Host selection behavior mediated by differential landing rates of the walnut twig beetle,Pityophthorus juglandis,and associated subcortical insect species,on two western North American walnut species,Juglans californica and J. major

The walnut twig beetle, Pityophthorus juglandis Blackman (Coleoptera: Scolytidae), vectors a phytopathogenic fungus, Geosmithia morbida Kolařík et al. (Hypocreales), which causes thousand cankers disease (TCD) in walnut (Juglans sp.) and wingnut (Pterocarya sp., both Juglandaceae) trees. We investigated an early point in disease inception in two walnut species – Juglans californica S. Wats. and Juglans major (Torr. ex Sitsgr.) Heller – native to riparian forests of the western USA by comparing P. juglandis flight and landing responses to small-diameter branch sections. Twenty unbaited branch sections (10 each of J. californica and J. major) were presented in a completely randomized design to populations of P. juglandis at the USDA Agricultural Research Service, National Clonal Germplasm Repository (NCGR) Juglans collection located at Wolfskill Experimental Orchards (Winters, CA, USA) and at the California State University, Chico, Agricultural Teaching and Research Center (ATRC, Chico, CA). These assays were carried out within a 4- to 6-year period when weekly flight surveys with aggregation pheromone-baited multiple funnel traps revealed that P. juglandis flight activity–abundance was higher at the NCGR than at the ATRC. For the landing rate assays, adhesive-coated acetate sheets were wrapped around the branch sections and exchanged weekly. Three assays were completed at the NCGR (assays 1–3), whereas one assay was completed at the ATRC (assay 4). Landing rates on these traps were compared between J. californica and J. major. Two additional assays (5 and 6) were completed at the NCGR to compare responses to branch sections of J. californica and to similarly sized cardboard tubes (negative control). All six assays were completed over a 4-year span during the 4- to 6-year weekly flight survey period. Pooled landing rates of male and female P. juglandis (assays 1–4) demonstrated a preference by both sexes for J. californica over J. major. In assay 5 there was no preference by males or females for J. californica over the negative control, perhaps due to the low flight activity–abundance of P. juglandis during the assay. When repeated at a time of higher flight activity–abundance (assay 6), male and female landing rates on J. californica exceeded those on the negative control. Females of the invasive fruit-tree pinhole borer (an ambrosia beetle), Xyleborinus saxeseni (Ratzeburg), and an invasive bark beetle, Hypothenemus eruditus Westwood (both Coleoptera: Scolytidae), showed relatively higher flight responses than either sex of P. juglandis during most assays, suggesting higher population densities of these two other invasive species at the two orchards or a greater sensitivity to host volatiles. Xyleborinus saxeseni and H. eruditus preferred to land on J. major over J. californica and on J. californica over the negative control. Similarly, an invasive longhorned beetle, Nathrius brevipennis (Mulsant) (Coleoptera: Cerambycidae), showed a significant preference for J. major over J. californica, but not for J. californica over the negative control. More male N. brevipennis were trapped than females at both study sites [sex ratio ranged from 5:1 (assay 6) to 39:1 (assay 4)], and flight occurred only in the spring and early summer months. Another ambrosia beetle trapped at the NCGR and ATRC, Xyleborus affinis Eichhoff, represented the first records of this species from western North America. In summary, flight responses recorded in some of our assays for P. juglandis and several other subcortical insects on Juglans indicate that host preference by these insects may be determined by long-range olfactory cues that do not involve pheromones.     

Life history and geographical distribution of the walnut twig beetle,Pityophthorus juglandis (Coleoptera: Scolytinae), in southern Europe

