Non-host Volatiles Research Articles

Semiochemical Disruption of the Pine Shoot Beetle, <I>Tomicus piniperda</I> (Coleoptera: Scolytidae)

Abstract The pine shoot beetle, Tomicus piniperda (Coleoptera: Scolytidae), is an exotic pest of pine in North America. We evaluated blends of semiochemical disruptants, which included nonhost volatiles and verbenone, for their ability to disrupt attraction of T. piniperda to traps baited with the attractant α-pinene and to Scots pine, Pinus sylvestris L., trap logs. In Michigan and in Ontario, Canada, a single blend of nonhost volatiles alone [comprised of 1-hexanol, (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, 3-octanol, and 1-octen-3-ol] or the nonhost volatile blend combined with verbenone significantly reduced attraction of T. piniperda to attractant-baited traps by 68–77%. Similarly, verbenone plus the nonhost volatile blend or a similar blend without 1-octen-3-ol also significantly reduced attack density of T. piniperda on pine trap logs by 56–74% in both Michigan and Ontario. Although relative responses between the different blends were slightly different between Michigan and Ontario, the recommended opera...

Olfactory recognition and behavioural avoidance of angiosperm nonhost volatiles by conifer‐inhabiting bark beetles

Abstract 1 When searching for suitable hosts in flight, especially in mixed forests, conifer‐inhabiting bark beetles will encounter not only suitable host trees and their odours, but also unsuitable hosts and nonhost trees. Rejection of these trees could be based on an imbalance of certain host characteristics and/or a negative response to some nonhost stimuli, such as nonhost volatiles (NHV).2 Recent electrophysiological and behavioural studies clearly indicate that conifer‐inhabiting bark beetles are not only able to recognize, but also to avoid, nonhost habitats or trees by olfactory means. Green leaf volatiles (GLV), especially C6‐alcohols, from the leaves (and partly from bark) of nonhost angiosperm trees, may represent nonhost odour signals at the habitat level. Specific bark volatiles such as trans‐conophthorin, C8‐alcohols, and some aromatic compounds, may indicate nonhosts at the tree species level. Flying bark beetles are also capable of determining whether a possible host is unsuitable by reacting to signals from conspecifics or sympatric heterospecifics that indicate old or colonized host tree individuals.3 Combined NHV signals in blends showed both redundancy and synergism in their inhibitory effects. The coexistence of redundancy and synergism in negative NHV signals may indicate different functional levels (nonhost habitats, species, and unsuitable hosts) in the host selection process. Combinations of NHV and verbenone significantly reduced the number of mass attacked host trees or logs on several economically important species (e.g. Dendroctonus ponderosae, Ips typographus, and I. sexdentatus).4 We suggest a semiochemical‐diversity hypothesis, based on the inhibition by NHV of bark beetle host‐location, which might partly explain the lower outbreak rates of forest insects in mixed forests. This ‘semiochemical‐diversity hypothesis’ would provide new support to the general ‘stability‐diversity hypothesis’.5 Natural selection appears to have caused conifer‐inhabiting bark beetles to evolve several olfactory mechanisms for finding their hosts and avoiding unsuitable hosts and nonhost species. NHV and unsuitable host signals have potential for use in protecting trees from attack. The use of these signals may be facilitated by the fact that their combination has an active inhibition radius of several metres in trap test, and by the observation of area effects for several trees near inhibitor soruces in tree protection experiments. Furthermore, incorporation of negative signals (such as NHV and verbenone) and pheromone‐based mass‐trapping in a ‘push–pull’ fashion may significantly increase the options for control against outbreaks of conifer‐inhabiting bark beetles, especially in high risk areas.

