Electrophysiological and Behavioral Responses of the Multicolored Asian Lady Beetle, <Emphasis Type="Italic">Harmonia axyridis</Emphasis> Pallas,to Sesquiterpene Semiochemicals

The role of two volatile sesquiterpenes, (E)-β-farnesene and (−)-β-caryophyllene, in the chemical ecology of the multicolored Asian lady beetle, Harmonia axyridis Pallas, was investigated by using both electrophysiological and behavioral techniques. (E)-β-Farnesene is the major component of the alarm pheromone of most aphid species, which are preyed on by H. axyridis. (−)-β-Caryophyllene was previously isolated from the headspace volatiles above overwintering and aggregated H. axyridis females. These sesquiterpenes elicited significant electroantennogram (EAG) activity from both H. axyridis male and female antennae. In a four-arm olfactometer, male and female H. axyridis were highly attracted toward (E)-β-farnesene, whereas only males were attracted to (−)-β-caryophyllene. In a bioassay technique that used a passively ventilated plastic box, both male and female H. axyridis aggregated in the (−)-β-caryophyllene-treated side of the box. These results support the potential usefulness of (E)-β-farnesene and (−)-β-caryophyllene in push–pull strategies that use H. axyridis as a biological control agent in aphid-infested sites or to control this new urban pest in residential structures.     

Essential Compounds in Herbivore-Induced Plant Volatiles that Attract the Predatory Mite <Emphasis Type="Italic">Neoseiulus womersleyi</Emphasis>

Carnivorous arthropods use volatile infochemicals emitted from prey-infested plants in their foraging behavior. Although several volatile components are common among plant species, the compositions differ among prey–plant complexes. Studies showed that the predatory mite Neoseiulus womersleyi is attracted only to previously experienced plant volatiles. In this study, we identified the attractant components in prey-induced plant volatiles of two prey–plant complexes. N. womersleyi reared on Tetranychus kanzawai-infested tea leaves showed significant preference for a mixture of three synthetic compounds [mimics of the T. kanzawai-induced tea leaves volatiles: (E)-β-ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), and (E,E)-α-farnesene] at a level comparable to that for T. kanzawai-induced tea plant volatiles. However, mixtures lacking any of these compounds did not attract the predatory mites. Likewise, N. womersleyi reared on T. urticae-infested kidney bean plants showed a significant preference for a mixture of four synthetic compounds [mimics of the T. urticae-induced kidney bean volatiles: DMNT, methyl salicylate (MeSA), β-caryophyllene, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene] at a level comparable to that for T. urticae-induced kidney bean volatiles. The absence of any of the four compounds resulted in no attraction. These results indicate that N. womersleyi can use at least four volatile components to identify prey-infested plants.     

Volatiles from a Mite-Infested Spruce Clone and Their Effects on Pine Weevil Behavior

Induced responses by Norway spruce (Picea abies) seedlings to feeding damage by two mite species were studied by analyzing the volatiles emitted during infestation. Four specimens of a Norway spruce (Picea abies L.) clone were infested with mites of Nalepella sp., another four with Oligonychus ununguis, and four were kept mite-free as controls. After a year of infestation, spruce volatiles were collected, analyzed, and identified using SPME-GC-MS. In addition, enantiomers of chiral limonene and linalool were separated by two-dimensional GC. Methyl salicylate (MeSA), (-)-linalool, (E)-β-farnesene, and (E,E)-α-farnesene were the main volatiles induced by both species of mites, albeit in different proportions. The ability of the main compounds emitted by the mite-infested spruces to attract or repel the pine weevil, Hylobius abietis (L.), was tested. (E)-β-farnesene was found to be attractive in the absence of spruce odor, whereas methyl salicylate had a deterrent effect in combination with attractive spruce odor. The other tested compounds had no significant effects on the behavior of the weevils.     

