Date of Award:

5-1-1976

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Donald W. Davis

Committee

Donald W. Davis

Committee

James MacMahon

Committee

B. Austin Haws

Abstract

Two species of spiders and 10 species of predatory insects were fed alfalfa weevil larvae in the laboratory. Most of the studies used instars III and IV, but some used II. Daily consumption records were kept. Experiments using both weevil larvae alone, and weevil larvae together with pea aphids and lygus bug nymphs, were included. Hippodamia convergens (adults and larvae), Coccinella transversoguttata (adults), Nahis ferus (adults), Nabis alternatus (adults), Chrysopa oculata (larvae), and Collops vittatus (adults) all clearly preferred aphids to either weevil larvae or lygus nymphs. In the absence of aphids, the two coccinellids fed on weevil larvae readily. Individually, C. transversoguttata was the better predator, but H. convergens was far more numerous in the fields, and consequently more important. The other four of the above predators did not accept larger larvae readily. The nabids fed readily on instar II larvae. The two spiders (Xysticus sp. and Tibellus oblongus), Collops bipunctata, and the European earwig (Forficula auricularia) were essentially nonselective predators. The earwig was numerous and ate many weevil larvae. It was probably second in overall importance after H. convergens. The only predator which appeared to prefer weevil larvae over alternate prey was Philonthus (probably fuscipennis). Individually, it was by far the most effective predator of weevil larvae studied, but it occurred in very low numbers in alfalfa fields in northern Utah.

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