Identification, synthesis, and behavioral activity of 5,11-dimethylpentacosane, a novel sex pheromone component of the greater wax moth, Galleria mellonella (L.)

A highly conserved plant volatile odorant receptor detects a sex pheromone component of the greater wax moth, Galleria mellonella (Lepidoptera: Pyralidae)

Odorant receptors (ORs) are key specialized units for mate and host finding in moths of the Ditrysia clade, to which 98% of the lepidopteran species belong. Moth ORs have evolved to respond to long unsaturated acetates, alcohols, or aldehydes (Type I sex pheromones), falling into conserved clades of pheromone receptors (PRs). These PRs might have evolved from old lineages of non-Ditrysian moths that use plant volatile-like pheromones. However, a Ditrysian moth called the greater wax moth, Galleria mellonella (a worldwide-distributed pest of beehives), uses C9-C11 saturated aldehydes as the main sex pheromone components (i.e., nonanal and undecanal). Thus, these aldehydes represent unusual components compared with the majority of moth species that use, for instance, Type I sex pheromones. Current evidence shows a lack of consensus in the amount of ORs for G. mellonella, although consistent in that the moth does not have conserved PRs. Using genomic data, 62 OR candidates were identified, 16 being new genes. Phylogeny showed no presence of ORs in conserved PR clades. However, an OR with the highest transcript abundance, GmelOR4, appeared in a conserved plant volatile-detecting clade. Functional findings from the HEK system showed the OR as sensitive to nonanal and 2-phenylacetaldehyde, but not to undecanal. It is believed that to date GmelOR4 represents the first, but likely not unique, OR with a stable function in detecting aldehydes that help maintain the life cycle of G. mellonella around honey bee colonies.

Nonanal, a new fall armyworm sex pheromone component, significantly increases the efficacy of pheromone lures

BACKGROUND

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a global pest that feeds on >350 plant species and severely limits production of cultivated grasses, vegetable crops and cotton. An efficient way to detect new invasions at early stages, and monitor and quantify the status of established infestations of this pest is to deploy traps baited with species-specific synthetic sex pheromone lures.

RESULTS

We re-examined the compounds in the sex pheromone glands of FAW females by gas chromatography-electroantennogram detector (GC-EAD), GC-mass spectrometry (MS), behavioral and field assays. A new bioactive compound from pheromone gland extracts was detected in low amounts (3.0% relative to (Z)-9-tetradecenyl acetate (Z9-14:OAc), the main pheromone component), and identified as nonanal. This aldehyde significantly increased attraction of male moths to a mix of Z9-14:OAc and (Z)-7-dodecenyl acetate in olfactometer assays. Adding nonanal to this two-component mix also doubled male trap catches relative to the two-component mix alone in cotton fields, whereas nonanal alone did not attract any moths. The addition of nonanal to each of three commercial pheromone lures also increased male catches by 53-135% in sorghum and cotton fields.

CONCLUSION

The addition of nonanal to pheromone lures should improve surveillance, monitoring and control of FAW populations. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Recent advances in the synthesis of insect pheromones: an overview from 2013 to 2022

Covering: 2013 to June 2022Pheromones are usually produced by insects in sub-microgram amounts, which prevents the elucidation of their structures by nuclear magnetic resonance (NMR). Instead, a synthetic reference material is needed to confirm the structure of the natural compounds. In addition, the provision of synthetic pheromones enables large-scale field trials for the development of environmentally friendly pest management tools. Because of these potential applications in pest control, insect pheromones are attractive targets for the development of synthetic procedures and the synthesis of these intraspecific chemical messengers has been at the core of numerous research efforts in the field of pheromone chemistry. The present review is a quick reference guide for the syntheses of insect pheromones published from 2013 to mid-2022, listing the synthesized compounds and highlighting current methodologies in organic synthesis, such as carbon-carbon coupling reactions, organo-transition metal chemistry including ring-closing olefin metathesis, asymmetric epoxidations and dihydroxylations, and enzymatic reactions.

Plasticity in life features, parasitism and super-parasitism behavior of Bracon hebetor, an important natural enemy of Galleria mellonella and other lepidopteran host species

The wasp, Bracon hebetor Say, is an important potential biocontrol agent of a wide range of lepidopteran insect species. The current study was subjected to compare these ectoparasitoid fitness traits on different host species belonging to the order Lepidoptera. Moreover, we determine the population dynamic with different host densities, sex ratio patterns, super-parasitism, longevity, paralysis success, and reproductive potential under laboratory conditions. Our results revealed that oviposition increased with an increase in host density, while the adult emergence and egg hatching were decreased due to the super-parasitism on host larvae. A higher male and female-biased population were observed when virgin and mated females offered fresh hosts. Adults' longevity was recorded more in females than males when kept only with bee honey + royal jelly + host larvae. The mean duration of egg-adult development was recorded higher on Galleria mellonella and lowest on Busseola fusca. The parasitization rate, super-parasitism, and cumulative fecundity of mated and virgin female wasps with different host species were observed higher on specific host Galleria mellonella while it was lower on Phthorimaea operculella. Furthermore, the parasitoids having mating experience preferred fresh, while the parasitoids' lack of mating experiences preferred paralyzed host under olfactometer test. Besides, this research has produced novel facts on the biology of parasitic wasp, B. hebetor that may guide the advancement of sustainable biological control programs to control lepidopteran pests.

