Jan Löfqvist

Olfactory Recognition of Host-Tree Susceptibility by Pine Shoot Beetles

Storm-fallen Scots pines with broken roots and trees with severed tops exude wound oleoresin. These trees are susceptible to bark beetles due to an injured vascular system that can not provide adequate oleoresin in order to resist new attacks by beetles [I]. Once a tree is attacked, most bark beetles use pheromone attractants to locate mates and often to overcome tree resistance through a mass attack [I, 21. It would be clearly advantageous for bark beetles to have evolved sensory systems for efficiently locating their host and in recognizing whether a particular host was less resistant than most healthy trees. However, little is known of how bark beetles select their host from among other plant and tree species [I], or what may attract the first individuals to a susceptible host. We have investigated the semiochemical basis of the mass aggregation of pine shoot beetles, Tomicus piniperda, on storm-injured Scots pine. We found that the beetle can recognize while still in flight a host tree and whether it is susceptible by means of olfaction of three plant monoterpenes evaporating from wound oleoresin. Scots pine logs infested with males and females of T. piniperda were tested in the forest of southern Sweden (Table 1, 1982) to determine their attractiveness to naturally swarming populations in the spring. The resulting catches of beetles indicate that there was a strong attraction to volatiles released from logs

Quantitative variation of pheromone components in the spruce bark beetleIps typographus from different attack phases

Ips typographus beetles were collected in the field, separated into eight attack phases (from beetles walking on the trunk of a tree under attack to those excavating gallery systems with a mother gallery longer than 4 cm), and immediately frozen in liquid nitrogen. 2-Methyl-3-buten-2-ol,cis- andtrans-verbenol, verbenone, myrtenol, trans-myrtanol, ipsenol, ipsdienol, and 2-phenylethanol were quantified from excised hindguts against an internal standard, heptyl acetate, in the extraction solvent. Methylbutenol, the pinene alcohols, and 2-phenylethanol showed the same pattern of variation between attack phases in males, with the largest amounts present before accepting females and then a fast decline. Ipsenol and ipsdienol were not detected in males before the females were accepted, and the amounts increased when the females start their egg laying. Verbenone occurred only in trace amounts. The beetles were sampled from five Norway spruce trees (Picea abies) of differing resin flow. The correlations between the nine pheromone components and five major host monoterpenes in the gut showed that the variation in the amount of methyl-butenol, ipsenol, and ipsdienol could not be explained by the variation in the amounts of host monoterpenes. In contrast over 80% of the quantitative variation ofcis-verbenol,trans-verbenol, and myrtenol was explained by the amount of α-pinene. The nine pheromone components from 36 individual males were also quantified. Both methylbutenol andcis-verbenol showed a large variation in both amounts and proportions. Females containedtrans-verbenol and traces of most other components found in males. When accepted by the male, they also contained a female-specific compound, β-isophorone. Behavioral and biosynthetic implications of the results are discussed.

Sex pheromone components of the turnip moth,Agrotis segetum

Analysis of female abdominal tips ofAgrotis segetum by means of GC-MS showed the presence of 13 aliphatic acetates and alcohols. (Z)-7-Dodecenyl acetate was found to be the main component in the extracts at amounts of about 1 ng/female. (Z)-9-Tetradecenyl acetate and (Z)-7-dodecenol were present to the extent of 49 and 19%, respectively, of the main component. Minor components could be identified as decyl acetate, (Z)-5-decenyl acetate, dodecyl acetate, (Z)-9-dodecenyl acetate, tetradecyl acetate, a tetradecenyl acetate, hexadecyl acetate, a hexadecenyl acetate, (Z)-5-decenol, and (Z)-9-tetradecenol. The presence and biological activity of decyl acetate, (Z)-5-decenyl acetate, and (Z)-7-dodecenyl acetate in the extracts could be detected by GC-EAD. Tested by EAG (Z)-5-decenyl acetate evoked the highest response among pheromone candidates, followed by (E)-5-decenyl acetate and (Z)-7-dodecenyl acetate. Single-cell recordings from 100 male antennal sensilla trichodea revealed receptorcells highly sensitive to (Z)-5-decenyl, (Z)-7-dodecenyl, (Z)-8-dodecenyl, and (Z)-9-tetradecenyl acetate as well as (Z)-5-decenol. The (Z)-5-decenyl, (Z)-7-dodecenyl, and (Z)-9-tetradecenyl acetate receptors were activated significantly also by female extracts. When tested in a tube olfactometer, a blend of decyl, (Z)-5-decenyl, (Z)-7-dodecenyl, and (Z)-9-tetradecenyl acetate evoked the same male response as did female glands.Tested in the field, this blend was more attractive than virgin females. Other authors previously reported many of the compounds identified in the present study. However, both quantitative and qualitative discrepancies exist among the various investigations, possibly due to the existence of geographical races.

