Antennal responses of four species of tree-killing bark beetles (Coleoptera: Scolytidae) to volatiles collected from beetles,and their host and nonhost conifers

Summary. Host selection in tree-killing bark beetles (Coleoptera: Scolytidae) is mediated by a complex of semiochemical cues. Using gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometric analyses, we conducted a comparative study of the electrophysiological responses of four species of tree-killing bark beetles, the Douglas-fir beetle, Dendroctonus pseudotsugae, Hopkins, the mountain pine beetle, D. ponderosae Hopkins, the spruce beetle, D. rufipennis Kirby, and the western balsam bark beetle, Dryocoetes confusus Swaine, to volatiles captured by aeration of 1) bole and foliage of four sympatric species of conifers, Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, lodgepole pine, Pinus contorta var. latifolia Engelm., interior spruce, Picea engelmannii x glauca, and interior fir, Abies lasiocarpa x bifolia, and 2) con- and heterospecific beetles at three stages of attack. We identified 13 monoterpenes in the conifers and nine compounds in the volatiles of beetles that elicited antennal responses. There was no qualitative difference in the terpene constitution of the four species of conifers and very little difference across beetle species in their antennal response to compounds from conifers or beetles. The lack of species-specific major or minor components in conifers suggests that beetles would need to detect differences in the ratios of different compounds in conifers to discriminate among them. Attraction to hosts and avoidance of nonhost conifers may be accentuated by perception of compounds emitted by con- and heterospecific beetles, respectively. The 22 compounds identified are candidate semiochemicals with potential behavioural roles in host location and discrimination.     

Dynamics of pheromone production and communication in the mountain pine beetle, Dendroctonus ponderosae Hopkins, and the pine engraver, Ips pini (Say) (Coleoptera: Scolytidae)

Summary. The mountain pine beetle, Dendroctonus ponderosae Hopkins, and the pine engraver, Ips pini (Say), often co-exist in lodgepole pine, Pinus contorta var. latifolia Engelmann. Intra- and interspecific semiochemical communication occurs in both species and their complete semiochemical repertoire and precise dynamics of pheromone production have not been elucidated. Porapak-Q extracts of captured volatiles from beetles of each species aerated at different attack phases (freshly emerged, pioneer sex alone in the log and both sexes paired in new galleries), followed by gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectroscopic analyses identified 17 compounds (seven compounds common to both species, six present in D. ponderosae and four present in I. pini) that excited the antennae of either or both species. Seven compounds for D. ponderosae and nine for I. pini had not been assessed for behavioural activity. In field trapping experiments, 2-phenylethanol produced by both species inhibited the response of D. ponderosae to its aggregation pheromones. exo- and endo-Brevicomin produced by D. ponderosae significantly decreased the response of I. pini to its aggregation pheromone ipsdienol. Nonanal, a ubiquitous compound found in the volatiles of lodgepole pine, various nonhosts and in both beetle species deterred the response of I. pini to ipsdienol. The occurrence of cis-verbenol, trans-verbenol and verbenone in emergent I. pini, and verbenone and 2-phenylethanol in emergent D. ponderosae suggests that these compounds may inhibit aggregation and induce dispersal following emergence. Termination of aggregation in D. ponderosae appears to depend on the production of frontalin in combination with changes in the relative ratios of verbenone, exo-brevicomin, trans-verbenol and 2-phenylethanol. In I. pini, the cessation of ipsdienol production by males is probably the main factor in terminating aggregation. Received 16 November 1999; accepted 7 August 2000     

A survey of antennal responses by five species of coniferophagous bark beetles (Coleoptera: Scolytidae) to bark volatiles of six species of angiosperm trees

