CHEMOECOLOGY (v.12, #4)
by Jacques Pasteels; Désiré Daloze (pp. 159-159).
Rich in phenomena-lacking in terms. A classification of kairomones
by Joachim Ruther; Torsten Meiners; Johannes L. M. Steidle (pp. 161-167).
Although the usefulness of the term kairomone was discussed controversially after its introduction, it is now widely accepted in chemical ecology. It is commonly used to describe a chemical that is pertinent to the biology of an organism (organism 1) and that when it contacts an individual of another species (Organism 2) evokes in the receiver a behavioural or physiological response that is adaptively favourable to organism 2 but not to organism 1. A look at the chemoecological literature reveals that chemicals classified by the mere term kairomone may have completely different biological functions for the receiving organism. Chemicals meeting the definition of a kairomone are used for the location of food sources and sexual mates, or may be used by potential prey or host organisms to decrease the negative impact of natural enemies. Thus, by describing those diverse mediators merely as kairomones, no information on the actual function of the chemical is given. When considering the terminology of pheromones, another diverse group of infochemicals mediating intraspecific interactions, further subdivision is common practice and useful to describe the multitude of different functions and thus, to prevent terminological confusion.¶The present paper demonstrates the diversity of kairomone-related ecological phenomena by several examples and proposes a further classification of kairomones according to the function for the benefiting organism, by introducing the terms foraging kairomone (used in the context of food location), enemy-avoidance kairomone (used to reduce the negative impact of natural enemies), sexual kairomone (used for sexual purposes), and aggregation kairomone (attracting/arresting both sexes of an organism). Additionally, discrimination of two groups of kairomones according to the effect on the benefiting organism is proposed leading to the terms primer kairomone (inducing physiological responses) and releaser kairomone (inducing behavioural responses). The intention of the proposed classification is to allow a more precise description of kairomones and thus, to aid the discussion of these compounds and to improve the readability of kairomone-related papers.
Keywords: Key words. Infochemical terminology — kairomone — foraging kairomone — enemy-avoidance kairomone — sexual kairomone — aggregation kairomone — primer kairomone omone — releaser kairomone — allomone
GC-EAG-analysis of volatiles from Brussels sprouts plants damaged by two species of Pieris caterpillars: olfactory receptive range of a specialist and a generalist parasitoid wasp species
by Hans M. Smid; Joop J.A. van Loon; Maarten A. Posthumus; Louise E.M. Vet (pp. 169-176).
Feeding by Pieris brassicae or P. rapae caterpillars on Brussels sprouts plants induces the emission of synomones that attract natural enemies of the caterpillars, Cotesia glomerata, a generalist parasitoid, and C. rubecula, a specialist on P. rapae. Previous research on this tritrophic system has identified a large number of volatiles in the headspace of herbivore-damaged Brussels sprouts plants, and this paper addresses the question which of these volatiles are perceived by the two parasitoid species. Headspace odors from both P. brassicae- and P. rapae-damaged Brussels sprouts plants were analyzed by coupled gas chromatography electro- antennogram (GC-EAG) detection. Twenty volatiles evoked consistent EAG reactions in the antennae of both species and nineteen of these volatiles could be identified with GC-MS. One component that could not be identified due to its low concentration, evoked EAG responses in antennae of C. rubecula only. Possible consequences for searching behavior of the two parasitoid species are discussed.
Keywords: Key words. Lepidoptera — Pieridae — Hymenoptera — Braconidae — Cotesia glomerata — Cotesia rubecula — Brussels sprouts — Brassicae oleracea — GC-EAG — tritrophic interactions — specialist — generalist
Agrobacterium-mediated transformation of Nicotiana attenuata, a model ecological expression system
by Tamara Krügel; Michelle Lim; Klaus Gase; Rayko Halitschke; Ian T. Baldwin (pp. 177-183).
Research into the genetic basis of the ecological sophistication of plants is hampered by the availability of transformable systems with a wealth of well-described ecological interactions. We present an Agrobacterium-mediated transformation system for the model ecological expression system, Nicotiana attenuata, a native tobacco that occupies the post-fire niche in the Great Basin Desert of North America. We describe a transformation vector and a transformation procedure that differs from the standard cultivated tobacco transformation protocols in its use of selectable markers, explants, media and cultivation conditions. We illustrate its utility in the transformations with genes coding for key enzymes in the oxylipin cascade (lipoxygenase, allene oxide synthase, hydroperoxide lyase) in antisense orientations and present high-throughput screens useful for the detection of altered phenotypes for the oxylipin cascade (green leaf volatiles and jasmonic acid after wounding).
Keywords: Key words. Nicotiana attenuata — Agrobacterium transformation — lipoxygenase — allene oxide synthase — hydroperoxide lyase — green leaf volatiles
Two herbivore-deterrent iridoid glycosides reduce the in-vitro growth of a specialist but not of a generalist pathogenic fungus of Plantago lanceolata L
by Hamida B. Marak; Arjen Biere; Jos M.M. van Damme (pp. 185-192).
