Field attraction of the vine weevil Otiorhynchus sulcatus to kairomones

Morphological and olfactory tree traits influence the susceptibility and suitability of the apple species Malus domestica and M. sylvestris to the florivorous weevil Anthonomus pomorum (Coleoptera: Curculionidae)

The florivorous apple blossom weevil, Anthonomus pomorum (Coleoptera: Curculionidae), is the most economically relevant insect pest of European apple orchards in early spring. Neither efficient monitoring nor ecologically sustainable management of this insect pest has yet been implemented. To identify heritable traits of apple trees that might influence the host selection of A. pomorum, we compared the susceptibility of apple tree species using infestation rates of the domesticated apple, Malus domestica (Rosaceae: Pyreae), and the European crab apple, M. sylvestris. We evaluated the suitability of the two apple species for A. pomorum by quantifying the mass of weevil offspring. Because volatile organic compounds (VOCs) emitted from flower buds of the domesticated apple have previously been suggested to mediate female weevil preference via olfactory cues, we conducted bioassay experiments with blossom buds of both apple species to explore the olfactory preference of adult weevils and, furthermore, identified the headspace VOCs of blossom buds of both apple species through GC-MS analysis. The infestation analysis showed that A. pomorum infested the native European crab apple more prevalently than the domesticated apple, which originated from Central Asia. The European crab apple also appeared to be better suited for weevil larval development than the domesticated apple, as weevils emerging from M. sylvestris had a higher body mass than those emerging from M. domestica. These field observations were supported by olfactory bioassays, which showed that A. pomorum significantly preferred the odor of M. sylvestris buds compared to the odor of M. domestica buds. The analysis of headspace VOCs indicated differences in the blossom bud volatiles separating several M. domestica individuals from M. sylvestris individuals. This knowledge might be employed in further studies to repel A. pomorum from M. domestica blossom buds.

Visual attraction of the European tarnished plant bug Lygus rugulipennis (Hemiptera: Miridae) to a water trap with LED light in chrysanthemum greenhouses and olfactory attraction to novel compounds in Y-tube tests

BACKGROUND

The European tarnished plant bug Lygus rugulipennis Poppius (Hemiptera: Miridae) can cause several types of damage to crops grown in greenhouses and fields, including flower abortion in eggplant, stem and fruit damage in cucumbers, and splits in chrysanthemums. Studies suggest that both male and female L. rugulipennis may be more attracted to traps based on visual attraction than pheromone-based trap. Therefore, the aim of this study was to evaluate the effectiveness of a water trap with LED lights and semiochemicals in trapping L. rugulipennis in the laboratory and greenhouse.

RESULTS

The results showed that water traps equipped with white LED light caught 20 - 30 times more bugs than did the sex pheromone-based traps in greenhouse experiment. During the week of peak flight, the LED water trap caught a total of 29 males and females, whereas the sex pheromone caught only one male. Among the semiochemicals tested in a Y-tube, both males and females were attracted to ß-caryophyllene, but not in the presence of the sex pheromone, whereas both males and females were attracted to pentyl butyrate in the presence of the sex pheromone. The pheromone plus bean plant odor was attractive to the insects, suggesting an interaction between plant odor and pheromone.

CONCLUSION

Overall, the findings of the study showed that the water trap with LED light could be an effective method for trapping L. rugulipennis in greenhouses. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Optimising Vine Weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), Monitoring Tool Design

Simple Summary

Vine weevil remains one of the most economically important insect pests of soft-fruit and ornamental crops globally. Growers currently lack effective monitoring systems to determine presence of vine weevil within crops, meaning that controls are often applied too late to prevent economic losses. Development of improved monitoring systems is currently hindered by a lack of knowledge of whether vine weevil adults select a monitoring tool based on its visual appearance. This study used paper cups as refuges to investigate the importance of colour, shape and position of entrances on monitoring tool efficacy. Results indicate that dark, tall refuges with entrances around their base were preferentially entered by adult vine weevil. This information provides the first steps towards developing improved designs for vine weevil monitoring tools.