Test of Semiochemical Mediated Host Specificity in Four Species of Tree Killing Bark Beetles (Coleoptera: Scolytidae)

We tested the hypothesis that nonhost conifers contain compounds that repel coniferophagous bark beetles (Coleoptera: Scolytidae) during host selection in four experiments (n = 10) involving paired trees baited with aggregation pheromones. Mountain pine beetles, Dendroctonus ponderosae Hopkins, and Douglas-fir beetles, Dendroctonus pseudotsugae Hopkins, were tested for discrimination between their respective hosts, lodgepole pine and Douglas-fir, and spruce beetles, Dendroctonus rufipennis Kirby, and western balsam bark beetles, Dryocoetes confusus Swaine, for discrimination between interior spruce and interior fir. Both host and nonhost conifers in a pair were baited with the same aggregation pheromone. Most baited host trees were successfully attacked and contained galleries with eggs or young larvae. Neither D. rufipennis nor D. confusus attempted to establish galleries on nonhosts. A few attacks were initiated on nonhosts by D. pseudotsugae and D. ponderosae, but most did not reach the phloem tissue, and in no case were they numerous enough to have produced a significant source of aggregation pheromone. Thus employing pheromone-baited nonhost trap trees would not be an effective management tactic. Higher trap catches in unbaited multiple funnel traps within 1 m of nonhost trees than in control traps 12.5 m away also indicated that there was no strong long range repellence caused by nonhost volatiles. Although this study was not designed to evaluate primary attraction to host trees, the lack of strong repellence from nonhost conifers partly supports the hypothesis of random landing followed by close range olfactory or gustatory rejection of nonhosts.

Comparative Behavioural Responses ofDryocoetes confususSwaine,Dendroctonus rufipennis(Kirby), andDendroctonus ponderosaeHopkins (Coleoptera: Scolytidae) to Angiosperm Tree Bark Volatiles

Synthetic, angiosperm bark-derived volatiles, which elicit antennal responses in a number of coniferophagous bark beetles (Coleoptera: Scolytidae), were tested in groups for their ability to disrupt the pheromone-positive response of the spruce beetle (SB), Dendroctonus rufipennis (Kirby), the western balsam bark beetle (WBBB), Dryocoetes confusus Swaine, and the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins, to attractant-baited traps. One complex mixture disrupted WBBB response to pheromone-baited multiple-funnel traps to a level not significantly different than that in unbaited control traps. No group of compounds, including a group of green leaf volatiles, was active in disrupting SB response, a result that contrasts other published findings and that is different from the behavioral responses that are elicited by nonhost volatiles in other species of coniferophagous bark beetles. For the MPB, the two green leaf alcohols, 1-hexanol and (Z)-3-hexen-1-ol, were highly disruptive. In addition, combinations of compounds from the group consisting of salicylaldehyde, benzaldehyde, nonanal, guaiacol, benzyl alcohol, and conophthorin acted to augment the disruptive activity of the green leaf alcohols.

Protection of lodgepole pine from attack by the mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Scolytidae) using high doses of verbenone in combination with nonhost bark volatiles

We evaluated the antiaggregation pheromone verbenone at low and high doses alone and with a seven-component repellent blend of nonhost angiosperm bark volatiles (NHVs) for their ability to deter attack by the mountain pine beetle, Dendroctonus ponderosae Hopkins. Release devices containing antiaggregants were deployed at 16 points on a 10-m grid in 40 × 40-m plots near Williams Lake, B.C. in June 2001. In 10 control plots with no antiaggregants, single pheromone-baited trees, at the plot centre were all mass-attacked by the mountain pine beetle by early October, as were 26.6% of the 432 lodgepole pines within the boundaries of the plots. In contrast, in plots treated with a high dose of verbenone plus NHVs, two of the central, pheromone-baited trees escaped any attack whatsoever, four of 10 plots had no surrounding trees attacked and only 2.1% of the total of 523 surrounding trees were mass-attacked. Density of attacked and mass-attacked trees was highest within 5 m of the central baited tree in all treatments, indicating that those beetles that breached the antiaggregant grid were then drawn toward the baited tree. Operational efficacy should thus be improved in the absence of baited trees within a treated area. We conclude that high-dose verbenone plus NHV treatments could be implemented operationally as a minor component of an integrated pest management strategy for large infestations, particularly in a push-pull tactic in which beetles are pushed from one area by the antiaggregant treatment and drawn into another with attractive baits. However, the principal use would be in the short-term protection of small, high-value stands or stands of high ecological or social value. Key words: Coleoptera, Scolytidae, Dendroctonus ponderosae, chemical ecology, verbenone, pest management

