Assessment of the In Vivo and In Vitro Release of Chemical Compounds from Vespa velutina

Vespa velutina has been rapidly expanding throughout Galicia since 2012. It is causing human health risks and well-known losses in the beekeeping sector. Control methods are scarce, unspecific, and ineffective. Semiochemicals are insect-derived chemicals that play a role in communication and they could be used an integrated pest management tool alternative to conventional pesticides. A previous determination of the organic chemical profile should be the first step in the study of these semiochemicals. HS-SPME in living individuals and the sting apparatus extraction followed by GC-MS spectrometry were combined to extract a possible profile of these compounds in 43 hornets from Galicia. The identified compounds were hydrocarbons, ketones, terpenes, and fatty acid, and fatty acid esters. Nonanal aldehyde appeared in important concentrations in living individuals. While pentadecane, 8-hexyl- and ethyl oleate were mainly extracted from the venom apparatus. Ketones 2-nonanone, 2-undecanone and 7-nonen-2-one, 4,8-dimethyl- were identified by both procedures, as was 1,7-Nonadiene, 4,8-dimethyl-. Some compounds were detected for the first time in V. velutina such as naphthalene, 1,6-dimethyl-4-(1-methylethyl). The chemical profile by caste was also characterized.

Electrophysiological Responses of Bactrocera kraussi (Hardy) (Tephritidae) to Rectal Gland Secretions and Headspace Volatiles Emitted by Conspecific Males and Females

Pheromones are biologically important in fruit fly mating systems, and also have potential applications as attractants or mating disrupters for pest management. Bactrocera kraussi (Hardy) (Diptera: Tephritidae) is a polyphagous pest fruit fly for which the chemical profile of rectal glands is available for males but not for females. There have been no studies of the volatile emissions of either sex or of electrophysiological responses to these compounds. The present study (i) establishes the chemical profiles of rectal gland contents and volatiles emitted by both sexes of B. kraussi by gas chromatography-mass spectrometry (GC-MS) and (ii) evaluates the detection of the identified compounds by gas chromatography-electroantennogram detection (GC-EAD) and -electropalpogram detection (GC-EPD). Sixteen compounds are identified in the rectal glands of male B. kraussi and 29 compounds are identified in the rectal glands of females. Of these compounds, 5 were detected in the headspace of males and 13 were detected in the headspace of females. GC-EPD assays recorded strong signals in both sexes against (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-ethyl-7-mehtyl-1,6-dioxaspiro[4.5]decane isomer 2, (E,Z)/(Z,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, and (Z,Z)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane. Male antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-methyl-6-pentyl-3,4-dihydro-2H-pyran, 6-hexyl-2-methyl-3,4-dihydro-2H-pyran, 6-oxononan-1-ol, ethyl dodecanoate, ethyl tetradecanoate and ethyl (Z)-hexadec-9-enoate, whereas female antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and 2-methyl-6-pentyl-3,4-dihydro-2H-pyran only. These compounds are candidates as pheromones mediating sexual interactions in B. kraussi.

The Venom Compound N-(3-methylbutyl)acetamide Attracts Several Polistes (Fuscopolistes) Species (Hymenoptera: Vespidae)

Polistes paper wasps in the Fuscopolistes subgenus (Hymenoptera: Vespidae) can be serious pests when they swarm at tall man-made structures. Chemical attractants may be useful to trap such paper wasps when they achieve pest status. Polistes venom has been shown to elicit a variety of behavioral responses in congeneric wasps, making it a source for potential chemical attractants. The compound N-(3-methylbutyl)acetamide is a principal volatile component in the venom of many female vespid wasps, including numerous Polistes species. We report the presence of N-(3-methylbutyl)acetamide in autumn gynes of Polistes metricus Say, Polistes bellicosus Cresson, and Polistes dorsalis (F.), as well as workers of Polistes aurifer (Saussure), P. bellicosus, P. metricus, and P. dorsalis. In field tests conducted in Florida, Georgia, South Carolina, and Washington, N-(3-methylbutyl)acetamide attracted male and female P. aurifer and P. metricus, as well as male P. dorsalis and P. bellicosus. Thus, N-(3-methylbutyl)acetamide may be a useful lure for trapping these paper wasps in pest situations.

Female volatiles as sex attractants in the invasive population of Vespa velutina nigrithorax

Due to its huge invasion potential and specialization in honeybee predation, the invasive hornet Vespa velutina nigrithorax represents a high-concern species under both an ecological and economical perspective. In light of the development of specific odorant attractants to be used in sustainable control strategies, we carried out both behavioural assays and chemical analyses to investigate the possibility that, in the invasive population of V. velutina nigrithorax, reproductive females emit volatile pheromones to attract males, as demonstrated in a Chinese non-invasive population. We focused on the secretions produced by sternal and venom glands; because of the volatility and complexity of their composition, both of them could potentially allow an attraction and a species-specific response, decreasing therefore non-target species by-catches. Results of chemical analyses and behavioural assays showed that venom volatiles, although population-specific, are unlikely candidates as male attractants since they do not differ in composition or in quantity between reproductive females and workers and do not attract males. Conversely, sternal gland secretion differs between female castes for the presence of some ketoacids exclusive of gynes already reported as sex pheromones for the non-invasive subspecies V. velutina auraria. Despite such a difference, males are attracted by the sternal gland secretion of both workers and gynes. These results provide a first step to understand the reproductive biology of V. velutina nigrithorax in its invasive range and to develop effective and sustainable management strategies for the species.

