Further observations on an insecticide-baitbox method for the control of sylvatic plague vectors; effect of prolonged filed exposure to DDT powder.

Abstract

A field experiment was conducted from July 1958 to February 1959 in the San Francisco Bay region to test the effect on flea populations of prolonged exposure of the native meadow vole, Microtus californicus, to 5% DDT powder in insecticide-bait-boxes. Previous studies had shown that two important vectors of sylvatic plague, Malaraeus telchinum and Hystrichopsylla linsdalei, could be controlled both on their hosts and in the host nests by this method. However, the question of possible resistance was postulated since the control of H. linsdalei on its host was inferior to control of other flea species.Bait-boxes with DDT powder were maintained in the field for 6 months. Records of flea populations on Microtus during this period showed equally good control of all flea species. Observations on vole nests at termination of the study revealed deposits of DDT and good control of all flea species in them. During the period of study, the evidence suggested that none of the flea species involved exhibited DDT resistance.The major portion of the field routine was done by Messrs A. R. Kinney and R. L. Martin. Flea identifications were made by Mr H. E. Stark. Analyses of nests and rodents for DDT were performed by Mr C. Cueto, Technical Development Laboratories, CDC, Savannah, Georgia.