Belowground Chemical Signaling in Maize: When Simplicity Rhymes with Efficiency

Maize roots respond to feeding by larvae of the beetle Diabrotica virgifera virgifera by releasing (E)-β-caryophyllene. This sesquiterpene, which is not found in healthy maize roots, attracts the entomopathogenic nematode Heterorhabditis megidis. In sharp contrast to the emission of virtually only this single compound by damaged roots, maize leaves emit a blend of numerous volatile organic compounds in response to herbivory. To try to explain this difference between roots and leaves, we studied the diffusion properties of various maize volatiles in sand and soil. The best diffusing compounds were found to be terpenes. Only one other sesquiterpene known for maize, α-copaene, diffused better than (E)-β-caryophyllene, but biosynthesis of the former is far more costly for the plant than the latter. The diffusion of (E)-β-caryophyllene occurs through the gaseous rather than the aqueous phase, as it was found to diffuse faster and further at low moisture level. However, a water layer is needed to prevent complete loss through vertical diffusion, as was found for totally dry sand. Hence, it appears that maize has adapted to emit a readily diffusing and cost-effective belowground signal from its insect-damaged roots.     

Plant Volatiles Influence Electrophysiological and Behavioral Responses of <Emphasis Type="Italic">Lygus hesperus</Emphasis>

Previous laboratory studies have shown that the mirid Lygus hesperus is attracted to volatiles emitted from alfalfa; feeding damage increases the amounts of several of these volatiles, and visual cues can enhance attraction further. The present study tested single plant volatiles in electrophysiological and behavioral trials with L. hesperus. Electroantennogram (EAG) analyses indicated that antennae responded to most plant volatiles included in the test, and that when gender differences were observed, males usually were more responsive than females. Antennal responses to the alcohols ((E)-3-hexenol, (Z)-3-hexenol, 1-hexanol), the acetate (E)-2-hexenyl acetate, and the aldehyde (E)-2-hexenal were among the strongest. Moderate responses were observed for (E)-β-ocimene, (E,E)-α-farnesene, (±)-linalool, and methyl salicylate. A dose dependent response was not observed for several terpenes (β-myrcene, β-caryophyllene, (+)-limonene, or both (R)-(+)- and (S)-(−)-α-pinenes). EAG responses, however, were not always consistent with behavioral assays. In Y-tube bioassays, males did not exhibit a positive behavioral response to any of the compounds tested. Instead, males were repelled by (E)-2-hexenyl acetate, (±)-linalool, (E,E)-α-farnesene, and methyl salicylate. In contrast, female L. hesperus moved upwind towards (R)-(+)-α-pinene, (E)-β-ocimene, and (E,E)-α-farnesene, and showed a negative response towards (Z)-3-hexen-1-ol, (S)-(−)-α-pinene, and methyl salicylate. This study emphasizes the use of multiple approaches to better understand host plant finding in the generalist herbivore L. hesperus.     

Plant Volatiles Enhance Behavioral Responses of Grapevine Moth Males, Lobesia botrana to Sex Pheromone

Plant volatiles play an important role in the lives of phytophagous insects, by guiding them to oviposition, feeding and mating sites. We tested the effects of different host-plant volatiles on attraction of Lobesia botrana males to the female-produced sex pheromone, in a wind tunnel. Addition of volatile emissions from grapevines or individual plant volatiles to pheromone increased the behavioral responses of L. botrana males over those to pheromone alone. At a low release rate (under-dosed) of pheromone, addition of (E)-β-caryophyllene, (Z)-3-hexenyl acetate, 1-hexanol, or 1-octen-3-ol increased all behavioral responses, from activation to pheromone source contact, while addition of (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-β-farnesene, (Z)-3-hexenol, or methyl salicylate affected only the initial behavioral responses. Dose–response experiments suggested an optimal release ratio of 1:1000 (sex pheromone: host plant volatile). Our results highlight the role of plant volatiles in the sensory ecology of L. botrana.     

