About 100 years ago, it was dicovered that insects transmitgrave, mainly tropical diseases - very much to theastonishment of the physicians of that time, who saw this asa new, possibly easy, way of eradicating the diseases byexterminating the vectors. For some years, DDT and otherthen new insecticides achieved great improvements, butsubsequently serious setbacks emerged:insecticide-resistance and anxiety about toxicity to man andanimals. In the past twenty years, serious efforts have beenmade tofind alternatives, with varying degrees of success.