Showing papers by "Peter Witzgall published in 2010"

Sex pheromones and their impact on pest management.

Abstract: The idea of using species-specific behavior-modifying chemicals for the management of noxious insects in agriculture, horticulture, forestry, stored products, and for insect vectors of diseases has been a driving ambition through five decades of pheromone research. Hundreds of pheromones and other semiochemicals have been discovered that are used to monitor the presence and abundance of insects and to protect plants and animals against insects. The estimated annual production of lures for monitoring and mass trapping is on the order of tens of millions, covering at least 10 million hectares. Insect populations are controlled by air permeation and attract-and-kill techniques on at least 1 million hectares. Here, we review the most important and widespread practical applications. Pheromones are increasingly efficient at low population densities, they do not adversely affect natural enemies, and they can, therefore, bring about a long-term reduction in insect populations that cannot be accomplished with conventional insecticides. A changing climate with higher growing season temperatures and altered rainfall patterns makes control of native and invasive insects an increasingly urgent challenge. Intensified insecticide use will not provide a solution, but pheromones and other semiochemicals instead can be implemented for sustainable area-wide management and will thus improve food security for a growing population. Given the scale of the challenges we face to mitigate the impacts of climate change, the time is right to intensify goal-oriented interdisciplinary research on semiochemicals, involving chemists, entomologists, and plant protection experts, in order to provide the urgently needed, and cost-effective technical solutions for sustainable insect management worldwide.

Flying the fly: long-range flight behavior of Drosophila melanogaster to attractive odors.

Abstract: The fruit fly, Drosophila melanogaster Meigen (Diptera: Drosophilidae), is a model for how animals sense, discriminate, and respond to chemical signals. However, with D. melanogaster our knowledge of the behavioral activity of olfactory receptor ligands has relied largely on close-range attraction, rather than on long-range orientation behavior. We developed a flight assay to relate chemosensory perception to behavior. Headspace volatiles from vinegar attracted 62% of assayed flies during a 15-min experimental period. Flies responded irrespective of age, sex, and mating state, provided they had been starved. To identify behaviorally relevant chemicals from vinegar, we compared the responses to vinegar and synthetic chemicals. Stimuli were applied by a piezoelectric sprayer at known and constant release rates. Re-vaporized methanol extracts of Super Q-trapped vinegar volatiles attracted as many flies as vinegar. The main volatile component of vinegar, acetic acid, elicited significant attraction as a single compound. Two other vinegar volatiles, 2-phenyl ethanol and acetoin, produced a synergistic effect when added to acetic acid. Geosmin, a microbiological off-flavor, diminished attraction to vinegar. This wind tunnel assay based on a conspicuous and unambiguous behavioral response provides the necessary resolution for the investigation of physiologically and ecologically relevant odors and will become an essential tool for the functional analysis of the D. melanogaster olfactory system.

Coding and interaction of sex pheromone and plant volatile signals in the antennal lobe of the codling moth Cydia pomonella.

Abstract: SUMMARY In the codling moth Cydia pomonella (Lepidoptera: Tortricidae) plant volatiles attract males and females by upwind flight and synergise the male response to the female-produced sex pheromone, indicating a close relationship between the perception of social and environmental olfactory signals. We have studied the anatomical and functional organisation of the antennal lobe (AL), the primary olfactory centre, of C. pomonella with respect to the integration of sex pheromone and host-plant volatile information. A three-dimensional reconstruction of the glomerular structure of the AL revealed 50±2 and 49±2 glomeruli in males and females, respectively. These glomeruli are functional units involved in the coding of odour quality. The glomerular map of the AL was then integrated with electrophysiological recordings of the response of individual neurons in the AL of males and females to sex pheromone components and behaviourally active plant volatiles. By means of intracellular recordings and stainings, we physiologically characterised ca . 50 neurons in each sex, revealing complex patterns of activation and a wide variation in response dynamics to these test compounds. Stimulation with single chemicals and their two-component blends produced both synergistic and inhibitory interactions in projection neurons innervating ordinary glomeruli and the macroglomerular complex. Our results show that the sex pheromone and plant odours are processed in an across-fibre coding pattern. The lack of a clear segregation between the pheromone and general odour subsystems in the AL of the codling moth suggests a level of interaction that has not been reported from other insects.

