Synthesis of the sex pheromone of the citrus mealybug, Pseudococcus cryptus

New esters from the essential oil of dry flowers of elder (Sambucus nigra L.)

BACKGROUND

Elder (Sambucus nigra L.) has relevance for the food, fragrance and pharmaceutical industries. Flowers of this species emit a very pleasant scent; for processing purposes, inflorescences are either collected from the wild or harvested from a cultivated crop. The study of elderflower-derived volatiles bears both phytochemical and commercial importance.

RESULTS

Three samples of dry elderflower essential oil obtained from laboratory-scale hydrodistillations were analyzed. By use of gas chromatography-mass spectrometry, synthesis and NMR studies of chromatographic fractions of a distillation water extract prepared in a semi-industrial scale steam distillation, 252 constituents of the oil were identified; 115 compounds were not previously reported as elderflower volatiles, seven of which were new natural esters. Particularly interesting were those of isosenecioic (3-methylbut-3-enoic) acid because these were never before found in the plant kingdom.

CONCLUSION

With these identifications, the known essential oil constituents accounted for 89.0-93.0% of the analyzed samples. Although the number of known S. nigra flower-derived volatiles is now quite high, further research (both analytical and olfactory) is needed to unveil all of the relevant contributions to the unique odor of elderflowers. © 2023 Society of Chemical Industry.

Sex Pheromone of the Invasive Mealybug Citrus Pest, Delottococcus aberiae (Hemiptera: Pseudococcidae). A New Monoterpenoid with a Necrodane Skeleton

Native to sub-Saharan Africa, Delottococcus aberiae De Lotto (Hemiptera: Pseudoccidae) is an invasive mealybug that has been recently reported in Europe, seriously damaging citrus production in eastern Spain. In this study, we isolated and determined the structure of the sex pheromone of D. aberiae, to provide a highly specific and effective lure for detecting, monitoring, and potentially controlling this pest. The volatile profile of D. aberiae virgin and mated females was studied by aeration and collection of effluvia in Porapak-Q. The resulting extracts were analyzed by gas chromatography coupled to mass spectrometry (GC-MS), revealing a candidate compound specific of virgin females. GC-MS and nuclear magnetic resonance spectroscopy data evidenced a new compound, (4,5,5-trimethyl-3-methylenecyclopent-1-en-1-yl)methyl acetate, with an unusual β-necrodol skeleton. This compound was synthesized and shown to be attractive to male D. aberiae in both laboratory and field experiments. A GC analysis using an enantioselective stationary phase and polarimetry analyses of the synthetic enantiomers showed the natural compound emitted by virgin females to be the - enantiomer.

Chemistry of the pheromones of mealybug and scale insects

This article comprehensively reviews the syntheses of all known sex pheromones of scales and mealybugs, describes how they were identified, and how the synthetic pheromones are used in insect management.

Sexual maturation and aging of adult male mealybug (Hemiptera: Pseudococcidae)

The physiological age of adult males of seven mealybug species was measured in relation to the elongation of the male pair of the waxy caudal filaments. These filaments begin to emerge after eclosion and reached their maximum length from 29.4-46.6 h. The studied males were divided into three age groups, expressed as percentages of the total waxy caudal filaments length. Attraction to a sex pheromone source was significantly higher in the oldest male group (maximum filaments growth) compared with youngest one. Only the oldest male group copulated successfully; few of the younger males tested displayed 'courtship' behavior towards conspecific virgin females. The calculated duration of the sexually active phase of the adult male life cycle varied among species ranging from 34.4 to 46.6 h. There were marked variations in the strength of attraction to a pheromone source according to time of day. There was a continuous decrease in sexual activity from morning to evening. Our findings reveal clear maturation periods for adult males of the seven studied species. The long immature phase of the adult male mealybug is probably also related to several physiological processes that are needed to complete male maturation. The most noticeable change is the elongation of the waxy caudal filaments. However, mating may be performed at any time ambient conditions are suitable. Whereas male mealybug flight towards a pheromone source is restricted to a few hours, the male may continue mating activity throughout its sexually active period.

Identification of the sex pheromone of the invasive scale Acutaspis albopicta (Hemiptera: Diaspididae), arriving in California on shipments of avocados from Mexico

As a result of relaxation of importation restrictions ordered by the Animal and Plant Health Inspection Service of the U.S. Department of Agriculture, shipments of fresh avocados from Mexico began entering California year-round in 2007, despite the fact that these shipments were heavily infested with a number of exotic and potentially invasive armored scale species that are not thought to be present in California. Here, we report the identification of the sex pheromone of one of these species, Acutaspis albopicta (Cockerell), from a quarantine colony of these insects initiated from specimens collected from commercial shipments of Mexican avocados. The compound was identified as [(1S,3S)-2,2-dimethyl-3-(prop-1-en-2-yl)cyclobutyl)]methyl (R)-2-methylbutanoate, and was similar in structure to the pheromones of several other scale and mealybug species. In laboratory bioassays, the pheromone was highly attractive to male scales in microgram doses. The pheromone will provide a very sensitive and selective tool for detection of the scale to try and prevent its permanent establishment in California.

Significance of chirality in pheromone science

Pheromones play important roles in chemical communication among organisms. Various chiral and non-racemic pheromones have been identified since the late 1960s. Their enantioselective syntheses could establish the absolute configuration of the naturally occurring pheromones and clarified the relationships between absolute configuration and bioactivity. For example, neither the (R)- nor (S)-enantiomer of sulcatol, the aggregation pheromone of an ambrosia beetle Gnathotrichus sulcatus, is behaviorally active, while their mixture is bioactive. In the case of olean, the olive fruit fly pheromone, its (R)-isomer is active for the males, and the (S)-isomer is active for the females. About 140 chiral pheromones are reviewed with regard to their stereochemistry-bioactivity relationships. Problems encountered in studying chirality of pheromones were examined and analyzed to think about possible future directions in pheromone science.

Sex pheromone of the pink hibiscus mealybug, Maconellicoccus hirsutus, contains an unusual cyclobutanoid monoterpene

Two compounds that together constitute the female sex pheromone of the pink hibiscus mealybug (PHM), Maconellicoccus hirsutus, were isolated, identified, and synthesized. They are (R)-2-isopropenyl-5-methyl-4-hexenyl (S)-2-methylbutanoate [common name is (R)-lavandulyl (S)-2-methylbutanoate] and [(R)-2,2-dimethyl-3-(1-methylethylidene)cyclobutyl]methyl (S)-2-methylbutanoate [which we refer to as (R)-maconelliyl (S)-2-methylbutanoate]. Maconelliol is an unusual cyclobutanoid monoterpene, and its structure has been established by enantioselective synthesis from precursors of known structure and configuration. A 1:5 synthetic mixture of the two RS esters (1 microg per rubber septum) proved to be a potent attractant of males in field bioassays. The pheromone component, maconelliyl 2-methylbutanoate, represents a heretofore undescribed natural product.