The soybean aphid, Aphis glycines, is attacked by a variety of insect predators in
Wisconsin soybean fields. This complex of beneficial insects appears to play a key role in
regulating soybean aphid populations. In 2001 and 2002, soybean aphid densities have been
highly variable and unpredictable from one area to the next. Much of this variability may be
due to the relative strength of local populations of aphid predators. Surveys conducted in these
two years indicate that the dominant aphid predator in Wisconsin soybeans is Harmonia
axyridis, known commonly as the multicolored Asian lady beetle. Both larval and adult lady
beetles feed upon soybean aphids. Field cage experiments in 2001 and 2002 measured the
effect of H. axyridis predation on soybean aphid population size. In both years, as few as one
beetle larva per seven soybean plants significantly reduced soybean aphid numbers. The
presence of these beetles at or above this level should therefore be noted when scouting for
soybean aphids.