Emission of Volatile Organic Compounds After Herbivory from <Emphasis Type="Italic">Trifolium pratense</Emphasis> (L.) Under Laboratory and Field Conditions

Plants emit a wide range of volatile organic compounds in response to damage by herbivores, and many of the compounds have been shown to attract the natural enemies of insect herbivores or serve for inter- and intra-plant communication. Most studies have focused on volatile emission in the laboratory while little is known about emission patterns in the field. We studied the emission of volatiles by Trifolium pratense (red clover) under both laboratory and field conditions. The emission of 24 compounds was quantified in the laboratory, of which eight showed increased emission rates after herbivory by Spodoptera littoralis caterpillars, including (E)-β-ocimene, the most abundant compound, (Z)-β-ocimene, linalool, (E)-β-caryophyllene, (E,E)-α-farnesene, 4,8-dimethyl-1,3,7-nonatriene (DMNT), 1-octen-3-ol, and methyl salicylate (MeSA). While most of these compounds have been reported as herbivore-induced volatiles from a wide range of plant taxa, 1-octen-3-ol seems to be a characteristic volatile of legumes. In the field, T. pratense plants with varying herbivore damage growing in established grassland communities emitted only 13 detectable compounds, and the correlation between herbivore damage and volatile release was more variable than in the laboratory. For example, the emission of (E)-β-ocimene, (Z)-β-ocimene, and DMNT actually declined with damage, while decanal exhibited increased emission with increasing herbivory. Elevated light and temperature increased the emission of many compounds, but the differences in light and temperature conditions between the laboratory and the field could not account for the differences in emission profiles. Our results indicate that the release of volatiles from T. pratense plants in the field is likely to be influenced by additional biotic and abiotic factors not measured in this study. The elucidation of these factors may be important in understanding the physiological and ecological functions of volatiles in plants.     

Vicia faba–Lygus rugulipennis Interactions: Induced Plant Volatiles and Sex Pheromone Enhancement

The profiles of volatile chemicals emitted by Vicia faba plants damaged by Lygus rugulipennis feeding, and by feeding plus oviposition, were shown to be quantitatively different from those released by undamaged plants. Samples of volatile chemicals collected from healthy plants, plants damaged by males as a consequence of feeding, plants damaged by females as a consequence of feeding and oviposition, plants damaged by feeding with mated males still present, and plants damaged by feeding and oviposition with gravid females still present, showed significant differences in the emission of hexyl acetate, (Z)-β-ocimene, (E)-β-ocimene, (E)-β-caryophyllene, and methyl salicylate. In particular, treatments with mated females present on plants had a significant increase in emission levels of the above compounds, possibly due to eggs laid within plant tissues or active feeding, compared with undamaged plants and plants damaged by males feeding, with or without insects still present. Furthermore, the pheromonal blend released by mated L. rugulipennis females, mainly comprising hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal, was enhanced when females were active on broad bean plants, whereas such an increase was not observed in males. Both sexes gave electroantennogram responses to green leaf volatiles from undamaged plants and to methyl salicylate and (E)-β-caryophyllene emitted by Lygus-damaged plants, suggesting that these compounds may be involved in colonization of host plants by L. rugulipennis. In addition, mated males and females were responsive to hexyl butyrate, (E)-2-hexenyl butyrate, and (E)-4-oxo-2-hexenal released by mated females on V. faba, indicating that these substances could have a dual function as a possible aggregation pheromone in female–female communication, and as a sex pheromone in female–male communication. An erratum to this article can be found at     

The Tea Weevil, <Emphasis Type="Italic">Myllocerinus aurolineatus</Emphasis>, is Attracted to Volatiles Induced by Conspecifics