Summary. Using Porapak Q traps, we collected the bark volatiles of six angiosperm trees native to British Columbia: black cottonwood, Populus trichocarpa Torr. & A. Gray (Salicaceae), trembling aspen, P. tremuloides Michx. (Salicaceae), paper birch, Betula papyrifera Marsh. (Betulaceae), bigleaf maple, Acer macrophyllum Pursh (Aceraceae), red alder, Alnus rubra Bong. (Betulaceae), and Sitka alder, A. viridis ssp. sinuata (Regel) á. L?ve & D. L?ve (Betulaceae). Utilising coupled gas chromatographic-electroantennographic detection analysis, the captured volatiles were assayed for antennal responses in five species of coniferophagous bark beetles (Coleoptera: Scolytidae), sympatric with most or all of the angiosperm trees: the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, the mountain pine beetle, D. ponderosae Hopkins, the spruce beetle, D. rufipennis (Kirby), the western balsam bark beetle, Dryocoetes confusus Swaine, and the pine engraver, Ips pini (Say). The identities of 25 antennally-active compounds were determined by coupled gas chromatographic-mass spectroscopic analysis, and co-chromatographic comparisons with authentic chemicals. The compounds identified were: hexanal, (E)-2-hexenal, (Z)-3-hexen-1-ol, 1-hexanol, heptanal, α-pinene, frontalin, benzaldehyde, β-pinene, 2-hydroxycyclohexanone, 3-carene, limonene, β-phellandrene, benzyl alcohol, (E)-ocimene, salicylaldehyde, conophthorin, guaiacol, nonanal, methyl salicylate, 4-allylanisole, decanal, thymol methyl ether, (E)-nerolidol, and dendrolasin. A number of these compounds are known semiochemicals that are active in the behaviour of other organisms, including bark beetles, suggesting a high degree of semiochemical parsimony. Antennally-active compounds ranged from seven in A. viridis to 17 in P. trichocarpa. The fewest number of compounds (9) were detected by I. pini and the largest number (24) were detected by D. pseudotsugae. Six compounds excited the antennae of all five species of bark beetles. The large number of antennally-active compounds detected in common by numerous bark beetles and present in common in numerous nonhost trees supports the hypothesis of olfaction-based recognition and avoidance of nonhost angiosperm trees during the process of host selection by coniferophagous bark beetles. Received 13 December 1999; accepted 14 March 2000     

Volatiles from the bark of trembling aspen, Populus tremuloides Michx. (Salicaceae) disrupt secondary attraction by the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae)

Summary. Coupled gas chromatographic-electroantennographic detection (GC-EAD) analysis of the Porapak Q-captured volatiles from the bark of trembling aspen, Populus tremuloides Michx., revealed four compounds that consistently elicited antennal responses by mountain pine beetles (MPBs), Dendroctonus ponderosae Hopkins. One of these, 1-hexanol, disrupted the capture of MPBs in multiple-funnel traps baited with the aggregation pheromones trans-verbenol and exo-brevicomin and the host kairomone myrcene, a blend of semiochemicals that mediates the secondary attraction response in which beetles mass attack and kill living pines. The other three EAD-active aspen bark volatiles, benzyl alcohol, benzaldehyde and nonanal, were inactive alone, but in binary and ternary combinations contributed to a disruptive effect in an additive and redundant manner when all four aspen bark volatiles were tested in all possible binary and ternary blends. The best ternary blend and the quarternary blend achieved ≥ 80% disruption. The quarternary blend enhanced the disruptive effect of the antiaggregation pheromone verbenone in traps, raising the disruptive effect to 98%, and also enhanced the inhibition of attack on attractant-baited lodgepole pines. This is the first demonstration of specific compounds from the bark of angiosperm trees that disrupt the secondary attraction response of sympatric coniferophagous bark beetles. The results support the hypothesis that such bark beetles are adapted to recognize and avoid non-host angiosperm trees by responding to a broad spectrum of volatiles that can act in various blends with equal effect. Received 27 October 1997; accepted 20 February 1998.     

GC-EAD responses to semiochemicals by eight beetles in the subcortical community associated with Monterey pine trees in coastal California: similarities and disparities across three trophic levels

