A semiochemical view of the ecology of the seed beetle Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae, Bruchinae)

The dried bean beetle, Acanthoscelides obtectus, is an economically important pest of stored legumes worldwide. Tracking the human-aided dispersion of its primary hosts, the Phaseolus vulgaris beans, it is now widespread in most bean-growing areas of the tropics and subtropics. In temperate regions where it can only occasionally overwinter in the field, A. obtectus proliferates in granaries, having multiple generations a year. Despite its negative impact on food production, no sensitive detection or monitoring tools exist, and the reduction of local populations still relies primarily on inorganic insecticides as fumigating agents. However, in the quest to produce more nutritious food more sustainably and healthily, the development of environmentally benign crop protection methods is vital against A. obtectus. For this, knowledge of the biology and chemistry of both the host plant and its herbivore will underpin the development of, among others, chemical ecology-based approaches to form an essential part of the toolkit of integrated bruchid management. We review the semiochemistry of the mate- and host-finding behaviour of A. obtectus and provide new information about the effect of seed chemistry on the sensory and behavioural ecology of host acceptance and larval development

Field response of two cetoniin chafers (Coleoptera, scarabaeidae) to floral compounds in ternary and binary combinations

Several synthetic floral lures have been described for the cetoniin scarabs Cetonia aurata aurata L. and Potosia cuprea Fabr. (Coleoptera, Scarabaeidae), exploiting their olfaction-guided behavioural preference for a wide range of flower volatiles. A ternary mixture of 3-methyl eugenol, 1-phenylethanol and (E)-anethol has previously been described as a powerful synthetic floral attractant for both C. a. aurata and P. cuprea. The first objective of the present research was to test whether isoeugenol and eugenol, with a very similar molecular structure to 3-methyl eugenol, can substitute 3-methyl eugenol in the ternary blend. All baited traps caught significantly more of both species than unbaited control traps, however, traps containing 3-methyl eugenol caught significantly more than those with either isoeugenol or eugenol. This indicates a fine tuning in behavioural response to 3-methyl eugenol. The second objective was to devise simpler attractant combinations for C. a. aurata and P. cuprea, based on previous field studies with synthetic floral compounds. Both C. a. aurata and P. cuprea showed strong attraction to the combination of 2-phenylethanol and 4-methoxyphenethyl alcohol, while the combination of 2-phenylethanol and 1,2,4-trimethoxybenzene resulted in medium-size catches, however, mostly catching P. cuprea. This level of selectivity may lead to the development of more selective lures for P. cuprea, and provide a better understanding of the feeding-related olfactory ecology of the two important pest chafer species

Metabolite-Based Resistance in Wheat Varieties to Aphid Virus Vectors: Progress and Future Opportunities

Cereal aphids Sitobion avenae and Rhopalosiphum padi are vectors for the barley yellow dwarf virus (BYDV) which, in addition to direct aphid damage, causes severe yield loss in wheat. Insecticides have commonly been used to control these pests. The advent of insecticide resistance spreading across aphid populations and the push to reduce insecticide use, however, requires new approaches to control aphid numbers. Screening studies have identified wheat varieties with natural product-based aphid resistance, which can act as an alternative to insecticides. Resistance induced by natural products include volatile organic compound-mediated (antixenotic) and development-modifying (antibiotic) processes. Full characterisation of these resistance mechanisms is still required and associated challenges, such as the influence of biotic and abiotic interactions, need to be addressed prior to their implementation into integrated pest management (IPM) or engineered into modern elite wheats. In this review, current literature on natural product-based S. avenae and R.padi resistance in wheat is discussed, outlining current knowledge gaps and challenges and highlighting future work required

Pheromone stereochemical specificity in the biology of the bean beetle Acanthoscelides obtectus

The dried bean beetle, Acanthoscelides obtectus, is a serious pest of legume crops, particularly Phaseolus vulgaris beans, and their management is challenging due to the beetle's cryptic larval stage. The major male-produced pheromone of A. obtectus is methyl (E,R)-2,4,5-tetradecatrienoate, crucial for female attraction, with the (S)-enantiomer emitted in smaller amounts (R:S ca. 9:1). Despite its identification half a century ago, it is still not commercially available for bruchid surveillance due to production and stability issues, with gaps in our knowledge relating to the bioactivity of the stereoisomers. We thus aim to clarify the behavioural specificity of the (R)- and (S)- enantiomers of methyl (E)-2,4,5-tetradecatrienoate, along with two commercially available isomers. Electrophysiological (EAG) assays with virgin females show that stereochemically pure methyl (E,R)-2,4,5-tetradecatrienoate is as EAG-active when part of the natural 9:1 or the racemic 1:1 blends, whereas the stereochemically pure (S)-enantiomer is inactive. Moreover, the structural analogues do not elicit significant EAG responses. Virgin females give positive behavioural responses in the olfactometer only to methyl (E,R)-2,4,5-tetradecatrienoate, but not to its antipode or the structural analogues. Furthermore, stereochemically pure methyl (E,R)-2,4,5-tetradecatrienoate elicits the same level of behavioural activity as the 9:1 blend. Curiously, presence of the (S)-enantiomer in equal proportions synergises female preference for stereochemically pure (R). These findings provide a better understanding of the pheromone biology of A. obtectus and create a platform for the development of pheromone trap-based surveillance with racemic methyl (E)-2,4,5-tetradecatrienoate