In September 2013, the walnut twig beetle (WTB) Pityophthorus juglandis Blackman, a species native to Mexico and south‐western USA, was recorded for the first time in Europe, in northern Italy. The collected adults were found to be vector of the fungus Geosmithia morbida Kola?ik, Freeland, Utley & Tisserat, an aggressive pathogen causing thousand cankers disease in walnut (Juglans spp.). To determine the geographical distribution of the WTB and the main aspects of biology, phenology and voltinism, an intensive survey of the main walnut plantations near the site of the first finding was conducted in 2014. The beetles began to fly with a mean air temperature of about 18°C (mid‐May) and continued until late October. Two partially overlapping generations occurred, with the second taking place in late September. The WTB was found in 14 of the 27 monitored walnut plantations. The infested sites were spread over four different non‐contiguous administrative provinces belonging to two regions (Veneto and Lombardy) of northern Italy. The most distant infested plantations were about 130 km apart along a west–east gradient, and about 70 km along a north–south gradient. In this respect, the distribution area of the WTB in northern Italy may be prudently estimated at about 4200 km². Molecular analysis of the collected individuals showed no genetic differences among the six sampled P. juglandis populations, suggesting that a few individuals might have arrived in Italy through a single introduction event and then spread over the territory. Given the quick mortality of infested walnuts and the wide distribution area, eradication strategies appear unrealistic. Possible strategies of biological control or local chemical treatments must be investigated.     

Walnut twig beetle landing rates differ between host and nonhost hardwood trees under the influence of aggregation pheromone in a northern California riparian forest

1. Host selection behaviour of the walnut twig beetle (WTB) among hardwood trees was investigated in a riparian forest in northern California by monitoring the landing rate of the beetle with sticky traps on branches baited with 3-methyl-2-buten-1-ol, the male-produced aggregation pheromone.
2. The assay was conducted over 7 days (22 May to 29 May 2017) and compared landing rates on branches of six nonhost species paired with northern California black walnut, Juglans hindsii (the host).
3. A total of 2242/1192 WTB were collected on branches of host/nonhost pairs, and more WTB landed on J. hindsii than on nonhosts in 42 of 58 instances. Female landing rate generally exceeded male landing rate, which underscores the influence of the male-produced synthetic pheromone in this system.
4. Landing rates of WTB males, females, and the combined sexes on boxelder, Acer negundo, and valley oak, Quercus lobata, did not differ significantly from the landing rates on J. hindsii, suggesting that these two nonhost riparian hardwoods do not repel WTB (in the context of the aggregation pheromone).
5. Significantly fewer WTB landed on Oregon ash, Fraxinus latifolia, river red gum, Eucalyptus camaldulensis, Fremont cottonwood, Populus fremontii, and red willow, Salix laevigata, than on J. hindsii, which suggests that these four nonhosts may repel one or both sexes of WTB in the context of the aggregation pheromone. Future analysis of the volatiles from these four hardwood species may lead to the discovery of semiochemical repellents for WTB.

     

Tribolium confusum responses to blends of cereal kernels and plant volatiles

In this study, we report on the behavioural responses of the Tribolium confusum to 6 blends of cereal volatiles. There were tested four doses (1 ng/min, 10 ng/min, 100 ng/min and 1000 ng/min in 50 μl of hexane applied on filter paper). A Y‐tube experiment revealed that T. confusum females and males were attracted to the blend 1, 4 and 5 at the concentrations between 1 and 10 ng/min. Confused T. confusum females and males were not attracted to any concentration of blend 2 and 3. Yet the beetle females and males were repelled by the highest concentrations (1000 ng/min) for all the blends tested and also by the concentration 100 ng/min of all the blends tested, except for blend 1 and 4. Females and males were also repelled by the three blend 6 concentrations tested (10, 100 and 1000 ng/min).     

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

Brandt's voles ( Microtus brandti ) are small native mammals that inhabit the grasslands of Inner Mongolia, China. The species is considered a pest, particularly during population outbreaks, which have increased in frequency since 1970 from 1 every 7 years to 1 every 3 to 5 years. Using historical records taken between 1948 and 1998, we found that there was significant correlation between years for which the monthly averages of the Southern Oscillation Index (SOI) were consistently high, and years in which outbreaks occurred. Also there was a tendency for outbreaks not to occur in years with precipitation above or below average. For some years at some sites, annual or biannual estimates are available for the density of Brandt's vole populations. We found that the seasonal rate of increase over the non-breeding season from autumn to spring was negatively correlated with the density in autumn. The rate of increase over the breeding season from spring to autumn was independent of the density in spring but instead, reflects the species' preference for habitat with short, sparse grass; populations do not persist in highly degraded grasslands or in tall, dense grassland. The link between outbreaks and climatic indices, and the numerical response of Brandt's voles to particular habitat characteristics, suggest that current grazing intensity tends to maintain grass at low height in years with average precipitation. The substantial increase in livestock numbers over the last 50 years appears to have increased the number of years when the balance of grazing and plant growth favours high rates of increase in Brandt's vole populations, and hence, there has been an increase in the frequency of outbreaks.     