Plant‐odour‐specific receptor neurones on the antennae of female and male Spodoptera littoralis

Abstract. Receptor neurones with high selectivity and sensitivity to plant odours were found within short sensilla trichodea on the antenna of both female and male Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) by using single‐sensillum recording techniques. In 112 sensilla from females and forty‐one from males, twenty‐four different receptor neurone types were characterized according to their specificity. Altogether, twenty‐six plant and three sex pheromone compounds were tested. Receptor neurones responding with high specificity to flower odours, green leaf volatiles, oviposition deterrents and other general host plant odours were identified. In twenty‐one receptor neurone types, responses were elicited by one or several plant compounds, and in three types responses were elicited by sex pheromone compounds. The majority of the receptor neurones responded to only one or two of the tested compounds. In general, only one of the two receptor neurones in a sensillum responded to any of the compounds tested. An exception was a receptor neurone responding to plant odours (green leaf volatiles) and another receptor neurone responding to a sex pheromone compound ([Z]‐7‐dodecenyl (acetate), which occurred in the same sensillum. The majority of the receptor neurones displayed a high sensitivity to plant odours. No morphological difference was identified the different sensillum types.

Attraction to pheromone sources of different quantity, quality, and spacing: Density-regulation mechanisms in bark beetleIps typographus

The density of bark-beetle colonization of a tree could be regulated by a quantitative effect of the pheromone signal from beetles in the tree (cessation of release of attractive pheromone) or by a qualitative effect (production of pheromone components inhibiting attraction). The quantitative hypothesis was tested onIps typographus by varying the release rate of the two known attractive compounds, 2-methyl-3-buten-2-ol (MB) and (4S)-cis-verbenol (cV). The highest number of beetles were captured at traps with the highest release rates. The catch was nearly proportional to the release of MB and cV at a distance between traps of 12 m or more. At 6-, 3-, and 1.5-m distances between traps deployed in a triangular arrangement there was still a good discrimination between release rates, but relatively more beetles, especially males, were caught on the blank. The lower release rates caught an equal sex ratio while the highest release rate caught only about 30% males. The qualitative hypothesis was tested by releasing the suspected inhibitors ipsdienol (Id) and ipsenol (Ie), from traps in the same amounts as cV. Only small effects were noted forI. typographus. However, the competitorI. duplicatus was attracted to Id and inhibited by Ie, while the predatorThanasimus formicarius was attracted to both compounds. On the other hand, when the ratio of Id or Ie to cV was 10∶1 or 0.1∶1 rather than 1∶1, they affected the numbers ofI. typographus attracted. A small amount of Id combined with the attractants increased trap catch, while large amounts of Id or Ie decreased attraction, especially when combined. Attack density regulation is modeled as an effect of both quantitative and qualitative mechanisms acting in sequence.

Differences in attraction to semiochemicals present in sympatric pine shoot beetles,Tomicus minor andT. piniperda.

The chemical ecology of host- and mate-finding in the pine shoot beetles,Tomicus minor andT. piniperda, was studied in southern Sweden. Beetles were collected in the field from defined attack phases on Scots pine. Using gas chromatography-mass spectroscopy, a number of oxygen-containing monoterpenes, e.g., 3-carene-10-ol, myrtenol,trans-verbenol, and verbenone, were identified from hindgut extracts of both sexes of both species. Compared toT. minor,T. piniperda contained additional compounds and in larger amounts. The amounts were highest in both species at the time when the beetles had bored into contact with the resin-producing xylem-phloem tissue. The synthesis of (1S,6R)-3-carene-10-ol by photooxidatipn of (+)-(1S,6R)-3-carene is described. In comparative electroantennogram (EAG) measurements on males and females of both species, the most active of the tested compounds wastrans-verbenol. Laboratory bioassays of walking beetles showed thatT. piniperda was attracted to uninfestèd pine logs.T. minor was more strongly attracted to pine logs infested with females than to uninfested pine logs, indicating a female-produced aggregation pheromone. Field tests confirmed thatT. piniperda was strongly attracted to pine logs. The attraction ofT. minor to logs was significant only when logs were combined with racemictrans-verbenol and (1S,6R)-3-carene-10-ol.T. minor was also attracted to a combination of these monoterpene alcohols alone. We suggest that host and mate location inT. piniperda is achieved by means of a kairomone composed of host monoterpenes, whileT. minor utilizes a primitive pheromone synergized by host odors. Evolution of host colonization strategies of the two beetles are discussed.

Pheromone dialects in European turnip moths Agrotis segetum

Female pheromone gland extracts from cultures of Agrotis segetum (Schiff.), originating from Sweden, France, Hungary and England were analysed for pheromone components and precursors (fatty acids). The pheromone blends were similar in the moths from the Swedish, English and Hungarian populations, whereas the French diverged with a much higher amount of (Z)-5-decenyl acetate relative to the homologous pheromone components (Z)-7-dodecenyl acetate and (Z)-9-tetradecenyl acetate. The frequency of receptor cells sensitive to (Z)-5-decenyl acetate on male antennae, was also highest in the French insects. In correspondence with the earlier reported behavioural significance of (Z)-5-decenyl acetate in the French turnip moth, this is indicative of a French pheromone dialect. The biosynthetic basis for the shift in pheromone production as well as ecological and evolutionary implications of the findings are discussed.