Abstract

Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), is an economically important insect pest of horticultural crops. To identify an effective and reliable monitoring system for adult vine weevil, this study investigated the influence of colour, height and entrance position on the efficacy of a model monitoring tool using modified paper cups as refuges. Vine weevil preferences were determined by the number of individuals recorded within a refuge. When provided with a binary choice between black or white refuges, vine weevil adults showed a preference for black refuges. Vine weevils provided with a range of coloured refuges (blue, green, red and yellow) in addition to black and white refuges showed a preference for black and blue over the other colours and white refuges in group choice experiments. Refuge height and entrance position also influenced vine weevil behaviour with individuals exhibiting a preference for taller refuges and those with entrance openings around the refuge base. These results provide insights into refuge selection by adult vine weevils, which can be exploited to improve monitoring tool design. The importance of developing an effective monitoring tool for vine weevil adults as part of an integrated pest management programme is discussed.

Vine Weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae), Management: Current State and Future Perspectives

Vine weevil, also known as black vine weevil, Otiorhynchus sulcatus, has been one of the most economically important pest species of global horticultural crops for the past five decades. This period has seen many changes in crop protection practices, including wide-scale adoption of biological controls such as entomopathogenic nematodes and fungi in place of conventional synthetic insecticides. Despite the experimental efficacy of these controls, growers continue to report significant crop losses associated with vine weevil infestation. We argue that simply switching from synthetic insecticides to biological controls, rather than using these controls as part of an integrated management program, is a key factor in the continued importance of this pest. An improved understanding of vine weevil biology and ecology is at the center of the development of truly integrated pest management programs. To this end, we identify opportunities created through recent vine weevil research and highlight key knowledge gaps in which further research may contribute to improved future management approaches.

The Synthesis of Pentyl Leaf Volatiles and Their Role in Resistance to Anthracnose Leaf Blight

Volatiles are important airborne chemical messengers that facilitate plant adaptation to a variety of environmental challenges. Lipoxygenases (LOXs) produce a bouquet of non-volatile and volatile oxylipins, including C₆ green leaf volatiles (GLVs), which are involved in a litany of plant physiological processes. GLVs are emitted by a diverse array of plant species, and are the best-known group of LOX-derived volatiles. Five-carbon pentyl leaf volatiles (PLVs) represent another widely emitted group of LOX-derived volatiles that share structural similarity to GLVs, however, relatively little is known about their biosynthesis or biological activity. In this study, we utilized PLV-deficient mutants of maize and Arabidopsis and exogenous PLV applications to elucidate the biosynthetic order of individual PLVs. We further measured PLVs and GLVs after tissue disruption of leaves by two popular methods of volatile elicitation, wounding and freeze-thawing. Freeze-thawing distorted the volatile metabolism of both GLVs and PLVs relative to wounding, though this distortion differed between the two groups of volatiles. These results suggest that despite the structural similarity of these two volatile groups, they are differentially metabolized. Collectively, these results have allowed us to produce the most robust PLV pathway to date. To better elucidate the biological activity of PLVs, we show that PLVs induce maize resistance to the anthracnose pathogen, Colletotrichum graminicola, the effect opposite to that conferred by GLVs. Further analysis of PLV-treated and infected maize leaves revealed that PLV-mediated resistance is associated with early increases of oxylipin α- and γ-ketols, and later increases of oxylipin ketotrienes, hydroxytrienes, and trihydroxydienes. Ultimately, this study has produced the most up-to-date pathway for PLV synthesis, and reveals that PLVs can facilitate pathogen resistance through induction of select oxylipins.

Isolation and identification of attractants from the pupae of three lepidopteran species for the parasitoid Chouioia cunea Yang

BACKGROUND

Chouioia cunea Yang (Hymenoptera: Eulophidae) is a parasitic wasp and natural enemy of several lepidopteran pests during their pupal stage. The volatiles from pupae of three hosts, Hyphantria cunea (Arctiidae), Antheraea pernyi (Saturniidae) and Lymantria dispar (Erebidae), were analyzed and compared to elucidate the chemical cues used by C. cunea to locate its hosts.

