Defensive secretion of Therea petiveriana: chemical identification and evidence of an alarm function

Alarm communication predates eusociality in termites

Termites (Blattodea: Isoptera) have evolved specialized defensive strategies for colony protection. Alarm communication enables workers to escape threats while soldiers are recruited to the source of disturbance. Here, we study the vibroacoustic and chemical alarm communication in the wood roach Cryptocercus and in 20 termite species including seven of the nine termite families, all life-types, and all feeding and nesting habits. Our multidisciplinary approach shows that vibratory alarm signals represent an ethological synapomorphy of termites and Cryptocercus. In contrast, chemical alarms have evolved independently in several cockroach groups and at least twice in termites. Vibroacoustic alarm signaling patterns are the most complex in Neoisoptera, in which they are often combined with chemical signals. The alarm characters correlate to phylogenetic position, food type and hardness, foraging area size, and nesting habits. Overall, species of Neoisoptera have developed the most sophisticated communication system amongst termites, potentially contributing to their ecological success.

Volatile compounds reveal age: a study of volatile organic compounds released by Chrysomya rufifacies immatures

Age determination of insects collected from vertebrate remains is an essential step in estimating time since colonization as related to the post-mortem interval. Long-established methods for making such estimates rely on determining age related to stage of development at the time of collection in relation to conditions experienced. However, such estimates are based on the completion of a stage of development. Methods allowing for more precise estimates of age (i.e., within a stage of development) are sorely needed. This study examined the potential of volatile organic compounds emitted by blow fly, Ch. rufifacies (Macquart), immatures to determine stage of development, which could potentially be used to estimate the age. Volatile organic compounds (VOCs) from the larval and pupal stages of Ch. rufifacies were collected by headspace solid-phase micro-extraction followed by gas chromatography-mass spectrometry (GC-MS). Analyses indicated 37 compounds shift quantitatively, as well as qualitatively, as the larvae and pupae age. Furthermore, compounds, such as 2-ethyl-1-hexanol, phenol, butanoic acid, hexadecanoic acid, octadecanoic acid, 2-methyl propanamide, and 2-methyl butanoic acid, serve as indicator compounds of specific stages within Ch. rufifacies development. This information could be important to determine if these compounds can be used in the field to predict the presence of certain developmental stages, in order to determine the potential of using volatile markers to estimate time of colonization.

Carabidae Semiochemistry: Current and Future Directions

Ground beetles (Carabidae) are recognized for their diverse, chemically-mediated defensive behaviors. Produced using a pair of pygidial glands, over 250 chemical constituents have been characterized across the family thus far, many of which are considered allomones. Over the past century, our knowledge of Carabidae exocrine chemistry has increased substantially, yet the role of these defensive compounds in mediating behavior other than repelling predators is largely unknown. It is also unclear whether non-defensive compounds produced by ground beetles mediate conspecific and heterospecific interactions, such as sex-aggregation pheromones or kairomones, respectively. Here we review the current state of non-exocrine Carabidae semiochemistry and behavioral research, discuss the importance of semiochemical research including but not limited to allomones, and describe next-generation methods for elucidating the underlying genetics and evolution of chemically-mediated behavior.

Prothoracic gland semiochemicals of green lacewings

Adult chrysopids have paired prothoracic glands (PG) that are thought to produce defensive secretions (allomones). We analyzed PG extracts of the following green lacewings from North and South America, Australia, and China: Ceraeochrysa cubana (Brazil); Chrysopa (= Co.) oculata, Co. nigricornis, Co. incompleta, Co. quadripunctata (USA), and Co. septempunctata (China); Chrysoperla (= Cl.) rufilabris (USA) and Cl. sp. (Brazil); Plesiochrysa ramburi and Mallada spp. (Australia). PG secretions are characteristic for species within a genus, except for Chrysopa spp. (Z)-4-Tridecene is ubiquitous, but (Z,Z)-4,7-tridecadiene is a major PG constituent in some Chrysopa spp. and in P. ramburi. Earlier reports that Co. oculata and Co. nigricornis produce 1-tridecene were shown to be in error. Chrysopa PG secretions are distinguished by the presence or absence of N-3-methylbutylacetamide, plus skatole (3-methylindole). Skatole is also identified for the first time from the Plesiochrysa and Ceraeochrysa. The PG secretion in Plesiochrysa ramburi is characterized by the presence of (Z)-4-undecene instead of (Z)-4-tridecene, and N-3-methylbutylpropanamide instead of the acetamide, resembling the PG secretions of Chrysopa nigricornis, Co. septempunctata and Co. incompleta. The chemotaxonomic value of PG semiochemicals is discussed, including evidence for subgroups within the genus Chrysopa as it now stands.