Development of lady beetle attractants from floral volatiles and other semiochemicals for the biological control of aphids

Aphids are among the most destructive phytophagous pests of host plants, because of their rapid reproduction, parthenogenesis, extensive crop damage, and the transmission of many plant viruses. Since lady beetles are important predatory natural enemies of aphids, developing lady beetle attractants to increase their field abundance is vital for aphid control. Floral volatiles and other semiochemicals are reportedly attractive to lady beetles. In this research, a total of 58 floral volatiles were tested by Y-tube olfactometer assays, among which 29 were highly attractive to both Harmonia axyridis (Coleoptera: Coccinellidae) and Coccinella septempunctata (Coleoptera: Coccinellidae). Meanwhile, the results of wind tunnel trials showed that only isoamyl acetate, α-humulene, trans-3-hexen-1-ol, methyl salicylate, and β-pinene lure these two species. Thereafter, 15 semiochemicals from pests, natural enemies, and pest-infested crops were mixed with the selected floral volatiles, to determine optimum formulations for attracting lady beetles through wind tunnels and further field trials. Eventually, formulas (1) α-humulene: β-pinene: methyl salicylate: trans-3-hexen-1-ol = 1:3:3:10; (5) α-humulene: β-pinene: methyl salicylate:1-nonanal = 1:3:3:10; (8) α-humulene: β-pinene: methyl salicylate: indole = 1:3:3:10 (1, 5, and 8 are labels used for the various formulations in field trials) were successfully verified to be attractive to lady beetles in both pumpkin and wheat fields. These formulations will be of great significance in developing integrated pest management strategies for aphid control.     

Plant volatiles mediate attraction to host and non-host plant in apple fruit moth, Argyresthia conjugella

Plant volatiles mediate host finding in insect herbivores and lead to host fidelity and habitat‐specific mating, generating premating reproductive isolation and facilitating sympatric divergence. The apple fruit moth, Argyresthia conjugella Zeller (Lepidoptera: Argyresthiidae), is a particularly suitable species to study the cues and behavioural mechanisms leading to colonization of a new host: it recurrently oviposits on the non‐host plant, apple Malus domestica Borkh. (Rosaceae), where the larvae cannot complete their development. The larval host of the apple fruit moth (Lepidoptera, Argyresthiidae), is rowan Sorbus aucuparia L. (Rosaceae). Fruit setting in rowan, however, fluctuates strongly over large areas in Scandinavia. Every 2–4 years, when too few rowanberries are available for egg laying in forests, apple fruit moth females oviposit instead on apple in nearby orchards, but not on other fruits, such as pear or plum. This poses the question of which cues mediate attraction to rowan and apple, and how apple fruit moth discriminates rowan from apple. Chemical analysis and antennal recordings showed that 11 out of 15 rowan volatiles eliciting an antennal response in A. conjugella females co‐occur in rowan and apple headspace, in a different proportion. In the field, A. conjugella was attracted to several of these plant volatiles, especially to 2‐phenyl ethanol, methyl salicylate, and decanal. Addition of anethole to 2‐phenyl ethanol had a strong synergistic effect, the 1 : 1 blend is a powerful attractant for A. conjugella males and females. These results confirm that volatiles common to both plants may account for a host switch in A. conjugella from rowan to apple. Some of the most attractive compounds, including 2‐phenyl ethanol, anethole, and decanal, which have been found in several apple cultivars, were not present in the headspace of the apple cultivar, Aroma, which is also susceptible to attack by A. conjugella. This supports the idea that the odour signal from apple is suboptimal for attraction of A. conjugella, but is nonetheless sufficient for attraction, during times when rowan is not available for egg laying.     