Many secondary plant compounds are involved in defense against both insect herbivores and pathogens. Two secondary plant compounds of Plantago lanceolata, the iridoid glycosides catalpol and its precursor aucubin, are well known for their deterrent effects on generalist and non-adapted specialist insect herbivores. We tested the effects of these compounds on the in-vitro growth of a specialist and generalist fungal pathogen of this host species. Two chemical forms of these iridoids were tested. The glycosides and their aglycones, the products of enzymatic conversion by specific $/Beta$-glucosidase enzymes. The glycosides enhanced growth of both the specialist fungus Diaporthe adunca and the generalist fungus Fusarium moniliforme var. subglutinans. The positive effect of these glycosides on the generalist fungus is in sharp contrast with the generally negative effects of these glysosides on generalist insect herbivores. The aglycones of aucubin and catalpol reduced the growth of the specialist fungus D. adunca, but, contrary to expectation, enhanced the growth of the generalist fungus F. moniliforme var. subglutinans. Effects of aucubin on D. adunca were stronger than effects of catalpol. This was true both for the growth stimulating effects of the glycosides and for the fungitoxic effects of the aglycones. We therefore expect that the effects of these iridoids in P. lanceolata on the specialist fungus will strongly depend on the ratio between catalpol and its precursor aucubin and the chemical form (glycoside or aglycone) in which these compounds are encountered by the fungus during growth. Our results suggest that iridoid glycosides in P. lanceolata can be used as defense against both herbivores and pathogens, but that their effects are highly specific with respect to the natural enemy species that is encountered.
Keywords: Key words. Chemical defense — plant-pathogen interactions — iridoid glycosides — aucubin — catalpol — Diaporthe adunca — Fusarium moniliforme — Plantago lanceolata
Comparative sensitivity to and consumption of methyl eugenol in three Bactrocera dorsalis (Diptera: Tephritidae) complex sibling species
by Suk-Ling Wee; Alwin Kah-Wei Hee; Keng-Hong Tan (pp. 193-197).
Sensitivities to methyl eugenol of three sibling species in the Bactrocera dorsalis complex were compared. The degree of species sensitivity to methyl eugenol, i.e. B. dorsalis > B. papayae > B. carambolae (in decreasing order), was concomitant with the species age-related response to methyl eugenol as previously reported. The ability to consume methyl eugenol by the three sibling species showed similar trend - the average ME consumption per male was 0.70 ml for B. dorsalis, 0.58 ml B. papayae and 0.18 μl B. carambolae. Results obtained were discussed in relation to area-wide control of fruit fly.
Keywords: Key words. Bactrocera dorsalis sibling species — B. carambolae — B. dorsalis — B. papayae — methyl eugenol sensitivity — consumption
De Novo terpenoid biosynthesis by the dendronotid nudibranch Melibe leonina
by Todd Barsby; Roger G. Linington; Raymond J. Andersen (pp. 199-202).
Stable isotope feeding studies using [1,2-13C2]-sodium acetate have demonstrated that 2,6-dimethyl-5-heptenal (1), a putative defensive allomone, is made by the Dendronotid nudibranch Melibe leonina via de novo biosynthesis.
Keywords: Key words. Chemical — defense nudibranch — biosynthesis — terpenoid
Effects of hydrolysable tannins on a herbivorous insect: fate of individual tannins in insect digestive tract
by Juha-Pekka Salminen; Kyösti Lempa (pp. 203-211).
We investigated the effects of four chemically characterised galloylglucoses (GGs, a subgroup of hydrolysable tannins) and their hydrolysis product, gallic acid (GA), on consumption and performance of larvae of the autumnal moth Epirrita autumnata. Larvae were fed with birch (Betula pubescens) leaves that had been painted individually with each of the compounds at two levels, 5 and 20 mg/g. In addition, we investigated the fates of the leaf-painted GGs and GA in the E. autumnata digestive tract by comparing phenolics in leaves consumed and in faeces. In general, GGs reduced leaf consumption by E. autumnata during the second and fourth instars, although there was high compound- and instar-specific variation. However, GGs did not affect the leaf consumption rates by the most voracious fifth instar larvae. This resulted in approximately the same loss of total biomass by the experimental tree, regardless of the nature and level of GGs enriched to its foliage. The characteristic fate of hydrolysable tannins, i.e. hydrolysis, was evidenced in the larval digestive tract for three of the four leaf-painted GGs. In addition to hydrolysis, the almost total absence of GGs in larval faeces was presumably related to the oxidation of GGs. The dose-dependent excretion percentage of ingested GA showed that it's faecal content should not be used, although it commonly is, to calculate the level of GG hydrolysis. Moreover, by comparing the non-uniform appearance of faecal tetragalloylglucoses, whether ingested as such or hydrolysed from pentagalloylglucose, we concluded that a major part of oxidation of GGs occurs before their hydrolysis in the digestive tract of E. autumnata. Criticism against the common use of tannic acid, a heterogeneous mixture of GA and GGs, in ecological studies is presented.
Keywords: Key words. Hydrolysable tannins — galloylglucoses — tannic acid — metabolism — birch — Betula pubescens — Epirrita autumnata
Apportionment of nuptial alkaloidal gifts by a multiply-mated female moth (Utetheisa ornatrix): eggs individually receive alkaloid from more than one male source
by Alexander Bezzerides; Thomas Eisener (pp. 213-218).
In the moth Utetheisa ornatrix the female is promiscuous and receives a nuptial gift of pyrrolizidine alkaloid (PA) by seminal infusion from each mate. The alkaloidal gifts are transmitted by the female to the eggs, which are protected as a result. We here show that individual eggs may receive PAs from more than one male source and that individual males have no assurance that the PA they themselves contribute to the female will find its way exclusively to eggs of their siring.
Keywords: Key words. Nuptial gift — paternal investment — female promiscuity — pyrrolizidine alkaloid — insect/plant interaction — Arctiidae
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