Summary.  Antennae of six sympatric bark and ambrosia beetles (Scolytidae), Dendroctonus valens LeConte, Gnathotrichus retusus (LeConte), Hylastes tenuis Eichhoff, Ips mexicanus (Hopkins), Ips plastographus maritimus Lanier, and Pseudohylesinus sericeus (Mannerheim), and two scolytid predators, Enoclerus sphegeus (F.) (Cleridae) and Lascontonus tuberculatus Kraus (Colydiidae), were analyzed by gas chromatographic-electroantennographic detection (GC-EAD) for their responses to synthetic Ips spp. pheromone components, and host and nonhost volatiles. The beetles emerged from cut logs of pitch canker-infected Monterey pine trees, Pinus radiata D. Don. There were significant disparities in EAD response patterns to the hemiterpene and monoterpene alcohol pheromone components that are typically produced by Ips spp. Antennae of I. p. maritimus responded strongly to ( ± )-ipsdienol, ( ± )-ipsenol, amitinol, and lanierone; antennae of I. mexicanus responded strongly to (1S,2S)-(–)-cis-verbenol, with weaker responses to ( ± )-ipsdienol, ( ± )-ipsenol, and amitinol; antennae of H. tenuis responded to (1S, 2R)-(–)-trans-ver-benol, with less pronounced responses to (–)-cis-verbenol and 2-methyl-3-buten-2-ol; and antennae of D. valens, G. retusus, and P. sericeus generally responded to all Ips spp. pheromone components except 2-methyl-3-buten-2-ol (D. valens and G. retusus) and E-myrcenol (G. retusus and P. sericeus). Ips mexicanus responded only to the (–)-enantiomers of ipsenol and ipsdienol, whereas I. p. maritimus responded to (–)-ipsenol, but to both the (+)- and (–)-enantiomers of ipsdienol. The antennae of the two predaceous insects (E. sphegeus and L. tuberculatus) responded to a range of the Ips spp. pheromone components. Host monoterpenes elicited no antennal responses from E. sphegeus, G. retusus, H. tenuis, and I. mexicanus, but several monoterpenes elicited various levels of responses from D. valens and I. p. maritimus antennae. Interestingly, antennae of female D. valens responded to (–), but not (+)-limonene. α- and β-Pinene elicited weak responses from L. tuberculatus antennae. EAD responses to selected nonhost volatiles were almost identical among the six scolytid species, with trans-conophthorin eliciting the strongest response in most cases, followed by three C₆- alcohols and two C₈-alcohols. The antennal responses by most of these species to linalool or geranylacetone were very weak; (E)-2-hexenal, (Z)-3-hexenyl acetate, and benzyl alcohol elicited almost no response. The response pattern of P. sericeus to nonhost volatiles differed slightly from the rest of the scolytids: a strong response to linalool, weaker response to the C₈-alcohols. The two predaceous Coleoptera generally had weak, but detectable, responses to nonhost volatiles, except for a relatively strong response to trans-conophthorin by L. tuberculatus. No notable differences in EAD responses were observed between males and females of the two Ips spp. Our results provide an electrophysiological baseline for future efforts to identify attractive and repellent semiochemicals (aggregation pheromones, host kairomones, or nonhost interruptants) for this guild of scolytids and their key predators that are associated with moribund and pitch canker- infected P. radiata.     

Comparison of the flower scent of the sexually deceptive orchid <Emphasis Type="Italic">Ophrys iricolor</Emphasis> and the female sex pheromone of its pollinator <Emphasis Type="Italic">Andrena morio</Emphasis>

Summary. Ophrys flowers mimic the female produced sex pheromone of their pollinator species to attract males for pollination. The males try to copulate with the putative female and thereby pollinate the flower. Using electrophysiological and chemical analyses, floral volatiles released by O. iricolor as well as the female sex pheromone of its pollinator species, Andrena morio are investigated. Overall, 38 peaks comprising 41 chemical compounds, were found to release reactions in the antennae of male A. morio bees. Analyses using coupled gas chromatography-mass spectrometry revealed the presence of alkanes and alkenes with 20 to 29 carbon atoms, aldehydes (C9 to C24) and two esters. Almost all of those compounds were found in similar proportions in both, the floral extracts of O. iricolor and cuticle surface extracts of A. morio females. The pattern of biologically active volatiles described here is very similar to that used by other Ophrys species pollinated by Andrena males.     

Adaptation of a four-arm olfactometer for behavioural bioassays of large beetles

Summary. We adapted a four-arm olfactometer (55 × 55 × 5.5 cm) for bioassays of large insects and its usefulness was evaluated by testing the responses of three beetles, the palm weevil Rhynchophorus palmarum (L.) (Coleoptera: Curculionidea) and two Dynast scarabs Strategus aloeus (L.) and Oryctes rhinoceros (L.) (Coleoptera: Scarabaeidae) to plant odours and aggregation pheromones. This olfactometer was coupled to a volatile delivery system dispensing highly volatile semiochemicals at constant concentrations. We materialized airflows in the olfactometer by discolouring sensitive papers with acid vapours under various conditions (air straighten by stainless steel grids in inputs and output, 500 ml/min per arm) to visualize air turbulence and to test air-tightness. The volatile delivery system can be used to mix and dispense a broad range of concentrations of semiochemicals in air from diluted aqueous solutions. It was calibrated by measuring the release of the pheromone using solid phase-microextraction (SPME). Dose-response curves to synthetic pheromone were obtained for O. rhinoceros of both sexes. Coupling the volatile delivery system to the fourarm olfactometer provided a system with which the responses of R. palmarum and S. aloeus to their synthetic aggregation pheromones and to natural plant volatiles could be readily observed and studied.     

