Pheromone chirality of african palm weevil,Rhynchophorus phoenicis (F.) and palmetto weevil,Rhynchophorus cruentatus (F.) (Coleoptera: Curculionidae)

Aggregation Pheromones of Weevils (Coleoptera: Curculionidae): Advances in the Identification and Potential Uses in Semiochemical-Based Pest Management Strategies

With approximately 83,000 species described, Curculionidae is the largest family of beetles, comprising more than 80% of all weevil species worldwide. Many species of Curculionidae attack a wide range of native and orchards crops, as well as globally important stored products such as grains, flour, and seeds, being responsible for significant environmental and economic losses. This work provides an overview of the research in the identification of aggregation pheromones of Curculionidae, and their potential contributions to the development of semiochemical-based pest management strategies. The synergistic effect of the host plant volatiles in the attractiveness of weevil pheromones is also briefly reported, demonstrating the important role of these additional attractants in the chemical communication of curculionids.

Perspectives for Synergic Blends of Attractive Sources in South American Palm Weevil Mass Trapping: Waiting for the Red Palm Weevil Brazil Invasion

Coupling several natural and synthetic lures with aggregation pheromones from the palm weevils Rhynchophorus palmarum and R. ferrugineus reveals a synergy that results in an increase in pest captures. The combined attraction of pure pheromones, ethyl acetate, and decaying sweet and starchy plant tissue increases the net total of mass-trapped weevils. The 2018 entrance of the red palm weevil (RPW) into South America has threatened palm-product income in Brazil and other neighboring countries. The presence of the new A1 quarantine pest necessitates the review of all available options for a sustainable mass-trapping, monitoring, and control strategy to ultimately target both weevils with the same device. The effective lure-blend set for the mass-trapping system will attract weevils in baiting and contaminating stations for entomopathogenic fungi that the same weevils will spread.

Attractiveness of host banana leaf materials to the banana weevil, Cosmopolites sordidus in Ghana for development of field management strategies

BACKGROUND

The banana weevil, Cosmopolites sordidus, has been frequently cited as the most challenging constraint to banana and plantain production, particularly in small-scale (smallholder) farming. For the development of a new, low-cost weevil management technology based on attractive host plant material, we previously identified (2R,5S)-theaspirane as the active component of attractive senesced banana leaves. In this new study, we used behavioural (olfactometer) bioassays with adult weevils to compare the attractiveness of four different developmental stages of banana leaves, i.e. unfolding (pale green), matured green (deep green), matured yellowing and senesced, to determine which leaf developmental stage would be most appropriate for use in weevil management. We also investigated the attractiveness of senesced leaf extracts prepared using different solvents to determine which solvent would be most appropriate for local production of leaf extracts. Coupled gas chromatography-electroantennography (GC-EAG) was then used with adult weevils to confirm the presence of (2R,5S)-theaspirane in attractive leaf extracts.

RESULTS

Of the leaf materials tested, only the odour of senesced leaf material was significantly attractive to adult weevils (P < 0.005). Furthermore, an extract of senesced material prepared using palm wine alcohol was significantly attractive (P < 0.05). Using coupled GC-EAG with weevil antennae, (2R,5S)-theaspirane was identified as a minor component with strong EAG activity within the palm wine alcohol extract.

CONCLUSION

The results suggest that palm wine alcohol extracts of senesced banana leaf material could be used to lure adult C. sordidus to traps in the field, as part of an ethnobotanical-based approach for C. sordidus management on smallholder farms. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Aggregation Pheromone of the Bearded Weevil, Rhinostomus barbirostris (Coleoptera: Curculionidae): Identification, Synthesis, Absolute Configuration and Bioactivity