Interruption of aggregation pheromone in Ips typographus (L.) (Col. Scolytidae) by non‐host bark volatiles

Abstract 1 The antennally active nonhost bark volatiles (NHVs): trans‐conophthorin (tC), C6‐alcohols (green leaf volatiles; GLVs) and C8‐alcohols, were tested for their ability to reduce attraction of the spruce bark beetle Ips typographus (L) (Col. Scolytidae) to its pheromone sources in both laboratory walking bioassy and field trapping experiments.2 In the walking bioassay with I. typographus females, individual NHVs such as tC, 3‐octanol and 1‐octen‐3‐ol, and the unsuitable host signal, verbenone (Vn), were inactive at the doses tested. However, the blend of C6‐alcohols (3GLVs) and all the binary, ternary, or quarternary blends significantly reduced the female attraction to the pheromone sources.3 In the field trapping experiments, individual NHV signals (tC, C6‐alcohols and C8‐alcohols) all reduced catch of I. typographus in pheromone‐baited traps, with their inhibitory effects similar to that of the known inhibitor, Vn. The binary, ternary or quarternary combinations of these NHV signals or Vn, all caused significantly stronger reductions in trap catches than the individual signals. The blends showed similar levels of interruption, except the binary blend of C8‐alcohols (2C8OH) and Vn.4 Difference in trapping mechanism between pipe traps (attraction and landing) and Lindgren funnel traps (attraction) did not affect the pattern of inhibition of these active NHV signals and Vn.5 These behaviourally active nonhost volatiles and Vn might be used effectively to protect spruce trees or stands against attacks by I. typographus.

Redundancy, synergism, and active inhibitory range of non‐host volatiles in reducing pheromone attraction in European spruce bark beetle Ips typographus

Host and habitat selection in flight by conifer bark beetles is governed by inhibition of attraction by non‐host volatiles (NHV), in addition to the well‐known attraction to kairomones from host plants and to aggregation pheromones from conspecifics. Antennally‐active NHV from angiosperm birch and aspen trees were field tested on the European spruce bark beetle, Ips typographus (L.), by pheromone baited traps in Sweden using release rates of NHV comparable to those from a non‐host tree. Trap catches were significantly reduced by 50‐70% by individual NHV: trans‐conophthorin, 3‐octanol and 1‐octen‐3‐ol from non‐host bark, 1‐hexanol and (Z)‐3‐hexen‐1‐ol from both leaves and bark and (E)‐2‐hexen‐1‐ol from leaves. Combined NHV signals in binary and ternary blends with the same overall release rates (ca 5 mg/day) showed both redundancy and synergism in their inhibitory effects. The redundancy occurred among individual green leaf alcohols (GLV‐alcohols or C6‐alcohols), C8‐alcohols, and between these two groups, while trans‐conophthorin and verbenone (Vn, from unsuitable host trees) showed significant synergistic effects between each other and with GLV‐alcohols or C8‐alcohols. The coexistence of redundancy and synergism in non‐host chemical signals may indicate different functional levels (non‐host habitats, species, and unsuitable host trees) of these negative volatile signals in the host selection process of conifer bark beetles. We showed an active inhibitory range (AIR) of a NHV‐blend plus Vn on a standard pheromone bait to be at least 2 m, by using a central pheromone trap and surrounding concentric barrier trap rings with radii of 1, 2, and 4 m. The influx of bark beetles flying across concentric rings within the AIR was reduced by 55–99%, depending on the distance to the central pipe trap. Our findings support the hypothesis that as mixed forests have greater semiochemical diversity than pure host stands; they disturb olfactory guided host choice, and may reduce the possibility of outbreaks of conifer‐infesting bark beetles. The synergistic effects as well as the active inhibitory range found in this study also suggest that optimal combinations of these NHV and verbenone may have potential in protecting forests against I. typographus by reducing or stopping attacks on suitable host trees. Mixed stands with higher semio‐chemical diversity disturb olfactory guided host choice and reduce the risk for outbreaks of specialist herbivores.. This ‘semiochemical‐diversity hypothesis’ provides new support to the general ‘stability‐diversity hypothesis’.

