If the infested trees are defoliated in the middle of their vegetative season, they are not able to accumulate enough reserves for winter and next spring. When the depletion of trees' reserves continues for several years, it decreases the fitness of trees, and finally it may result in trees death as can be documented in Czech Republic and Hungary (Szaboky, 1997; V. Skuhravy and M. Mraz, personal communication). However, the most of the horse-chestnuts are able to coop with this treat and the damage is most thoughtful from an aesthetic point of view. But a serious threat can be expected especially for the trees in cities and along busy routes, which are exposed also to other stress factors (salt, air pollution, and heavy metals) and there, economic, safety, and ecological consequences might be serious. Also trees attacked by the miner can be more prone to infection with dangerous fungus Guignardia aesculli which results in leaf coiling and necrosis. In addition, the C. ohridella can attack another tree species as it was recently documented with maple (Gregor et al., 1998). Today the chestnut protection against this serious pest is unsatisfactory. Raking and burning of litter from infested trees in the fall and spring or spraying of infested trees with insecticides are the only methods available by now. The litter leaves can not be completely removed from all places and burning of large amounts of the litter produce enormous quantity of greenhouse gases. Insecticides, used against larval (chitinase inhibitors e.g. Dimiline®) and adult (pyrethroides Karate®, Vaztak®) stages, are rather effective, but their use poses an ecological hazard and requires proper timing for the highest effectiveness. Cost for such a treatment is estimated to be 5-30 USD/tree.

There are numerous examples of successful IPM strategies based on sex pheromones (Wyat, 1997). Three of them seem to be the most promising for the horse-chestnut:

1) Sex pheromone baited sticky traps for monitoring of the population density of C. ohridella to determine the proper time for insecticide spraying. As the males emerge several days earlier than females (Kalinová et al., unpublished) the detection of first-generation males will give us enough time for application of insecticide against unmated or just mated females before oviposition. This combination of monitoring and spraying will substantially reduce the first generation of the pest and decrease their expansion in the following generations.

2) Male confusion technique (Carde and Minks, 1995). The principle of this method is permeation of tree-surrounding air with higher doses of synthetic pheromone with the aim to disrupt chemically mediated mating behavior, respectively to confuse and disable males to locate females for matting. The high activity of the pheromone at very low concentrations, as was documented (Svatoš et al., 1999), is a promising prerequisite for the success. It means that low amounts of the synthetic pheromone could be used.

3) Using of pheromone-baited traps contaminated with insecticide (trap-and-kill), pathogens, fungus or insect growth regulators. The contaminated males are vectors which transfer the biologic agents to other conspecifics (females). The two later mentioned methods will required rather intensive experiments to test their efficacy and proper design. Their practicability must be further investigated and the implementation can be expected in the season 2002-3.

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