Chemoecology最新文献

The purpose of the present study was to investigate the influence of cultivation parameters on the growth of leafcutter ant associated actinomycete Pseudonocardia sp. These bacteria live in a very specialized symbiosis with the leafcutter ant Acromyrmex octospinosus and fungi of the genus Leucoagaricus. Pseudonocardia are known to produce antibiotics but are very hard to grow as a result of the complexity of their symbiosis. The bacteria were grown on yeast-malt-extract agar and the influence of pH, temperature conditions and the addition of chitin and a cuticular hydrocarbon (CHC) solution specific to leafcutter ants on the growth of Pseudonocardia and other bacteria inhabiting the leafcutter ants´ surface was tested. The best growth rate of Pseudonocardia was achieved by cultivation at 28 °C in a medium with pH 7 supplemented with chitin and CHC solution. Additionally, these conditions inhibited the growth of other competitive bacteria. This is the first report on the optimization of growth media for leafcutter ant associated Pseudonocardia adjusted to the conditions found on the ants´ cuticle.

Social organisation of eusocial insects requires efficient communication among conspecifics, involving various signals. Among them, Cuticular Hydrocarbons Compounds are used like chemical signals for recognition processes. These semiochemical compounds, which can vary qualitatively and quantitatively, form an individual chemical signature carrying identity of each congeners which contribute to the social cohesion of the colony members. In this study, we analysed the chemical signature of workers of the eusocial and invasive Vespidae species, the Yellow-legged hornet, Vespa velutina nigrithorax. The chemical communication system between hornets’ workers is relatively unknown and their social organisation poorly documented. However, a strong chemical heterogeneity between castes and colonies have been previously identified in the Yellow-legged hornet, suggesting a possible chemical diversity between workers. Our results showed a strong chemical heterogeneity mainly explained by their colonial origin, as previously described, but also by their behaviour at a given time. In this study, four behaviours have been reported in the field and could be assigned to a workers’ sub-caste: animal foragers, builders, defenders and material foragers. A chemical separation of individuals into two groups have been observed, where animal foragers exhibit a clear separation of their chemical profiles compared to their counterparts. Also, animal foragers had more alkenes and fewer branched alkanes than the other workers. This exploratory study demonstrates that workers of this invasive hornet species present different cuticular profiles, probably used in both inter and intra-specific recognition phenomena. This is therefore a first step towards understanding the chemical communication involved in the social organisation of hornet workers.

The surface tension of chemical compounds is a crucial parameter in many interfacial processes of importance in sexual communication through odorants. To date, it has not been measured for any insect sex pheromone, including those from worldwide pests or well-studied organisms. Instead, it can be retrieved from dedicated black-box software, which delivers poorly described theoretical calculations and lacks clarity regarding error values. Using the low variability in the chemical structures of the sex pheromones from several moth species as an asset to avoid compounding effects, we estimated their surface tension using the pendant drop method, a well-known method in soft matter chemistry and physics yet seldom used by biologists despite being well suited for small samples. We examined 12 compounds: Z8-12:OH, E7Z9-12:Ac, E8E10-12:Ac, Z8-12:Ac, E8-12:Ac, E10Z12-16:Ald, E10Z12-16:OH, Z11-16:Ald, E3Z8Z11-14:Ac, Z9-14:Ac, Y11Z13-16:Ac, Z11-16:Ac. The species associated with these pheromones include the pests Lobesia botrana, Cydia splendana, Grapholita molesta, Bombyx mori, Cydolima perspectalis, Tuta absoluta, Spodoptera frugiperda, Thaumetopoea pityocampa and Mamestra brassicae. The measured values, ranging from 26 to 31 mN/m, are in accordance with the stated values in the available ACD/ChemSketch software and with our own theoretical predictions based on their densities and Parachor calculations, known as Macleod’s formula.

