The rare European click beetle, Elater ferrugineus L., develops exclusively in old, hollow deciduous trees. As a result of massive habitat loss caused by modern forestry, it is threatened throughout its entire distribution range and regarded as an indicator species for undamaged natural forests. As E. ferrugineus lives cryptically and its populations are frequently overlooked, we investigated its sex pheromone to develop a reliable detection tool. Pheromone gland extracts of single female E. ferrugineus were examined by using gas chromatography-mass spectrometry (GC-MS). All samples contained 7-methyloctyl 5-methylhexanoate, 7-methyloctyl octanoate, 7-methyloctyl 7-methyloctanoate, and 7-methyloctyl (Z)-4-decenoate in a ratio of approximately 1:1:3:3. Structures of all four esters, which have not been reported as pheromone compounds before, were confirmed by synthesis. A blend of the components was tested in the field and proved to be attractive for E. ferrugineus males, which were found to swarm exclusively during the day. This blend provides a noninvasive and effective monitoring method for this cryptic species, promising future collection records of E. ferrugineus in regions where it exists below the limit of detection by conventional collecting methods.

SUMMARY Male insects may increase their chance of successful reproduction by releasing pheromones that attract females or elicit sexual acceptance. In parasitic wasps, male pheromones have been suggested for a few species but no chemicals have been identified so far. Here we report the first identification of a male sex pheromone in parasitic Hymenoptera. In abdomens of male jewel wasps, Nasonia vitripennis Walker, we found a mixture of(4R,5R)- and(4R,5S)-5-hydroxy-4-decanolide (HDL), which was released intermittently and attracted virgin females, but no males, in an olfactometer bioassay. However, only a few minutes after copulation mated females avoided the male-derived pheromone. Neither preference nor avoidance was shown by mated females after 24 h and even after they had been allowed to oviposit for 6 days. Nasonia vitripennis females normally mate only once. Thus,their variable response to the sex attractant depending on the mating status makes sense from an evolutionary perspective. Firstly, it increases the chance of virgins to be inseminated. Secondly, by terminating the response or even avoiding the male pheromone, mated females decrease the probability of encountering males and being disturbed by their courtship activities when searching for new oviposition sites.

Based on analysis of pheromone gland extracts, highly attractive new baits have been developed for three click beetle pests. That for Agriotes brevis is a mixture of geranyl butanoate and (E,E)-farnesyl butanoate, and that for A rufipalpis and A sordidus contains geranyl hexanoate alone. From known data from species populating Russia, optimized bait compositions for species in Central and Western Europe were developed as follows: geranyl octanoate + geranyl butanoate for A lineatus, geranyl isovalerate for A litigiosus, geranyl hexanoate + geranyl octanoate for A obscurus, geranyl butanoate alone for A sputator and (E,E)-farnesyl acetate alone for A ustulatus. Although slight differences were found in gland contents with A litigiosus var laichartingi and fenotypus typicus, nevertheless there were no differences in response to the optimum bait. There were no differences in pheromone composition or response to the optimized bait between the two morphological forms ('black' and 'red') of A ustulatus. As a result of these studies, highly effective pheromone baits are now available for monitoring and population reduction in all important pest click beetle species in Central and Western Europe.

Polyploidy has played a key role in plant evolution and diversification. Despite this, the processes governing reproductive isolation among cytotypes growing in mixedploidy populations are still largely unknown. Theoretically, coexistence of diploid and polyploid individuals in sympatric populations is unlikely unless cytotypes are prezygotically isolated through assortative pollination. Here, we investigated the pre-mating barriers involved in the maintenance of three co-occurring cytotypes from the genus Gymnadenia (Orchidaceae): tetraploid and octoploid G. conopsea and tetraploid G. densiflora. We assessed differences in flowering phenology, floral morphology, and visual and olfactory cues, which could lead to assortative mating. Gas chromatography coupled with Electronic supplementary material The online version of this article (electroantennographic detection was used to identify scent compounds with physiological activity in the two main pollinators, Deilephila porcellus and Autographa gamma. The importance of olfactory cues was also assessed in the field by analysing the moths' responses to the olfactory display of the plants, and by following the pollinator's behaviour on artificial arrays. Our complex approach demonstrated that the coexistence of Gymnadenia cytotypes in mixed-ploidy populations was only partly explained by differences in floral phenology, as cytotypes with overlapping flowering (i.e., octoploid G. conopsea and tetraploid G. densiflora) might freely exchange pollen due to only 1 mm differences in spur lengths and the lack of assortative behaviour of pollinators. While floral colour among the cytotypes was similar, floral scent differed significantly. Though both pollinator species seemed to physiologically detect these differences, and the floral scent alone was sufficient to attract them, pollinators did not use this cue to discriminate the cytotypes in the field. The absence of premating barriers among cytotypes, except partial temporal segregation, suggests the existence of other mechanisms involved in the cytotypes' coexistence. The genetic differences in ITS sequences among cytotypes were used to discuss the cytotype's origin.

Summary The response of the forest cockchafer, Melolontha hippocastani F. (Coleoptera, Scarabaeidae), towards volatiles emitted by different host plants and conspecifics was tested in field experiments during the flight period at dusk. Funnel traps containing artificially damaged leaves from the host plants Carpinus betulus L. and Quercus rubra L., as well as from the non‐host plant Prunus serotina Ehrh. caught significantly more beetles than empty control traps. On the other hand, traps baited with undamaged leaves from Q. rubra did not catch significantly more beetles than empty controls. Leaves from C. betulus damaged by beetle feeding did not attract more beetles than artificially damaged leaves. By use of gas chromatography coupled with electroantennographic detection (GC‐EAD) electrophysiological responses of males and females were shown for 18 typical plant volatiles. A synthetic mixture of selected typical green plant volatiles was also highly attractive in the field. A total of 9982 beetles was caught during the field experiments, among them only 33 females. This suggests that attraction to damaged foliage during flight period at dusk is male‐specific. Field experiments testing the attractiveness of female M. hippocastani towards conspecific males by employing caged beetles and beetle extracts indicated that males of M. hippocastani use a female‐derived sex pheromone for mate location. On wired cages containing either unmated feeding females, or unmated females without access to foliage, or feeding males in combination with extracts from unmated females, significantly more males landed during the flight period than on comparable control cages containing feeding males or male extracts. A possible scenario of mate location in M. hippocastani involving feeding‐induced plant volatiles and a female‐derived sex pheromone is discussed.