[9] Ragsdale et al. (2004) noted that the soybean aphid probably arrived in North America earlier than 2000, but remained undetected for a period of time.

[1] Venette and Ragsdale (2004) suggested that Japan probably served as the point of origin for the soybean aphid's North American invasion.

[10] By 2003, the soybean aphid had been documented in Delaware, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New York, North Dakota, Ohio, Pennsylvania, South Dakota, Virginia, West Virginia, and Wisconsin.

[12] In two studies, the quantity of overwintering eggs had a strong positive correlation with the severity of soybean aphid outbreaks in the following spring.

[3][citation needed] Colonization of buckthorn by soybean aphids in the spring can lead to curling of leaves and twigs.

During this stage, small colonies of soybean aphids appear patchy, occurring on single plants scattered throughout a field.

[13][17] Damage to a soybean plant during this initial stage is a result of stylet-feeding and can include curling and stunting of leaves and twigs, physiological delays, and underdevelopment of root tissue.

[20] Extremely high population growth rates can be achieved under optimal conditions, with a colony doubling in size in as few as 1.3 days.

Heavy infestations of soybean aphids may cause plant stunting, distorted foliage, premature defoliation, stunted stems and leaves, reduced branch, pod, and seed numbers, lower seed weight, and underdevelopment of root tissue.

[3][13][19] When populations of soybean aphids increase, a need arises for apterae to produce alate offspring to seek out new hosts.

[22] Decreased body size and lowered fecundity can be induced in soybean aphids when populations reach very high densities.

[22] As host plant quality begins to deteriorate in late August and early September, soybean aphids take on a paler color and experience decreased growth and reproductive rates.

[3] Factors that positively affect the production of gynoparae and male alatae include declining host plant quality, shortened day length, and lowered temperatures.

[3] As buckthorn experiences increased feeding pressure by oviparae, volatile emissions from the plant are significantly decreased, possibly serving as a defense mechanism to inhibit further colonization by soybean aphids.

An experiment further reinforced this relationship by demonstrating that soybean aphids can develop on red clover in a laboratory setting.

Myers et al. (2005a) hypothesized that potassium-stress in the laboratory may lead to increased nitrogen availability for soybean aphids.

Viruses spread by soybean aphids are typically vectored non-persistently, which allows for disease transmission in the first moments of stylet penetration.

For example, nymphs have higher rates of metabolism than other life stages, ingest more phloem, and are thus exposed to larger quantities of antibiotic compounds.

[42][43][44][45][46][47][48] Exclusion cage experiments have provided evidence that predators can play an important role in suppression of the soybean aphid.

[42][43][49] One of the most important predators of soybean aphids in North America is the insidious flower bug (Orius insidiosus (Say)).

[50][51] Fox et al. (2004) hypothesized that the impact from this predator early in the season could be attributed to small plant size and sparse canopies, which aid the insidious flower bug by reducing foraging time and decreasing the number of places soybean aphids can hide (i.e., enemy-free space).

[51] Another group of predators that plays a key role in suppression of populations of soybean aphids in North America is lady beetles (Coccinellidae spp.).

[55] In addition, increases in populations of lady beetles have the ability to inhibit colony growth of soybean aphids throughout the growing season.

[53] As generalist predators, lady beetles are able to feed on alternate prey when soybean aphids are at low densities.

[40] Other characteristics of lady beetles that are advantageous in times of soybean aphid scarcity include developmental delays of certain life stages, decreased body weights, and reduced clutch sizes.

[13][60][61] Although seed-applied treatments have proven to be a convenient delivery method for insect control, studies have experienced inconsistent results regarding their efficacy against the soybean aphid.

[59][65] Evidence indicates that foliar insecticide applications can reduce symptoms associated with soybean aphid infestations, including curled leaves, shortened stems, stunted plants, and premature defoliation.

[59] Foliar insecticide applications can work detrimentally if nontarget effects are experienced, such as the unintended death of beneficial natural enemies.