortly after it was found and several sources were quickly identified in the USDA soybean germplasm collection. Characterization of resistance expression and mapping of resistance genes in resistant germplasm accessions resulted in the identification of six named soybean aphid resistance genes: Rag1, rag1c, Rag2, Rag3, rag4, and Rag5 (proposed). Simple sequence repeat markers flanking the resistance genes were identified, facilitating efforts to use marker-assisted selection to develop resistant commercial cultivars. Saturation or fine-mapping with single nucleotide polymorphism markers narrowed the genomic regions containing Rag1 and Rag2 genes. Two potential NBS-LRR candidate genes for Rag1 and one NBS-LRR gene for Rag2 were found within the regions. Years before the release of the first resistant soybean cultivar with Rag1 in 2009, a soybean aphid biotype, named biotype 2, was found that could overcome the resistance gene. Later in 2010, biotype 3 was characterized for its ability to colonize plants with Rag2 and other resistance genes. At present, three biotypes have been reported that can be distinguished by their virulence on Rag1 and Rag2 resistance genes. Frequency and geographic distribution of soybean aphid biotypes are unknown. Research is in progress to determine the inheritance of virulence and develop DNA markers tagging virulence genes to facilitate monitoring of biotypes. With these research findings and the availability of host lines with different resistance genes and biotypes, the soybean aphid-soybean pest-host system has become an important model system for advanced research into the interaction of an aphid with its plant host, and also the tritrophic interaction that includes aphid endosymbionts.

Resistance and virulence in the soybean- Aphis glycines interaction

Parasitoids and predatory flies that can attack soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in soybean, Glycine max (L.) Merr., fields were identified 3 to 4 yr after the aphid was first sighted in the north central United States. We detected 15 species by exposing soybean aphid to ovipositing parasitoids and predatory flies at two locations in southern Michigan. The species detected were (in order of the number of specimens recovered from high to low) Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae), Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae), Allograpta obliqua Say (Diptera: Syrphidae), Aphidius colemani Viereck (Hymenoptera: Braconidae), Eupeodes americanus Wiedemann (Diptera: Syrphidae), Leucopis glyphinivora Tanasijtshuk (Diptera: Chamaemyiidae), Aphelinus asychis Walker (Hymenoptera: Aphelinidae), Sphaerophoria contigua Macquart (Diptera: Syrphidae), Binodoxys kelloggensis Pike, Starý & Brewer (Hymenoptera: Braconidae), Eupeodes volucris Osten Sacken (Diptera: Syrphidae), Paragus hemorrhous Meigen (Diptera: Syrphidae), Toxomerus marginatus Say (Diptera: Syrphidae), Aphelinus albipodus Hayat & Fatima (Hymenoptera: Aphelinidae), Syrphus rectus Osten Sacken (Diptera: Syrphidae), and Praon sp. (Hymenoptera: Braconidae). These species were capable of finding, attacking, and completing development on soybean aphid in soybean fields. Based on a literature review, host aphid ranges of the species detected varied widely, with a tendency toward broader host ranges. These data add to the existing information on the predatory complex currently known to attack soybean aphid in the north central United States. Implications for biological control of soybean aphid are discussed.

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J. R. Vockeroth

Papers

Hymenopteran Parasitoids and Dipteran Predators Found Using Soybean Aphid After Its Midwestern United States Invasion