Emission of oilseed rape volatiles after pollen beetle infestation; behavioural and electrophysiological responses in the parasitoid <Emphasis Type="Italic">Phradis morionellus</Emphasis>

Summary. The pollen beetle, Meligethes aeneus, is an important pest of oilseed rape, Brassica napus. Larvae of this species feed only in the buds and flowers of Brassicaceae. One important natural enemy of this beetle is the parasitoid Phradis morionellus that attacks larvae in buds and flowers and also feeds on the flowers. The preferences for odours of non-infested and infested rape were tested for both starved and fed parasitoids in Y-tube olfactometer experiments. The volatile blend released from pollen beetle-infested and non-infested flowering rape and from pollen beetle larvae was identified and quantified. Gas chromatography-electroantennodetection analyses were performed with female P. morionellus. Parasitoids in both treatment groups preferred infested rape, but the proportion of responding female P. morionellus was significantly lower for the group that was starved. Six of the 20 volatiles identified were released at higher rates from infested rape than from non-infested. None of these compounds was found in pollen beetle larvae headspace. P. morionellus antennae detected both major and minor components in the volatile blend. The volatiles released at a significantly higher rate from infested rape and detected by P. morionellus antennae were (Z)-3-hexenylacetate, (Z)-3-hexenol, 3-butenyl isothiocyanate and (E,E)-α-farnesene.     

Comparative electrophysiological analysis of plant odor perception in females of threePapilio species

Summary Antennae of femalePapilio butterflies perceive many volatile plant constituents with widely differing, constituent-specific sensitivities. We compared the responses of threePapilio species to volatiles from host and non-host plants to assess species-specificity and the degree of evolutionary conservatism in olfactory responses.Since previous studies had demonstrated that the polar constituents in odor fromDaucus carota stimulate oviposition behavior inPapilio polyxenes, we collected headspace volatiles fromD. carota, Pastinaca sativa (both Apiaceae) andArtemisia dracunculus (Asteraceae) and separated the polar fraction of these volatiles by gas chromatography. GC-coupled electroantennograms (GC-EAG) were recorded from the speciesPapilio polyxenes, P. machaon hippocrates andP. troilus. In addition, the responses of the three species to five compounds known as generally occurring constituents of plant odor were recorded. The relative sensitivities for these compounds were nearly identical in all threePapilio species. The response spectra to the separated plant volatiles also showed considerable similarities among the species.From the limited set of GC peaks evoking a response in one of the species, 64% (D. carota), 44% (P. sativa) and 29% (A. dracunculus) also evoked a response in both of the other species. The responses of the two closely related Apiaceae feeders (P. polyxenes, P. m. hippocrates) to volatiles fromD. carota were more similar to each other than was either to the response ofP. troilus, which feeds on Lauraceae. However, this was not true for the responses to volatiles fromP. sativa. The least congruence among the three species was found in the responses to volatiles fromA. dracunculus, a non-host for all of them. The differences and similarities found in the response profiles of the threePapilio species are discussed with respect to evolutionary adaptation to host odor versus evolutionary conservatism in adaptation of olfactory receptors.     

Male-biassed response of garden chafer, Phyllopertha horticola L., to leaf alcohol and attraction of both sexes to floral plant volatiles

Summary. Field tests were performed to evaluate the response of the garden chafer, Phyllopertha horticola (Coleoptera: Scarabaeidae) to known scarab attractants and to investigate the influence of trap colour and height on the number of captured beetles. Both sexes were attracted by a lure mixture composed of geraniol, eugenol, and 2-phenylethyl propionate (PEP) (ratio 3:7:3). When testing floral volatiles individually, only geraniol, eugenol and methyl anthranilate but not PEP was attractive. Response of garden chafer to (Z)- 3-hexen-1-ol was strongly male-biassed. Both the response to floral volatiles and (Z)-3-hexen-1-ol was increased by using funnel traps with yellow instead of grey vanes. Traps positioned at 50 and 125 cm above ground captured significantly more garden chafers than those at 200 cm. The strongly male-biassed response to (Z)-3-hexen-1-ol suggests that in P. horticola (subfamily Rutelinae) orientation towards plant volatiles emitted upon mechanical damage of plants is part of the male mate finding strategy as recently demonstrated for cockchafers of the genus Melolontha (subfamily Melolonthinae). Possible application of plant volatiles for control of P. horticola is discussed.     