Evaluating companion planting and non-host masking odors for protecting roses from the Japanese beetle (Coleoptera: Scarabaeidae).

Effectiveness of companion planting, and use of nonhost masking odors were evaluated under field conditions for protecting roses against the Japanese beetle, Popillia japonica Newman. Three reputedly effective companion species, rue (Ruta graveolens L.), zonal geranium (Pelargonium x hortorum Bailey), and garlic chives (Allium scheonparum L.) were interplanted with roses in replicated garden plots. Numbers of beetles on these roses were compared with rose-only control plots on 6 d during beetle flight. The masking odor hypothesis was tested by hanging mesh bags of aromatic herbs or other sources of reputedly repellent nonhost volatiles around potted roses in the field. Treatments included crushed red pepper (Capsicum frutescens L.), fennel seeds (Foeniculm vulgare Miller), crushed spearmint (Mentha picata L.), cedar shavings (Juniperus sp.), osage orange fruits (Maclura pomifera (Raif) Schneid.), and fleshy gingko seeds (Gingko biloba L.). No treatment significantly reduced numbers of beetles relative to the controls. Interplanting with geraniums significantly increased numbers of Japanese beetles on roses. Similarly, roses surrounded by sachets with fennel seeds, cedar shavings, crushed red pepper, or osage orange fruits had significantly more beetles than the control plants on two or more sample dates. Our results suggest that the use of companion or reputedly repellent plants or plant odors probably will be ineffective for protecting roses or other highly-susceptible ornamentals from P. japonica. Use of such tactics in an effort to discourage other garden pests might even increase Japanese beetle damage in those plantings.

Disruption by conophthorin of the kairomonal response of sawyer beetles to bark beetle pheromones.

Antennally active nonhost angiosperm bark volatiles were tested for their ability to reduce the response of three common species of coniferophagous wood-boring Cerambycidae to attractant-baited multiple funnel traps in the southern interior of British Columbia. Of the nonhost volatiles tested, only conophthorin was behaviorally active, disrupting the attraction of sawyer beetles, Monochamus spp., to traps baited with the host volatiles alpha-pinene and ethanol and the bark beetle pheromones ipsenol and ipsdienol. Conophthorin did not affect the attraction of sawyer beetles to the host kairomones alpha-pinene and ethanol in the absence of bark beetle pheromones, nor did it have any behavioral effect on adults of Xylotrechus longitarsis, which were not attracted to bark beetle pheromones. These results indicate that conophthorin does not act as a general repellent for coniferophagous Cerambycidae, as it seems to do for many species of Scolytidae, but has the specific activity of disrupting the kairomonal response of sawyer beetles to bark beetle pheromones.

Fine structure of antennal sensilla basiconica and their detection of plant volatiles in the eucalyptus woodborer, Phoracantha semipunctata Fabricius (Coleoptera: Cerambycidae)

The ultrastructure and distribution pattern of two types of basiconic sensilla (I and II) on the antennal flagellum of both sexes of Phoracantha semipunctata (Coleoptera: Cerambycidae) was investigated by scanning and transmission electron microscope. Both types are thin-walled multiporous sensilla and occur mostly along the anterior border of the Fl1–Fl6 flagellomeres, while on the distal flagellomeres (Fl7–Fl9) they are more evenly distributed on both surfaces. Clusters of sensilla basiconica II are found on the distal half of the anterior border of the Fl1–Fl6 flagellomeres. Sensilla basiconica I have one bipolar sensory cell with a branched distal dendrite, whereas the sensilla basiconica II contain two bipolar sensory cells with branched distal dendrites. No sexual dimorphism was found in the fine structure and distribution pattern of both types of sensilla basiconica. Responses from single sensory cells to host and non-host plant odors were examined, using gas chromatography linked with electrophysiological recordings. Most cells associated with each sensillum type were narrowly tuned, each specialized for the detection of one or two chemically related compounds. No clear functional distinction between the two morphological types of sensilla was found, although the few cells that responded specifically to non-host volatiles were associated with sensilla basiconica II.

