Colonization of soybean aphid, Aphis glycines (Homoptera: Sternorrhyncha: Aphididae) is of concern to soybean growers in Minnesota. An objective of this study was to determine when aphids were first detected in soybean at a statewide level by taking random samples during the growing season from all counties where soybean is grown. From these samples, we hypothesized that spatial data might provide indirect evidence of where soybean aphid successfully overwintered. In addition, we might understand when distribution from soybean to soybean might occur by examining the proportion of alatoid nymphs in the samples. In 2002, soybean aphids were first detected in late June in the lower third of the state. But by early July, soybean aphids were found evenly dispersed in Minnesota. Since apterae were collected in the June samples, the data suggest that soybean aphid successful overwintered throughout much of Minnesota in 2001-2002. Peak abundance of alatoid nymphs was 11-17 August, indicating summer migrations are highest after soybeans are setting and filling pods. The cause for alatoid formation and summer migration observed in 2002 was not clear. In 2003 we experimentally manipulated conditions favorable for alatoid formation. Factors such as temperature, photoperiod, plant quality, and crowding were examined independently and in combinations to understand those factors that trigger alatoid nymph formation.
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