The tea weevil, Myllocerinus aurolineatus (Voss) (Coleoptera: Curculionidae), is a leaf-feeding pest of Camellia sinensis (O.Ktze.) with aggregative behaviors that can seriously reduce tea yield and quality. Although herbivore-induced host plant volatiles have been shown to attract conspecific individuals of some beetle pests, especially members of the Chrysomelidae family, little is known about the volatiles emitted from tea plants infested by M. aurolineatus adults and their roles in mediating interactions between conspecifics. The results of behavioral bioassays revealed that volatile compounds emitted from tea plants infested by M. aurolineatus were attractive to conspecific weevils. Volatile analyses showed that infestations dramatically increased the emission of volatiles, (Z)-3-hexenal, (Z)-3-hexenol, (E)-β-ocimene, linalool, phenylethyl alcohol, benzyl nitrile, indole, (E, E)-α-farnesene, (E)-nerolidol, and 31 other compounds. Among the induced volatiles, 12 chemicals, including γ-terpinene, benzyl alcohol, (Z)-3-hexenyl acetate, myrcene, benzaldehyde, (Z)-3-hexenal, and (E, E)-α-farnesene, elicited antennal responses from both sexes of the herbivore, whereas (E)-β-ocimene elicited antennal responses only from males. Using a Y-tube olfactometer, we found that six of the 13 chemicals, γ-terpinene, benzyl alcohol, (Z)-3-hexenyl acetate, myrcene, benzaldehyde, and (Z)-3-hexenal, were attractive to both males and females; two chemicals, (E/Z)-β-ocimene and (E, E)-α-farnesene, were attractive only to males; and four chemicals, (E)-4,8-dimethyl-1,3,7-nonatriene, phenylethyl alcohol, linalool, and (Z)-3-hexenol, were attractive only to females. The findings provide new insights into the interactions between tea plants and their herbivores, and may help scientists develop new strategies for controlling the herbivore.     

<Emphasis Type="Italic">cis</Emphasis>-Jasmone Elicits Aphid-Induced Stress Signalling in Potatoes

Elicitation of plant defense signaling that results in altered emission of volatile organic compounds (VOCs) offers opportunities for protecting plants against arthropod pests. In this study, we treated potato, Solanum tuberosum L., with the plant defense elicitor cis-jasmone (CJ), which induces the emission of defense VOCs and thus affects the behavior of herbivores. Using chemical analysis, electrophysiological and behavioral assays with the potato-feeding aphid Macrosiphum euphorbiae, we showed that CJ treatment substantially increased the emission of defense VOCs from potatoes compared to no treatment. Coupled GC-electroantennogram (GC-EAG) recordings from the antennae of M. euphorbiae showed robust responses to 14 compounds present in induced VOCs, suggesting their behavioral role in potato/aphid interactions. Plants treated with CJ and then challenged with M. euphorbiae were most repellent to alate M. euphorbiae. Principal component analysis (PCA) of VOC collections suggested that (E)-2-hexenal, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), (E)-β-farnesene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), methyl salicylate (MeSA), CJ, and methyl benzoate (MeBA) were the main VOCs contributing to aphid behavioral responses, and that production of TMTT, (E)-β-farnesene, CJ, and DMNT correlated most strongly with aphid repellency. Our findings confirm that CJ can enhance potato defense against aphids by inducing production of VOCs involved in aphid-induced signalling.     

Volatile Emissions from Aesculus hippocastanum Induced by Mining of Larval Stages of Cameraria ohridella Influence Oviposition by Conspecific Females

Larval stages of the horse chestnut leafminer Cameraria ohridella can completely destroy the surface of horse chestnut leaves, Aesculus hippocastanum. This study investigated the effect of the degree of leaf browning caused by the insect’s larvae on olfactory detection, aggregation, and oviposition of C. ohridella adults. The influence of A. hippocastanum flower scent on oviposition of the first generation was also evaluated. Utilizing gas chromatography coupled with parallel detection by mass spectrometry and electroantennography (GC-MS/EAD), more than 30 compounds eliciting responses from antennae of C. ohridella were detected. Oviposition and mining by C. ohridella caused significant changes in the profile of leaf volatiles of A. hippocastanum. After oviposition and subsequent mining by early larval stages (L1–L3), substances such as benzaldehyde, 1,8-cineole, benzyl alcohol, 2-phenylethanol, methyl salicylate, (E)-β-caryophyllene, and (E,E)-α-farnesene were emitted in addition to the compounds emitted by uninfested leaves. Insects were able to detect these compounds. The emitted amount of these substances increased with progressive larval development. During late larval stages (L4, L5) and severe loss of green leaf area, (E,E)-2,4-hexadienal, (E/Z)-linalool oxide (furanoid), nonanal, and decanal were also released by leaves. These alterations of the profile of volatiles caused modifications in aggregation of C. ohridella on leaves. In choice tests, leaves in early infestation stages showed no significant effect on aggregation, whereas insects avoided leaves in late infestation stages. Further choice tests with leaves treated with single compounds led to the identification of substances mediating an increase or decrease in oviposition.     