Protection of lodgepole pines from mass attack by mountain pine beetle, Dendroctonus ponderosae, with nonhost angiosperm volatiles and verbenone

AbstractA number of angiosperm nonhost volatiles (NHVs) and green leaf volatiles (GLVs) were tested alone and as supplements to the antiaggregation pheromone, verbenone, for their ability to disrupt attack by the mountain pine beetle (MPB), Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae), on lodgepole pine, Pinus contorta Dougl. ex Loud. var. latifolia Engel. Preliminary experiments led to a refined NHV blend [benzyl alcohol, guaiacol, benzaldehyde, nonanal, salicylaldehyde, and conophthorin] and a refined GLV blend [(Z)‐3‐hexen‐1‐ol and (E)‐2‐hexen‐1‐ol]. In a 20‐replicate experiment, NHV and GLV groups both singly, and verbenone alone, significantly reduced MPB mass attack on pheromone‐baited trees and on trees within 5 m of the pheromone‐baited trees. Both blends in combination with verbenone reduced the number of mass attacked, baited trees to three out of 20 compared to 20 out of 20 of the baited controls. Each binary combination was also effective at reducing mass attack. In these experiments, all tested repellents were released from devices stapled to trees at the same point as the pheromone bait, suggesting that the repellency could have been to a point source, rather than to the whole tree. Therefore, in two further experiments bands of release devices were wrapped around the treated trees and the pheromone bait was removed from the treated trees. In one experiment, when the aggregation pheromone bait was suspended between pairs of trees treated with the NHV blend plus GLV blend plus verbenone, only three out of 25 treated pairs had mass attack on at least one member of the pair. In the other 60‐replicate experiment, with no pheromone baits present, attack occurred on 13 untreated and 11 banded trees, all in the path of a large advancing infestation. However, the mean attack density on the banded trees was significantly reduced to a level below the 40 attacks m−2 of bark surface required to kill a healthy lodgepole pine. As a result of these experiments, operational trials are recommended.

Non-Host Volatiles Disrupt the Response of the Stenographer Bark Beetle, Ips sexdentatus (Coleoptera: Scolytidae), to Pheromone-Baited traps and Maritime Pine Logs

Non-host volatiles (NHV) were tested on antennae of Ips sexdentatus with coupled gas chromatographic-electroantennographic detection (GC-EAD). Significant antennal responses were found to aggregation pheromone components, ipsdienol and amitinol, an attraction inhibitor, verbenone, and non-host bark volatiles extracted from Betula pendula, including trans-conophthorin (tC) and alcohols. The tC, a blend of three green leaf alcohols (C6-alcohols), and a blend of two bark alcohols (C8-alcohols) were tested in combination for their ability to disrupt the attraction of the stenographer bark beetle to pheromone-baited traps, unbaited and pheromone-baited maritime pine logs. The strongest disruptive effect resulted from the addition of the tC combined with the blends of NHV alcohols at high release rate, achieving an 83% reduction in trap catches, 89% reduction of attacks on unbaited pine logs, and 60% on baited logs. It is proposed that the two types of NHV have an additive effect, tC playing a major role in pheromone disruption while the alcohols would interrupt host specific signals. The results suggest that I. sexdentatus uses both bark and green leaf volatiles from non-host tree species in the host selection process. These NHV are promising disruptants, which could be used to prevent stenographer bark beetle attacks on log piles or standing trees in forest. A mixture of conifers and broad-leaved species would also disturb olfactory guided host selection supporting the assumption that more diverse forests are less prone to pest insect outbreaks.