Attraction of female grapevine moth to common and specific olfactory cues from 2 host plants

Abstract: In herbivorous insects with more than 1 host plant, attraction to host odor could conceptually be mediated by common compounds, by specific compounds released by each plant or by combinations of common and specific compounds. We have compared the attraction of female grapevine moth, Lobesia botrana, with specific and common (shared) odors from 2 different plants: a wild host (Daphne gnidium) and a recently colonized host (Vitis vinifera). Odor blends eliciting female attraction to V. vinifera have previously been identified. In this study, olfactory cues from D. gnidium were identified by electroantennographic detection and chemical analysis. The attraction of mated females to synthetic odor blends was then tested in a wind tunnel bioassay. Female attraction was elicited by a blend of compounds released by both from D. gnidium and V. vinifera and by 2 blends with the compounds released specifically from each host. However, more complete odor blends of the 2 plants elicited stronger attraction. The common compounds in combination with the specific compounds of D. gnidium were the most attractive blend. This blend was tested with the common compounds presented both in the ratio emitted by D. gnidium and by V. vinifera, but there was no difference in female attraction. Our findings suggest that specific as well as common plant odor cues play a role in L. botrana host recognition and that there is plasticity in attraction to partial blends. The results are discussed in relation to mechanisms behind host odor recognition and the evolution of insect-plant associations.

Pheromone communication channels in tortricid moths: lower specificity of alcohol vs. acetate geometric isomer blends.

Abstract: Discrimination of conspecific and heterospecific signals is a key element in the evolution of specific mate recognition systems. Lepidopteran pheromone signals are typically composed of several compounds that synergize attraction of conspecific and inhibit attraction of heterospecific males. Blends convey specificity, but not their single components, that are typically shared by several species. Many sex pheromones are blends of geometric or positional isomers of straight-chain acetates, while species-specific blends of analogous alcohols have not been described. We have, therefore, studied the attraction of tortricid moths to the geometric isomers (E,E)-, (E,Z)-, (Z,E)- and (Z,Z)-8,10-dodecadien-1-ol. Only one species responding to these alcohols seemed to be attracted to a blend of two isomers, while most species are attracted to only one alcohol isomer. Lack of a pronounced synergist or antagonist effect of the other geometric isomers explains the lack of specific attraction to isomer blends and reduces accordingly the number of specific communication signals composed of these alcohols. In comparison, many more species respond to the analogous (E,E)-, (E,Z)-, (Z,E)- and (Z,Z)-8,10-dodecadienyl acetates and their binary blends. The acetate isomers all play a behavioural role, either as attractants, attraction synergists or antagonists, and thus promote specific communication with acetate blends. Male moths seem to discriminate the acetate isomers with greater precision than the analogous alcohols. It is proposed that discrimination is facilitated by steric differences between the four acetate isomers, as compared to the more uniform steric properties of the alcohols.

Flight tunnel response of codling moth Cydia pomonella to blends of codlemone, codlemone antagonists and pear ester.

Abstract: Upwind orientation flights of codling moth males Cydia pomonella L. to a single source of sex pheromone (E,E)-8,10-dodecadienol (codlemone) are significantly reduced when blending it with pheromone antagonists, either with codlemone acetate, (E,E)-8,10-dodecadienyl acetate, or with the codlemone isomer (E,Z)-8,10-dodecadienol. However, once activated by a pheromone stimulus, males no longer distinguish between a pheromone source and these antagonistic blend sources. This shows that the pheromone stimulus required for the initiation of an upwind flight response differs from the stimulus for maintaining upwind flight and landing at the source. In contrast to pheromone antagonists, males discriminate between pheromone alone and a blend source of pheromone and the plant volatile pear ester, ethyl (2E,4Z)-2,4-decadienoate. This indicates a difference in the detection and neural integration of pheromone and plant volatile stimuli.