Date of Award:

5-1-1985

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

D. W. Davis

Committee

D. W. Davis

Committee

B. A. Haws

Committee

R. S. Albrechtsen

Abstract

Four wheat fields in northern Utah were sampled sequentially during 1982 and 1983 for aphid species and their predators. Feeding tests were conducted in the greenhouse and laboratory using two aphid species and lygus bug nymphs as prey with six different predator species. Three dominant aphid species were collected in both winter and spring wheat. They were: the English grain aphid Macrosiphum avenae (Fabr.), the greenbug Schizaphis graminum (Rondani), and the rose grass aphid Acyrthosiphum dirhodum (Walker). Four other aphid species were collected in relatively small numbers during the summer. They were: the western wheat aphid Diuraphis tritici (Gillette), the cowpea aphid Aphis medicaginis Koch, Aphis setarius (Thomas), and a new record for Utah, Sipha elegans (Del Guercio). Three aphid species were collected from winter wheat during the fall. They were: the corn leaf aphid Rhopalosiphum maidis (Fitch), the oat bird-cherry aphid Rhopalosiphum padi (Linn.), and few M. avenae. Most of the aphid species started to appear in the fields during early May, reaching a peak during late July on winter wheat, or early August on spring wheat. Coccinellid adults and larvae, especially Hippodamia convergens Guerin, were the most common and effective aphid predators in the fields. H-abid adults and nymphs were second. These were mostly Nabis alternatus Parsh.. Chrysopids, syrphids and European earwigs were scarce in the fields and appeared mostly during the latter part of the season. Spiders and predacious thrips were abundant during the season, but laboratory tests showed that they did not feed on wheat aphids. Ladybird beetle larvae and adults, and chrysopid larvae consumed the highest numbers of English grain aphids in the laboratory tests. Hippodamia larvae, chrysopid larvae, H. convergens adults, N. alternatus adults and nymphs, and syrphid larvae consumed a mean 54.5, 48, 41, 31.5, 21.5 and 20 of M. avenae, respectively, during 24 hours. Hippodamia larvae, chrysopid larvae, and H. convergens adults showed a significant preference for M. avenae over lygus bug nymphs. N. alternatus adults and nymphs showed no preference. N. alternatus adults and H. convergens adults showed a significant preference for M. avenae over A. dirhodum. N. alternatus nymphs and Hippodamia larvae did not show any preference. C. transversoguttata adults showed a nonsignificant preference for A. dirhodum over M. avenae.

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