Olfactory responses of Ips duplicatus from inner Mongolia, China to nonhost leaf and bark volatiles.

Leaf and bark volatiles from nonhost angiosperm trees were tested on Ips duplicatus by gas chromatographic-electroantennographic detection (GC-EAD) and by pheromone-baited traps in Sweden and Inner Mongolia, China, respectively. GC-EAD analysis of the headspace volatiles from fresh bark chips of Betula pubescens revealed trans-conophthorin, two green leaf volatiles (GLVs): 1-hexanol and (Z)-3-hexen-1-ol, and two C8 alcohols: 3-octanol and 1-octen-3-ol, that consistently elicited antennal responses by I. duplicatus. The identification of these EAD-active compounds was confirmed in further GC-EAD recordings with synthetic mixtures. Antennal responses were also found to synthetic (E)-2-hexen-1-ol and linalool, which have been identified from the leaves of nonhost birch and aspen species. No antennal responses of I. duplicatus were found to hexanal, (E)-2-hexenal, and (Z)-3-hexyl acetates. In field trapping experiments, blends of EAD-active green leaf alcohols or C8 alcohols, or transconophthorin alone resulted in significant reductions (27-60%) in the number of I. duplicatus captured compared with pheromone-baited traps. The unsuitable host compound, verbenone (Vn), also significantly reduced trap catches by up to 60% in both experiments. The strongest disruptive effect resulted from the addition of the combination of green leaf alcohols, C8 alcohols, and verbenone to the pheromone trap, which caused an 84% reduction in trap catch. The blend of two green leaf aldehydes plus the acetate increased the trap catches in 1998 and had no negative or positive effects in 1999. Our results suggest that these nonhost volatiles (NHVs) are important olfactory signals used by I. duplicatus in host selection. They may have great significance in developing semiochemical-based management programs for I. duplicatus by reducing or stopping attacks on suitable hosts.

Potential for Nonhost Volatiles as Repellents in Integrated Pest Management of Ambrosia Beetles

Semiochemical-based mass trapping of the striped ambrosia beetle, Trypodendron lineatum (Olivier) (Coleoptera: Scolytidae), has been the cornerstone of an integrated pest management (IPM) programme for ambrosia beetles on the British Columbia coast since 1981. However, there is no available tactic of protecting logs from attack that could be incorporated into the IPM programme. We tested nonhost volatiles (NHVs) from the bark of angiosperm trees for their ability to disrupt catches of T. lineatum in multiple-funnel traps baited with the aggregation pheromone lineatin. In one set of experiments, a blend of 1-hexanol and benzyl alcohol caused 77.9% and 80.0% reduction in captures of males and females, respectively, and in another a blend of methyl salicylate and salicylaldehyde caused reductions of 65.0% for males and 66.9% for females. All four NHVs combined caused reductions in captures for males and females of 82.3% and 81.4%, respectively, not much greater than to the blend of 1-hexanol and benzyl alcohol. However, because both blends were active alone, their redundancy when combined lends confidence to the selection of the four-component blend for operational testing. Although disruption was increased when a 16-component NHV blend was tested, or when (±)−(E)-conophthorin was added to the four-component blend, addition of more compounds to the four-component blend was not considered operationally or economically justifiable. When deployed from low-density polyethylene tubes stapled along the length of pheromone-baited conifer logs, this blend caused prolonged and significant reductions in landing by T. lineatum and also by Gnathotrichus sulcatus (LeConte) and G. retusus (LeConte) (Coleoptera: Scolytidae). However, attacking beetles generally overcame the NHV treatment by the end of the flight period, leading to similar attack densities on treated and control logs. Therefore, we recommend that further operational investigations explore using repellent NHVs in combination with disruptive visual, tactile or gustatory stimuli.

