Biomedical subjects

John F Tooker

Publications and source records attributed to John F Tooker.

5 recordsLinked to original sources

PubMed2007

Jasmonate, salicylate, and benzoate in insect eggs.

Jasmonic acid (JA) and salicylic acid (SA) are key molecules in the initiation of plant defensive responses to attack by herbivores and pathogens, respectively. Our previous work has shown that JA occurs at high concentrations in eggs and neonates of lepidopteran species. Here, we extend our analyses to eggs of 15 non-lepidopteran insect species spanning eight orders, again screening for JA, but also including SA and one of its metabolic precursors, benzoic acid. We detected all three compounds in eggs of almost all the species examined. Moreover, concentrations of these compounds were variable across species, suggesting that species accumulate and/or utilize the compounds differently. Eggs of the fruit-feeding fly Rhagoletis pomonella contained the greatest concentrations of all three compounds, which appear to be common in fruit. The presence of these plant-derived compounds in eggs may serve defensive or other functions for insects, and could conceivably trigger plant defensive responses after oviposition.

Animals↗

PubMed2006

Jasmonate in lepidopteran larvae.

Jasmonic acid (JA) is a key molecule initiating plant defensive responses to herbivory. Our previous work has shown that this phytohormone is often present at high concentrations in eggs and neonates of lepidopteran species. In this work, we document the concentrations of JA found in various tissues of larval H. virescens fed on artificial diets with varying JA concentrations and on transgenic tobacco lines with different capabilities of producing JA. At high JA concentrations, excess jasmonate appeared to be voided in frass, but significant amounts were found in most larval tissues we analyzed as well as in regurgitant. At lower concentrations, caterpillars excreted less JA and appeared to accumulate relatively greater amounts of JA in their tissues. In both experiments, substantial amounts of JA were found in labial salivary glands, a notable result since JA is an important signaling molecule involved in the induction of plant defenses.

Animals↗

PubMed2005

Jasmonate in lepidopteran eggs and neonates.

Jasmonic acid (JA) is a key molecule initiating plant defensive responses to attack by pathogens and herbivores. This phytohormone is produced at sites of insect damage and is ingested by feeding insects, but its subsequent occurrence in insect tissues remains to be studied. We report the presence of JA in eggs and neonates of all nine lepidopteran species that we screened, representing four superfamilies and five families of Lepidoptera. Concentrations of JA in some lepidopteran species far exceeded those found in most plant species. Levels of JA varied significantly among species and between eggs and neonates of the same species. In some cases, eggs contained significantly more JA than neonates, but for at least one species (Lymantria dispar) neonates had more JA than their eggs despite lacking food upon emergence. The presence of JA in eggs and neonates across a wide taxonomic range may indicate that JA has an undescribed function in insects.

Animals↗

PubMed2004

Stereochemistry of host plant monoterpenes as mate location cues for the gall wasp Antistrophus rufus.

In spring, adult males of the gall wasp Antistrophus rufus L. emerge from inconspicuous galls in stems of their host plant Silphium laciniatum L. and search for sites on stems where females will later emerge. The behavior of males suggests that they use olfaction rather than visual or tactile cues in searching for mates. In an earlier publication, we reported that galls of A. rufus were associated with changes in enantiomeric ratios of alpha- and beta-pinene emitted by plant stems, and hypothesized that monoterpene stereochemistry served as a mate location cue for adult males. Here, we support this hypothesis with bioassays that demonstrate that males can discriminate between galled and ungalled stems, as well as between blends of synthetic monoterpenes with ratios of enantiomers representative of galled and ungalled stems.

Animals↗

PubMed2002

Altered host plant volatiles are proxies for sex pheromones in the gall wasp Antistrophus rufus.

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 (alpha-pinene, beta-pinene, and camphene) than did S. terebinthinaceum. Ratios of "+" and "-" enantiomers of alpha- and beta-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.

Journal Article↗