The effect of temperature on Culex pipiens pipiens, Cx. p. quinquefasciatus, and reciprocal hybrids of the two was investigated by monitoring the DV/D ratios of these stocks maintained at 15.6 degrees C and 23.9 degrees C over 10 generations. Little variation occurred in mean values of the parental subspecies at either temperature. At 23.9 degrees C, the mean ratios for both hybrid lines rose from an intermediate value to a level well above the accepted minimum for Cx. p. quinquefasciatus (0.4), and the proportion of individuals identifiable as that subspecies increased 16-fold. At 15.6 degrees C, hybrid mean DV/D ratios decreased to or below the pipiens maximum value (0.2), and the proportion of pipiens individuals increased 4 to 5 times. The need to monitor closely the status of Cx. pipiens hybrid colonies is evident.
