Chemoecology最新文献

The Argentine ant is one of the five worst invasive ants. Recently it has been shown that one of the main compounds of its pygidial gland, iridomyrmecin, is used as a venom against competitors and enemies. Here, we explore the variability in the quantities of iridomyrmecin of individual workers, along a range of locations pertaining to both its native and invasive ranges, in order to know whether its venom could have contributed to the differential invasion success of European supercolonies. We specifically compared the amount of iridomyrmecin among supercolonies in the native range and among three invasive supercolonies: the Main supercolony (the most extended worldwide), the Corsican and the Catalonian supercolonies (both with a restricted distribution in Europe). Our main result is that the variability of the iridomyrmecin is very high. Looking at mean values, we found that the amount of iridomyrmecin of the Main supercolony was the lowest while the highest corresponded to the Corsican supercolony, with the Catalonian and the native range supercolonies having intermediate values. However, variability in the values within each supercolony was similar between supercolonies. This suggests that the success of a given invasive supercolony may not be explained by higher quantities of this defensive compound. Our results open the way for exploring the connection between defensive compounds and the invasion success of this global invader.

The subfamily Gonyleptinae is the second largest in Gonyleptidae, harboring over 100 species. Gonyleptinae is polyphyletic, nestled in the clade K92, and despite its richness, several species of that subfamily have not had their chemicals of the defensive secretions analyzed. Among these are Gonyleptes curticornis (Mello-Leitão, 1940) and G. horridus Kirby, 1819, the latter being particularly important, because it is the type species of the genus, which in turn names the subfamily Gonyleptinae. Gonyleptes horridus is also used in many phylogenetic analyses, be it using morphological or molecular data. The chemical study of the secretions of these two species by GC–MS and ¹H NMR showed the presence of 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl)-methylbutanone, 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl) isobutanone and 4-methyl-1-hepten-3-one in both species. On the other hand, 4-methyl-1-hexen-3-one was observed only in G. curticornis, and 7-methyl-2-octanol is exclusive of G. horridus. All vinyl-ketones identified have already been described for Gonyleptidae. We ran an Ancestral Character State Reconstruction (ASR) analysis under three different conditions to infer the evolution of the identified compounds (based on modified characters of a previous study) and their chemical nature (multistate character, either as alkylphenol, benzoquinone or vinyl-ketone) on a modified Gonyleptidae phylogeny. Our results corroborate previous studies that alkylphenol is the ancestral most condition, changing to benzoquinone in the ancestor of Gonyleptidae or even earlier in a grassatorean ancestor depending on the analysis. Vinyl-ketones are a synapomorphy of K92. We briefly discuss character codifications and use of weights of ASR analyses of specific compounds, which were inconclusive. 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl) isobutanone is shared by both Gonyleptes species and described for the genus Sodreana Mello-Leitão, 1922. 1-(6-(1-methyl-propyl)3,4-dihydro-2H-pyran-2yl)2-methylbutanone and 4-methyl-1-hepten-3-one are also shared by both Gonyleptes species and described for Moreiranula saprophila. From a taxonomic standpoint, combinations of specific compounds might help to diagnose supraspecific groups but given our limited sample, such decision should be taken with care and further tested. Finally, 7-methyl-2-octanol is described for the first time in Gonyleptidae, emphasizing the chemical diverse nature in the K92 clade.

In social insects, juvenile hormone (JH) affects the degree of ovarian development, reproductive status, and temporal polyethism in workers. JH also contributes to determining the epicuticular chemical composition, which differentiates the castes of queens and workers. However, a few studies have evaluated the action of JH on behavioral ontogeny, cuticular chemical profile, and oocyte length and width, especially in social wasps of independent foundation. Therefore, the following hypotheses were tested: (i) topical application of JH changes the behavioral ontogeny of newly emerged workers; and (ii) changes might be detected in the cuticular chemical composition and oocyte length and width of newly emerged females receiving topical application of JH. The treatment consisted of application of JH, at a concentration of 25 µg.µL⁻¹ in acetone, to 1-day-old Mischocyttarus consimilis workers. The application of JH to newly emerged M. consimilis females significantly altered oocyte length and width, with effects on behavioral ontogeny and the cuticular chemical compounds signaling these parameters in the colony. No effects of the solvent on female physiology were observed, reinforcing that the observed changes were due to the specific effects of JH.

