Ecological Impact of Parathion in Soybeans

An application of ethyl parathion to flowering soybeans reduced populations of predatory arthropods by 66 percent 6 days posttreatment. Egg and larval parasites of the green cloverworm, Plathypena scabra (F.), the most abundant caterpillar species, also were reduced. The green cloverworm population decreased by 83 percent 6 days after the applica· tion. Populations of secondary pests and detritus feeders Similarly were affected. Most species made a remarkable comeback and reached checkfield levels or higher 4 weeks after treatment. The population of green cloverworms increased to a maximum level 2.3 times higher than in the check field during pod fill, apparently caused by decreased predation and parasitism of eggs and early instars. Survival of the resurgent population was low, however, and few 6th instars were noted in either the treated or check fields. Percent defoliation and yield did not differ in the two fields.