RESULTS

The attraction of C. cunea to H. cunea pupae has no obvious association with the types of plant leaves consumed by H. cunea before pupation. C. cunea exhibited the strongest attraction to the pupae of H. cunea, followed by those of A. pernyi and L. dispar based on behavioral experiments. Gas chromatography-mass spectrometry and GC-electroantennography (GC-EAD) analyses showed that these three host pupae consisted of essentially the same active volatile components but at different relative amounts. Active components derived from these pupae by GC-EAD were alkanes from C12 to C27, and C. cunea showed different levels of attraction to different single compounds.

CONCLUSION

Host location by C. cunea primarily depends on common compounds emanating from the pupae of several host species. The relative amount of each component varies across host species, guiding host preferences by C. cunea. Optimal blends of several components were identified. Understanding the chemical cues used by C. cunea to locate its host could increase the possibility of developing attractants for parasitic wasps and subsequently increasing the parasitism rate of C. cunea on various hosts. © 2019 Society of Chemical Industry.

Catch me if you can: the influence of refuge / trap design, previous feeding experience, and semiochemical lures on vine weevil (Coleoptera: Curculionidae) monitoring success

BACKGROUND

Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), is one of the most economically important pest species of berry and ornamental crops globally. Monitoring this nocturnal pest can be difficult and time consuming and the efficacy of current tools is uncertain. Without effective monitoring tools, implementation of integrated pest management strategies is challenging. This study tests the relative efficacy of a range of vine weevil monitoring tools. Whether host-plant volatiles and weevil feeding experience influence vine weevil capture is also tested.

RESULTS

Monitoring tool efficacy differed overall between the six monitoring tool designs tested and ranged from catches of 0.4% to 26.7% under semi-field conditions. Previous feeding experience influenced vine weevil behavior. In yew conditioned populations, 39% of the weevils responded to and were retained in the trap baited with yew foliage while 37% of weevils from Euonymus fortunei conditioned populations responded to and were retained in the trap baited with E. forunei foliage. A simple synthetic lure consisting of (Z)-2-pentenol + methyl eugenol also increased vine weevil catches compared with an unbaited trap.

CONCLUSION

Demonstrating differences in the efficacy of different monitoring tool designs is an important first step for developing improved methods for monitoring vine weevil populations within crops. This study presents the first direct comparison of vine weevil monitoring tool designs and indicates that trap efficacy can be improved by baiting with host-plant material or a synthetic lure based on host-plant volatiles. © 2019 Society of Chemical Industry.

Electrophysiological and Behavioral Responses of Adult Vine Weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae), to Host Plant Odors

Vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae), is an economically important pest species in many soft-fruit and ornamental crops. Economic losses arise from damage to the roots, caused by larvae, and to the leaves, caused by adults. As adults are nocturnal and larvae feed below ground, infestations can be missed initially, with controls applied too late. In the absence of a vine weevil sex or aggregation pheromone, the development of an effective semiochemical lure for better management of this pest is likely to focus on host-plant volatiles. Here, we investigate the electrophysiological and behavioral responses of adult vine weevils to volatile organic compounds (VOCs) originating from their preferred host plant Euonymus fortunei, and synthetic VOCs associated with this host when presented individually or as blends. Consistent electroantennographic responses were observed to a range of generalist VOCs. Behavioral responses of weevils to VOCs, when presented individually, were influenced by concentration. Vine weevil adults showed directional movement toward a mixture of seven plant volatiles, methyl salicylate, 1-octen-3-ol, (E)-2-hexenol, (Z)-3-hexenol, 1-hexanol, (E)-2-pentenol, and linalool, even though no, or negative, responses were recorded to each of these compounds presented individually. Similarly, vine weevils showed directional movement toward a 1:1 ratio mixture of (Z)-2-pentenol and methyl eugenol. Results presented here point to the importance of blends of generalist compounds and their concentrations in the optimization of a lure.

