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BACKGROUND\ud \ud The banana weevil, Cosmopolites sordidus, has been frequently cited as the most challenging constraint to banana and plantain production, particularly in small‐scale (smallholder) farming. For the development of a new, low‐cost weevil management technology based on attractive host plant material, we previously identified (2R,5S)‐theaspirane as the active component of attractive senesced banana leaves. In this new study, we used behavioural (olfactometer) bioassays with adult weevils to compare the attractiveness of four different developmental stages of banana leaves, i.e. unfolding (pale green), matured green (deep green), matured yellowing and senesced, to determine which leaf developmental stage would be most appropriate for use in weevil management. We also investigated the attractiveness of senesced leaf extracts prepared using different solvents to determine which solvent would be most appropriate for local production of leaf extracts. Coupled gas chromatography–electroantennography (GC–EAG) was then used with adult weevils to confirm the presence of (2R,5S)‐theaspirane in attractive leaf extracts. \ud \ud \ud RESULTS\ud \ud Of the leaf materials tested, only the odour of senesced leaf material was significantly attractive to adult weevils (P < 0.005). Furthermore, an extract of senesced material prepared using palm wine alcohol was significantly attractive (P < 0.05). Using coupled GC–EAG with weevil antennae, (2R,5S)‐theaspirane was identified as a minor component with strong EAG activity within the palm wine alcohol extract. \ud \ud \ud CONCLUSION\ud \ud The results suggest that palm wine alcohol extracts of senesced banana leaf material could be used to lure adult C. sordidus to traps in the field, as part of an ethnobotanical‐based approach for C. sordidus management on smallholder farms. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

BACKGROUND: The response of virgin females of the legume pest Acanthoscelides obtectus (Coleoptera: Bruchidae) to\ud headspace extracts of volatiles collected from flowers of a nectar plant, Daucus carota, was investigated using behaviour\ud (four-arm olfactometry) and coupled gas chromatography–electroantennography (GC-EAG).\ud RESULTS: Odours from inflorescences were significantly more attractive to virgin female beetles than clean air. Similarly, a sample\ud of volatile organic compounds (VOCs) collected by air entrainment (dynamic headspace collection) was more attractive to beetles\ud than a solvent control. In coupled GC-EAG experiments with beetle antennae and the VOC extract, six components showed EAG\ud activity. Using coupled GC–mass spectrometry (GC–MS) and GC peak enhancement with authentic standards, the components\ud were identified as -pinene (S:R 16:1), sabinene, myrcene, limonene (S:R 1:3), terpinolene and (S)-bornyl acetate. Females preferred\ud the synthetic blend of D. carota EAG-active volatiles to the solvent control in bioassays. When compared directly, odours of D.\ud carota inflorescences elicited stronger positive behaviour than the synthetic blend.\ud CONCLUSION: This is the first report of behaviourally active volatiles linked to pollen location for A. obtectus, and development\ud of the six-component blend is being pursued, which could underpin the design of semiochemical-based field management\ud approaches against this major pest of stored products.

The mechanisms of host shift in phytophagous insects are poorly understood. Among the many proposed processes involved, sexual selection via semiochemicals has recently been suggested. This hypothesizes that sexual communication using pheromones is modified as a result of development on a new host, and such plant-induced phenotypic divergence in mate recognition cues can lead to reproductive isolation between host lines. We tested this hypothesis on Acanthoscelides obtectus, an oligophagous bruchid of Phaseolus vulgaris beans worldwide, which also develops in acceptable non-hosts, such as chickpea (Cicer arietinum L.). Male sex pheromone blends of the bean, chickpea and chickpea/bean host lines during artificially induced host shifts showed different composition. Bean-reared females did not distinguish between blends, whereas chickpea and chickpea/bean females preferred the chickpea male pheromone. However, electrophysiological (EAG) responses to male odour of antennae of the three female host lines were similar, all preferring bean-reared males. Egg-laying choice tests revealed a uniform preference for bean seeds across female host lines, even after multiple generations, whereas larvae did not distinguish between bean and chickpea seeds. We conclude that the development of divergent chemical signalling systems during host shifts does not facilitate the evolution of host races in A. obtectus, because oviposition preferences remain unaffected.

BACKGROUND\ud \ud Agrilus bigutattus (Fabricius) is a forest pest of increasing importance in the United Kingdom. The larvae damage weakened native oaks and are thought to contribute to premature tree death. Suspected links with acute oak decline (AOD) are not yet confirmed, but AOD-predisposed trees appear to become more susceptible to A. biguttatus attack. Thus, management may be necessary for control of this insect. To explore the possibility of monitoring beetle populations by baited traps, the host tree volatiles regulating A. biguttatus–oak interactions were studied.\ud \ud \ud RESULTS\ud \ud Biologically active volatile organic compounds in dynamic headspace extracts of oak foliage and bark were identified initially by coupled gas chromatography–electroantennography (GC-EAG) and GC–mass spectrometry (GC-MS), and the structures were confirmed by GC coinjection with authentic compounds. Of two synthetic blends of these compounds comprising the active leaf volatiles, the simpler one containing three components evoked strongly positive behavioural responses in four-arm olfactometer tests with virgin females and males, although fresh leaf material was more efficient than the blend. The other blend, comprising a five-component mixture made up of bark volatiles, proved to be as behaviourally active for gravid females as bark tissue.\ud \ud \ud CONCLUSIONS\ud \ud These initial results on A. biguttatus chemical ecology reveal aspects of the role of attractive tree volatiles in the host-finding of beetles and underpin the development of semiochemically based surveillance strategies for this forest insect.

Conserving populations of environmentally vulnerable insect species requires a greater understanding of the factors that determine their abundance and distribution, which requires detailed knowledge of their population and community ecology. Chemical ecological tools such as pheromones can be used for non-destructive monitoring of scarab beetle populations, enabling European countries to detect and, in some cases, map the range of some of these species, proving a valuable technique for monitoring elusive saproxylic beetles. In this paper, we investigated the behavioural and chemical ecology of the noble chafer, Gnorimus nobilis L., a model insect species of conservation concern across a Europe-wide distribution, and a red-listed UK Biodiversity Action Plan priority species. We identified a potential pheromone of adult beetles using electrophysiological recordings, behavioural measurements and field trials in the UK. Gnorimus nobilis is highly unusual in that although both sexes produce, at high metabolic cost, the natural product 2-propyl (E)-3-hexenoate, it only attracts males. This pattern of chemical signalling makes the classification of the compound, based on current semiochemical terminology, somewhat problematic, but in our view, it should be termed an aggregation pheromone as a consequence of the production pattern. Since both sexes emit it, but apparently only males respond positively to it, 2-propyl (E)-3-hexenoate may reflect an intermediate evolutionary stage towards developing into a sex-specific signal. From an applied perspective, our study provides a model for the non-invasive surveillance of cryptic vulnerable insect species, without the need for habitat searching or disturbance, and continuous human monitoring.