The development of strains or races of insects that are resistant to insecticides is a serious obstacle to the progress of chemical pest control. In many cases recommendations at first viewed as offering a permanent solution for an entomological problem have had to be abandoned within a very few years. Until the general relationships governing insccticidnl resistance are reduced to an orderly and understandable basis, the permanent soIution nf an insect pest control problem by chemical treatment is largelv an unjustifiable expectation.

It is difficult to obtain accurate records of the occurrence of bird-lice and especially those associating them with correctly identified hosts. For this reason it is considered the following records of bird-lice, taken from birds in Ontario, may be of interest and should be published.

The collections were made by the author and Messrs. A. A. Wood and D. A. Arnott and one or two other persons. The specimens are in the collection of the Dominion Entomological Laboratory, Chatham, Ontario.

The correct identifications of North American species of leafhoppers of the genus Macrosteles (sensu lato) are important because of the economic significance of one of them as a carrier of a virus disease of many species of plants. In the past, such identifications have been difficult to make because the extent of the variation in colour, markings, and structure that occurs has not been appreciated fully, because some species were misidentified in previous revisions, and because there were a number of unrecognized species in the fauna.