Polygraphus proximus, a four-eyed fir bark beetle, is an invasive bark beetle species which has caused extensive damage to forests of Abies sibirica in southern and western Siberia and to Abies species in the European part of Russia. There is a high risk that the pest insect will spread to areas where it is currently not considered present, such as the European Union. In these areas, it threatens to attack conifer forests of various species which may result in major environmental and economic impact. The aim of this study was to identify pheromone components of P. proximus that can be used as pheromone baits. Males and females of P. proximus were allowed to bore into the bark of stem sections of Abies sibirica at the laboratory, and volatiles were collected with solid-phase microextraction (SPME). Analyses of these extracts with gas chromatography-mass spectrometry (GC–MS) revealed several sex-specific compounds. In total, twelve male-specific compounds and one female-specific compound were identified. The major male-specific compound determined by GC peak area was (Z)‐2‐(3,3‐dimethylcyclohexylidene)‐ethanol [(Z)-DMCHE] and the minor male-specific compounds were 3-methyl-3-buten-1-ol, 3-methyl-2-buten-1-ol, 3-methyl-2-butenal, benzyl alcohol, fragranol, 7-methyl-3-methylene-6-octen-1-ol, (Z)- and (E)-2-(3,3-dimethylcyclohexylidene)-acetaldehyde, geraniol, geranial and papayanol. The only female-specific compound was identified as 1-hexanol. Two of the male-specific compounds, (Z)‐DMCHE and 3-methyl-2-buten-1-ol were shown to attract males and females of P. proximus in field studies. Thus, we now for the first time can present the structures of two male-specific components that are biologically active parts of P. proximus aggregation pheromone. However, some chemical communication overlap between P. proximus and P. subopacus needs to be further investigated as (Z)‐DMCHE also attracted males and females of P. subopacus.

Juvenile hormone (JH) has important functions that regulate insect life. In adult individuals, it induces gonadotropic and behavioral changes. Manipulating JH levels helps to understand how it influences insect physiology. The effects of JH on Epiponini swarm-founding wasps have shown contrasting results, affecting reproduction, chemical compound expression, behavior, and age polyethism. In this study, we investigated whether JH affects reproductive physiology and production of fertility cues in a swarm-founding wasp species Polybia occidentalis in an age-controlled experimental setup. We treated newly emerged females with methoprene (JH analogue) and precocene-I (JH inhibitor) to determine their effects on ovary activation and cuticular hydrocarbon (CHC) expression. Furthermore, we compared the chemical profiles of treated workers with those of queens. Our results show that methoprene and precocene-I affected the CHC production in P. occidentalis. Additionally, females treated with methoprene were chemically more similar to queens than precocene- and acetone-treated females. Methoprene affected ovarian status (increasing ovary activation). These results suggest that different levels of JH reflect changes in chemical and reproductive traits in P. occidentalis females. Furthermore, we point out the existence of fertility cues in this Epiponini wasp.

Allelopathic plants release secondary compounds into the soil that then suppress the growth of nearby plants. Allelopathy has been shown for the invasive Japanese knotweed (Fallopia japonica) and Bohemian knotweed (F. × bohemica). The aggressive and dominant invaders represent a serious threat to the local plant communities outside their native range. Here, we analysed the phenols in the knotweed rhizomes using nuclear magnetic resonance. We also evaluated the allelopathic potential of methanol extracts of F. japonica and F. × bohemica rhizomes and compared these with the effects of the individual knotweed phenols resveratrol, epicatechin and emodin, and their mixture. Rhizomes of both knotweeds contained similar amounts of epicatechin and emodin, with 24% higher resveratrol in F. × bohemica. Only the F. × bohemica methanol extract inhibited radish (Raphanus sativus) seed germination. After 3 days of treatments with 10% (w/v) extracts of both knotweeds, radish seedlings showed up to 70% shorter roots. In contrast, root growth of seedlings treated with the individual phenols resveratrol, epicatechin and emodin, and their mixture, was inhibited by up to 30%, similar to the 1% knotweed extracts. Biochemical parameters of oxidative stress also increased in the roots of treated seedlings, with high levels of malondialdehyde in particular indicating lipid peroxidation. Total antioxidative capacity was also increased in seedlings exposed to 0.6 mg/mL resveratrol and emodin. This study shows higher allelopathic potential of the knotweed methanol extracts compared to the individual phenols and their mixture.