Sexually differentiated functions of female-produced pheromone of the black chafer <Emphasis Type="Italic">Holotrichia loochooana loochooana</Emphasis> (Sawada) (Coleoptera: Scarabaeidae)

Summary. Both male and female Holotrichia loochooana loochooana (Sawada) (Coleoptera: Scarabaeidae) were attracted with female-produced pheromone, anthranilic acid (2-aminobenzoic acid), in the field. Male chafers were observed to apparently directly locate cotton balls impregnated with 1 to 10 mg of pheromone. In contrast, females never directly oriented to the treated balls but landed 0.2-1.5 m away and exposed their abdominal glands in a calling posture, which occasionally resulted in aggregation of both females and males. This suggested the mating aggregation of this species could be primarily induced by pheromone released by females. A hypothesis for adaptability of female aggregation is proposed and discussed.     

Sex pheromones and their potential role in the evolution of reproductive isolation in small ermine moths (Yponomeutidae)

Summary Sex pheromone communication in the nine European species of small ermine moths (Yponomeuta) is reviewed in regard to the potential role of pheromones in the speciation process. Six of the nine species studied (viz.,Y. evonymellus, Y. cagnagellus, Y. padellus, Y. irrorellus, Y. plumbellus, andY. vigintipunctatus) use a mixture of (E)-11-and (Z)-11-tetradecenyl acetate in different ratios as primary pheromone components, with combinations of tetradecyl acetate, (Z)-9-tetradecenyl acetate, (Z)-11-hexadecenyl acetate and the corresponding alcohols of the acetates as additional pheromone components. Analysis of (Z)- to (E)-11-tetradecenyl acetate ratios produced by individual females of these species demonstrated significant variation among females of all species. However, the ranges of ratios produced byY. cagnagellus, Y. irrorellus, andY. plumbellus, sharing the same host-plant species, spindle tree, did not overlap. Niche separation of all six species mentioned required consideration of at least one additional pheromone component or of temporal aspects. The remaining three species,i.e. Y. malinellus, Y. mahalebellus andY. rorellus, have pheromones that differ qualitatively.Biosynthetic routes to the pheromone components identified are proposed on the basis of fatty acid pheromone precursors found in the pheromone glands. A phylogenetic tree for the genus is constructed based on allozyme frequency data and changes in pheromone composition are superimposed on this tree. We suggest that the ancestral ermine moth pheromone is a mixture of (Z)-11- and (E)-11-tetradecenyl acetate and the corresponding alcohols, and a scenario of how present-day patterns evolved is outlined. The pheromone differences among the three species using spindle tree as their host-plant might have evolved throughreproductive character displacement upon secondary contact between populations that had already diverged genetically in allopatry. Pheromone differences within the so-calledpadellus-complex (includingY. cagnagellus, Y. mahalebellus, Y. malinellus, Y. padellus, andY. rorellus) in which species might have originated sympatrically, may have evolved byreinforcing selection as these species still hybridise and produce viable offspring when confined in cages. The role of pheromones in reproductive isolation amongYponomeuta species is emphasised by (1) the function of pheromone components of some of the species as behavioural antagonists to other species, (2) the cross-attraction under experimental conditions between allochronic species with similar pheromones, and (3) the formation of hybrids in the laboratory between species that are isolated in nature by pheromone differences.     

Multiple feeding stimulants in <Emphasis Type="Italic">Sinapis alba</Emphasis> for the oligophagous leaf beetle <Emphasis Type="Italic">Phaedon cochleariae</Emphasis>