Insects and plants have been part of an evolutionary arms race that has led plants to produce toxins as defense and insects to sequester these chemical compounds. Pyrrolizidine alkaloids (PAs) are secondary plant chemical metabolites, and some herbivorous insects have evolved biochemical mechanisms to tolerate, sequester, and use PAs against predators and parasitoids. Several tiger moth species (Erebidae: Arctiinae) have gone one step further by transferring PAs acquired during mating to their eggs or using them as precursors of sexual pheromones, thereby making PAs an essential element in sexual selection. Although tiger moths are well known to use PAs for defense, a comprehensive qualitative and quantitative systematic review of PA research on tiger moths has yet to be conducted. To identify areas of past research focus and future research potential, we analyzed 108 studies retrieved from an exhaustive search on the Web of Science. Through a scientometric analysis, we synthesized available literature, examining authors, journals, countries and keywords with the aim of providing researchers tools to navigate the current literature more effectively. Using a systematic review approach, we evaluated the frequency of moth species studied and host plant diet, along with their research topic, allowing us to identify major knowledge gaps. We show that the number of publications decreased after 2015, and most research has focused on a few moth species and research topics. Our results provide valuable insights that can help direct research efforts to further the development of knowledge about PAs in Arctiinae.

The chemical composition of cuticular hydrocarbons differs qualitatively and quantitatively among insect species. These differences convey species-specific information about host suitability to foraging parasitoids, enabling them to discriminate between the host and non-host species. Specialist parasitoids that parasitize fewer host species are predicted to use host-specific cues compared to generalists that have evolved to use common cues present in multiple potential host species. Here, we tested the above hypothesis by evaluating two parasitoids with varying levels of host specificity, Microplitis croceipes (specialist) and Cotesia marginiventris (generalist), for their responses to cuticular extracts of three caterpillar species, Chloridea virescens, Helicoverpa zea, and Spodoptera exigua. First, we compared the cuticular profiles of the three caterpillar species and found that C. virescens and H. zea were qualitatively similar in cuticular composition, whereas S. exigua differed qualitatively and quantitatively from the other two. In contact bioassays, both parasitoid species were behaviorally arrested by the host cuticular extracts, with specialist M. croceipes able to discriminate between the cuticular extracts of its host and non-host caterpillar species. Assessment with the coupled gas chromatography-electroantennogram detection (GC-EAD) revealed qualitative and quantitative differences in parasitoids’ antennal responses to the components of cuticular extracts of host species, with M. croceipes showing greater antennal response than generalist C. marginiventris. The data implicated 13-methylhentriacontane as a probable host-specific kairomone used by specialist M. croceipes. These results suggest that specialist parasitoids like M. croceipes may exploit the differences in the composition of cuticular chemicals of caterpillars as cues for host recognition and discrimination.

Herbivorous insects require mechanisms to deal with defence compounds produced by their host plants. Despite an array of secondary compounds associated with defence, eucalypts are hosts to many insect species that readily obtain nutrients also produced by these plants. Gonipterus weevils are foliage-feeding eucalypt specialists as larvae and adults, with a notable characteristic of protecting their eggs with a hardened frass-like substance. The aim of this study was to assess plant, weevil frass and egg capsule chemistry to determine how the weevil eliminates plant secondary metabolites. We hypothesised that noxious compounds would be metabolised prior to elimination and that egg capsules would be composed of frass and additional substances. Weevils were fed on Eucalyptus globulus plants for seven days, with their frass and egg capsules collected daily, and the damaged, first, fully-expanded leaves of the host collected at the end of the assay. Compounds present in each sample were extracted in hexane and analysed by gas chromatography-mass spectrometry. The most abundant compounds in each sample were waxes and terpenoids, and metabolism of 1,8-cineole was evident, with two metabolites that may have semiochemical activity. Comparative analysis revealed significant differences between all samples, with shared compounds varying in relative proportions and exclusive compounds in sample type. These findings contribute to the understanding of Gonipterus physiology and highlight the differences between frass and the cover of egg capsules.

