Klaus Peschke

A review of myrmecophily in ant nest beetles (Coleoptera: Carabidae: Paussinae): linking early observations with recent findings.

Myrmecophily provides various examples of how social structures can be overcome to exploit vast and well-protected resources. Ant nest beetles (Paussinae) are particularly well suited for ecological and evolutionary considerations in the context of association with ants because life habits within the subfamily range from free-living and predatory in basal taxa to obligatory myrmecophily in derived Paussini. Adult Paussini are accepted in the ant society, although parasitising the colony by preying on ant brood. Host species mainly belong to the ant families Myrmicinae and Formicinae, but at least several paussine genera are not host-specific. Morphological adaptations, such as special glands and associated tufts of hair (trichomes), characterise Paussini as typical myrmecophiles and lead to two different strategical types of body shape: while certain Paussini rely on the protective type with less exposed extremities, other genera access ant colonies using glandular secretions and trichomes (symphile type). We compare these adaptations with other taxonomic groups of insects by joining contemporary research and early sources and discuss the possibility of an attracting or appeasing effect of the secretion. Species that are ignored by their host ants might use chemical mimicry instead. Furthermore, vibrational signals may contribute to ant–beetle communication, and chemical signals have proven to play a role in host finding. The powerful defense chemistry of paussines as “bombardier beetles” is not used in contact with host ants. We attempt to trace the evolution of myrmecophily in paussines by reviewing important aspects of the association between paussine beetles and ants, i.e. morphological and potential chemical adaptations, life cycle, host specificity, alimentation, parasitism and sound production.

Defensive secretion of the tenebrionid beetle, Blaps mucronata: physical and chemical determinants of effectiveness.

SummaryThe primary components of the defensive secretions ofBlaps mucronata (Tenebrionidae) are two quinones (methyl-p-benzoquinone and ethyl-p-benzoquinone) and the hydrocarbon 1p-n-tridecene. The hydrocarbon is shown, by comparison with longer- and shorter-chainn-alkanes and 1-n-alkenes, to be optimally suited as carrier of the quinones, and as a surfactant that promotes spread of secretion over the beetles body following discharge from the gland openings at the abdominal tip. As shown from repellency tests with ants (Monomorium pharaonis) and topical irritancy tests with cockroaches (Periplaneta americana), the antiinsectan potency of the secretion derives as much from the hydrocarbon as from the quinones.

Cuticular hydrocarbons and female sex pheromones of the rove beetle, Aleochara curtula (Goeze) (Coleoptera:Staphylinidae)

The cuticular hydrocarbons of the staphylinid beetle, Aleochara curtula, have been analysed by gas chromatography and by combined gas chromatography-mass spectrometry and comprise n-alkanes, n-alkenes, monomethylalkanes and dimethylalkanes, ranging from C21 to C29. The separation and identification of isomeric internally branched monomethylalkanes and dimethylalkanes was supported by computerized mass-chromatography. (Z)7-Heneicosene and (Z)7-tricosene were isolated and characterized as the main components of the female sex pheromone by liquid column chromatography, HPLC, molecular sieve inclusion, hydrogenation and quantitative capillary gas chromatography of male and female hydrocarbons. The position and configuration of the double bonds were established by formation of monomethoxy derivatives and i.r.-spectroscopy. The sex pheromone isolation procedure was monitored by a bioassay (males grasping with genitalia towards dosed models). Synthetic (Z)7-heneicosene (2 μg/female) and (Z)7-tricosene (12 μg/female) gave high sexual response rates, whereas (Z)9-heneicosene and (Z)9-tricosene released little or no response. A dose-response curve with an optimal concentration of individual pheromone components (2 μg) is described. Synthetic (S)isomers proved to be much less effective.

Comparison of tarsal and cuticular chemistry in the leaf beetle Gastrophysa viridula (Coleoptera: Chrysomelidae) and an evaluation of solid-phase microextraction and solvent extraction techniques

Tarsal substrate adhesion in insects is based on the effect of a thin film of liquid in the contact zone, which is deposited as droplets on the surface an insect has walked on, but as yet, little is known about the chemical composition of the liquid. In the present study, interference reflection microscopical images of the tarsal contact and footprints of Gastrophysa viridula (Coleoptera: Chrysomelidae) are depicted and the chemical composition of tarsal liquids and cuticular components are investigated by means of solid-phase microextraction and solvent extraction of whole beetles and footprints. Based on this comparative methodical approach, we are first to provide evidence from direct sampling for the chemical congruence of cuticular lipids and tarsal liquid in beetles. Furthermore, differences resulting from the applied sampling techniques are assessed and advantages of the respective methods are discussed.

Ethyl 4-Methyl Heptanoate: A Male-Produced Pheromone of Nicrophorus vespilloides

Sexually mature male beetles of the genus Nicrophorus (Coleoptera: Silphidae) exhibit a conspicuous behavior, recognized as pheromone-releasing activity. Laboratory and field studies demonstrated that females are attracted to males that exhibit this behavior, both on or off reproductive resources. Here, we report the results of a study in which volatile chemicals released by calling Nicrophorus vespilloides were collected by solid-phase microextraction and analyzed by using coupled gas chromatography–mass spectrometry. These analyses revealed that ethyl 4-methyl heptanoate and (E)-geranylacetone are emitted by males that engage in the behavior. In the field, traps baited with racemic ethyl 4-methyl heptanoate caught roughly equal numbers of male and female N. vespilloides. Some male and female Nicrophorus vespillo and male Nicrophorus humator were also caught in traps baited with this compound. Traps baited with (E)-geranylacetone did not catch significant numbers of beetles.