Attraction of Lygus rugulipennis and Adelphocoris lineolatus to synthetic floral odour compounds in field experiments in Hungary (Heteroptera: Miridae)

Field experiments were carried out to ascertain whether synthetic floral odour compounds were attractive for two pest bug species. The European tarnished plant bug (Lygus rugulipennis Poppius) has been reported to damage various crops (e.g. strawberry, sugarbeet, alfalfa, cucumber), and the alfalfa plant bug (Adelphocoris lineolatus (Goeze)) is considered as a pest of alfalfa and Bt-cotton. In our field tests, traps baited with phenylacetaldehyde caught significantly more L. rugulipennis than unbaited traps. In addition, A. lineolatus was also attracted to phenylacetaldehyde-baited traps. When testing other, EAG active compounds, (E)-cinnamaldehyde attracted A. lineolatus as well. This compound was also attractive for L. rugulipennis, however, to a lesser extent than phenylacetaldehyde. When the two compounds were presented in combination, no synergistic or inhibitory effect was detected in either species. By attracting both sexes of both species, these new attractants may prove to be useful and provide the basis for further development of new lures for agricultural use

Solvent extraction of PDMS tubing as a new method for the capture of volatile organic compounds from headspace

Polydimethylsiloxane (PDMS) tubing is increasingly being used to collect volatile organic compounds (VOCs) from static biological headspace. However, analysis of VOCs collected using PDMS tubing often deploys thermal desorption, where samples are considered as ‘one-offs’ and cannot be used in multiple experiments. In this study, we developed a static headspace VOC collection method using PDMS tubing which is solvent-based, meaning that VOC extracts can be used multiple times and can be linked to biological activity. Using a synthetic blend containing a range of known semiochemicals (allyl isothiocyanate, (Z)-3-hexen-1-ol, 1-octen-3-one, nonanal, (E)-anethol, (S)-bornyl acetate, (E)-caryophyllene and pentadecane) with differing chemical and physicochemical properties, VOCs were collected in static headspace by exposure to PDMS tubing with differing doses, sampling times and lengths. In a second experiment, VOCs from oranges were collected using PDMS sampling of static headspace versus dynamic headspace collection. VOCs were eluted with diethyl ether and analysed using gas chromatography – flame ionization detector analysis and coupled GC – mass spectrometry analysis. GC-FID analysis of collected samples showed that longer PDMS tubes captured significantly greater quantities of compounds than shorter tubes, and that sampling duration significantly altered the recovery of all tested compounds. Moreover, greater quantities of compounds were recovered from closed compared to open systems. Finally, analysis of orange headspace VOCs showed only a few qualitative differences in VOCs recovered compared to dynamic headspace collections, although quantities sampled using PDMS tubing were lower. In summary, extraction of PDMS tubing with diethyl ether solvent captures VOCs from the headspace of synthetic blends and biological samples, and the resulting extracts can be used for multiple experiments linking VOC content to biological activity

KLP+ ("hat") trap with semiochemical lures suitable for trapping two diabrotica spp. exotic to Europe.

The KLP+ (“hat”) trap baited with pheromone or floral lures is a highly efficient non-sticky trap for the western corn rootworm, Diabrotica v. virgifera. We tested the suitability of this trap design for the related species, D. speciosa and D. barberi, baited with their respective lures. Both species are exotic to Europe: the former inhabits South America, and the latter occurs in some parts of North America. In screening tests performed in Brazil, several synthetic floral compounds and their combinations were found to be attractive to D. speciosa. However, the greatest effect was recorded for the previously described attractant 1,4-dimethoxybenzene. When the most active compounds in the preliminary test, 2-phenylethanol, methyl anthranilate, eugenol or benzaldehyde were added to 1,4-dimethoxybenzene, no synergistic effects were observed. When1,4-dimethoxybenzene was formulated in three types of polyethylene (PE) dispensers in KLP+traps, PE bag dispensers were superior to two types of PE vial dispenser, and caught hundreds of D. speciosa. Unbaited traps caught only negligible numbers. There was an interesting non-target effect. KLP+ traps with 1,4-dimethoxybenzene caught large numbers of the cornsilk fly, Euxesta eluta, which is known as a maize pest. For D. barberi, both a pheromone and a potent floral lure are already known. In tests with KLP+ traps, we found that the pheromone and floral lures can be applied together in the same trap to maximize both male and female catches. In conclusion, for early detection programs in Europe, the application of KLP+ traps baited with 1,4-dimethoxybenzene in PE bag dispensers could be recommended for D. speciosa, and KLP+ traps with dual (pheromone and floral) lures for D. barberi. In the case of D. barberi, one should note that the lures also show some attraction for D. v. virgifera, and the ratio of D. barberi vs. D. v. virgifera in the catch will be pre- dominantly determined by the relative population densities at the given site