Candidate genes involved in spiroacetal biosynthesis in the oriental fruit fly, Bactrocera dorsalis

Spiroacetals are widespread in nature as components of volatile semiochemical secretions from many insect species. The general pathway for spiroacetal biosynthesis in Bactrocera sp. is preliminarily established, but many genes involved in this pathway remain to be characterized. By analyzing transcriptomes of the rectal glands (RGs) from immature and mature females of the oriental fruit fly, Bactrocera dorsalis, a set of genes encoding two acetyl-CoA carboxylases (ACCs), two fatty acid synthases (FASs), eight desaturases (DESs), twelve fatty acyl-CoA reductases (FARs), seventy-two cytochrome P450 enzymes (CYPs), and twenty-three odorant binding proteins (OBPs) were identified. We investigated the expression of candidate genes in immature and mature stages based on the RNA-seq data and Real-time quantitative PCR. Expression profiling revealed that some of these genes were primarily expressed in female rectal glands among different tissues, and were up-regulated in mature females. Semi-quantitative RT-PCR assays were also adapted to examine tissue-specific expression of selected candidate genes. Additionally, their putative functions in spiroacetal synthesis and transportation are proposed. Our study provided large-scale sequence information for further functional studies on spiroacetal biosynthetic pathways.

Variation in Venoms of Polybia Paulista Von Ihering and Polybia Occidentalis Olivier (Hymenoptera: Vespidae), Assessed by the FTIR-PAS Technique

Wasps are able to synthesize toxic compounds known as venoms, which form a part of a mechanism to overcome prey and also to defend their colonies. Study of the compounds that constitute these substances is essential in order to understand how this defense mechanism evolved, since there is evidence that the venoms can vary both intra- and interspecifically. Some studies have used liquid and gas chromatography as a reliable technique to analyze these compounds. However, the use of Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) to analyze the variations in venom's chemical profile has been proposed recently. This study evaluated whether the FTIR-PAS technique is effective for assessing the role of environmental factors on intra- and interspecific differences in the venom of the wasps Polybia paulista Von Ihering and Polybia occidentalis Olivier by FTIR-PAS. The colonies were collected in three municipalities of Mato Grosso do Sul, Brazil, in different types of environments. The results showed that the venoms of P. paulista and P. occidentalis differed significantly in profile. In addition, the intraspecific differences in the venom's chemical profile of P. paulista are related to the type of environment where they nested, regardless of the geographical distance between the nests. The FTIR-PAS technique proved to be reliable and effective to evaluate the variations in the venom's chemical profile in social wasps.

Ecology and Evolution of Communication in Social Insects

Insect life strategies comprise all levels of sociality from solitary to eusocial, in which individuals form persistent groups and divide labor. With increasing social complexity, the need to communicate a greater diversity of messages arose to coordinate division of labor, group cohesion, and concerted actions. Here we summarize the knowledge on prominent messages in social insects that inform about reproduction, group membership, resource locations, and threats and discuss potential evolutionary trajectories of each message in the context of social complexity.

Tree resin composition, collection behavior and selective filters shape chemical profiles of tropical bees (Apidae: Meliponini)

The diversity of species is striking, but can be far exceeded by the chemical diversity of compounds collected, produced or used by them. Here, we relate the specificity of plant-consumer interactions to chemical diversity applying a comparative network analysis to both levels. Chemical diversity was explored for interactions between tropical stingless bees and plant resins, which bees collect for nest construction and to deter predators and microbes. Resins also function as an environmental source for terpenes that serve as appeasement allomones and protection against predators when accumulated on the bees' body surfaces. To unravel the origin of the bees' complex chemical profiles, we investigated resin collection and the processing of resin-derived terpenes. We therefore analyzed chemical networks of tree resins, foraging networks of resin collecting bees, and their acquired chemical networks. We revealed that 113 terpenes in nests of six bee species and 83 on their body surfaces comprised a subset of the 1,117 compounds found in resins from seven tree species. Sesquiterpenes were the most variable class of terpenes. Albeit widely present in tree resins, they were only found on the body surface of some species, but entirely lacking in others. Moreover, whereas the nest profile of Tetragonula melanocephala contained sesquiterpenes, its surface profile did not. Stingless bees showed a generalized collecting behavior among resin sources, and only a hitherto undescribed species-specific "filtering" of resin-derived terpenes can explain the variation in chemical profiles of nests and body surfaces from different species. The tight relationship between bees and tree resins of a large variety of species elucidates why the bees' surfaces contain a much higher chemodiversity than other hymenopterans.