Correlated changes in breeding status and polyunsaturated cuticular hydrocarbons: the chemical basis of nestmate recognition in the burying beetle Nicrophorus vespilloides?

Nestmate recognition in eusocial insects has received a lot of attention in the last decades. Recognition in subsocial species, in contrast, has been ignored almost completely and consequently, and little is known about proximate mechanisms of recognition in subsocial systems. We studied one subsocial species, the biparental brood caring burying beetle Nicrophorus vespilloides, an interesting model organism for studies of recognition because of its ability to discriminate between breeding partners and conspecific competitors. Recognition appears to be based on a chemical cue closely linked to the breeding status of individuals. Breeding and non-breeding beetles consistently differ in their relative proportions of polyunsaturated cuticular hydrocarbons. To investigate the function of these polyenes in the burying beetles’ recognition system, we quantified their concentration on the cuticle during the early state of a breeding attempt and tested the response of breeding beetles in corresponding behavioural experiments. We observed a rapid increase in the proportion of polyunsaturated hydrocarbons of both males and females after they were provided with a carcass suitable for reproduction. Furthermore, we found that the relative amount of polyenes on an individual’s surface was closely correlated with its chance of being accepted as breeding partner. Our results support the idea that polyunsaturated hydrocarbons are involved in breeding partner recognition in N. vespilloides, functioning as a signal that conveys information about the individual’s breeding status. Breeding females have greater amount of polyenes than breeding males, and females ingest more carrion during the first days on the carcass, which supports our hypothesis that precursors for the respective polyenes are derived from ingested carrion.

Food Wrapping with the Postpharyngeal Gland Secretion by Females of the European beewolf Philanthus triangulum

Ground-nesting animals share their habitat with countless microorganisms that can play important roles as pathogens or competitors for food resources. Thus, species that store food in the soil, either for themselves or for their progeny, must protect these resources against microbial degradation. Females of the European beewolf, Philanthus triangulum, hunt honeybees as provisions for their brood and store the paralyzed prey in their subterranean nests. A previous study had shown that females lick the surface of prey before oviposition and that this licking treatment delays mold growth. Here, we showed that females apply large amounts of a secretion from their postpharyngeal glands onto the surface of their prey during the licking behavior. Inhibition-zone assays showed that comparatively large amounts of the gland secretion had no direct antimycotic effect. We discuss our findings with regard to other possible mechanisms of the postpharyngeal gland secretion against fungal growth.

Interaction of liquid epicuticular hydrocarbons and tarsal adhesive secretion in Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae)

Species of various insect orders possess specialised tarsal adhesive structures covered by a thin liquid film, which is deposited in the form of footprints. This adhesive liquid has been suggested to be chemically and physiologically related to the epicuticular lipid layer, which naturally covers the body of insects and acts as the prime barrier to environmental stresses, such as desiccation. The functional efficiency of the layer, however, is jeopardised by partial melting that may occur at physiological temperatures. In this study, light microscopic images of elytral prints show that the epicuticular lipid layer of the Colorado potato beetle Leptinotarsa decemlineata actually is partially liquid and chemical investigations reveal the high similarity of the epicuticular hydrocarbon pattern and the tarsal liquid. By means of chemical manipulation of the surface hydrocarbon composition of live beetles, the substance exchange between their tarsal adhesive hairs and the body surface is monitored. Histological sections of L. decemlineata tarsi, furthermore, reveal glandular cells connected to individual adhesive setae and departing from these results, an idea of a general mechanism of tarsal secretion is developed and discussed in a functional–ecological context.

The Chemistry of the Postpharyngeal Gland of Female European Beewolves

Females of the European beewolf, Philanthus triangulum, possess a large glove-shaped gland in the head, the postpharyngeal gland (PPG). They apply the content of the PPG to their prey, paralyzed honeybees, where it delays fungal infestation. Here, we describe the chemical composition of the gland by using combined GC-MS, GC-FTIR, and derivatization. The PPG of beewolves contains mainly long-chain unsaturated hydrocarbons (C23–C33), lower amounts of saturated hydrocarbons (C14–C33), and minor amounts of methyl-branched hydrocarbons (C17–C31). Additionally, the hexane-soluble gland content is comprised of small amounts of an unsaturated C25 alcohol, an unknown sesquiterpene, an octadecenylmethylester, and several long-chain saturated (C25, C27) and unsaturated (C23–C27) ketones, some of which have not yet been reported as natural products. Surprisingly, we found a dimorphism with regard to the major component of the PPG with some females having (Z)-9-pentacosene, whereas others have (Z)-9-heptacosene as their predominant component. The biological relevance of the compounds for the prevention of fungal growth on the prey and the significance of the chemical dimorphism are discussed.

Congruence of epicuticular hydrocarbons and tarsal secretions as a principle in beetles

Within beetles, those species that are adapted to life on plants have developed widened tarsi with specialised hairy attachment structures. The capability to adhere to smooth surfaces is based on a liquid film on the surface of these structures, the composition of which is similar to the cuticular lipids. By means of a cluster analysis based on chemical similarities between samples obtained from tarsi or elytra of 35 species using solid phase microextraction, the present study strongly suggests that this chemical congruence is a principle in beetles. This supports the idea of tarsal liquids being part of the cuticular lipid layer and contributes to the understanding of liquid-mediated attachment systems.