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Acknowledgment in Memorium. This paper is dedicated to Ernie Hughes, who pioneered the scientific development of the NIST gas SRM program, and who contributed so much of his technical knowledge to numerous interactions with experts in the gas analysis field, worldwide. In the present study, Ernie carried out the analyses of the NPL standards and supplied the SRMs that were analyzed by NPL, but passed away before this paper could be written. His unique insight into the requirements for accuracy in gas standards and trace gas analysis will be sorely missed by his many friends and scientific colleagues both in the United States and abroad.Registry No. CO, C02, Literature Cited(1) Davenport, A. J.; Freshwater, F.; King, J. H.; Merrifield, D. R.; Partridge, R. H.; Woods, P. T. NPL Quantum Metrology Report: Analyses of Reference Gas Mixtures for the Community Bureau of Reference, Commission of European Communities; January 1985.

The composition of the volatile oil obtained from the hydrodistillation of the leaves of Psidium guajava L., growing in Nigeria, was studied by GC-MS. Forty-two compounds, representing more than 90% of the volatile mixture, were identified. The significant compounds were limonene (42.1%) and β-caryophyllene (21.3%).

We describe a previously uncharacterized function for changes in plant chemistry induced by phytophagous insects: to provide cues for mate location. Larvae of the gall wasp Antistrophus rufus Gillette (Hymenoptera: Cynipidae) feed within inconspicuous galls inside the flowering stems of the prairie perennials Silphium laciniatum L. and Silphium terebinthinaceum Jacquin (Asteraceae). Adult male A. rufus emerge before females and are challenged with locating mates that are sequestered within dead plant stems that occur in a matrix of dead vegetation. Allozyme studies revealed complete reproductive isolation between wasp subpopulations in the two plant species. In laboratory bioassays, males responded only to their natal plant species, antennating the stem surface. Males from S. laciniatum also responded to hexane extracts of S. laciniatum stems, and extracts contained much higher concentrations of monoterpenes (␣-pinene, ␤-pinene, and camphene) than did S. terebinthinaceum. Ratios of ''؉'' and ''؊'' enantiomers of ␣-and ␤-pinene approximated 50:50 for nongalled S. laciniatum stems but strongly differed from 50:50 in galled stems, with ''؉'' and ''؊'' enantiomers strongly dominant in different plants. In bioassays, male wasps from S. laciniatum responded to a synthetic blend of the monoterpenes in enantiomeric ratios characteristic of galled stems. Male A. rufus rely entirely on olfaction to locate females within stems in a complex prairie habitat, and gall wasps themselves apparently influence the plant to modify ratios of monoterpene enantiomers. These plant volatiles serve as a signal for males, acting as a sex pheromone proxy for females concealed within plant tissues.Hymenoptera ͉ Cynipidae ͉ insect ͉ mate location ͉ volatiles P hytophagous insects may induce release of plant volatile chemicals that relay information across trophic levels. For example, induced plant volatiles can attract natural enemies of herbivores (e.g., refs. 1 and 2), discourage oviposition by conspecific herbivores to prevent intraspecific competition between larvae (3), or serve both functions (4). Volatile compounds associated with insect-feeding damage also induce physiological resistance in conspecific plants (5) or across plant species (6). In this paper, we describe a previously uncharacterized function for changes in plant chemistry induced by phytophagous insects: to provide cues for mate location. Although earlier studies have revealed that plant volatiles play an important role in insect mate location (e.g., refs. 7 and 8), ours is to our knowledge the first to suggest that insects alter the chemical composition of plant volatile bouquets for purposes of mate location.Antistrophus rufus larvae feed within galls inside the flowering stems of four species of Silphium that occur in prairies of the Midwestern United States (9, 10). These galls form entirely within the stem and are not discernable externally. Silphium laciniatum L. and Silphium terebinthinaceum Jacquin cooccur throughout the Midwest, including at our prairie study s...