Date of Award:

5-1-1995

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Edward W. Evans

Committee

Edward W. Evans

Committee

Diane G. Alston

Committee

William A. Brindley

Abstract

The larval endoparasitoid, Bathyplectes curculionis (Thomson), is a major enemy of the alfalfa weevil, Hypera postica (Gyllenhal), which is the most serious pest of alfalfa in North America. The effectiveness of B. curculionis as a biological control agent may be influenced by the availability of adult food sources. One potential source of carbohydrates, aphid honeydew, has been shown to increase fecundity and longevity in some parasitic Hymenoptera. Pea aphids, Acyrthosiphon pisum (Harris), are often present in Utah alfalfa agricultural systems and their honeydew may act as a food source for B. curculionis. Laboratory experiments were performed to evaluate the effect of pea aphid and artificial honeydew (sucrose water) on the longevity, fecundity, and foraging behavior of B. curculionis. Adult wasps enclosed with alfalfa and pea aphids lived almost twice as long as wasps enclosed with alfalfa alone. In a related experiment, female B. curculionis were allowed to feed on pea aphid honeydew, artificial honeydew, or water alone for two days and were then dissected to determine the number of eggs in a lateral oviduct. Egg production was slightly greater in females given either artificial or pea aphid honeydew than in those given only water. The results from the laboratory foraging behavior experiment, in which female wasps were allowed to choose alfalfa with or without pea aphid honeydew, were inconclusive. Field experiments (with caged and uncaged alfalfa) were performed to determine the effect of artificial honeydew spray on B. curculionis parasitism rates. Parasitism rates of alfalfa weevil larvae were higher in caged plants sprayed periodically with artificial honeydew than in caged plants sprayed with water alone. The results from uncaged field experiments, in which the plots were sprayed periodically with artificial honeydew, were inconclusive. Aphid honeydew as a carbohydrate food source increases wasp longevity and fecundity, and may increase parasitism rates in the field. Hence, the presence of pea aphids in moderate numbers in an alfalfa field may actually improve biological control of the alfalfa weevil.

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