The young workers (in three days) of five races of Apis mellifera ligustica- ZAU — 1 Italian honey bee (Ea), Chinese Italian honey bee (Eb), American Italian honey bee (Em), Italian Italian honey bee (Ee) and Australian Italian honey bee (Eo) have been used to study the genotype, genotype frequency, allele frequency, heterozygous and homzygous degrees of the malate dehydrogenase Ⅱ (MDH Ⅱ ) isozymes with polyacrylamide gel isoelectrofocusing (IEF-PAGE). There are six genotypes (a/a, a/b, a/c, b/b, b/c, c/ c) in MDH Ⅱ that is coded by three alleles： a，b and c. All of them are found in Ea, Eb and Ee; four (a/b, a/c, b/c, c/c) are found in Eo; three (a/c, b/c, c/c) in Em.The genotype frequencies are aa (0.022), ab (0.028), ac (0.296), bb (0.007), be (0.140), cc (0.508) in Ea; aa (0.003), ab (0.011), ac(0.117), bb (0.006), be (0.156), cc (0.706) in Eb; aa (0.033), ab (0.203), ac (0.224), bb(0.021), be (0.252), cc (0.267) in Ee; aa (0.000), ab (0.000), ac (0.313), bb (0.000), be(0.253), cc (0.433) in Em; aa (0.000), ab (0.006), ac (0.011), bb (0.000), be (0.172), cc (0.811)in Eo. The allele frequencies are a (0.184), b (0.091), c (0.726) in Ea; a (0.067), b (0.090), c (0.717) in Em; a (0.008), b (0.089), c (0.903) in Eo. The heterozygosities (H) of the MDH Ⅱ locus equal to 0.464 in Ea; 0.284 in Eb; 0.679 in Ee; 0.566 in Em; 0.189 in Eo.

The results of test-independence show that there are significant differences in the distributions of genotype frequency, gene frequency, heterozygous and homozygous degrees among five races of Apis mellifera.