Volatile Emissions from <Emphasis Type="Italic">Alnus glutionosa</Emphasis> Induced by Herbivory are Quantitatively Related to the Extent of Damage

Plant volatile organic compounds (VOCs) elicited in response to herbivory serve as cues for parasitic and predatory insects. Knowledge about quantitative relationships between the extent of herbivore-induced damage and the quantities of VOCs released is scarce. We studied the kinetics of VOC-emissions from foliage of the deciduous tree Alnus glutinosa induced by feeding activity of larvae of the geometrid moth Cabera pusaria. Quantitative relationships between the intensity of stress and strength of plant response were determined. Intensity of biotic stress was characterized by herbivore numbers (0–8 larvae) and by the amount of leaf area eaten. The strength of plant response was characterized by monitoring (i) changes in photosynthesis, (ii) leaf ultrastructure, and (iii) plant volatiles. Net assimilation rate displayed compensatory responses in herbivore-damaged leaves compared with control leaves. This compensatory response was associated with an overall increase in chloroplast size. Feeding-induced emissions of products of the lipoxygenase pathway (LOX products; (E)-2-hexenal, (Z)-3-hexenol, 1-hexanol, and (Z)-3-hexenyl acetate) peaked at day 1 after larval feeding started, followed by an increase of emissions of ubiquitous monoterpenes peaking on days 2 and 3. The emission of the monoterpene (E)-β-ocimene and of the nerolidol-derived homoterpene 4,8-dimethyl-nona-1,3,7-triene (DMNT) peaked on day 3. Furthermore, the emission kinetics of the sesquiterpene (E,E)-α-farnesene tended to be biphasic with peaks on days 2 and 4 after start of larval feeding. Emission rates of the induced LOX products, of (E)-β-ocimene and (E,E)-α-farnesene were positively correlated with the number of larvae feeding. In contrast, the emission of DMNT was independent of the number of feeders. These data show quantitative relationships between the strength of herbivory and the emissions of LOX products and most of the terpenoids elicited in response to feeding. Thus, herbivory-elicited LOX products and terpenoid emissions may convey both quantitative and qualitative signals to antagonists of the herbivores. In contrast, our data suggest that the feeding-induced homoterpene DMNT conveys the information “presence of herbivores” rather than information about the quantities of herbivores to predators and parasitoids.     

From Terpenoids to Aliphatic Acids: Further Evidence for Late-Instar Switch in Osmeterial Defense as a Characteristic Trait of Swallowtail Butterflies in the Tribe Papilionini

We compared the chemical compositions of the osmeterial secretions of fourth and fifth (last) instars of eight swallowtail species of the tribe Papilionini. Four species (Papilio demoleus, P. polytes, P. paris, and P. macilentus) are Asian Rutaceae-feeding swallowtails. The other four (Chilasa epicydes, C. agestor, P. troilus, and P. glaucus) represent more distant clades within the Papilionini and species with larval hosts in other plant families. We conducted a quantitative analysis for six species, but only qualitative analysis for P. glaucus and C. agestor. In all eight species, regardless of larval host plant, secretions of the fourth instar principally consisted of mono- and sesquiterpene hydrocarbons, whereas those of the fifth instar comprised aliphatic acids and their esters. Consistent with earlier findings, our results suggest that this “heterogeneous” pattern of osmeterial chemistry, not seen in other tribes, may characterize the Papilionini as a whole. Unlike those of most Papilio species, the fourth and fifth instars of Chilasa species resemble each other in body coloration. Thus, the heterogeneous osmeterial pattern is not necessarily associated with color change in papilionid larvae. The major terpenoids identified in fourth instar larval secretions from the six species were α-pinene, sabinene, β-myrcene, limonene, β-phellandrene, (Z)-β-ocimene, (E)-β-ocimene, p-mentha-1,4(8)-diene, β-elemene, β-caryophyllene, (E)-β-farnesene, (3Z,6E)-α-farnesene, (Z)-α-bisabolene, germacrene-A, (E)-α-bisabolene, and germacrene-B. The profiles for individual species differed both qualitatively and quantitatively from one another, and certain species also secreted methyl 3-hydroxy-n-butyrate and oxygenated sesquiterpenes in relatively large proportions. Secretions from fifth instars were composed of varying proportions of isobutyric, 2-methylbutyric, and acetic acids, and methyl and ethyl (minor) esters of both isobutyric and 2-methylbutyric acids. The heterogeneity of osmeterial chemistry in the tribe Papilionini may represent fine-tuning of chemical defense in response to shifting predation pressures as the larvae age and grow.     