Summary. In earlier investigations on host plant discrimination of leaf beetles glucosinolates were described as feeding stimulants for the Brassicaceae specialist Phaedon cochleariae F. (Coleoptera: Chrysomelidae). However, since these findings could not be confirmed in later studies offering 2-propenylglucosinolate in concentrations corresponding to those detected in host plant leaf material, the identification of feeding stimulants of this leaf beetle species remained unclear. In order to investigate which compounds of the host plant Sinapis alba (Brassicaceae) are involved in feeding stimulation, leaf extracts of different polarities were tested in bioassays with adults of P. cochleariae. Number of feeding beetles and net consumption rates were highest on pea leaves painted with methanol extracts of S. alba, whereas weak feeding responses were also detectable for hexane extracts. In subsequent bioassay-guided fractionations of methanol extracts with semi-preparative high performance liquid chromatography, two distinct fractions, one containing glucosinolates and another containing flavonoids, were found to stimulate beetles to feed to variable degrees. Other collected fractions had zero activity. The combination of both active fractions evoked significantly higher consumption rates and stimulated more beetles to feed than fractions tested individually. At least one compound of each fraction, among these the main glucosinolate of S. alba, 4-hydroxybenzylglucosinolate, act additively. Effects of two different naturally-occurring ratios of glucosinolates and flavonoids on the strength of feeding responses were investigated by use of extracts of two sets of host plants differently exposed to radiation. One set was outdoors-exposed, whereas the second set was kept in the greenhouse. However, the feeding behaviour of P. cochleariae was not affected by the significantly different relative compositions of both compound classes in the host material. In conclusion, mustard leaf beetles need a combination of distinct plant metabolites acting in concert for feeding stimulation, whereby the mere presence of these stimulants, but probably not the ratio of involved compounds, determines their feeding response.     

Aggregation pheromone compounds of the black larder beetle Dermestes haemorrhoidalis Kuster (Coleoptera: Dermestidae)

Gas chromatography with simultaneous flame ionisation and electroantennographic detection (GC–EAD) and gas chromatography with mass spectrometry analysis (GC–MS) of abdominal extracts of adult male Dermestes haemorrhoidalis Kuster (Coleoptera: Dermestidae) revealed the presence of electrophysiologically and behaviourally active compounds to its conspecific males and females. Isopropyl dodecanoate (3), isopropyl (Z)-9-tetradecenoate (5), isopropyl tetradecanoate (6), isopropyl (Z)-9-hexadecenoate (7) and isopropyl hexadecanoate (8) were detected in male abdominal extracts only. Analysis of collected male headspace volatiles revealed the presence of six EAD-active compounds (3), (5), (6) and isopropyl tridecanoate (4) plus two unidentified compounds (1) and (9). Synthetic compounds (3), (4), (5), (6) and (7) showed EAD activity with antennae of both sexes in contrast to synthetic (8) which showed EAD activity with female antennae only. Male and female antennae of D. haemorrhoidalis reacted with high receptor potentials to isopropyl (Z)-9-dodecenoate (2), although this compound itself was detected in neither male nor female abdominal extracts or headspace volatiles. Petri dish bioassays indicated that male abdominal extracts and compounds (2), (3), (5) and (6) aroused and attracted conspecific male and female beetles significantly (P < 0.05) compared to female extracts. These results suggested the presence of a male-produced aggregation pheromone in D. haemorrhoidalis. Field assays with any of the described compounds, however, did not result in attraction of this beetle in significant numbers.     

Sesquiterpene Hydrocarbons: Kairomones with a releaser effect in the sexual communication of the white-spotted longicorn beetle, <Emphasis Type="Italic">Anoplophora malasiaca</Emphasis> (Thomson) (Coleoptera: Cerambycidae)

Summary.  We conducted a series of experiments with the white-spotted longicorn beetle Anoplophora malasiaca (Thomson), and its host plant, Citrus unshiu, to examine the origin of the sesquiterpene hydrocarbons (SHCs; including β-elemene, β-caryophyllene, α-humulene, α-farnesene, and several unidentified compounds) that are contained in the elytra of the beetles and act as an attractant. In the laboratory, mechanically wounded citrus branches, as well as those fed upon by A. malasiaca, attracted males more frequently than intact branches. Solid phase microextraction (SPME) and subsequent analyses by gas chromatography (GC) analyses detected measurable SHCs from the air around both mechanically wounded and beetle-infested branches, as well as trace amounts from intact branches. The SHCs were also detected for a certain time from beetles that had fed on the citrus branches, but the amounts decreased rapidly after they were removed from the host. This decrease generally corresponded with a reduction of attractiveness of the beetles in a behavioural assay. Isolated females acquired the SHCs after exposure to, but not upon contact with, other females that had fed on C. unshiu branches. We hypothesize that the citrus SHCs are adsorbed in, retained on, and released from the wax layer of the beetle elytra. Since these compounds are released from branches when beetles feed, they may indirectly signal the presence of beetles to others in the field. The high response rate to SHCs by males is likely representing mate searching behavior. The SHCs act as kairomones with a releaser effect in the communication system of A. malasiaca. Hiroe Yasui, Toshiharu Akino, Midori Fukaya: These authors contributed equally to this article.     

