Host Plant Biology
More than 100 species of Rhamnus exist worldwide, and most of these species are native to temperate regions of the Northern Hemisphere. Rhamnus species are plentiful in North America. Two confirmed Rhamnus species that support overwintering of soybean aphids in North America are common buckthorn (Rhamnus cathartica) of exotic origin and alderleaf buckthorn (Rhamnus alnifolia) of native origin. Another widespread Rhamnus species of exotic origin in North America is alder buckthorn (Rhamnus frangula); however, neither mature oviparae nor eggs have been documented on this potential host.
In an experiment to determine alternate primary hosts for soybean aphids, only members of the genus Rhamnus were able to support development of soybean aphids. In Asia, where the soybean aphid is native, dominant primary hosts include Japanese buckthorn (Rhamnus japonica) and Dahurian buckthorn (Rhamnus davurica). One study indicated certain plant species may play a role in bridging colonization of soybean from buckthorn. One such species that is readily available in early spring is red clover (Trifolium pratense). An experiment further reinforced this relationship by demonstrating that soybean aphids can develop on red clover in a laboratory setting.
The most common secondary host in both Asia and North America for soybean aphids is soybean. Soybean has been cultivated in Asia for 4,000 to 5,000 years and in the United States since 1904. Du et al. (1994) demonstrated that the primary method by which soybean aphids locate soybean is through olfactory chemical signaling. Interference by non-host odors diminished the ability of soybean aphids to locate and colonize soybean.
Deleterious effects of soybean aphids on soybean can be highly variable and are influenced by factors like soybean aphid density, plant stage, plant density, and temperature. In addition, soil nutrient conditions within a soybean field may play some role in the development of infestations of soybean aphids. For example, in a laboratory experiment, soybean aphids that fed on potassium-deficient soybean experienced increased fecundity and survivorship. Field experiments failed to corroborate this finding. Myers et al. (2005a) hypothesized that potassium-stress in the laboratory may lead to increased nitrogen availability for soybean aphids. Yield data taken from this experiment showed that potassium-stress in conjunction with infestation by soybean aphids caused significant yield loss.
Specificity for soybean aphids to feed on soybean has been demonstrated by Han and Yan (1995) in an experiment utilizing an electrical penetration graph. While no difference in the amount of time spent probing between soybean and other non-host plants was observed, the ingestion of phloem by soybean aphids was either greatly reduced or did not happen at all on non-host plants. Nevertheless, some alternate secondary hosts have been observed for soybean aphids. The most widespread of these alternate secondary hosts is wild soybean (Glycine soja), which has been known to support colonies of soybean aphids in Asia. In Korea and the Philippines, kudzu (Pueraria montana) and tropical kudzu (Pueraria javanica) have been described as alternate secondary hosts, respectively.
Read more about this topic: Soybean Aphid
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