Soybean Aphid (Aphis glycines), Homoptera

Soybean Aphid biology & life cycle

The soybean aphid is one of the foremost insect pests of soybeans in Canada. It has a complex life cycle with several generations per year and requires two species of host plant to complete its life cycle: common buckthorn and soybeans. In the fall, soybean aphids lay eggs on common buckthorn (a woody shrub or small tree). These eggs overwinter and hatch in the spring, giving rise to wingless females. These females reproduce without mating, producing more females. Two generations live on buckthorn before the third generation develop wings and fly to colonize on soybeans.

The aphids continue to produce wingless generations until the soybean aphids become crowded. Winged adults are then produced in the next generation to disperse to other plants or fields. As fall approaches, females start to produce winged males and females that fly to buckthorn to mate and produce eggs.

Aphids can migrate into fields throughout the summer from nearby fields or from far distances (e.g, the United States) via storm fronts. Populations can grow to extremely high levels under favorable environmental conditions. Early-planted fields are prone to early season infestations from aphids moving from buckthorn in the spring. Late-planted fields are prone to summer migration of adults coming from other soybean fields. Fields under drought stress or potassium deficiency can be more prone to injury.

Identifying Soybean Aphid

Soybean Aphid: eggs

Eggs of the soybean aphid are difficult to find because you can't see them with the naked eye. The eggs are tucked down along buckthorn buds. The nymphs will feed on those buds in the early spring when they hatch.

Soybean Aphid: larvae

Young aphids, or nymphs, look the same as adults, but are much smaller and wingless. They appear as very light green dots on plants.

Soybean Aphid: adult

The adult soybean aphid is small in size, approximately 1.5 mm, and difficult to see without the use of a 10X or greater magnifier. They may be winged or wingless, and are pale greenish-yellow with black cornicles (“tailpipes”) and a pale yellow “tail.”

Adult aphids have piercing-sucking mouthparts and typically feed on new tissue on the undersides of leaves near the top of recently colonized soybean plants. Later in the season, aphids can be found on all parts of the plant, feeding primarily on the undersides of leaves, but also on stems and pods.

Once populations reach threshold levels, aphids can cause the plants to abort flowers, become stunted, reducing pod and seed production and quality. Yield loss is greatest when soybeans are in the early R stages (R1-R2), when flowers can abort and impact pod establishment. Peak infestations during the pod fill stage (R3) and beyond can result in smaller seed size and a reduction in seed quality.

Soybean Aphid: management

• Seed treatments for the control of other soil insect pests may provide early-season protection from early infestations of soybean aphids. Once soybeans enter the R1 stage, seed treatments are no longer present in the plants and require foliar applications if thresholds are reached.
• Scout each field every seven to 10 days during R1 until the crop is well into the R6 stage. Scout fields more frequently (every three to four days) as aphid populations approach the threshold. Look at 20 random plants across the field, avoiding field edges. Turn leaves over on each trifoliate of the plant to count the number of aphids on the leaves and stems.
• Look for the presence of aphid natural enemies such as lady beetles, green lacewings, insidious flower bugs, aphid mummies, fuzzy aphids, and other insect predators. Predators and parasitoids may keep low or moderate aphid populations in check.
• Use the free Aphid Advisor app (www.aphidapp.com) to determine if control is necessary or if natural enemies are abundant enough to keep aphid populations below threshold.
• Apply foliar insecticide when threshold of "250 aphids per plant with increasing populations" has been reached in the R1-R5 stage of soybeans. A minimum of two field visits is required to confirm that aphid populations are increasing.
• If aphid populations do not appear to be on the increase above 250 per plant, do not apply insecticide, as it will kill off the beneficial insects that are keeping the aphid population in check. Aphids are then likely to increase quickly in the absence of their predators and could easily reach threshold.
• Scout fields after insecticide application to ensure that aphid populations do not rebound or secondary pests, particularly spider mite populations, do not flare up.