Sex pheromone communication of tentiform leaf-miners <Emphasis Type="Italic">Phyllonorycter insignitella</Emphasis> and <Emphasis Type="Italic">Ph. nigrescentella</Emphasis> from two related species groups

Summary.  Females of both species start their pheromone-releasing activity on the second day after emergence at the beginning of the photophase. During the present work, a peak of calling activity with close to 100% of active Ph. nigrescentella females was registered 1.5 hour after the light had been put on. The high pheromone release behaviour with 50% active females lasted for 3 hours. The calling activity of the group of females was about 6 h/day. The beginning of a photophase under laboratory conditions or an early morning in nature is a common period for sex pheromone release in the genus Phyllonorycter. (8Z,10E)-tetradecadien-1-yl acetate (8Z,10E-14:Ac), (8Z,10E)-tetradecadien-1-ol (8Z,10E-14:OH) and (8E,10Z)-tetradecadien-1-yl acetate (8E,10Z-14:Ac) in the ratio 96:4:traces as well as 8Z,10E-14:Ac and 8Z,10E-14:OH in the ratio 88:12 collected by Solid Phase Micro Extraction (SPME) were found to be specific for the calling periods of virgin Phyllonorycter insignitella and Ph. nigrescentella females respectively. Field trapping experiments demonstrated that all three compounds are important for the attraction of Ph. insignitella males while only 8Z,10E-14:Ac is the essential sex pheromone component for Ph. nigrescentella. The pheromone activity of all three compounds is reported for the first time. Addition of either 8Z,10E-14:OH or 8E,10Z-14:Ac to 8Z,10E-14:Ac did not have a significant effect on the attraction of Ph. nigrescentella males, while the efficiency of the three component blend was 5 times lower as compared to that of 8Z,10E-14:Ac. Our data demonstrate that 8Z,10E-14:OH and 8E,10Z-14:Ac play a dual function, they are minor sex pheromone components of Ph. insignitella essential for attraction of conspecific males and show an allelochemical, antagonistic effect on Ph. nigrescentella males and, thus, ensuring specificity of the mate location signal in two related Phyllonorycter species.     

Aggregation pheromone ofCarpophilus freemani (Coleoptera: Nitidulidae): A blend of conjugated triene and tetraene hydrocarbons

Summary Males ofCarpophilus freemani Dobson (Coleoptera: Nitidulidae) produce an aggregation pheromone to which both sexes fly in a wind-tunnel bioassay. The major pheromone component (ca. 30 ng per male per day in volatile collections) was identified as (2E,4E,6E)-5-ethyl-3-methyl-2,4,6-nonatriene. A minor component, (2E,4E,6E,8E)-7-ethyl-3,5-dimethyl-2,4,6,8-undecatetraene, was 3–10% as abundant as the major triene and was 5–20% as active when compared at relative doses ranging from natural proportions to 1:1. These compounds act synergistically: a mixture of major and minor components in natural proportions attracted more than twice as many beetles as the major component alone, and the mixture fully accounted for the activity of male-derived volatile collections. Six other male-derived conjugated hydrocarbons, ranging from 2% down to 0.04% as abundant as the major component, were also identified. These are (in order of decreasing bioassay activity when compared on an equal-weight basis): (3E,5E,7E)-6-ethyl-4-methyl-3,5,7-decatriene, (2E,4E,6E)-5-ethyl-3-me-thyl-2,4,6-octatriene, (3E,5E,7E,9E)-8-ethyl-4,6-dimethyl-3, 5,7,9-dodecatetraene, (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6, 8-undecatetraene, (3E,5E,7E)-5-ethyl-7-methyl-3,5,7-undecatriene, and (2E,4E,6E)-3,5-dimethyl-2,4,6-nonatriene. All structure identifications were confirmed by synthesis. In the wind tunnel, the pheromone acted synergistically with host-type volatiles such as propyl acetate, valeric acid, and ethanol. This concept was verified by fields tests in California, in which there was dramatic synergism between the pheromone and fermenting host materials. Pheromone biosynthesis is discussed.     

