Soybean aphid season under way
When populations reach high levels during the summer, winged females are produced that migrate to other soybean fields. Like a number of other insect species (e.g., potato leafhoppers), these migrants can be caught up in weather patterns, moved great distances, and end up infesting fields far from their origin. These summer migrants likely have been the major source of infestations in Nebraska the past several years.
Soybean Aphid Natural Enemies
The soybean aphid has many insect predators. The most visible is the multicolored Asian lady beetle, but the tiny (1/10-inch long) insidious flower bug (or Orius) is the most commonly occurring and important predator. It feeds on a variety of small insects and spider mites. Naturally occurring predators, primarily the insidious flower bug, can significantly slow soybean aphid population growth, particularly during hot July weather. Resident populations of predators also help reduce the rate of successful colonization of soybeans by the soybean aphid. Other common predators include green lacewing, brown lacewing, damsel bugs or Nabids, and spined soldier bugs, among others.
Other groups of natural enemies include parasitoids and pathogens. The presence of aphid “mummies” (light brown, swollen aphids) indicates the presence of parasitoids. These mummies harbor immature parasitoids, which will become adults, emerge from the mummy, and parasitize more aphids. The presence of “fuzzy” aphid carcasses indicates fungal pathogens are present, which occasionally can lead to dramatic reductions of aphid populations.
Soybean Aphid Injury to Soybean
Soybean aphids injure soybeans by removing plant sap with their needle-like mouthparts. Symptoms of soybeans infested by soybean aphid may include yellowed, distorted leaves and stunted plants. A charcoal-colored residue also may be present on the plants. This is sooty mold that grows on the honeydew that aphids excrete. Honeydew by itself makes leaves appear shiny. Soybean plants appear to be most vulnerable to aphid injury during the early reproductive stages. Heavy aphid infestations during these stages can cause reduced pod and seed counts.
Soybean Aphid Occurrence in Nebraska
Soybean aphids have been reported in most soybean producing regions of Nebraska, although the highest and most economically damaging populations typically occur in northeast Nebraska.
In much of the soybean aphid’s range, significant aphid infestation often has occurred in the early vegetative stages of soybean. These infestations then undergo rapid population growth to reach high populations during the flowering stages (R1, R2). During most years in Nebraska, however, very few aphids have been found during the vegetative stages. This may be in part because in Nebraska we have less of the soybean aphid’s overwintering host, common buckthorn, than states further east and north do. We usually find a few aphids in late June to early July, but it is usually mid-July, when soybeans are entering or in R3 (beginning pod stage), before we begin to regularly find aphids.