Variation in Herbivore and Methyl Jasmonate-Induced Volatiles Among Genetic Lines of <Emphasis Type="Italic">Datura wrightii</Emphasis>

Many plant species produce volatile organic compounds after being damaged by herbivores. The production of volatiles also may be induced by exposing plants to the plant hormone, jasmonic acid, or its volatile ester, methyl jasmonate. This study addresses the induction of the production volatile organic compounds among genetic lines of Datura wrightii. Within populations, some plants produce glandular trichomes, whereas others produce nonglandular trichomes, and trichome phenotype is controlled by a single dominant gene. Glandular trichomes not only confer resistance to some herbivorous insects, but they also inhibit many natural enemies of those herbivores. Because of the potential benefit of natural enemies that use volatile cues to find individuals of the non-glandular phenotype, it is reasonable to ask if plants of D. wrightii that differ in trichome morphology might produce different blends of volatile compounds. Volatile compounds were collected from eight genetic lines of plants that had been backcrossed for three generations. Volatiles were collected from pairs of sibling plants before and after insect damage or treatment with methyl jasmonate. Within each pair, one sib expressed glandular trichomes and the other expressed nonglandular trichomes. Overall, plants produced an array of at least 17 compounds, most of which were sesquiterpenes. Total production of volatiles increased from 3.9- to 16.2-fold among genetic lines after insect damage and from 3.6- to 32-fold in plants treated with methyl jasmonate. The most abundant compound was (E)-β-caryophyllene. This single compound comprised from 17 to 59% of the volatiles from insect-damaged plants and from 24 to 88% of the volatiles from plants treated with methyl jasmonate, depending upon genetic line. The production of (E)-β-caryophyllene by the original male parents of the eight genetic lines was significantly related to the mean production of their third-generation backcross progeny indicating that the variation in the production of (E)-β-caryophyllene was inherited. Blends did not differ qualitatively or quantitatively between sibs expressing glandular or nonglandular trichomes.     

Identification of Host Attractants for the Ethiopian Fruit Fly, <Emphasis Type="Italic">Dacus ciliatus</Emphasis> Loew

The Ethiopian fruit fly, Dacus ciliatus, is an oligophagous pest of cucurbit crops, particularly melons, cucumbers, and marrows (summer squash). The present study aimed to identify host attractants for D. ciliatus and was guided by a behavioral bioassay and an electrophysiological assay. We tested volatile compounds from the fruits of a host plant, ripe and unripe Galia melon, Cucumis melo var. reticulates. Both sexes were attracted to melon volatiles. Those of ripe melon were preferred. Gas chromatography-electroantennographic detection analysis of the behaviorally active ripe melon volatiles consistently showed that 14 compounds elicited similar antennal responses from both sexes. Twelve compounds were identified by gas chromatography-mass spectrometry (GC-MS) using GC-MS libraries, retention indices (RI), and authentic standards. The electrophysiological activities of the compounds that were present at sufficient levels for identification, benzyl acetate, hexanyl acetate, (Z)-3-hexenyl acetate, (Z)-3-octenyl acetate, octanyl acetate, (Z)-3-decenyl acetate, and (E)-β-farnesene, were evaluated at six different dosage levels by using electroantennography (EAG). Benzyl and hexanyl acetates elicited dose responses only in males, while other tested compounds elicited dose responses in both sexes. The strongest responses were observed for doses between 100 ng and 10 μg. The dose response, in terms of attractiveness to synthetic compounds within the active range (as determined by EAG), also was evaluated in the behavioral bioassay. Synthetic acetates were attractive to both sexes when tested individually. Significant attraction was observed when individual compounds were applied in the bioassay arena at doses of 0.5–1 μg/dispenser. Blends of compounds in equal proportions also were attractive to the insects. The most attractive blend was a mixture of four or five identified acetates. The addition of an equal proportion of (E)-β-farnesene to this mixture had a deterrent effect.     

