Regulation of the Damson-Hop Aphid(Phorodon Humuli(Schrank)) on Hops (Humulus lupulusL.) by Predators

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Abstract
Summary The development of Phorodon humuli populations was studied on hops cv Cobbs during 1971 and 1972. Plants not treated with an insecticide in 1971 were completely defoliated by late July. Half of the experimental plants in 1971 and all of the experimental plants in 1972 were treated at the end of June with 120 ml of 1% dimefox. When the effect of the insecticide had diminished, aphid populations increased on plants from which predators were excluded by sleeve-cages, but decreased on uncaged plants and caged controls. At harvest on uncaged strings there were averages of 1 aphid per 10 cones in 1971 and 3 aphids per cone in 1972. Forficula auricularia L., Anthocoris nemorum (L.) and A. nemoralis (F.) were the most abundant predators when aphid populations declined. In 1972 predators (mostly anthocorids) reduced aphid populations on plants from which earwigs (F. auricularia) and non-flying predators were excluded, but more slowly than on controls.

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