Date of Award:

5-1-2000

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Edward W. Evans

Committee

Edward W. Evans

Committee

Jennifer W. MacAdam

Committee

Diane G. Alston

Committee

Kimberly A. Sullivan

Committee

Frank J. Messina

Abstract

In a series of field and laboratory experiments, I explored the trade-off between self-maintenance and current reproduction for the parasitoid Bathyplectes curculionis (Thomson)(Hymenoptera: Ichneumonidae), an economically important natural enemy of the alfalfa weevil, the most significant pest in forage alfalfa. Floral nectars, pea aphid honeydew, and artificial foods such as sugar sprays are likely to assist B. curculionis in meeting its self-maintenance needs. Once these needs are met then B. curculionis females may be more likely to search for hosts to parasitize. However, these foods must not only be available, but accessible, of high quality, and detectable, to be of benefit to the wasp. Sugar sprays applied to alfalfa increased the number of B. curculionis adults throughout the first crop of alfalfa and elevated the rate of parasitism late in the first crop. A significant interaction between local abundance of aphids (and their honeydew) and the application of sugar spray indicated that sugar sprays may be redundant when numbers of pea aphids are high. In a Y-tube olfactometer, hungry wasps preferred odors of dandelions and fed wasps preferred the odor of the host plant, alfalfa, suggesting a readiness to host search only in fed wasps. Females did not behave similarly, however, when phacelia was substituted for dandelion as the floral odor source. The unfed wasps showed no preference for phacelia odor to that of alfalfa. Although the wasps lived significantly longer when fed dandelion nectar than phacelia nectar, surprisingly, neither availability of whole dandelions nor phacelia flowers had a notable impact on wasp longevity. Floral morphology probably limited access to the nectar. Virgin wasps outlived mated wasps when provided either dandelion or phacelia flowers. Wasps fed honey water lived much longer than wasps feeding at flowers; mated wasps fed honey lived longer than unmated wasps. Although pea aphid honeydew is a potential food in the field, it is unlikely that B. curculionis actively seeks out this food. Olfactometer experiments indicated that these wasps had no naïve response to the odor of pea aphids but can associatively learn pea aphid odor. But when the odors of pea aphids and alfalfa are mixed together, the wasp could not distinguish between alfalfa with pea aphids from alfalfa without aphids. A parasitoid's competing needs for self-maintenance and current reproduction may be balanced if these wasps are provided with high-quality carbohydrate foods that are physically accessible, and easily located in close association with hosts.

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