Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

Abstract

Outer row embryos of the southern green stick bug, Nezara viridula (L.), orient toward the center of the egg mass; inner row embryos do not. Embryonic orientation was mediated by stimuli provided by the glue which holds the egg mass together. Physical and chemical orientation cues associated with the glue were present only on the inner surfaces of outer row eggs; other eggs received no such differential stimuli and therefore oriented as a function of the oviposition behavior of the female. Embryonic orientation assured that upon hatching, outer row nymphs received the stimulation necessary for arrestment and inclusion in the first instar aggregation. The hatching of N. viridula was a function of a temperature dependent, photoperiodically entrained rhythm. Hatching within an egg mass was synchronized by the interaction of emerging nymphs stimulating hatching in adjacent eggs and not due to independent timing of eclosion in each egg. In addition to timing eclosion at the onset of light, the photoperiodic rhythm may have functioned to synchronize development so that all eggs in an egg mass were simultaneously capable of hatching when stimulated by the emergence of siblings. In first instar N. viridula, olfactory and visual cues caused attraction while visual and tactile cues caused arrestment. Using chemical, behavioral, and developmental data, n-tridecane was identified as a bifunctional pheromone of first instars; it was the primary component in whole-body extracts and the only volatile found in air extracts. Olfactometry with whole-body extracts and n-tridecane demonstrated that high concentrations were repellent and probably function to alarm and disperse aggregations, and low concentrations were attractive and function to induce aggregation. The adaptive functions of aggregation in first instar N. viridula include: decreased mortality through facilitation of water intake and prevention of desiccation, accelerated development through thermal conservation, and decreased predation through pooling of chemical defenses. Aggregation does not alter food intake or provide contact with essential symbiotes, and groups of nymphs have poorer adherence to a substrate than do isolated individuals.

Pages

147

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