Caste differences in venom volatiles and their effect on alarm behaviour in the paper wasp Polistes dominulus (Christ)

Foundresses and workers of Polistes paper wasps show slight morphological and physiological differences. However, after the emergence of the workers, the castes can be readily discriminated by their behaviour: the dominant foundress is the principal egg-layer, whereas workers perform different tasks linked to colony development. Previous studies have demonstrated in this genus that defence of the colony by the workers is more effectively carried out by a collective response elicited by venom volatiles used as alarm pheromones. In the present study, gas chromatography–mass spectrometry analyses of the venom volatiles of foundresses and workers of Polistes dominulus (Christ) show predominantly quantitative differences. Spiroacetals, mainly(E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, are significantly higher in the venom volatiles fraction of workers, whereas the amount of N-(3-methylbutyl)acetamide is almost double in foundresses. On the basis of the chemical results, behavioural assays were performed on fifteen field colonies to test the alarm response of the resident wasps to venom extracts from foundresses and workers. Our behavioural results suggest that worker venom has a stronger alarm effect on the colonies than that of the foundresses, which seems unable to elicit the complete alarm response ending with a final attack and sting. The venom volatiles of P. dominulusworkers serve mainly to alarm the colony whilst those of foundresses may also be linked to additional functions related to conspecific interactions.

Volatiles from the venom of five species of paper wasps (Polistes dominulus, P. gallicus, P. nimphus, P. sulcifer and P. olivaceus)

The venom volatiles of five paper wasp species, four European belonging to the subgenus Polistes sensu stricto (P. dominulus, P. gallicus, P. nimphus, P. sulcifer) and one belonging to the Asian subgenus Gyrostoma (P. olivaceus), have been sampled by headspace solid phase micro-extraction and analysed by gas chromatography-mass spectrometry. The venom volatile components of Polistes wasps have never been fully investigated before, although the presence of some spiroacetals has been previously reported in literature. The composition of the venom was qualitatively and quantitatively different among the analysed species with the major substances tentatively identified, on the basis of their mass spectra, as: spiroacetals, mainly 2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, two amides, N-(3-methylbutyl)acetamide and N-(3-methylbutyl)propanamide and acetates of saturated, mono- and di-unsaturated 2-alcohols with an odd number of carbon atoms in the chain. The acetate of a di-unsaturated 2-alcohol, present in two isomeric forms, identified as (E)- and (Z)-5-tangerinol has never been reported in literature for insects. Propanoates of the same 2-alcohols were only found in the venom of P. gallicus. Both the amides and the above-mentioned spiroacetal have been already shown to be alarm pheromones in other social wasps, while the acetates and propanoates have ever been reported in this taxon.

Biosynthesis and Identification of Volatiles Released by the Myxobacterium Stigmatella aurantiaca

The volatiles released by agar plate cultures of two strains of the myxobacterium Stigmatella aurantiaca (strains Sg a15 and DW4/3-1) were collected in a closed-loop stripping apparatus (CLSA) and analyzed by GC-MS. Large numbers of substances from different compound classes (ketones, esters, lactones, terpenes, and sulfur and nitrogen compounds) were identified; several of them are reported from natural sources for the first time. The volatiles 2-methyltridecan-4-one (17), its isomer 3-methyltridecan-4-one (20), and the higher homologue 2-methyltetradecan-4-one (18) were identified in the extracts of both strains and were synthesized. In addition, strain Sg a15 produced 2,12-dimethyltridecan-4-one (19), 2-methyltridec-2-en-4-one (23), and a series of phenyl ketones, among them 1-phenyldecan-1-one (14) and 9-methyl-1-phenyldecan-1-one (16), whereas strain DW4/3-1 emitted traces of 10-methylundecan-2-one (21). The biosynthesis of 14 and 16 was examined in feeding experiments with deuterated precursors carried out on agar plate cultures. The leucine-derived starter unit isovalerate was shown to be incorporated into 16, as was phenylalanine-derived benzoic acid into both 14 and 16. The results point to formation both of the phenyl ketones and of the structurally related aliphatic ketones through an unusual head-to-head coupling between a starter unit such as benzoyl-CoA and a fatty acyl-CoA, followed by decarboxylation.