Pea Aphid1 Injury to Resistant and Susceptible Alfalfa In the Field2

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,\Ifalfas resistant and susceptible to Acyrthosiphon pisum (Harris), were compared under both natural and artificial infestations in the field. Plants with little injury were identified and paired with adjacent, severely damaged plants in a heavily infested 'Cody' alfalfa field in which most top growth had been killed. Plants selected for lack of injury showed resistance in laboratory tests. Increases in forage yields for resistant over susceptible plants on successive cuttings in 1968 and 1969 were 211, 188, 107, 114, and 78%. Increased yield apparently was due to resistance, because in absence of pea aphids, clonal propagules of susceptible plants yielded more than did resistant plants.

When infested with aphids in field cages, a resistant strain 'KS 6' produced 72% more forage than did susceptible Cody. For KS 6, both numbers and weights of pea aphids were depressed.

Resistant 'Kanza' and susceptible Cody were compared in varietal yield trials at different locations and in years with various intensities of pea aphid infestations. At a location in 1968, when the infestation was severe, Kanza forage yields were 167% of Cody, compared with 99 to 125% in previous and subsequent years when pea aphids were not of economic importance. In 1968, at 2 locations where aphid populations were low, Kanza yields were 103 and 109% of Cody, compared with 155 and 188% at heavily infested locations, Kanza also out yielded Cody in protein and carotene after heavy infestations in 1968.

Our results indicated that pea aphids cause losses in forage quality as well as in quantity and that losses are reduced by resistant cultivars.

Document Type: Research Article

Publication date: April 1, 1971

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  • Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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