Methyl Salicylate,a Soybean Aphid-Induced Plant Volatile Attractive to the Predator <Emphasis Type="Italic">Coccinella septempunctata</Emphasis>

Induced volatiles provide a signal to foraging predatory insects about the location of their prey. In Iowa, early in the growing season of soybean, Glycine max, many predacious seven-spotted lady beetles, Coccinella septempunctata, were observed on plants with heavy infestations of soybean aphid, Aphis glycines. We studied whether the attraction of this beetle is caused by the release of specific volatile compounds of soybean plants infested by aphids. Volatile compounds emitted by soybean plants infested by aphids were compared with those of undamaged, uninfested, and artificially damaged plants. Gas chromatography–mass spectrometry analyses revealed consistent differences in the profiles of volatile compounds between aphid-infested soybean plants and undamaged ones. Significantly more methyl salicylate was released from infested plants at both the V1 and V2 plant growth stages. However, release patterns of two other induced plant volatiles, (d)-limonene and (E,E)-α-farnesene, differed between the two plant growth stages. Gas chromatographic–electroantennographic detection of volatile extracts from infested soybean plants showed that methyl salicylate elicited significant electrophysiological responses in C. septempunctata. In field tests, traps baited with methyl salicylate were highly attractive to adult C. septempunctata, whereas 2-phenylethanol was most attractive to the lacewing Chrysoperla carnea and syrphid flies. Another common lady beetle, the multicolored Asian lady beetle, Harmonia axyridis, showed no preference for the compounds. These results indicate that C. septempunctata may use methyl salicylate as the olfactory cue for prey location. We also tested the attractiveness of some selected soybean volatiles to alate soybean aphids in the field, and results showed that traps baited with benzaldehyde caught significantly higher numbers of aphids.     

(<Emphasis Type="Italic">E,E</Emphasis>)-α-Farnesene,an Alarm Pheromone of the Termite <Emphasis Type="Italic">Prorhinotermes canalifrons</Emphasis>

The behavioral and electroantennographic responses of Prorhinotermes canalifrons to its soldier frontal gland secretion, and two separated major components of the secretion, (E)-1-nitropentadec-1-ene and (E,E)-α-farnesene, were studied in laboratory experiments. Behavioral experiments showed that both the frontal gland secretion and (E,E)-α-farnesene triggered alarm reactions in P. canalifrons, whereas (E)-1-nitropentadec-1-ene did not affect the behavior of termite groups. The alarm reactions were characterized by rapid walking of activated termites and efforts to alert and activate other members of the group. Behavioral responses to alarm pheromone differed between homogeneous and mixed groups, suggesting complex interactions. Antennae of both soldiers and pseudergates were sensitive to the frontal gland secretion and to (E,E)-α-farnesene, but soldiers showed stronger responses. The dose responses to (E,E)-α-farnesene were identical for both soldiers and pseudergates, suggesting that both castes use similar receptors to perceive (E,E)-α-farnesene. Our data confirm (E,E)-α-farnesene as an alarm pheromone of P. canalifrons.     

