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Final Report Summary - HOST SHIFT (Olfactory correlation of rapid host plant shift in the European corn borer)

Insects possess a highly-developed sense of smell and live, as far as they are concerned, in a world dominated by odors. The goal of this research project was to study the neuroethological basis and evolution of olfaction in insects, using European corn borer (ECB) as a model, which has two pheromone races producing and detecting opposite ratio of the two pheromone components (Z and E-race). Additionally, this species is an economically important pest in the northern hemisphere. The existence of two clearly differentiated pheromone strains intrigued the curiosity of the chemical ecologists, especially since these pheromone strains seem to be fixed to different host plants. One pheromone strain strongly prefers ancestral host plants such as hop (Humulus lupulus) and mugwort (Artemisia vulgaris), whereas the other strain has shifted to maize (Zea mays) since its introduction in Europe in the 16th century. The goal of this research project was to study the neuroethological basis and evolution of olfaction according to host plant shift in insects, using ECB as a model. The aim was to characterize the olfactory component of this host plant divergence using a multidisciplinary approach, including insect electrophysiology, chemical analysis, insect peripheral neurophysiology, central neuroanatomy, behavioral and field tests. Besides establishing the colonies of both strains of the ECB in the laboratory, Dr. Kárpáti used a four-way volatile collection setup to collect odors from different host plants, such as hop, maize and mugwort. To identify the key host plant compounds from the previously collected volatiles, which are active on the different strains’ female antennae peripheral electrophysiological measurements were carried out. Dr. Kárpáti was able to distinguish the key compounds from the odor bouquet, which were physiologically active compare the two strains. He also identified the molecular structure of the previously classified key compounds. To verify the behavioral output of the identified compounds and their mixtures, which can attract females he carried out insect wind tunnel bioassay. The end of the project Dr. Kárpáti was able to develop a synthetic mixture of the host plant compounds, which can attract ECB Z-strain females in the wind tunnel. These results can be useful in novel monitoring control strategies of this pest species.
In 2012, a new pest, the spotted wing drosophila (Drosophila suzukii), has been arrived in Hungary and caused enormous damages in fruit production. Therefore, Dr. Kárpáti’s group focused on this pest to find an environmentally friendly plant protection way against this pest using olfactory based solutions. First time they were able to detect and publish the spices in Hungary as a first record. Since 2012 his aim is to understand the neuroethological background of olfaction of the spotted wing drosophila and to develop a species-specific monitoring method based on host plant volatiles.
During this project, his research group is also focused on another new, invasive pest in Europe, the box tree moth (Cydalima perspectalis), which causes damages on box trees since 2007. They investigated the oviposition-repellent effect of larval frass volatiles. Volatiles emanated by larval frass evoked antennal responses on both male and female antennae; specific compounds with this activity were identified as guaiacol, (±)-linalool and veratrol. These compounds were found to be detected by individual chemosensilla located on the antennae. A synthetic mixture of these volatiles, when applied on boxwood plants, significantly reduced the number of laid eggs demonstrating the blend’s oviposition-repellent effect.
Kárpáti’s research group was also able to identify the female produced pheromone composition of another invasive European pest, the European pepper moth (Duponchelia fovealis). This pest causing damages in green houses on horticultural pest. Using coupled gas chromatographic-electroantennographic detection analysis and coupled gas chromatography–mass spectrometry of the female gland extract we revealed three antennally active peaks, which were (Z)-11-hexadecenal (Z11–16:Ald), (E)-13-octadecenal (E13–18:Ald) and (Z)-13-octadecenal (Z13–18:Ald). The approximate ratio of E13–18:Ald, Z13–18:Ald and Z11–16:Ald in the crude pheromone gland extract was 10:1:0.1, respectively. Single sensillum recordings showed that there was one sensory neuron that responded with high amplitude spike to both E13–18:Ald and Z13–18:Ald, while another neuron housed in the same sensillum responded to Z11–16:Ald. Field evaluation of the identified compounds indicated that the highest number of caught males was achieved when E13–18:Ald, Z13–18:Ald and Z11–16:Ald were present in baits in the same ratio as in the female gland extract. This pheromone can be used in a monitoring strategy and could potentially lead to the development of mating disruption.
All results have importance for understanding mechanisms and constrains in insect olfaction; with significance within basic research by contributing to our general understanding of the olfactory sense, as well as in future applications within applied research e.g. when designing biological traps for pest species.

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Life Sciences
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