The bearded weevil, Rhinostomus barbirostris (Coleoptera: Curculionidae: Dryophthorinae), attacks coconut trees, oil palms and other species of Arecaceae. Besides direct damage, R. barbirostris may be a vector of diseases in coconut and oil palms, such as stem bleeding (resinosis) and red ring disease. Currently, the only method to control this weevil is by visual observation of damage and removal of infected plants. Semiochemical-based trapping could improve the effectiveness of monitoring and management of R. barbirostris. In comparisons of volatiles released by R. barbirostris males and females by gas chromatography (GC) two male-specific compounds were observed. GC-mass spectrometry (MS) and GC-Fourier transform-infrared (FTIR) analyses of the natural compounds suggested these were diastereoisomers of 5-hydroxy-4-methylheptan-3-one, also known as sitophilure, a pheromone component of other dryophthorine species. Synthesis of the mixture of all four stereoisomers of sitophilure was performed in two steps, and the chemical structures were confirmed by comparing GC retention times and MS and FTIR spectra of natural and synthetic compounds. The absolute configurations of the two male-specific compounds were elucidated by enantioselective GC; the major component was the (4S,5R)-isomer, and the minor component (4S,5S)-sitophilure. In analyses by GC-electroantennography (EAG) the antennae of male and female R. barbirostris only responded to the (4S,5R)-isomer of the synthetic sitophilure. The stereoisomeric mixture of sitophilure was attractive to both sexes of R. barbirostris in laboratory experiments in the presence of sugar cane volatiles, and a similar result was obtained in a preliminary field trapping test.

Yakushinamides, Polyoxygenated Fatty Acid Amides That Inhibit HDACs and SIRTs, from the Marine Sponge Theonella swinhoei

Yakushinamides A (1) and B (2), prolyl amides of polyoxygenated fatty acids, have been isolated from the marine sponge Theonella swinhoei as inhibitors of HDACs and SIRTs. Their planar structures were determined by interpretation of the NMR data of the intact molecules and tandem FABMS data of the methanolysis products. For the assignment of the relative configurations of the three contiguous oxymethine carbons in 1 and 2, Kishi's universal NMR database was applied to the methanolysis products. During the assignments of relative configurations of the isolated 1-hydroxy-3-methyl moiety in 1 and the isolated 1-hydroxy-2-methyl moiety in 2, we found diagnostic NMR features to distinguish each pair of diastereomers. The absolute configurations of 1 and 2 were determined by a combination of the modified Mosher's method and Marfey's method. Although the modified Mosher's method was successfully applied to the methanolysis product of 1, this method gave an ambiguous result at C-20 when applied to the methanolysis product of 2, even after oxidative cleavage of the C-14 and C-15 bond.

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.

Chirality of israeli pine bast scale,Matsucoccus josephi (homoptera: Matsucoccidae) sex pheromone

The absolute configuration of the sex pheromone of the Israeli pine bast scale,Matsucoccus josephi, was determined as (2E,5R,6E,8E)-5,7-dimethyl-2,6,8-decatrien-4-one, designated here asR-E with 10% (2E,5S,6E,8E)-5,7-dimethyl-2,6,8-decatrien-4-one, designated asS-E. The chirality of the quantitatively minorZ isomer was (2E,5R,6Z,8E)-5,7-dimethyl-2,6,8-decatrien-4-one (R-Z). Chiral assignments were made by comparative gas chromatographic (GC) analysis of naturalM. josephi pheromone with stereoselectively synthesized stereoisomers on a chiral Cyclodex-B column, which separated the enantiomers with baseline resolution. In gas chromatographic-electroantennographic detection (GC-EAD) analysis of the racemicZ andE isomers, the latter elicited the stronger antennal response by maleM. josephi. In GC-EAD of all four stereoisomers, employing the chiral column,R-E was the most active stereoisomer. In field testsR-E attracted 10 times more males ofM. josephi than didS-E. The racemicE/Z pheromone mixture, containing all four stereoisomers in approximately equal amounts, attracted as many maleM. josephi as did an equivalent amount ofR-E, indicating that the other stereoisomers are not inhibitory. The same keto-diene moiety with the same chiral center and configuration in all three known Matsucoccidae sex pheromones implies a common biosynthetic pathway and phylogenetic relationship.