ELECTROPHYSIOLOGICAL AND BEHAVIOURAL RESPONSES OF TOMICUS PINIPERDA AND TOMICUS MINOR (COLEOPTERA: SCOLYTIDAE) TO NON-HOST LEAF AND BARK VOLATILES

AbstractLeaf and bark volatiles from non-host birches, Betula pendula Roth. and Betula pubescens Ehrh. (Betulaceae), and aspen, Populus tremula L. (Salicaceae), were tested on spring-dispersing Tomicus piniperda (L.) and Tomicus minor (Hart.) by gas chromatographic – electroantennographic detection (GC–EAD) and by attractant-baited traps in southern Sweden. GC–EAD analysis of the head-space volatiles from fresh bark chips of B. pendula revealed two green leaf alcohols, 1-hexanol and (Z)-3-hexen-1-ol, that consistently elicited antennal responses by T. piniperda and T. minor. Further analyses with synthetic mixtures showed that the antennae of these two Tomicus species also responded to other green leaf alcohols, such as (E)-2-hexen-1-ol found from the non-host leaves, and C8-alcohols, 3-octanol and 1-octen-3-ol, from bark of non-host birches and aspen. No antennal responses of the Tomicus species were observed to green leaf C6-aldehydes and C6-acetate or to non-host bark volatiles like trans-conophthorin, benzaldehyde, salicylaldehyde, and benzyl alcohol. In field trapping experiments, blends of electrophysiologically active green leaf alcohols or C8-alcohols resulted in reductions (> 60%) in the number of T. piniperda captured compared with that for the kairomone-baited trap. When these two blends were combined, trap catch was further reduced (90%), which was not significantly different from that for the blank control. Neither the blend of two green leaf aldehydes plus the acetate nor the bark compounds trans-conophthorin or benzyl alcohol reduced trap catches. Tomicus minor had a response pattern similar to that of T. piniperda. Hylurgops palliatus (Gyll.) (Coleoptera: Scolytidae) was attracted to the combination of kairomone and verbenone but not to kairomone and was not affected by the blends of green leaf volatiles. Our results suggest that selected leaf–bark C6-alcohols and the bark C8-alcohols may have potential in developing semiochemical-based management programs against both pine shoot beetles by repelling them from suitable breeding and feeding sites.

Bark volatiles from nonhost angiosperm trees of spruce bark beetle, Ips typographus (L.) (Coleoptera: Scolytidae): Chemical and electrophysiological analysis

Volatiles from bark of three nonhost angiosperm trees of Ips typographus (Coleoptera: Scolytidae) (Betula pendula, B. pubescens, and Populus tremula) were collected by headspace sampling and direct solvent extraction in June 1998, and identified and quantified by coupled gas chromatographic-mass spectrometry (GC-MS). Only small amounts of bark volatiles were detected in the aerations in situ from undamaged stems of the nonhost trees. In headspace volatiles from bark chips the two birch species had a similar odour profile, with two sesquiterpene hydrocarbons, α-zingiberene and α-santalene, as the most dominant components. Bark of P. tremula emitted significantly less sesquiterpenes and more green leaf volatiles (GLVs) than the two birch species did. Solvent extraction of fresh bark gave similar volatile composition for the two birches compared to the headspace of bark chips, but large differences were found in P. tremula. Coupled gas chromatographic-electroantennographic detection analysis (GC-EAD) of the headspace volatiles from fresh bark chips of the three nonhost species revealed five compounds that consistently elicited antennal responses by I. typographus. The strongest antennal responses were elicited by trans-conophthorin, (5S,7S)-(–)-7-methyl-1,6-dioxaspiro[4.5]decane with optical purity of ca. 90% (S,S). The other four antennally active bark volatiles were 1-hexanol, (Z)-3-hexen-1-ol, 3-octanol and 1-octen-3-ol, which had similar electroantennogram (EAG) dose-response curves and response thresholds. (±)-trans-Conophthorin showed a different, linear EAG dose-response curve, with a 10 times lower response threshold than the other GC-EAD active compounds, similar to the pheromone component, (−)-(4S)-cis-verbenol. These results suggest that not only the green leaf alcohols from leaves of the angiosperm trees but also the nonhost bark volatiles could be used by I. typographus as long-range olfactory cues to discriminate between its conifer host and the nonhosts, birch and aspen.