Investigating the threat to Sitka spruce from Ips typographus: discrimination and colonization of Britain's principal commercial conifer by a damaging forest pest

BACKGROUND: Ips typographus (L.), the eight-toothed spruce bark beetle (Coleoptera: Scolytinae), has devastated European Norway spruce (Picea abies) forests in recent years. For the first time, I. typographus has established localised breeding populations in Britain, where Sitka spruce (P. sitchensis) is a critical component of plantation forestry. The interactions between Norway spruce and I. typographus are well understood, but relatively little is known about the susceptibility of Sitka spruce to the beetle. This study aimed to determine whether I. typographus would select Sitka, compared to Norway spruce, as a host for breeding, and to study the chemical ecology underlying these host preferences. RESULTS: Host choice assays were conducted in the laboratory using freshly cut spruce logs, and then verified in the field in an area with an endemic population of I. typographus. Overall, colonisation and breeding success were found to be similar in cut Sitka and Norway spruce material. The response of I. typographus, reared on both Norway and Sitka spruce, to headspace extracts of aged and fresh Norway and Sitka spruce billets was tested behaviourally using four-arm olfactometry. Odours of aged wood from the two species were equally attractive, and fresh Sitka was more attractive than fresh Norway spruce. Antennal responses to Norway Spruce and Sitka Spruce billet headspace extracts were located using GC-EAG and identified by coupled GC-mass spectrometry and GC co-injection with authentic standards. Norway- and Sitka spruce-reared beetles did not differentiate between synthetic Norway or Sitka spruce blends and responded similarly. CONCLUSION: These findings suggest I. typographus will select and colonise cut Sitka as readily as cut Norway spruce, with implications for its establishment risk in Sitka-growing regions. The study advances the understanding of the role of both host-emitted volatile organic compounds (VOCs) and induced host preference in host selection by I. typographus

Development of a Synthetic Floral Lure for Pollen Beetles (Coleoptera: Nitidulidae)

Pollen beetles (Coleoptera: Nitidulidae) rank among the most important pests of oilseed rape (Brassica napus). For their timely detection in early spring, yellow sticky or water pan traps are used; however, it has been suggested that the addition of chemical lures to attractive visual cues could improve trap efficacy. During the course of field trials in Hungary, we have developed a 3-component synthetic floral lure consisting of (E)-anethol þ (E)-cinnamyl alcohol þ (E)-cinnamyl acetate, which attracted large numbers of pollen beetles into large capture-capacity fluorescent yellow funnel traps. There was no apparent difference between the pollen beetle species Brassicogethes aeneus F. 1775 (earlier Meligethes aeneus), Brassicogethes viridescens F. 1775, Brassicogethes coracinus Sturm 1845 and Fabogethes nigrescens Sturm 1845 in their responses to the 3-component lure, which can therefore be used to trap all of them. Funnel traps with the new ternary floral lure were more efficient in catching beetles than those with lures containing 2-phenethyl isothiocyanate, a previously described plant-derived attractant for pollen beetles. However, the effect of the addition of the isothiocyanate to the ternary blend was not completely clear from these experiments and thus requires further studies

Characterisation of aphid antixenosis in aphid-resistant ancestor wheat, Triticum monococcum

BACKGROUND: Due to the increasing presence of insecticide resistance across cereal aphid populations, new aphid management strategies, including the engineering of host resistance to aphids into commercial wheat varieties, are required. Previous studies have identified ancestor wheat, Triticum monococcum accessions MDR045 and MDR049, with resistance against the grain aphid, Sitobion avenae. To test the hypothesis that resistance can be accounted for by antixenosis (reduced attractiveness of host plants) via the release of repellent volatile organic compounds (VOCs), we explored the response of S. avenae to MDR045 and MDR049 following S. avenae herbivory, using behaviour and electrophysiology experiments. RESULTS: In four-arm olfactometry assays, alate S. avenae showed aphid-density dependent reduced preference to VOC extracts from T. monococcum MDR045 and MDR049. By contrast, alate S. avenae showed aphid-density dependent increased preference to extracts from hexaploid wheat, T. aestivum var Solstice and T. monococcum MDR037. Coupled gas chromatography-electroantennography (GC-EAG), using the antennae of alate S. avenae, located 24 electrophysiologically active compounds across all tested accessions. Synthetic blends created from 21 identified EAG-active compounds confirmed bioactivity of corresponding VOC extracts in four-arm olfactometry assays against alate S. avenae. CONCLUSION: Our data suggest that resistance of T. monococcum MDR045 and MDR049 to S. avenae can be at least partially accounted for by antixenosis, through antennal perception of specific repellent VOC blends induced by S. avenae feeding behaviour