Effects of bark beetle pheromones on the attraction of Monochamus alternatus to pine volatiles

Abstract We evaluated the attraction of Monochamus alternatus Hope (Coleoptera: Cerambycidae), Dryocoetes luteus Blandford and Orthotomicus erosus Wollaston (Coleoptera: Curculionidae: Scolytinae) to multiple-funnel traps baited with the pine volatiles, ethanol and (+)-α-pinene and the bark beetle pheromones, ipsenol and ipsdienol. M. alternatus were attracted to traps baited with ethanol and (+)-α-pinene but not those baited with ipsdienol and ipsenol. Ipsdienol and ipsenol decreased catches of M. alternatus in traps baited with ethanol and (+)-α-pinene. Traps baited with either binary combinations of ethanol and (+)-α-pinene or ipsdienol and ipsenol were attractive to D. luteus and O. erosus. The addition of ipsenol and ipsdienol to traps baited with ethanol and (+)-α-pinene synergized attraction of O. erosus but not D. luteus.     

Responses of stored-product Anobiidae to pheromone lures and plant-derived volatiles

Experiments were conducted in different locations to investigate responses of adult Stegobium paniceum and Lasioderma serricorne (Col., Anobiidae) to different commercially available or prototype fabrications of their female‐produced sex pheromones. The results showed that the number of S. paniceum captured in traps baited with the commercially available lures was significantly higher than those captured in traps baited with the prototype stegobinone lures. The three commercially available brands of serricornin lures investigated were equally effective in capturing L. serricorne. In a related study, we conducted a 9‐week trapping experiment to determine if responses of L. serricorne to serricornin can be enhanced by the presence of host plant odours. Traps were baited with serricornin alone, serricornin plus dried red chilli (Capsicum frutescens L.) or red chilli alone. The results showed that the number of beetles captured in traps baited with a combination of serricornin and chilli volatiles were significantly higher than in traps baited with pheromone or chilli volatiles alone, indicating that potential exist for improved monitoring or mass trapping of L. serricorne by combining pheromone with plant‐derived volatiles present in Capsicum spp.     

The role of beetle and host volatiles in host colonization in the European oak bark beetle, Scolytus intricatus (Ratzeburg) (Col., Scolytidae)

Abstract:  To understand the role of chemical signals involved in Scolytus intricatus (Ratzeburg) (Col., Scolytidae) host colonization, the attractiveness of intact and beetle colonized host material was investigated in the field and in the laboratory. In the field, chemical signals operating at long range were investigated by means of sticky traps. In the laboratory, close-range chemical interactions were investigated with an arena olfactometer. Field experiments showed no differences in the attractiveness between infested and non-infested host material. On the contrary, laboratory experiments revealed higher attractiveness of infested host and beetle-produced frass in comparison with intact host and mechanically produced sawdust respectively. Laboratory data also disclosed the attractiveness of beetle extracts of both sexes. Our data show that: (1) host kairomones play an important role during host colonization, and that (2) S. intricatus does not use a sex-specific secondary attractant system. Differences between results of field and laboratory trials are discussed.     

棉铃虫齿唇姬蜂对植物挥发物和寄主性信息素腺体化合物的EAG反应

测试了棉铃虫齿唇姬蜂Campoletis chlorideae Uchida对58种植物挥发物和5种寄主性信息素腺体化合物的EAG反应。在100 μg的刺激剂量下,棉铃虫齿唇姬蜂对C₅～C₇脂肪醇的EAG反应最强,碳链延长或缩短都将导致反应的降低;对脂肪醛、酮、酸和酯都有一定的反应。棉铃虫齿唇姬蜂对萜烯的EAG反应很低,对氧化萜的反应普遍升高。3种芳香化合物均可激起棉铃虫齿唇姬蜂较强的EAG反应。剂量反应曲线表明,具有EAG活性的化合物激起的反应强度与化合物的剂量呈正相关,而2种萜烯——α-蒎烯和反式石竹烯,在测定的剂量范围内EAG活性都很低。棉铃虫齿唇姬蜂对寄主性信息素腺体化合物也有EAG反应,用100 μg和1 000 μg的寄主性信息素刺激,雄蜂的反应可比雌蜂的反应高出1倍。对植物挥发物在棉铃虫齿唇姬蜂寻找寄主中的作用进行了讨论。     

Field trapping of the flathead oak borer Coroebus undatus (Coleoptera: Buprestidae) with different traps and volatile lures

