Abstract
The genetic basis of malate dehydrogenase (MDH), an esterase ( alpha -Est 3) in the citrus red mite Panonychus citri and P. osmanthi was studied by polyacrylamide gel electrophoresis and crossing experiments. Based on the banding patterns and the phenotype segregation ratio, MDH-1 appeared as a dimeric enzyme of a single locus composed of three codominant alleles (S, M and F) in P. citri. alpha -Est 3, also a dimeric enzyme regulated by two codominant alleles (S and F), was polymorphic in some populations of P. citri, and the frequency of the F allele was higher in southwestern populations than in other populations. The F allele of P. osmanthi, a mite that superficially resembles P. citri, was observed in only one population and all others were fixed for the S allele. At the MDH-1 locus, all populations of P. osmanthi and P. citri were fixed for the M allele with one exceptional population of P. citri. In this population, most females exhibited a single band of the MM homozygote, but one female showed three bands of the SM heterozygote and two females showed three bands of the MF heterozygote. Thus, little geographical variation was found in allele distribution at the MDH-1 locus, but some variation was detected at the alpha -Est 3 locus only in P. citri.