Abstract
Analytical studies on dieldrin resistance in field populations of larvae of Culex pipiens were done adopting two test methods. One is the so-called "ld-p line test". If a field population consisted of two or three component populations being homogeneous in susceptibility or resistance to a insecticide, and if each ld-p line (log dosage-probit mortality regression line) were separated independently, the ld-p line, or more correctly the curve, obtained from the mixed population would show one or two plateaus, flat portion parallel to the horizontal axis (see Fig.1 and Fig.2). Analyzing the position of the plateaus experimentally get from the curve, the genetical configuration of the mixed population and the component ld-p lines, such as RR, RS, SS can be estimated. By analyzing 10 field populations of C. pipiens larvae, the configuration ratios of RR (homozygous resistants), RS (heterozygous hybrids) and SS (homozygous susceptibles) to dieldrin was estimated, which were shown in Fig.3 and summarized in Fig.4 and Table 2. The other method is the so-called "discriminating test", the outline of which is as follows : Egg rafts collected from breeding sources in field were reared to 3rd or 4th stage larvae in separate bowls. Thirty (pallens type and fatigans type) or fifteen (molestus type) larvae were tested with two discriminating dosages, i. e., 0.02ppm and 0.3ppm (0.1ppm in Koniya population) of dieldrin. With 0.3ppm (0.1ppm in Koniya population), almost all of RR may be alive and all of RS and SS may be dead, and with 0.02ppm, almost all of SS may be dead and all of RS and RR may be alive. So, the rafts consisted of only RR and of only SS can be discriminated from those consisted of two or three components. In these cases, the rafts consisted of only RR may be produced from RR(P)×RR(P); and those of only SS from SS(P)×SS(P). If the frequency of RR and SS factor in P was supposed to be a and c, respectively, the appearance ratio of RR and SS rafts to all the egg rafts was admitted to be a^2 and c^2, respectively. As a^2 and c^2 can be available experimentally by the discriminating test mentioned above, a, b and c can be calculated (in this case, b=1-a-c), and RR(F_1), RS(F_1) and SS(F_1) can be calculated by the formula shown in Table 3. The configuration ratios of RR, RS and SS components in five field populations estimated by the discriminating test were listed in Table 4. In Table 5, the configuration ratios estimated by ld-p line test and by discriminating test were listed. Those methods estimated by two different tests were in good accord with each other. Summarizing the data mentioned above, it appeared surely that dieldrin resistance in larvae of Culex pipiens showed a monofactorial mode of inheritance, with the resistant factor partially dominant. This was confirmed by the crossing experiments with susceptibles and resistants, which will be reported in the other paper.
