Behavioral and Physiological Aspects of Self-Selection by the Corn Earworm, Heliothis Zea
Cohen, Randy Wade
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Permalink
https://hdl.handle.net/2142/71103
Description
Title
Behavioral and Physiological Aspects of Self-Selection by the Corn Earworm, Heliothis Zea
Author(s)
Cohen, Randy Wade
Issue Date
1987
Department of Study
Entomology
Discipline
Entomology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Entomology
Abstract
Larvae of the corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), prefer to feed on corn silks as early instars but change their feeding preference to corn kernels as they mature. Within the corn kernel, final instar larvae prefer to feed on germ but will always eat some of the endosperm. In the laboratory, germ-fed larvae grow more efficiently than endosperm-feeders, eating less food and completing the final stadium somewhat sooner. However, larvae that feed on endosperm live much longer as adults and produce more eggs in their lifetime than do adults from germ-fed larvae. Thus, in nature, corn earworm larvae strike a balance between larval and adult needs by ingesting entire kernels.
Final instar Heliothis zea larvae self-select a complete and balanced diet from two nutritionally incomplete diets, one lacking only casein and the other lacking only sucrose. The physiological processes regulating nutrient self-selection in animals have not been fully elucidated, but recent evidence in mammals links the production of the neurotransmitter serotonin (5-hydroxytryptamine) with carbohydrate feeding. It is well-known that serotonin is present in insect nervous systems. High performance liquid chromatography analysis reveals that H. zea fed on sucrose or starved have increased brain serotonin levels. Larvae feeding on a diet with casein but lacking sucrose or on a nutritionally complete 80:20 (casein:sucrose) diet contain much lower levels of brain serotonin. Incorporation of a serotonin antagonist (p-chlorophenylalanine) in the diet of self-selecting H. zea larvae reduces brain serotonin levels and produces an 85% increase in sucrose consumption, whereas addition of an agonist (tryptophan) results in a 10% decrease in sucrose consumption accompanied by a relatively large but not statistically significant increase in brain serotonin. The data suggest that serotonin may be involved in a physiological feedback loop monitoring nutrient need.
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