Albert K. MINKS, P. van DEVENTER and S. VOERMAN
Research Institute for Plant Protection (IPO-DLO), P.O. Box 9060, 6700 GW
Wageningen, The Netherlands.
It is estimated that in 1995 mating disruption has worldwide been applied on approximately 250.000 ha of outdoor cultures: 80% in cotton, 10% in grapes, and the remaining 10% is divided between pome and stone fruits, and vegetables.
In 1995 we have started effectivity tests of mating disruption on the nohuid moth Chrysodeixis chalcites in heated greenhouses, in which sweet peppers (paprika) are grown. This moth species of subtropical origin was accidentily introduced into the Dutch greenhouses and became a serious pest in the year-round cultures of particularly sweet pepper and tomato. Insecticidal control of the larvae is problematic, as this must be compatible with the current biological control system of sucking insects, as aphids, thrips and whiteflies, and spider mites. Additionally, effective parasites and/or predators are not available.
Our tests were conducted at three sites: 1) two greenhouses at IPO, with a surface area of each ± 180 m2, 2) four greenhouses at the research station for greenhouse vegetables of each ± 450 m2 at Horst, and 3) two commercial greenhouses of ± each 1 ha at Horst. At all three sites pheromone dispensers were applied in half of the greenhouses at the same density of 600 dispensers/ha, and the other half served as non-treated control. Each dispenser contained 75 mg Z7-12:Ac + 15 mg Z9-14:Ac, the optimum pheromone blend for attraction of C. chalcites. The dispensers used were of the polymeric type developed by the TNO Plastics and Rubber Research Institute, at Delft The Netherlands. Evaporation characteristics of the dispensers have been detemmined by GC-analysis of residual contents and also by direct measurements of the pheromone concentration in the air in the various greenhouses by means of a portable EAG-apparatus. Details will be reported by van der Pers et al. in another presentation in this symposium.
The effects of the mating disruption treatment were assessed in various ways: a) capture of "native" male moths and recapture of released male moths by pheromone traps, b) determination of the mating frequency of tethered female moths and c) measurement of the feeding damage by C. chalcites caterpillars in the crop. The latter assessment method was of particular use in the IPO-greenhouses, where we could make several releases of pairs of C. chalcites.
We conclude from the results of these first tests that mating disruption is clearly effective in protecting the crop from feeding damage of C. chalcites larvae. Further research is underway to establish the lowest possible pheromone dosage and to see whether or not application of only the major component of the pheromone blend is feasible. We also want to find out at which moth density mating disruption is still applicable in greenhouse conditions. Furthemmore, the effect of opening of the top windows for ventilation in summer on mating disruption must be established. And, finally, Spodoptera exigua, another important noctuid pest in Dutch greenhouse cultures, will be included in our further testing.