Abstract: The morphology of the larva of Frontopsylla nakagawai borealosinica (Fnb) Liu, Wu et Chang, 1986 was studied and compared with other five congeneric species: F. spadix spadix (Fss), F. elatoides intermedia (Fei), F. elatoides elatoides (Fee), F. aspiniformis (Fa) and F. frontalis baibacina (Ffb). The number of mandibular teeth for each species is: 5 (Fnb), 5-6 (Fss), 5 (Fei), 5 (Fee), 5 (Fa) and 9 (Ffb). The number of occipital setae: 4(6) (Fnb), 4(4) (Fss), 4(12) (Fei), 6(6) (Fee), 4(6) (Fa) and 4(10) (Ffb). The number of setae of 1-5 abdominal segments in the posterior pringcipal row: 10(2) (Fnb), 10(2) (Fss), 8(4) (Fei), 8(4) (Fee), 10(2) (Fa) and 8(4) (Ffb). The number of setae of fore/hind rows on anal comb: 4-6/20-24 (Fnb), 4/14-16 (Fss), 10-12/20-26 (Fei), 4/28-30 (Fee), 5-9/18-20 (Fa) and 2/14-17 (Ffb). The number of strut setae per side: 8-11 (Fnb), 8-11 (Fss), 18-20 (Fei), 18-20 (Fee), 15 (Fa) and 7-9 (Ffb). The shapes of egg burst by dorsal view are like the shape of shoe except that of F. frontalis baibacina, which is like the shape of table tennis bat. Based on all characters listed above, F. nakagawai borealosinica has closer relationship with F. spadix spadix with a distinguishable character, the number of setae of hind row on anal comb. It is obvious that these six species of Frontopsylla can be classified to two groups according to the number of mandibular teeth and the shape of egg burst: one group consisting of one single species, F. frontalis baibacina, and another group consisting of the rest species. This grouping is congruent with that based on adult morphology.

Key words: Siphonaptera, Leptopsyllidae, Frontopsylla nakagawai borealosinica, larval morphology