Graduate Thesis Or Dissertation
 

Pheromone-mediated behavior of adult Douglas-fir tussock moths, Orgyia pseudotsugata (McD.) (Lepidoptera: Lymantriidae)

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  • The sinuous flight behavior of male Douglas-fir tussock moths, Orgyia pseudotsugata, (McD.), is characterized by positive anemotaxis and positive chemoklinotaxis and varies depending on distance from the pheromone source, population density, and time of day. Visual cues play a minor role in close-range orientation to a pheromone source, but males do respond to heat energy equivalent to the internal body temperature of the females. A female may be simultaneously courted by two or more males, and a male may remain by the female after mating. Males and females can mate more than once, and there appears to be a minimum time-span which must elapse between consecutive matings by the same male. This probably limits males to one mating per evening. Egg viability is the same for single and multiple matings. Mated females wait for a period of time before laying their eggs and may interrupt oviposition to mate again. An unmated female may lay a portion of her eggs before mating or complete oviposition without copulating. Comparisons of average elapsed courtship, copulation, preoviposition (the period between copulation and egg laying) and oviposition times for laboratory-reared and wild New Mexico moths revealed that pre-oviposition is longer in laboratory moths; but courtship, copulation, and oviposition are the same. Under the prevailing field study conditions, females lived up to seven days but their ability to attract males dropped after three days and the probability that they would mate dropped after two days. Attractancy of male flight is also influenced by temperature and the inhibitory effect of rainy weather. The decline in attractancy is due to a reduction in the amount of pheromone present and a loss of the ability to release the pheromone. Furthermore, at least 20% of the unmated females were not attractive.
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