Specialist Leaf Beetle Larvae Use Volatiles from Willow Leaves Infested by Conspecifics for Reaggregation in a Tree

Young, gregariously living larvae of the willow leaf beetles Plagiodera versicolora are known to exhibit characteristic aggregation-dispersion-reaggregation behavior and local fidelity to a host tree. In this study, we investigated whether plant volatiles induced by feeding P. versicolora larvae were involved in the reaggregation behavior. Under laboratory conditions, we conducted dual-choice bioassays and found that the first and second instars discriminated between volatiles from leaves infested by larvae and volatiles from uninfested leaves. The discriminative behavior was dependent on both the time leaves were infested and the age of discriminating larvae. First and second instars preferred odor from 1-d-infested leaves to odor from uninfested leaves, whereas third instars (solitary stage) did not discriminate between these volatile blends. Odor from 2-d-infested leaves was preferred to odor from 1-d-infested leaves by first instars, whereas odor from leaves infested for 3 d was not attractive to these very young larvae. Neither was odor of leaves infested for 1 d and then left uninfested for 1 or 2 d attractive to young larvae. The data suggest that the first and second instars use volatiles from a leaf newly infested by conspecific larvae as one of the reaggregation cues. We detected several herbivore-induced compounds in the headspace of the attractive leaves. Among those, a mixture of synthetic (E)-β-ocimene, (Z)-β-ocimene, allo-ocimene, and linalool was found to attract the larvae.     

Leaf Volatile Emissions of <Emphasis Type="Italic">Betula pendula</Emphasis> during Autumn Coloration and Leaf Fall

Deciduous trees remobilize the nitrogen in leaves during the process of autumn coloration, thus providing a high quality food source for aphids preparing to lay over-wintering eggs. It has been suggested that aphids may use volatile organic compounds (VOCs) to: (a) select leaves where nutrient remobilization has started and induced defenses are reduced; and (b) detect the time of leaf abscission. We analyzed VOCs emitted by the foliage of Betula pendula Roth. during autumn coloration and from leaf litter just after leaf fall. We tested the hypothesis that costly, photosynthesis-related terpenes and other herbivore-induced VOCs related to attraction of aphid parasitoids and predators are reduced during the coloration process. We also investigated if the VOC emission profile of abscising leaves is different from that of early stage yellowing leaves. Enemy-luring compounds (E)-β-ocimene, linalool, and (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) were emitted only from the green foliage. Methyl salicylate (MeSa), known to recruit predatory bugs and attract migrant aphids, was emitted until the first stage of color change. Cis-3-hexenol, an indicator of cellular disintegration, became dominant in the emissions from abscising leaves and from fresh leaf litter. We discuss the ecological significance of the observed changes in birch leaf VOC profiles during the process of autumn senescence.     

Volatiles from Psylla-Infested Pear Trees and Their Possible Involvement in Attraction of Anthocorid Predators

Previous work showed that anthocorid predators aggregate around gauze cages containing Psylla-infested trees in a pear orchard. Because anthocorids responded to odor from Psylla-infested leaves in a laboratory test, it was hypothesized that these aggregative responses in the field were triggered by olfaction of compounds associated with Psylla injury. We present chemical analyses of volatiles from damaged and undamaged plants and studies on behavioral responses of anthocorid predators to compounds released by damaged plants. Leaf headspace volatiles from clean and Psylla-infested pear trees were collected on Tenax and identified by GC-MS after thermodesorption. Twelve volatiles were found exclusively in headspace samples from Psylla-infested leaves. Six were present in significantly higher quantities in samples from infested leaves: the monoterpene, (E,E)-α-farnesene, the phenolic, methyl salicylate, and the green leaf compounds, (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol, 1-hexyl-acetate, and 1-penten-3-ol. These compounds are known to be produced by plants, and damage by pear psyllids seems to trigger their emission. Blend composition varied and was partly correlated with tree or leaf age and degree of Psylla infestation. To study whether compounds associated with leaf injury elicit olfactory responses in anthocorid predators, apple-extracted (E,E)-α-farnesene, synthetic methyl salicylate, and (Z)-3-hexen-1-yl acetate were offered in a Y-tube olfactometer to field-collected adult Anthocoris spp. Significant positive responses were found to both the monoterpene and the phenolic, but not to the green leaf volatile. The results lend support to the hypothesis that predator attraction to herbivore-infested pear trees is mediated by herbivory-induced plant volatiles.