The flathead oak borer Coroebus undatus F. (Coleoptera: Buprestidae) is one of the primary pests of cork oak Quercus suber L. in the Mediterranean region causing great economic losses to the cork industry. Very little is known about its biology and behavior and, so far, no control measures have been established. We present the results of a pilot study aimed to develop an efficient trapping method for monitoring this harmful pest. In a 3‐year field study, purple‐colored prism traps baited with a mixture of green leaf volatiles (GLVs) from the host have been shown the most effective combination to catch C. undatus adults (solely females) compared to other trap and lure types tested. Wavelength and reflectance measurements revealed that purple traps exhibit reflectance peak values similar to those found in the abdominal and elytral cuticle of both sexes, suggesting the involvement of visual cues for mate location in this species. The data presented are the first to demonstrate captures of adults of the genus Coroebus by an attractant‐based trapping method.     

Relationship between a host plant compound,myrcene and pheromone production in the bark beetle, IPS paraconfusus

The pheromonal components, ipsenol and ipsdienol were found in increasing quantities in hindguts of only the male sex of Ips paraconfusus following exposure of both sexes to a series of increasing concentrations of myrcene vapour. Hindguts of female and male beetles contained similar quantities of myrcene and other volatile compounds associated with myrcene exposure. Unexposed beetles of both sexes did not contain detectable amounts of any volatile compound. This indicates that myrcene induces or is a precursor for sex-specific pheromone biosynthesis.     

Olfactory antennal responses to plant volatiles in apterous virginoparae of the vetch aphidMegoura viciae

Electroantennogram (EAG) responses were recorded from apterous virginoparae of the vetch aphidMegoura viciae Buckton (Homoptera, Aphididae) to more than eighty volatile compounds in order to investigate its sensory ability to perceive plant odours. The response profile ofM. viciae reveals a differential sensitivity for the array of plant volatiles tested. The whole group of general green leaf volatiles is very stimulatory. In addition to (E)-2-hexenal, the following compounds of this group elicit large EAG responses: (E)-2-heptenal, 1-octenol-3, hexyl acetate, (Z)-3-hexenyl acetate, hexanol-1, hexanal, 2-heptanone and 3-octanone. Relatively large EAGs are also produced by 4-methoxybenzaldehyde (p-anisaldehyde), hexanonitrile, heptanonitrile, 1,6-hexanedithiol, butyl isothiocyanate, 4-pentenyl isothiocyanate, (−)-(1S)-β-pinene, (+)-(S)-carvone, (−)-(R)-carvone, α-terpineol, linalool and citronellal. The nitriles are the most effective of all plant volatiles tested. Structure-activity relationships occur in various groups of chemicals and members of the green leaf volatiles, benzaldehydes, isothiocyanates and monoterpenes are ranked accordingly. In the group of green leaf volatiles, aliphatic aldehydes are more stimulating than the corresponding alcohols. EAG responses to series of saturated aliphatic alcohols and aldehydes reveal that C₆ and C₇ compounds are the most stimulatory. Dose-response curves show that the rank order of EAG response amplitudes hardly changes at lower dosages. It is concluded thatM. viciae perceives general plant volatiles as well as more-specific components, such as nitriles and isothiocyanates, associated with the odour blends of non-host plant species.     

Electrophysiological and behavioural responses of Scyphophorus acupunctatus (Col., Curculionidae) to Agave tequilana volatiles

Abstract:  The weevil Scyphophorus acupunctatus Gyllenhal (Col., Curculionidae) is the most important insect pest of cultivated agaves in Mexico. The objective of this study was to search for potential attractants for this weevil species from the freshly cut fleshy leaves of healthy Agave tequilana Weber var. Blue plants. Combined gas chromatography-electroantennography (GC-EAD) analysis of A. tequilana volatile extracts showed that seven peaks elicited antennal responses from males and females. Five of these peaks were identified by gas chromatography-mass spectrometry (GC-MS) as o -xylene, α -pinene, 3-carene, γ -terpinene and linalool. Electroantennogram (EAG) records of both sexes to 1-, 10- and 100- μ g-stimulus load of these five compounds showed that there was a dose effect on the EAG responses for linalool, 3-carene and α -pinene, but not for γ -terpinene and o -xylene. There were no sexual differences between male and female EAG responses to any of the compounds tested. Y-tube olfactometer bioassays of the compounds showed that males and females were attracted to α -pinene, 3-carene, γ -terpinene and/or linalool at doses of 1 and 10  μ g, while weevils were repelled by linalool at a dose of 100  μ g.     

