DIRK EBBINGHAUS-1,2, ALFRED ELBERT-1, MICHAEL
LINDEMANN-1, PETER M. LÖSEL-1, JÜRGEN
SCHERKENBECK-1, ERHARD WEBER-1, CLAUS P.W. ZEBITZ-2
1- Bayer AG
Central Research Division, Agricultural Centre Monheim Building 6220,
D-40789 Monheim, Germany
2- University of Stuttgart-Hohenheim
Institut of Phytopathology, Otto-Sander-Str.5, D-70599 Stuttgart, Germany
It is known that E8,E10-dodecadienol (Codlemone), the main component of the sex pheromone emitted by females of C. pomonella elicits both a strong behavioural and electrophysiological response in codling moth males. The role of the minor components in improving the attractiveness of pheromone baited traps is reported by several authors-1,2,3, while Mc Donough and coworkers-4 could not find any evidence for enhanced responses. Trap catches were also improved when a mixture of green leaf volatiles (GLVs) was added to Codlemone-5. Our aim was to investigate the role of minor sex pheromone components and host plant odours in male moth attraction, using electrophysiological and behavioural bioassays.
A 7-component blend based on Einhorn and coworkers' analysis-3 of a sex pheromone gland extract was prepared. In view of inhibitory effects attributed to isomers of Codlemone-4,6 the E8,Z10-isomer was not included in the blend. A steam distillate of apples was also prepared.
Electroantennograms recorded from the antennae of males offered the pheromone test blend at a range of different concentrations did not differ from the response to the same absolute amounts of Codlemone alone. Coupled GC-EAD recordings were used to investigate electrophysiological responses of antennae from male moths to single components of the blend. While the EAD showed a very strong response to Codlemone, its sensitivity to dodecanol was very slight and no response to tetradecanol or any of the other components was detected.
By scanning electron microscopy of both male and female antennae at least 5 different types of sensilla have so far been identified. Single Cell recordings with tungsten electrodes showed that cells responding preferentially to Codlemone were located in the Sensilla trichodea. No cells responding to dodecanol (12-OH) or tetradecanol (14-OH) were found in Sensilla trichodea. However, Sensilla auricillica of both, male and female C. pomonella occasionally contained cells tuned to 12-OH and 14-OH. Experiments conducted in a windtunnel showed no increase in trap catches for male codling moths offered the 7-component blend compared to codlemone alone. However, males were caught in significantly greater numbers in sticky traps baited with rubber septa containing both Codlemone and an apple steam distillate. The distillate alone proved unattractive to males.
The weak electrophysiological response associated with minor pheromone components so far tested, correlates with the behavioural test results and prevents us from confirming a role for 12-OH and 14-OH in long distance orientation behaviour of codling moth males to calling females. The presence of host plant odours in contrast, does appear to enhance the attractiveness of Codlemone to male moths.
Work currently in progess in our laboratory aims to identify substances from extracts of the host plant which may interact with the sex pheromone cue.
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