RESUMO
Previous studies have shown that the boll weevil, Anthonomus grandis, is attracted to constitutive and conspecific herbivore-induced cotton volatiles, preferring the blend emitted by cotton at the reproductive over the vegetative stage. Moreover, this preference was paralleled by the release of the acyclic homoterpenes (tetranorterpenes) (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) in Delta Opal cotton being higher at the vegetative than at the reproductive stage. Here, we evaluated whether this difference in release of acyclic homoterpenes also occurred in other cotton varieties, and if boll weevils could recognize these compounds as indicators of a specific cotton phenological stage. Results showed that cotton genotypes CNPA TB-90, BRS-293 and Delta Opal all produced higher levels of DMNT and TMTT at the vegetative stage than at the reproductive stage and that these homoterpenes allowed for principal component analysis separation of volatiles produced by the two phenological stages. Electroantennograms confirmed boll weevil antennal responses to DMNT and TMTT. Behavioral assays, using Y-tube olfactometers, showed that adding synthetic homoterpenes to reproductive cotton volatiles (mimicking cotton at the vegetative stage in terms of homoterpene levels) resulted in reduced attraction to boll weevils compared to that to unmodified reproductive cotton. Weevils showed no preference when given a choice between plants at the vegetative stage and the vegetative stage-mimicked plant. Altogether, the results show that DMNT and TMTT are used by boll weevils to distinguish between cotton phenological stages.
Assuntos
Comportamento Animal/efeitos dos fármacos , Terpenos/química , Terpenos/farmacologia , Gorgulhos/efeitos dos fármacos , Animais , Bioensaio , Feminino , Genótipo , Gossypium/genética , Gossypium/metabolismo , Masculino , Terpenos/metabolismoRESUMO
Chinavia and Nezara spp. stink bugs (Heteroptera: Pentatomidae) include over100 species, with highest diversity in Afrotropical and Neotropical regions. Species thus far studied in these genera utilize trans-(Z)-(4 S)-bisabolene epoxide (BE) and cis-(Z)-(4 S)-BE as major sex pheromone components, with species specificity ensured by different ratios of the two compounds. Gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS) analyses of a volatiles from C. ubica males revealed the presence of two BE isomers in approximately a 90:10 ratio, which were shown by microprobe (1) H NMR to be cis-(Z)-BE and trans-(Z)-BE isomers, respectively. Analyses of volatiles from C. impicticornis males suggested the presence of a single isomer, trans-(Z)-BE, in high purity (>90 %). The absolute configurations of the isomers produced by C. ubica and C. impicticornis were determined using chiral GC analysis (ß-DEX column). Oxidative microchemistry of synthetic standards of cis-(Z)-(4 S)-BE and trans-(Z)-(4R)-BE, and volatiles from male of C. ubica, revealed the absolute stereochemistry of the cis-(Z)-BE to be (1R,2 S,4 S) [cis-(Z)-(4 S) for short]. Similarly, analyses of trans-(Z)-(4 S)-BE and cis-(Z)-(4R)-BE standards, and volatiles from males of C. ubica and C. impicticornis, revealed the absolute stereochemistry of the trans-(Z)-BE to be (1 S,2R,4 S) [trans-(Z)-(4 S) for short]. Olfactometer bioassays with synthetic BEs confirmed attraction of female C. ubica and C. impicticornis to conspecific synthetic pheromone, but not to heterospecific synthetic pheromone. Chinavia impicticornis appeared not to discriminate behaviorally between the conspecific pheromone and its enantiomer. Coupled GC-electroantennography with antennae from females suggested that C. ubica and C. impicticornis possess olfactory receptors for both cis-(Z)-(4 S)-BE and trans-(Z)-(4 S)-BE. The results in this study confirm that C. ubica and C. impicticornis, as for other Chinavia and Nezara spp., utilize cis-(Z)-(4 S)-BE and trans-(Z)-(4 S)-BE as sex pheromone components, with different ratios guaranteeing species specificity. Furthermore, the results suggest that the absolute stereochemistry of BEs may be less important for conspecific recognition than the relative stereochemistry between the epoxide group and the alkyl substituent on the bisabolene ring.