Diapause Dynamics and Host Plant Suitability of Papilio zelicaon (Lepidoptera: Papilionidae)

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Abstract
The swallowtail butterfly P. zelicaon Lucas is generally univoltine in habitats where it feeds on native species of Umbelliferae. In lowland areas of California [USA] where it uses introduced species of Foeniculum and Citrus, it is multivoltine. Diapause induction is primarily regulated by photoperiod. Long days (> 14 h light) prevent pupal diapause while short days (12 h light) induce diapause. Critical photophase varies with latitude of the population, being longest (13.5 h light) in central California multivoltine populations and shortest (12 h light) in multivoltine populations from southern California. Univoltine populations had more than 50% diapause at the long photophase (14L) tested. Selection at 14L:10D, 23.5.degree. C for low diapause in a laboratory stock originating from central California multivoltine females lowered the critical photophase from 13.5L to 13.0L. Diapause development and termination are primarily regulated by temperature. A sufficient period of chilling at the optimum 11.degree. C temperature was necessary for maximum frequency of diapause termination. Numerous pupae from the low diapause stock eclosed without a chilling treatment, but no progeny from field-collected females did so. Weaker diapause intensity in the low diapause laboratory stock and southern California populations suggests that linkage exists between the genetic controls regulating diapause induction and diapause termination. Diapause incidence in progeny from females which had diapaused was significantly greater than that in nondiapause females. Consequences of adult oviposition preference for F. vulgare were examined by comparing the suitability of Foeniculum for larval growth with another introduced but nonpreferred host, Conium maculatum. Conium was less suitable in almost all respects as a host plant, producing higher larval and pupal mortality, decreased pupal weights and increased frequency of diapause.