Jan N. C. VAN DER PERS-1, J.W. KLIJNSTRA-2 and J.J. de VLIEGER-2
1-Syntech/VDP Laboratories, P.O.Box 1547, 1200 BM Hilversum, The Netherlands.
2-TNO Plastics and Rubber Research Institute, Crop Protection Research,
P.O.Box 6031, 2600 JA Delft, The Netherlands.
An important parameter for the success of mating disruption is the emission rate of the synthetic pheromone formulation and thus the concentration of pheromone released in the air. Conventional methods of measuring aerial concentrations are based either on trapping the pheromone in cartridges containing a suitable adsorbent followed by gas chromatographic analysis, or on measuring the loss of pheromone in the dispensers over time. However, application of these methods is limited by their complexity and high costs. We have developed therefore, a pheromone measuring apparatus based on the electroantennogram (EAG) technique that is suitable for routine use outside the laboratory.
The device is small, light-weight, and it can be operated by non-specialists. A male antenna of the species under study is excised and placed in a holder provided with contact pads. Contact between the ends of the antenna and the input circuit of the amplifier is established using a non-drying electrically conductive gel. The holder with the antenna is placed in the device in a completely closed compartment. A miniature air pump maintains a constant, charcoal-filtered air flow over the antenna. Pressing a button activates a valve by which a short puff (0.3 s) of unfiltered air is passed over the antenna. After a pre-set time (5 s) a puff of air from a built-in reference cartridge containing a synthetic pheromone component is presented to the antenna. The responses to the reference are used to indicate the decline in antennal sensitivity during the measurements. The EAG signals evoked by the air puff and the reference compound are recorded on a portable tape recorder, which is also used to record voice comments during the measurements.
In 1995 EAG measurements were conducted inside conditioned greenhouses in which sweet peppers (paprika) are grown. Pheromone dispensers for mating disruption on the noctuid moth Chrysodeixis chalcites were applied in half of the greenhouses at a density of 600 dispensers/ha; the other half served as non-treated controls. The non-treated greenhouses provided the reference plant odour background necessary to measure the EAG response to plant odours only. EAG measurements in pheromone-treated greenhouses were alternated with measurements in the nontreated greenhouses. The EAG response to the pheromone in the treated green houses was calculated by substraction of the EAG to plant odours only in the nontreated greenhouses.
In 1996 tests were started in greenhouses provided with dispensers having four increasing pheromone release rates. EAG measurements were made starting from the moment of dispenser application and continuing at regular intervals.
All EAG measurements were compared to the data obtained by release rate analysis of the dispensers used, as well as to data provided by biological assessment of the effect of the mating disruption, details of which will be reported by Minks et al. in another presentation during this symposium.
From the EAG data collected so far, we conclude that the portable EAG sensor is a practical and reliable device for measuring pheromone release rates in greenhouses.