Identification of the Aggregation Pheromone of the Date Palm Root Borer Oryctes agamemnon

Sex Pheromone of the Azalea Mealybug With a Non-Terpene Structure

Mealybug females release sex pheromones to attract conspecific males for mating. It is critical for mealybug males, which are fragile and short-lived, to respond to the pheromone of their species without time- and energy-consuming cross-attractions to other species. Thus, mealybug pheromone systems are considered to have evolved to be species-specific with unique structures in each species and offer an opportunity to study the diversity of pheromone chemistry that mediates intersexual courtship signals. More than 20 mealybug pheromones are reported to be monoterpenes in general, with only one exception, a hemiterpene alcohol esterified with a medium-chain fatty acid (MCFA), found in the Matsumoto mealybug, Crisicoccus matsumotoi. However, it is unknown whether this is truly exceptional, or if similar compounds are used in other related mealybugs. In this study, we isolated and characterized the pheromone of an allied species, the azalea mealybug C. azaleae. Using gas chromatography-mass spectrometry, nuclear magnetic resonance spectroscopy, and bioassays with synthetics, the pheromone was shown to be composed of isopropyl (E)-7-methyl-4-nonenoate, isopropyl (E)-7-methyl-4-octenoate, and ethyl (E)-7-methyl-4-nonenoate. Surprisingly, the structures of these compounds do not include hemiterpene nor monoterpene motifs but have methyl-branched MCFA parts that are similar to an acid moiety of the C. matsumotoi pheromone. This study implies irregular events for the divergence of pheromone structures in ancestors of the genus Crisicoccus and other mealybugs.

Identification of Components of the Aggregation Pheromone of the Guam Strain of Coconut Rhinoceros Beetle, Oryctes rhinoceros, and Determination of Stereochemistry

The coconut rhinoceros beetle, Oryctes rhinoceros (Linnaeus 1758) (Coleoptera: Scarabaeidae: Dynastinae) (CRB), is endemic to tropical Asia where it damages both coconut and oil palm. A new invasion by CRB occurred on Guam in 2007 and eradication attempts failed using commonly applied Oryctes rhinoceros nudivirus (OrNV) isolates. This and subsequent invasive outbreaks were found to have been caused by a previously unrecognized haplotype, CRB-G, which appeared to be tolerant to OrNV. The male-produced aggregation pheromone of the endemic, susceptible strain of O. rhinoceros (CRB-S) was previously identified as ethyl 4-methyloctanoate. Following reports from growers that commercial lures containing this compound were not attractive to CRB-G, the aim of this work was to identify the pheromone of CRB-G. Initial collections of volatiles from virgin male and female CRB-G adults from the Solomon Islands failed to show any male- or female-specific compounds as candidate pheromone components. Only after five months were significant quantities of ethyl 4-methyloctanoate and 4-methyloctanoic acid produced by males but not by females. No other male-specific compounds could be detected, in particular methyl 4-methyloctanoate, 4-methyl-1-octanol, or 4-methyl-1-octyl acetate, compounds identified in volatiles from some other species of Oryctes. Ethyl 4-methyloctanoate elicited a strong electroantennogram response from both male and female CRB-G, but these other compounds, including 4-methyloctanoic acid, did not. The enantiomers of ethyl 4-methyloctanoate and 4-methyloctanoic acid were conveniently prepared by enzymatic resolution of the commercially-available acid, and the enantiomers of the acid, but not the ester, could be separated by gas chromatography on an enantioselective cyclodextrin phase. Using this approach, both ethyl 4-methyloctanoate and 4-methyloctanoic acid produced by male CRB-G were shown to be exclusively the (R)-enantiomers whereas previous reports had suggested male O. rhinoceros produced the (S)-enantiomers. However, re-examination of the ester and acid produced by male CRB-S from Papua New Guinea showed that these were also the (R)-enantiomers. In field trapping experiments carried out in the Solomon Islands, both racemic and ethyl (R)-4-methyloctanoate were highly attractive to both male and female CRB-G beetles. The (S)-enantiomer and the corresponding acids were only weakly attractive. The addition of racemic 4-methyloctanoic acid to ethyl 4-methyloctanoate did significantly increase attractiveness, but the addition of (R)- or (S)-4-methyloctanoic acid to the corresponding ethyl esters did not. Possible reasons for the difference in assignment of configuration of the components of the CRB pheromone are discussed along with the practical implications of these results.

Attraction of Adults of Cyclocephala lunulata and Cyclocephala barrerai (Coleoptera: Scarabaeoidea: Melolonthidae) towards Bacteria Volatiles Isolated from Their Genital Chambers

In the study of the chemical communication of adults of the Melolonthidae family, bacteria have been observed in the epithelium of the genital chamber; possibly, bacteria are involved in the production of sex attractants in their hosts. Therefore, it is important to identify the volatile organic compounds from bacteria (VOCsB) released by these microorganisms and study the biological activity stimulated by VOBCs in adults of Melolonthidae. In this study, bacteria were isolated from the genital chamber of Cyclocephala lunulata and Cyclocephala barrerai, from which VOCsB were extracted using static headspace solid-phase microextraction (SHS-SPME) and dynamic headspace Super Q solid-phase extraction (DHS-SPE) and analyzed using gas chromatography-mass spectrometry. The effect of VOCsB on the hosts and conspecifics was evaluated utilizing an olfactometer and electroantennography (EAG). Two species of Enterobacteria were isolated from the genital chamber of each female species, and VOCsB derived from sulfur-containing compounds, alcohols, esters, and fatty acids were identified. An attraction response was observed in olfactometry studies, and antennal responses to VOCsB were confirmed in EAG bioassays. With these results, new perspectives on the relationship between these beetles and their bacteria emerge, in addition to establishing a basis for management programs in the future.