Ant venom has several functions, including predation, communication, defense against predators, and action against pathogens. There is a scarcity of data about ant venom components that could provide support for understanding the mechanisms of action. The objective here was to identify the amino acids and proteins in the venom of the predatory ant Ectatomma brunneum and to evaluate its antimicrobial activity. The amino acids were analyzed by liquid chromatography, with diode array detection, and were identified using amino acid standards. The two-dimensional (2D) gel electrophoresis fractionation approach was used to identify the proteins, together with MALDI-TOF/TOF mass spectrometry and protein databases. The antimicrobial activity of the venom was evaluated using the minimum inhibitory and minimum microbiocidal concentrations. The venom of E. brunneum contained free amino acids, with a high amount of alanine. The 2D gel analysis showed 104 spots, of which 21 were identified and classified according to biological function, as follows: venom proteins, nontoxic reservoir protection, cellular maintenance proteins, and proteins with unknown function. The venom showed antimicrobial activity, inhibiting the growth of all the bacteria and fungi tested. The results provide new insights into ant venom components and antimicrobial activity.

Within the genus Hyles, Euphorbia feeding appears to have evolved twice independently, in H. euphorbiae but also in H. nicaea, a species which had not been studied for its detoxification processes before. Euphorbia is known to contain toxic secondary metabolites, including diterpene esters, preventing most herbivores from feeding on them. We investigated the metabolisation of the standard phorbol ester Phorbol 12-myristate 13-acetate (TPA) and the diterpenes contained in Euphorbia cyparissias by the two species Hyles euphorbiae and Hyles nicaea (subspecies nicaea). For the first time, we report (1) The gut disposition of Hyles n. nicaea for this standard phorbol ester, which is commonly used in cancer and tumour research and (2) The disposition of the food plant tiglinaes of Euphorbia cyparissias after gut passage in both species and (3) Tigliane metabolites in the frass of TPA and of E. cyparissias feeding larvae. For both species around 5–25% of the TPA dose was recovered in the frass of the larvae, along with the metabolites phorbol and phorbol-13-acetate in very small amounts and traces. While the amounts of phorbol found did not differ much between the species frass, phorbol-13-acetate could be found in higher amounts in Hyles n. nicaea frass, indicating a difference in metabolisation. Moreover, enzymatic hydrolysis of TPA to phorbol-13-acetate and phorbol are postulated not to be the main metabolisation pathway, seeing that the amounts found only represent a small fraction of the TPA dose consumed.

Semiochemicals released by predators (i.e. “kairomones”) may be useful for prey species. Knowledge on functional use of olfaction to detect kairomones and the consequent antipredator behaviour remains scant in birds, especially in raptors. The study population of Eurasian kestrels Falco tinnunculus canariensis inhabits the island of Tenerife, and man is one of its main predators, destroying clutches and stealing nestlings. Man and kestrels have evolved in sympatry or, at least, have been sharing the habitat for a long time. Parent kestrels were exposed to chemical cues: human fresh urine (predator), cologne (odorous control), or water (odourless control) in the nest when provisioning for nestlings. They did not display clear signs of aggressive antipredator behaviour when in contact with kairomones released by a non-present human predator. With human urine, they visited less, arrived earlier the first time in the trial, but their refusal percentage dropped significantly, and they spent more time inside the nest than those containing cologne or water. Females, especially, visited those nests highest above the ground less times regardless of substance. Interactions among some environmental (e.g. nest height, variations in human urine odour) and behavioural factors (e.g. neophobic response) could influence kestrel behaviour regarding kairomones. Kestrels would exhibit commensurate responses according to the magnitude of predation risk faced. We suggest kestrels do not ultimately react through behavioural defence mechanisms based on chemical cues from human predators, although it remains unclear if they respond to these chemical cues in other ways.