A vast diversity of parasites associates with ants. Living in and around ant nests of these organisms must overcome ant colony defenses. As ant defensive behavior is mainly mediated by species-specific cuticular hydrocarbons (CHCs) or alarm pheromones, and ant-associated parasites can either crack their hosts’ chemical communication code by modifying their own CHC profiles or use pro-active strategies like chemical weaponry for distraction and repellency. While the chemical nature of ant–parasite interactions has been intensively studied for highly host-specific parasites, the chemical-deceptive strategies of the rather rare ant-resembling heteropterans are unknown. To gain insight into this system, I studied the bug Scolopostethus pacificus (Barber 1918) which can be found near the nests of the ecologically dominant and aggressive velvety tree ant (Liometopum occidentale, Emery 1895). Using behavioral, chemical, and molecular approaches, I disentangled the relationship of S. pacificus and its host ant. Chemical profiling of the bug and the ant revealed that the bug does not make use of CHC insignificance or mimicry, but instead uses a cocktail of volatile compounds released from its metathoracic glands that likely moderates encounters with its aggressive host. Feeding trials with armed and artificially disarmed bugs revealed a defensive function of the gland exudates. Targeted molecular gut barcoding showed that S. pacificus does not feed on L. occidentale. These results suggest that chemical weaponry, rather than a chemical code-cracking CHC matching or chemical insignificance, enables S. pacificus to get along with and live in close proximity to its host ant.

The scent gland secretion of an undetermined species of Prionostemma from Costa Rica was analyzed by gas chromatography–mass spectrometry and shown to consist of medium-chain carboxylic acids (mainly octanoic acid) and a ß-hydroxy-carboxylic acid, eventually identified as myrmicacin (= (R)-3-hydroxydecanoic acid). While scent gland secretions in harvestmen have traditionally been considered to be products of de novo synthesis, we here provide evidence for the unusual case of sequestration-derived scent gland constituents: at least myrmicacin appears to be sequestered from leaf-cutter ants that constitute a part of the prey of the Prionostemma-species herein investigated. This is the first report on the scent gland chemistry of the sclerosomatid subfamily Gagrellinae as well as on a possible sequestration mechanism in harvestmen.

Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) is a notorious pest of rice, Oryza sativa L. (Poaceae). Sex pheromones and host-plant volatiles can trap C. medinalis separately. To improve the trap efficiency of synthetic sex pheromone blend, we first tested the synergistic effect of 8 host-plant volatiles, including 2-phenylethanol, 1-hexanol, 1-heptanol, (Z)-3-hexenal, (E)-2-hexenal, octanal, valeraldehyde, and methyl salicylate, on the attraction of C. medinalis to the female-produced sex pheromones in electroantennography. The addition of (E)-2-hexenal, methyl salicylate, valeraldehyde, and (Z)-3-hexenal increased electroantennogram response of C. medinalis to sex pheromones. Further behavioral testing in wind tunnel experiments indicated that additive (E)-2-hexenal or methyl salicylate stimulated the landing behaviors of both male and female C. medinalis compared with sex pheromones alone. Field evaluations showed that mixtures of sex pheromones and (E)-2-hexenal /methyl salicylate resulted in significantly higher catches to male moths than sex pheromones alone. Using 1:1 and 1:10 combinations of the sex pheromones and (E)-2-hexenal, the attraction of C. medinalis to mixtures showed a synergistic effect of 95% and 110%, respectively. Furthermore, 1:1 and 1:10 mixtures of the sex pheromones and methyl salicylate exhibited a synergistic effect of 69% and 146%, respectively. These results may provide the basis for developing efficient pest management strategies against C. medinalis using host-plant volatiles and insect sex pheromones.