Volatiles Emitted by Calling Males of Burying Beetles and Ptomascopus morio (Coleoptera: Silphidae: Nicrophorinae) Are Biogenetically Related

In burying beetles, Nicrophorus spp. (Coleoptera: Silphidae: Nicrophorinae) mate finding is mediated by male produced volatile compounds. To date, pheromone components of only two species have been identified. In an attempt to better understand the evolution of male pheromone signaling in burying beetles, we investigated the male released volatiles of ten Nicrophorus species and one closely related nicrophorine species, Ptomascopus mori. Volatiles emitted by calling males were collected in the laboratory by means of solid phase micro extraction and analyzed using gas chromatography coupled with mass spectrometry. Identified volatiles included short chain esters of 4-methylcarboxylic acids, terpenoids, and some other aliphatic compounds. The long-range volatile signals of the burying beetle species included in this study are blends of two to seven components. We found that methyl or ethyl esters of 4-methylheptanoic acid and 4-methyloctanoic acid are produced by eight of the ten investigated Nicrophorus species. These esters may play a key role in chemical communication. Their widespread occurrence suggests that these compounds did not evolve recently, but appeared relatively early in the phylogeny of the genus. Although Ptomascopus is considered the sister genus of Nicrophorus, P. morio males do not produce any of the Nicrophorus compounds, but release 3-methylalkan-2-ones, which are absent in Nicrophorus. A better understanding of the evolution of burying beetle pheromones, however, will only be possible once more species have been studied.

Synthetic Co-Attractants of the Aggregation Pheromone of the Date Palm Root Borer Oryctes agamemnon

Laboratory and field investigations to identify and evaluate plant co-attractants of the aggregation pheromone of the date palm pest Oryctes agamemnon are reported. Volatiles emitted by freshly cut palm core and palm core with feeding males, were collected, analyzed by gas chromatography coupled to mass spectrometry and evaluated in olfactometers alone or combined with synthetic pheromone. A collection of palm odor without male effluvia was attractive alone and enhanced attraction to synthetic pheromone in an olfactometer similar to that to a collection of palm odor emitted with feeding males and containing natural pheromone. Behavioral responses to collections of palm volatiles were correlated to the amount of volatiles material in them. Enhancement of the attractiveness of the pheromone was not correlated to chemicals specific to beetle feeding. The chemicals common to the active collections extracts were benzoate esters, mostly ethyl benzoate, anisole derivatives and sesquiterpenes. Blends of the most abundant components of the extracts were evaluated for enhancement of the attractiveness of pheromone (1 μg) in olfactometers at 1 or 10 μg doses. The mixtures were further evaluated by field trapping in Tunisia at 3-10 mg/day using reference (6 mg/day) or experimental pheromone formulations. A mixture of ethyl benzoate, 4-methylanisole and farnesol (1:1:1 w/w at 6.5 mg/day) enhanced captures in pheromone baited traps in 2014 and 2015 and this mixture was as active as the natural palm bait. The practical prospect of the result for the management for O. agamemnon, and other palm beetles is discussed.

Draft Genome of the Scarab Beetle Oryctes borbonicus on La Réunion Island

Beetles represent the largest insect order and they display extreme morphological, ecological and behavioral diversity, which makes them ideal models for evolutionary studies. Here, we present the draft genome of the scarab beetle Oryctes borbonicus, which has a more basal phylogenetic position than the two previously sequenced pest species Tribolium castaneum and Dendroctonus ponderosae providing the potential for sequence polarization. Oryctes borbonicus is endemic to La Réunion, an island located in the Indian Ocean, and is the host of the nematode Pristionchus pacificus, a well-established model organism for integrative evolutionary biology. At 518 Mb, the O. borbonicus genome is substantially larger and encodes more genes than T. castaneum and D. ponderosae. We found that only 25% of the predicted genes of O. borbonicus are conserved as single copy genes across the nine investigated insect genomes, suggesting substantial gene turnover within insects. Even within beetles, up to 21% of genes are restricted to only one species, whereas most other genes have undergone lineage-specific duplications and losses. We illustrate lineage-specific duplications using detailed phylogenetic analysis of two gene families. This study serves as a reference point for insect/coleopteran genomics, although its original motivation was to find evidence for potential horizontal gene transfer (HGT) between O. borbonicus and P. pacificus. The latter was previously shown to be the recipient of multiple horizontally transferred genes including some genes from insect donors. However, our study failed to provide any clear evidence for additional HGTs between the two species.