Effectiveness and persistence of the oviposition deterring pheromone of Pieris brassicae in the field
1987
Klijnstra, J.W. | Schoonhoven, L.M.
In small-scale field experiments the potency of the oviposition deterring pheromone (ODP) of Pieris brassicae as a pest control agent has been studied. In a field cage containing control and ODP-treated cabbage plants, single females were released and their behaviour observed until they had selected an oviposition site. In experiments without ODP-treated plants, oviposition occurred evenly on plants throughout the cage. In the presence of the pheromone, oviposition was concentrated on plants along two sides of the cage. The distribution of oviposition attempts on control and treated plants in pheromone experiments, however, was not significantly different from that in the control experiments. This means that under these field conditions, i.e. within a cage, the ultimate effectiveness of the pheromone is nil. However, the duration of pre-oviposition behaviour and the mean number of landings during the site-selection process by ovipositing females were both found to be significantly increased in the presence of the pheromone. The ODP also affected the relative number of landings on control plants, which was higher in the pheromone runs than in the control runs. Without pheromone, females released from the center of the cage tended to fly to the sides of the cage. The presence of ODP stimulates this flight behaviour and, moreover, discourages females from returning to the center of the cage, thereby reducing oviposition on central plants in the field plot. Laboratory experiments with leaves from treated field plants indicated persistence of the pheromone under field conditions for at least 5 days. It is concluded that in the field the ODP acts as a modifier of female pre-oviposition behaviour and stimulates dispersal activity, rather than giving absolute protection against P. brassicae oviposition.
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