The Importance of Methyl-Branched Cuticular Hydrocarbons for Successful Host Recognition by the Larval Ectoparasitoid Holepyris sylvanidis

Cuticular hydrocarbons (CHCs) of host insects are used by many parasitic wasps as contact kairomones for host location and recognition. As the chemical composition of CHCs varies from species to species, the CHC pattern represents a reliable indicator for parasitoids to discriminate host from non-host species. Holepyris sylvanidis is an ectoparasitoid of beetle larvae infesting stored products. Previous studies demonstrated that the larval CHC profile of the confused flour beetle, Tribolium confusum, comprises long chain linear and methyl-branched alkanes (methyl alkanes), which elicit trail following and host recognition in H. sylvanidis. Here we addressed the question, whether different behavioral responses of this parasitoid species to larvae of other beetle species are due to differences in the larval CHC pattern. Our study revealed that H. sylvanidis recognizes and accepts larvae of T. confusum, T. castaneum and T. destructor as hosts, whereas larvae of Oryzaephilus surinamensis were rejected. However, the latter species became attractive after applying a sample of T. confusum larval CHCs to solvent extracted larvae. Chemical analyses of the larval extracts revealed that CHC profiles of the Tribolium species were similar in their composition, while that of O. surinamensis differed qualitatively and quantitatively, i.e. methyl alkanes were present as minor components on the cuticle of all Tribolium larvae, but were absent in the O. surinamensis CHC profile. Furthermore, the parasitoid successfully recognized solvent extracted T. confusum larvae as hosts after they had been treated with a fraction of methyl alkanes. Our results show that methyl alkanes are needed for host recognition by H. sylvanidis.

3,7-Dimethylpentadecane: a Novel Sex Pheromone Component from Leucoptera sinuella (Lepidoptera: Lyonetiidae)

Leucoptera sinuella is a leaf-miner moth present in several regions in the world, which has been recently introduced into Chile. The larvae feed exclusively on the leaves of poplar and willow trees, and the damage caused by the feeding behavior poses a threat to the wood-producing industry. Besides, L. sinuella larvae invade nearby orchards for pupation, causing rejections in Chilean fresh fruit for export. Here we report the identification of the female-produced sex pheromone of L. sinuella as a first step towards the development of pheromone-based methods for pest management of this species. First, we analyzed hexane extracts of the abdominal glands of virgin females by gas chromatography coupled with mass spectrometry and identified the major compound in these extracts to be 3,7-dimethylpentadecane, while minor compounds in the extracts proved to be 3,7-dimethyltetradecane and 7-methylpentadecane. Structure assignments were carried out by comparison of retention times and mass spectra of the natural products with those of authentic reference samples. Second, we conducted field tests, which showed that traps baited with synthetic 3,7-dimethylpentadecane were significantly attractive to males in a dose-dependent response. Our results also showed that a mixture of 3,7-dimethylpentadecane, 3,7-dimethyltetradecane, and 7-methylpentadecane in proportions similar to those found in gland extracts was the most attractive lure.

Mating-based regulation and ligand binding of an odorant-binding protein support the inverse sexual communication of the greater wax moth, Galleria mellonella (Lepidoptera: Pyralidae)

In moths, sex pheromones play a key role in mate finding. These chemicals are transported in the antennae by odorant-binding proteins (OBPs). Commonly, males encounter conspecific females; therefore, several OBPs are male-biased. Less is known, however, about how the olfactory system of moths has evolved toward inverse sexual communication, ie where females seek males. Therefore, the objective of this study was to identify the profile of OBPs and their expression patterns in the bee hive pest, Galleria mellonella, a moth that uses inverse sexual communication. Here, OBP-related transcripts were identified by an RNA Sequencing (RNA-Seq) approach and analysed through both Reverse Transcription Polymerase Chain Reaction (RT-PCR) in different tissues and quantitative real-time PCR for two states, virgin and postmating. Our results indicate that G. mellonella has 20 OBPs distributed amongst different tissues. Interestingly, 17 of the 20 OBPs were significantly down-regulated after mating in females, whereas only OBP7 was up-regulated. By contrast, 18 OBP transcripts were up-regulated in males after mating. Additionally, binding assays and structural simulations showed general odorant-binding protein 2 (GOBP2) was able to bind sex pheromone components and analogues. These findings suggest a possible role of OBPs, especially GOBPs, in the inverse sexual communication of G. mellonella, with gene expression regulated as a response to mating.

