The larval food range of the black swallowtail, Papilio polyxenes, is restricted naturally to plants of the family Umbelliferae. When larvae were reared on celery leaves cultured in solutions of sinigrin (a chemical occurring in various species of Cruciferae), feeding rates were not significantly affected but growth and development were substantially reduced. At concentrations of 0.1% (fresh weight of leaf) or higher, sinigrin caused 100% larval mortality. These findings suggest that the larval feeding niche of P. polyxenes is bounded in part by chemical barriers of a toxicological as well as a behavioral nature. They also provide further evidence that sinigrin and other mustard oil glucosides serve a defensive function in plants of the family Cruciferae.
INTRODUCTIONThe data ,are generally presented as a mean and standard error for the larvae in any particular treatment group. The various experimental parameters and indices were subjected to one-way analysis of variance to determine differences in efficiencies or developmental rates anaong the various larval oo.d plants.
RESULTSVarious plant parameters differed greatly among the four Asclepias species offered to the monarch larvae ( The proportion .of ingested foo,,d which was digested and ,assimilat, ed ('assimilation efficiency') averaged about 5o% for all experimental host plants, except for d. syriaca which was significantly higher (P(o.os) with a mean of approximately 58% (Table 2). The efficiency with which ingested matter was converted to biomass ranged ro,m 29.59% for larvae reaved on d. syriaca to 6.39% fo.r larvae reared on d. tuberosa (P
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