Cherry Bark Tortrix, Enarmonia Formosana: Olfactory Recognition of and Behavioral Deterrence by Nonhost Angio- and Gymnosperm Volatiles

We tested the hypothesis that males and females of the cherry bark tortrix (CBT), Enarmonia formosana, antennally perceive and behaviorally respond to volatiles from nonhost plants. Volatiles from flowering cherry trees, Prunus serrulata Kwanzan, and from nonhost trees, including trembling aspen, Populus tremuloides, grand fir, Abies grandis, Norway spruce, Picea abies, and Scots pine, Pinus sylvestris, were captured on Porapak Q and extracts analyzed by coupled gas chromatographic–electroantennographic detection (GC-EAD). Compounds that elicited responses from male and female antennae were identified by coupled GC–mass spectrometry (MS) and by comparative GC-MS and GC-EAD with authentic standards. In field cage and field experiments, nonanal from aspen trees and (±)-α-pinene from coniferous trees were effective in reducing captures of male CBT in pheromone-baited traps and deterring oviposition by female CBT on cherry blocks. Recognition of nonhost volatiles, such as nonanal and α-pinene, may allow male and/or female CBT to avoid trees that provide inadequate concealment from predators during calling, resting, and copulation and that are unsuitable for oviposition and development of offspring. Nonhost volatiles may also be exploited for control of CBT by disrupting both mate- and host-finding.

Habitat Preferences of Three Congeneric Braconid Parasitoids: Implications for Host-Range Testing in Biological Control

Abstract Cotesia flavipes, C. sesamiae, and C. chilonis are parasitoids of stemboring noctuids and pyralids of gramineous plants. We tested the response of these parasitoids to volatiles from a range of host and nonhost grasses and volatiles from nongrass, nonhost plants. We found that the three species were differentially attracted to grasses and that their preference patterns were consistent with host/host–plant records from the field. None of the three species was attracted to volatiles from nongrass plants. For two of the three parasitoids, grasses that were damaged by a host were more attractive than undamaged grasses and damaged, previously less-favored grasses became more attractive than undamaged, previously favored grasses. Damage by a host did not increase the attraction of nongrass plants to parasitoids. We suggest that, for certain parasitoids, testing preference for habitat plants could help to determine their ecological host range and therefore aid in matching parasitoids to target crops, as well as streamlining testing for impacts against nontarget species.

Behavioral and electrophysiological responses of Aphids to host and nonhost plant volatiles

Alate and apterous virginoparae ofAphis fabae Scop, and alate virginoparae ofBrevicoryne brassicae (L.), walking in a linear track olfactometer, were attracted by odor from leaves of their host plants.A. fabae responded to odor from undamaged but not damaged bean leaves. Gynoparae (autumn migrants) ofA. fabae, however, did not respond to their host plant (spindle,Euonymus europaeus) odor. Odors of certain nonhost plants masked the attractiveness of the host plant leaves, but tansy (Tanacetum vulgare) and summer savory (Satureja hortensis) volatiles repelledB. brassicae andA. fabae, respectively. 3-Butenyl isothiocyanate attractedB. brassicae andLipaphis erysimi (Kalt.), the latter species being more sensitive in both behavioral and electrophysiological studies. Isothiocyanate receptors were found on the antennae ofA. fabae, which was repelled by these compounds, 4-pentenyl isothiocyanate being the most active.

Preferences of matedHeliothis virescens andH. subflexa females for host and nonhost volatiles in a flight tunnel

In flight-tunnel bioassays, mated femaleHeliothis subflexa (Gn.) moths demonstrated in dual-choice tests a significant preference for volatiles from an extract of their only known host,Physalis spp. (groundcherry). However,H. virescens (F.), a polyphagous species, responded positively by anemotaxis to extracts from susceptible tobacco, cotton,Desmodium tortuosum (host plants), and groundcherry, a nonhost.H. virescens females did not fly to volatiles emanating from an extract of a resistant tobacco cultivar.