Sequestration of plant pyrrolizidine alkaloids by chrysomelid beetles and selective transfer into the defensive secretions

Summary Oreina cacaliae andO. speciosissima (Coleoptera, Chrysomelidae) sequester in their elytral and pronotal defensive secretions pyrrolizidine alkaloids (PAs) as Noxides (PA N-oxides). The PA N-oxide patterns found in the beetles and their host plants were evaluated qualitatively and quantitatively by capillary gas chromatography/mass spectrometry (GC-MS). Of the three host plantsAdenostyles alliariae (Asteraceae) is the exclusive source for PA N-oxide sequestration in the defensive secretions of the beetles. With the exception of O-acetylseneciphylline the N-oxides of all PAs ofA. alliariae, i.e. senecionine, seneciphylline, spartioidine, integerrimine, platyphylline and neoplatyphylline were identified in the secretion. PA N-oxides typical ofSenecio fuchsii (Asteraceae) were detected in the bodies of the beetles but not in their secretion. No PAs were found in the leaves of the third host plant,Petasites paradoxus (Asteraceae). The results suggest the existence of two distinctive storage compartments for PA N-oxides in the beetle: (1) the defensive secretion, containing specifically PA N-oxides acquired fromA. alliariae; (2) the body of the beetle, sequestering additionally but less selectively PA N-oxides from other sources,e.g. S. fuchsii or monocrotaline N-oxide fed in the laboratory. The concentration of PA N-oxides in the defensive secretion is in the range of 0.1 to 0.3 mol/1, which is more than 2.5 orders of magnitude higher than that found in the body of the beetle. No significant differences exist in the ability of the two species of beetles to sequester PA N-oxides fromA. alliariae, althoughO. speciosissima, but notO. cacaliae, produces autogenous cardenolides. A negative correlation seems to exist between the concentrations of plant-derived PA N-oxides andde novo synthesized cardenolides in the defensive secretion ofO. speciosissima.     

Behavior and ecology of Old World Luperini beetles of the genusAulacophora (Coleoptera: Chrysomelidae)

Summary The attraction of Old World leaf beetles in the genusAulacophora to kairomones and parakairomones which are effective lures for New WorldDiabrotica andAcalymma were investigated. Beetles captured on sticky traps baited with single and multicomponent lures were no different from the control traps for two species ofAulacophora. Yellow colored traps and squash blossoms are attractive toAulacophora beetles which detect sub-microgram quantities of cucurbitacins on silica gel. Leaf feeding behavior and flight activity data are correlated with varietal preference of threeAulacophora species. The common response byDiabrotica andAulacophora to cucurbitacins reinforces the two groups' coevolutionary association with the Cucurbitaceae. The apparent lack of a common response toCucurbita blossom volatiles suggests recent evolutionary pathways are substantially different for these two groups of beetles.     

Mother’s choice of the oviposition site: balancing risk of egg parasitism and need of food supply for the progeny with an infochemical shelter?

Summary. Oviposition site selection of herbivorous insects depends primarily on host plant presence which is essential for offspring survival. However, parasitoids can exploit host plant cues for host location. In this study, we hypothesised that herbivores can solve this dilemma by ovipositing within high plant diversity. A diverse plant species composition might represent an ‘infochemical shelter’, as a potentially complex volatile blend can negatively affect the host location ability of parasitoids. We examined this exemplarily for the egg-laying response of the generalist leaf beetle, Galeruca tanaceti, in relation to (1) host plant availability and (2) plant species diversity in the field. Further, we investigated the effect of odours from mixed plant species compositions on (3) leaf beetle oviposition site selection and on (4) the orientation of its specialised egg parasitoid, Oomyzus galerucivorus. In the field, egg clutch occurrence was positively related to the presence and quantity of two major host plants, Achillea millefolium (yarrow) and Centaurea jacea, and to the number of herbaceous plant species. In two-choice bioassays, female beetles oviposited more frequently on sites surrounded by an odour blend from a diverse plant species composition (including yarrow) than on sites with a pure grass odour blend. In the presence of yarrow odour and an odour blend from a diverse plant mixture (including yarrow) no difference in the oviposition response was recorded. Experienced parasitoid females were attracted to yarrow odours, but showed no response when yarrow odours were offered simultaneously with odours of a non-host plant. In conclusion, it could be shown in laboratory bioassays that the parasitoid responds only to pure host plant odours but not to complex odour blends. In contrast, the herbivore prefers to oviposit within diverse vegetation in the field and in the laboratory. However, the laboratory results also point to a priority of host plant availability over the selection of a potential ‘infochemical shelter’ for oviposition due to high plant diversity.