A summary of recent insecticidal tests on some insects of medical importance in Taiwan.

The author describes some investigations carried out on a number of insects of medical importance in Taiwan (six species of Anopheles, one species of Culex, one of Aëdes, two subspecies of Musca domestica and one species of Cimex) with the object of finding out whether resistance to DDT and BHC had developed among them as a result of the insect-control campaigns which have been in operation in the island since 1948.Of the anophelines, certain strains of A. minimus and A. h. sinensis were found to have a relatively high and statistically significant tolerance to DDT, but whether this can be regarded as developed resistance remains to be ascertained. As to the other insects examined, some strains exhibited statistically significant differences in tolerance to DDT; in certain cases, however, the ancestors of the tolerant strains had never been exposed to DDT, and it has not been possible yet to find an explanation for this phenomenon.No significant difference in susceptibility to gamma-BHC was shown by three strains of Cimex hemipterus, two of which had previously been exposed to mixtures of DDT and BHC and one of which had not.