Attractiveness of host volatiles combined with background visual cues to the tea leafhopper,Empoasca vitis

The tea green leafhopper, Empoasca vitis (Göthe) (Hemiptera: Cicadellidae), is a serious pest of tea plants. We examined the behavioral responses of E. vitis adults to odors from the shoots of three host plants in a Y‐tube olfactometer with background visual cues. The host plants were tea [Camellia sinensis (L.) Kuntze (Theaceae)], peach [Prunus persica (L.) Siebold & Zucc. (Rosaceae)], and grapevine [Vitis vinifera L. (Vitaceae)]. Volatiles from the shoots were analyzed. Both yellow‐green and gold backgrounds enhanced the olfactory responses of E. vitis adults to tea plant odors, and this enhancement was stronger under a high light intensity. On the yellow‐green background, E. vitis adults significantly preferred the odors from shoots of the three host plants compared with clean air. Moreover, E. vitis adults preferred grapevine odor over the tea plant odor. The volatile blends of the three plant species were distinctly different. Peach plant shoots emitted the greatest amount of volatiles, whereas grapevine shoots released the greatest diversity of compounds. These results provide evidence that background visual cues could enhance the response of E. vitis adults to host‐plant volatiles. The leafhoppers can discern different host odors, suggesting the possibility of using peach plant and grapevine odors to monitor and manage this pest in tea plantations.     

Diapause status of females affects attraction of male pear psylla, Cacopsylla pyricola, to volatiles from female-infested pear shoots

A companion study showed that male pear psylla, Cacopsylla pyricola (Förster) (Homoptera: Psyllidae) were attracted to volatiles from pear shoots infested with post-diapause females. The present study compared the behavioral response of males to diapause and post-diapause females. Assays were done using a Y-tube olfactometer. We collected male and female winterform psylla from pear orchards at regular intervals between late October (early diapause) and late February (post-diapause). Female-infested shoots were not attractive to males until the February samples, coinciding with ovarian maturation and onset of mating in the field. A second set of assays was done in which we manipulated diapause status in the laboratory either by exposing psylla to a long-day photoperiod or by treating insects with an insect growth regulator, fenoxycarb. In the photoperiod experiments, both short-day and long-day males preferentially selected long-day (post-diapause) females over short-day (diapause) females. Fenoxycarb-treated males preferred fenoxycarb-treated (post-diapause) females over untreated (diapause) females; untreated males showed no preferences. Results support observations made elsewhere that male winterform pear psylla perceive and are attracted to volatile odors associated with pear shoots infested with post-diapause females.     

Synthetic host volatiles increase efficacy of trap cropping for management of Colorado potato beetle, Leptinotarsa decemlineata (Say)

Abstract 1 The attractiveness of pitfall traps baited with a synthetic host volatile attractant to colonizing adult Colorado potato beetle, Leptinotarsa decemlineata (Say) was evaluated in a field setting. 2 Significantly more postdiapause, colonizing adult L. decemlineata were captured in baited than unbaited pitfall traps. 3 The potential for this synthetic kairomone to enhance the efficacy of trap cropping as a management tool was evaluated by comparing conventionally managed plots with like‐sized plots bordered by either attractant‐treated trap crop or untreated trap crop. 4 More postdiapause, colonizing adults, egg masses and small larvae were present in attractant‐treated trap crops than in untreated trap crops. 5 There were no significant differences in egg mass and small larvae densities between plots bordered by attractant‐treated trap crops and conventionally managed plots, but there were significantly fewer large larvae and adult beetles in conventionally managed plots. 6 Plant canopy area of conventionally managed plots was significantly greater than in plots bordered by either type of trap crop. 7 Yields for conventionally managed plots and plots bordered by attractant‐treated trap crops did not differ, and less insecticide (44%) was applied to plots bordered by attractant‐treated trap crops.     