Structure, chirality, and field testing of a male-produced aggregation pheromone of Asian palm weevilRhynchophorus bilineatus (Montr.) (Coleoptera: Curculionidae)

4-Methyl-5-nonanol is a male-produced aggregation pheromone of the Asian palm weevil,Rhynchophorus bilineatus (Montr.). The pheromone was identified by coupled gas chromatographic-electroantennographic detection (GC-EAD) and coupled GC-mass spectrometric (MS) analyses of male-and female-produced volatiles. Analyses by GC-EAD and GC-MS of weevil-produced and stereoselectively synthesized isomers of 4-methyl-5-nonanol on a Cyclodex B column, which separated isomers with baseline resolution, revealed that only (4S,5S)-4-methyl-5-nonanol is EAD active and produced by the males. In field experiments in Papua New Guinea, (4S,5S)-4-methyl-5-nonanol and a racemic mixture of disatereoisomers of it enhanced attraction of male and female weevils to sugarcane-baited traps. (4S,5S)-4-Methyl-5-nonanol is also an aggregation pheromone of two other Asian palm weevils.R. ferrugineus (Oliv.) andR. vulneratus (Panz.). The stereoisomeric mixture of 4-methyl-5-nonanol is currently used to manage populations ofR. bilineatus in Papua New Guinea.

Pheromone chirality of asian palm weevils,Rhynchophorus ferrugineus (Oliv.) andR. vulneratus (Panz.) (Coleoptera: Curculionidae)

Production of 4-methyl-5-nonanol, and 4-methyl-5-nonanone by two sympatric Asian palm weevils,Rhynchophorus ferrugineus (Oliv.) andR. vulneratus (Panz.) suggested that enantiospecificity of either compound could impart species specificity of pheromone communication. Weevil-produced, racemic 4-methyl-5-nonanol and 4-methyl-5-nonanone and their stereoselectively synthesized optical isomers were subjected to gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometry (MS) on a chiral Cyclodex-B column. Only theS,S stereoisomer of 4-methyl-5-nonanol was EAD active and was produced by bothR. ferrugineus andR. vulneratus. Production and EAD activity of (S)-4-methyl-5-nonanone exceeded that of its antipode in both weevils. In field experiments in Java. (4S, 5S)-4-methyl-5-nonanol and the stereoisomeric mixture were equally attractive. The 4R,5R stereoisomer was inactive. The corresponding ketone enantiomers neither enhanced nor reduced attraction to (4S,5S)-4-methyl-5-nonanol. Lack of apparent differences betweenR. ferrugineus andR. vulneratus pheromones suggests that synonomy of both weevils should be considered unless other pre- or postzygotic reproductive isolating mechanisms are disclosed in future studies.

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.

Field evaluation of plant odor and pheromonal combinations for attracting plum curculios

The attractiveness of different synthetic host odors and a synthetic aggregation pheromone (grandisoic acid [GA]) to overwintered adult plum curculios (PCs), Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), was examined using two types of traps (sticky panels and black pyramids) placed in border areas surrounding an unsprayed section of an apple orchard in Massachusetts. In 2001, we evaluated the response of PCs to three synthetic fruit volatiles (benzaldehyde [BEN], ethyl isovalerate [EIV], and limonene [LIM]) assessed alone and in combination with GA, as well as the response to GA alone and a no-odor (control) treatment. BEN was the only host volatile that synergized the response of PCs to GA for both trap types. For both trap types, GA was as attractive to PCs as a single component as when in combination with either EIV or LIM. In 2002, four release rates of BEN (0, 2.5, 10, and 40 mg/day) and two release rates of GA (1 and 2 mg/day) were evaluated for attractiveness to PCs using panel and pyramid traps. For panel traps, an increase in amount of GA released (from 1 to 2 mg/day) was associated with a 35% increase in captures. However, PC captures by pyramid traps were similar regardless of the amount of GA released. For panel traps, 10 and 40 mg/day of BEN were the most attractive release rates regardless of the amount of GA released. For pyramid traps baited with GA. PC captures were enhanced by the presence of BEN, regardless of release rate. In 2003, GA at 1 mg/day + BEN at 80 mg/day of release did not enhance PC captures by panel traps relative to lower release rates of BEN. Pyramid traps releasing GA at 1 mg/day performed best when baited with BEN at 10 mg/day of release; a release rate of 80 mg/day of BEN decreased the attractiveness of the binary combination of BEN + GA. Combined results suggest that BEN at 10 mg/day + GA at 1 mg/day of release constitutes an attractive lure that may improve the effectiveness of monitoring traps for PCs.