Candidate chemosensory genes identified from the greater wax moth, Galleria mellonella, through a transcriptomic analysis

The greater wax moth, Galleria mellonella Linnaeus (Lepidoptera: Galleriinae), is a ubiquitous pest of the honeybee, and poses a serious threat to the global honeybee industry. G. mellonella pheromone system is unusual compared to other lepidopterans and provides a unique olfactory model for pheromone perception. To better understand the olfactory mechanisms in G. mellonella, we conducted a transcriptomic analysis on the antennae of both male and female adults of G. mellonella using high-throughput sequencing and annotated gene families potentially involved in chemoreception. We annotated 46 unigenes coding for odorant receptors, 25 for ionotropic receptors, two for sensory neuron membrane proteins, 22 for odorant binding proteins and 20 for chemosensory proteins. Expressed primarily in antennae were all the 46 odorant receptor unigenes, nine of the 14 ionotropic receptor unigenes, and two of the 22 unigenes coding for odorant binding proteins, suggesting their putative roles in olfaction. The expression of some of the identified unigenes were sex-specific, suggesting that they may have important functions in the reproductive behavior of the insect. Identification of the candidate unigenes and initial analyses on their expression profiles should facilitate functional studies in the future on chemoreception mechanisms in this species and related lepidopteran moths.

Losing the Arms Race: Greater Wax Moths Sense but Ignore Bee Alarm Pheromones

The greater wax moth, Galleria mellonella L., is one of main pests of honeybees. The larvae burrow into the wax, damaging the bee comb and degenerating bee products, but also causes severe effects like driving the whole colony to abscond. In the present study, we used electroantennograms, a Y maze, and an oviposition site choice bioassay to test whether the greater wax moth can eavesdrop on bee alarm pheromones (isopentyl acetate, benzyl acetate, octyl acetate, and 2-heptanone), to target the bee colony, or if the bee alarm pheromones would affect their preference of an oviposition site. The results revealed that the greater wax moth showed a strong electroantennogram response to these four compounds of bee alarm pheromones even in a low concentration (100 ng/μL), while they showed the highest response to octyl acetate compared to the other three main bee alarm components (isopentyl acetate, benzyl acetate, and 2-heptanone). However, the greater wax moth behavioral results showed no significant preference or avoidance to these four bee alarm pheromones. These results indicate that bees are currently losing the arms race since the greater wax moth can sense bee alarm pheromones, however, these alarm pheromones are ignored by the greater wax moth.

The Biology and Control of the Greater Wax Moth, Galleria mellonella

The greater wax moth, Galleria mellonella Linnaeus, is a ubiquitous pest of the honeybee, Apis mellifera Linnaeus, and Apis cerana Fabricius. The greater wax moth larvae burrow into the edge of unsealed cells with pollen, bee brood, and honey through to the midrib of honeybee comb. Burrowing larvae leave behind masses of webs which causes galleriasis and later absconding of colonies. The damage caused by G. mellonella larvae is severe in tropical and sub-tropical regions, and is believed to be one of the contributing factors to the decline in both feral and wild honeybee populations. Previously, the pest was considered a nuisance in honeybee colonies, therefore, most studies have focused on the pest as a model for in vivo studies of toxicology and pathogenicity. It is currently widespread, especially in Africa, and the potential of transmitting honeybee viruses has raised legitimate concern, thus, there is need for more studies to find sustainable integrated management strategies. However, our knowledge of this pest is limited. This review provides an overview of the current knowledge on the biology, distribution, economic damage, and management options. In addition, we provide prospects that need consideration for better understanding and management of the pest.

Chiral methyl-branched pheromones

Insect pheromones are some of the most interesting natural products because they are utilized for interspecific communication between various insects, such as beetles, moths, ants, and cockroaches. A large number of compounds of many kinds have been identified as pheromone components, reflecting the diversity of insect species. While this review deals only with chiral methyl-branched pheromones, the chemical structures of more than one hundred non-terpene compounds have been determined by applying excellent analytical techniques. Furthermore, their stereoselective syntheses have been achieved by employing trustworthy chiral sources and ingenious enantioselective reactions. The information has been reviewed here not only to make them available for new research but also to understand the characteristic chemical structures of the chiral pheromones. Since biosynthetic studies are still limited, it might be meaningful to examine whether the structures, particularly the positions and configurations of the branched methyl groups, are correlated with the taxonomy of the pheromone producers and also with the function of the pheromones in communication systems.