Ovarian development of Agrilus planipennis: effects of age and mating status and influence on attraction to host volatiles

Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a major pest of ash trees, Fraxinus spp. (Oleaceae), in North America. This study investigated the timing of reproductive development in female beetles and the influence of female reproductive maturity on attraction to host volatiles. Based on dissections of females of increasing age, females with access to males for mating, and thus presumed mated, developed mature eggs only after 18–24 days. In contrast, female beetles reared without access to males, and thus unmated, did not develop mature eggs at any age. Chemical analysis of cuticular hydrocarbons detected the contact sex pheromone, 9‐methyl‐pentacosane, in cohorts of females which were 8–9 days old and older, supporting previous research that this compound signals sexual maturity to males. Results from field‐trapping bioassays demonstrated that stage of female reproductive maturity influenced their attraction to host volatiles: females caught on traps baited with foliar volatiles contained eggs and ovarioles that were significantly less developed than those on traps baited with bark sesquiterpenes. However, our results revealed that females with immature stages of ovarioles and undeveloped eggs, such as those observed in unmated females, were rarely ever caught on traps baited with either of the host volatile lures. Further research on host compounds attractive to immature females is critical for early detection and possible control of A. planipennis populations during the extended pre‐oviposition period.     

Attraction of the grasshopper, Melanoplus sanguinipes, to host plant odors and volatile components

The attraction of the polyphagous grasshopper, Melanoplus sanguinipes (F.), to odors from plant foliage or to chemical components of these odors was tested in a glass Y-tube olfactometer. Humidified air was passed at equal flow rates through a sample chamber containing plant material and an empty control chamber and then through the Y-tube to the holding chamber containing the test insect. Solutions of volatile chemicals in water were metered at a constant rate into the sample air stream with a syringe pump. Insects moving upwind were recorded after entering either the sample or control arm of the Y-tube. Both nymphs and adults were strongly attracted to the odor of chopped and intact seedling foliage of perennial ryegrass and wheat. Chopped leaves but not intact leaves of sorghum and alfalfa also were significantly attractive. The major components of ryegrass odor from both chopped and stem-cut leaves were Z-hex-3-en-1-yl acetate, Z-hex-3-en-1-ol, and pent-1-en-3-ol, in that order, with lesser amounts of E-hex-2-enal. Chopped leaves released many more minor components. The major components when tested individually or in binary and ternary mixtures were significantly attractive to grasshoppers compared to humidified air but not to the degree of whole plant odor. However, a quartenary mixture simulating the odor blend had levels of attractancy equal to that of chopped grass odor. Blends of these 5- and 6-carbon unsaturated alcohols, esters, and aldehydes volatilizing from green plants probably play an important role as olfactory cues for orientation of grasshoppers to food plants.

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Résumé L'attraction de M. sanguinipes (F.) par l'odeur du feuillage et des composés chimiques de ces odeurs a été examinée dans un olfactomètre en tube de verre en Y. Des flux identiques d'air humidifié étaient introduits dans une enceinte contenant le matériel végétal et dans une enceinte témoin, et, via le tube en Y, dans l'enceinte contenant l'insecte à étudier. Des solutions aqueuses de substances volatiles étaient introduites à un taux constant dans le courant d'air grâce à une seringue. Les insectes se déplaçant contre le vent étaient enregistrés après pénétration dans une branche déterminée du tube en Y. Larves et adultes étaient fortement attirés par l'odeur de feuillage intact ou coupé de semis de Lolium perenne et de blé (Triticum aestivum). Les feuilles coupées, mais non les feuilles intactes de sorgho (Sorghum bicolor) et de luzerne (Medicago sativa) étaient, elles aussi, significativement attractives. Les principales substances constituant de l'odeur de feuilles de Lolium perenne, tant coupées qu'intactes, étaient dans l'ordre de Z-hex-3-en-1-yl acétate, le Z-hex-3-en-1-ol et le pent-1-en-3-ol, et dans une moindre mesure, E-hex-2-enal. Les feuilles coupées libéraient beaucoup plus de composés secondaires. Les principaux constituants testés, seuls ou en mélanges binaires ou ternaires, étaient significativement attractifs, mais moins que l'odeur totale de la plante. Toutefois, un mélange quaternaire, simulant le mélange odorant, avait le même pouvoir attractif que l'odeur de la plante entière. L'union de ces alcools, esters et aldéhydes à 5- et 6-carbones non saturés, volatilisés à partir des plantes vertes, jouent probablement un grand rôle comme signaux orientateurs lors de l'attraction des criquets par leur plantes alimentaires.