Chemical investigations of volatile kairomones produced by Hyphantria cunea (Drury), a host of the parasitoid Chouioia cunea Yang

In tritrophic 'plants-herbivores-natural enemies' systems, there are relatively few reports concerning the role(s) of kairomones in pupal parasitism. Chouioia cunea Yang (Hymenoptera: Eulophidae), an endoparasitic chalcid wasp, parasitizes pupae of the fall webworm (Hyphantria cunea Drury). The role of host-related kairomones was investigated using electroantennogram (EAG) and behavioral techniques. Chemicals from some host stages (pupae) and host by-products (frass), induced arrestment behavior of female parasitoids, while chemicals from prepupae, were inactive. Gas chromatography-mass spectrometry analysis of volatiles collected from pupae, frass and prepupae using solid-phase microextration revealed seven compounds with carbon chain lengths ranging from C4 to C20. All of the chemicals elicited significant EAG responses in C. cunea. Y-tube olfactometer bioassays demonstrated a significant positive response of mated female C. cunea to 1-dodecene. These data provide a better understanding of the host location mechanisms of pupal parasitoid.

Influence of Two Acyclic Homoterpenes (Tetranorterpenes) on the Foraging Behavior of Anthonomus grandis Boh

Previous studies have shown that the boll weevil, Anthonomus grandis, is attracted to constitutive and conspecific herbivore-induced cotton volatiles, preferring the blend emitted by cotton at the reproductive over the vegetative stage. Moreover, this preference was paralleled by the release of the acyclic homoterpenes (tetranorterpenes) (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) in Delta Opal cotton being higher at the vegetative than at the reproductive stage. Here, we evaluated whether this difference in release of acyclic homoterpenes also occurred in other cotton varieties, and if boll weevils could recognize these compounds as indicators of a specific cotton phenological stage. Results showed that cotton genotypes CNPA TB-90, BRS-293 and Delta Opal all produced higher levels of DMNT and TMTT at the vegetative stage than at the reproductive stage and that these homoterpenes allowed for principal component analysis separation of volatiles produced by the two phenological stages. Electroantennograms confirmed boll weevil antennal responses to DMNT and TMTT. Behavioral assays, using Y-tube olfactometers, showed that adding synthetic homoterpenes to reproductive cotton volatiles (mimicking cotton at the vegetative stage in terms of homoterpene levels) resulted in reduced attraction to boll weevils compared to that to unmodified reproductive cotton. Weevils showed no preference when given a choice between plants at the vegetative stage and the vegetative stage-mimicked plant. Altogether, the results show that DMNT and TMTT are used by boll weevils to distinguish between cotton phenological stages.

A host-plant-derived volatile blend to attract the apple blossom weevil Anthonomus pomorum - the essential volatiles include a repellent constituent

BACKGROUND

Plant volatiles are promising cues for trapping pest insects. This study started with a recently identified complex blend released by prebloom apple trees and aimed to reduce the number of compounds in the blend while maintaining the attraction of the target pest, the apple blossom weevil Anthonomus pomorum. An evaluation was made to determine whether attraction to plant volatiles is a general feature in this species.

RESULTS

Laboratory-based bioassays with field-collected weevils demonstrated repellency by volatiles from the non-host walnut, indicating that preference for plant odours is not a general feature in this species. By a subtractive bioassay approach, the original number of compounds in the apple-plant-released blend was stepwise reduced from 12 to 6 while maintaining weevil attraction. This resulting blend was as attractive as the full blend and as a blossom-bud-carrying apple twig. It was found to be composed of two synergistically interacting constituents, of which the first containing benzenoids was behaviourally inactive, and the second comprising the remaining compounds was even repellent.

CONCLUSIONS

This study enhances knowledge of the interaction of behaviourally effective constituents in complex odour blends and contributes to the development of an efficient monitoring system involving plant volatiles for the apple blossom weevil.