Odour similarities between the slave-keeping ants Formica sanguinea and Polyergus rufescens and their slaves Formica fusca and Formica rufibarbis

Abstract The volatile compounds of degassed gasters have been identified in four formicine ants; the slave-keeper Formica sanguinea Latr., its slaves Formica fusca L. and Formica rufibarbis F., and the slave-keeper Polyergus rufescens (Latr.), which keeps the same species as slaves as does F. sanguinea. We have mainly investigated the worker ants, but in F. sanguinea also females and males have been analysed. All substances found in the gasters of workers of F. sanguinea and F. rufibarbis have proved to be secreted by Dufours gland. Most probably also all compounds identified in F. fusca and P. rufescens emanate from this gland. Besides aliphatic hydrocarbons of varying chain length, the volatile constituents of the secretion of Dufours gland from females and workers of F. sanguinea are shown to be n-decyl-, n-undecyl-, and n-dodecylacetate. The corresponding alcohols occur as minor components. Moreover, one isomer of farnesene is found. In F. fusca we have identified the same farnesene isomer and eight aliphatic hydrocarbons. The ther slave-species, F. rufibarbis, is shown to secrete the same acetates as F. sanguinea, plus 2-tridecanone and eight aliphatic hydrocarbons. In P. rufescens we have identified the main component as being the same farnesene isomer as previously found in F. sanguinea and F. fusca. We have also found two aliphatic hydrocarbons, whereas two smaller peaks in the gas chromatogram still remain unidentified. The volatile compounds from single gasters of worker ants of F. sanguinea have also been analysed and considerable quantitative variations were found in the components of different specimens.

Leaf Volatiles from Nonhost Deciduous Trees: Variation by Tree Species, Season and Temperature, and Electrophysiological Activity in Ips typographus

The leaf volatiles emitted from four nonhost tree species of Ips typographus, i.e. Betula pendula, B. pubescens, Populus tremula, and Sambucus nigra, were collected outdoors by headspace sampling in situ and analyzed by GC-MS. Three major classes of compounds, aliphatics [mainly green-leaf volatiles (GLVs)], monoterpenes, and sesquiterpenes, existed in all the deciduous tree species investigated. In June, when the bark beetles are searching in flight for host trees, GLVs mainly consisting of (Z)-3-hexenyl acetate and (Z)-3-hexen-1-ol were the dominant constituents in B. pendula and S. nigra. In B. pubescens and P. tremula, sesquiterpenes (and their derivatives) and monoterpenes made up the major part of whole volatile blends, respectively. Surprisingly, sesquiterpene alcohols and other oxides released from B. pubescens in considerable amounts were not found in the closely related species, B. pendula. By August, both the total volatiles and individual compounds significantly decreased, mainly due to the maturation of leaves, since the light intensity and temperatures during sampling were the same as in June. There were almost no volatiles detected from P. tremula and S. nigra leaves in August. The total emissions from these deciduous species were significantly different among the species, with B. pubescens releasing 5–10 times more than other species. Under the conditions of constant light intensity and humidity, emissions of both total volatiles and most individual components of severed B. pendula and S. nigra branches (with fresh leaves) increased according to a saturation curve from 16°C to 40°C. Ips typographus antennae responded strongly to green leaf alcohols: (Z)-3-hexen-1-ol, 1-hexanol, and (E)-2-hexen-1-ol, but not to aldehydes or acetates in GC-EAD analyses of B. pendula and B. pubescens leaf volatiles. No antennal responses to monoterpenes, sesquiterpenes, or sesquiterpene oxides were found. These three antennally active GLVs emitted from nonhost tree leaves might be indicators of a wrong habitat in the host selection of conifer bark beetles.

Pheromone variation among eastern European and a western Asian population of the turnip mothAgrotis segetum.

The female sex pheromone composition and the male electro-physiological response with respect to the three main sex pheromone components, (Z)-5-decenyl acetate, (Z)-7-dodecenyl acetate, and (Z)-9-tetradecenyl acetate, were investigated in populations ofAgrotis segetum from Armenia and Bulgaria. The percentage composition of the female-produced pheromone was 1∶52∶47 and 1∶42∶57 for the respective populations. Corresponding male receptor frequencies were 9∶90∶1 and 6∶92∶2. EAG response profiles of the male antennae were similar for the two populations. The populations from Armenia and Bulgaria differed from the earlier investigated French and Swedish populations, which have larger amounts of (Z)-5-decenyl acetate in gland extracts and have a majority of (Z)-5-decenyl acetate-sensitive receptors. Investigation of receptor frequencies on antennae of male Hungarian moths showed that individuals could be classified as either Swedish or Armenian/Bulgarian type. Males of the Swedish type were preferentially attracted to the three-component pheromone blend, whereas blends of (Z)-7-dodecenyl and (Z)-9-tetradecenyl acetate, and (Z)-7-dodecenol [pure or in mixture with (Z)-5-decenol] attracted the Armenian/Bulgarian type. The nature of pheromone variation among European and Asian populations of the turnip moth and possible mechanisms maintaining the variation are discussed.