Morphology of bursa of Heterorhabditis spp.

By Khuong Nguyen

The bursa of Heterorhabditis spp. is a structure that needs to be studied to see if it can be used for identification to species of this group of nematode.

In general, the genital papillae (bursal papillae) 1 to 6 (counting from anterior end of bursa) are constant for all species of Heterorhabditis studied, while papillae 7-9 are variable. Bursa of H. megidis, H. zealandica, and H. marelatus, has nine pairs of bursal papillae as usually described in the genus Heterorhabditis with the formula 1, 2, 3, 3 (one single papilla and three groups with 2, 3, and 3 papillae with very few variations). The terminal group of H. zealandica is different from that of other species: the middle papilla is much shorter than others. The bursa of H. bacteriophora also has 1, 2, 3, 3 bursal papillae, but the terminal group is variable in some strains: it is mostly stable in strain GA2, more variable in strain Argentina and highly variable in strain HP88. The arrangement of bursal papillae for H. mexicana n. sp. is 1, 2, 3, 2. The terminal group of papillae has only 2 pairs of papillae in 70% of the 40 observed specimens as stated in the description of the male. The arrangement of bursal papillae in H. indica is 1, 2, 3, ?. The terminal group of papillae (?) is variable. For both strains, from either Asia or America, we have not observed any male with 3 complete pairs as seen in H. megidis, H. zealandica, H. marelatus and H. bacteriophora . Photographs, Fig. 6E1- E4 and Fig. 6F1- F4 show variation of bursal papillae in the terminal group of papillae of H. indica. The Indian strain of H. indica has an unpredictable number of pairs of papillae in its terminal group. This observation is similar to that of Poinar et al. (1992). In the original description of H. indica, it was stated that the eighth and ninth pairs are often absent but if present are modified in being short, narrow or swollen. For the Mexican strain of H. indica, three papillae on one side and two on the other side were observed more often. We did not have samples of H. brevicaudis for this study; and the population of H. downesi was lost after we collected DNA for sequencing. In the original description, both H. brevicaudis (Liu, 1994) and H. downesi (Stock et al., 2002) have 9 pairs of bursal papillae.

Figure 1. Bursa of Heterorhabditis spp., ventral views, showing bursal papillae. A1, A2: H. megidis, ventral and lateral views showing 4 groups of bursal papillae (1, 2, 3, 3) and 3 papillae in terminal group; B1, B2: H. zealandica strain Florida and NZH3 respectively, ventral views showing 3 papillae in terminal group with the central papillae much shorter than others; C1, C2: H. marelatus, ventral views with little variation; D1, D2: H. bacteriophora strain GA2 and HP88 respectively, with 3 pairs of papillae in terminal group; E, F: H. indica (E1-E4 = strain India, F1-F4 = strain Mexico) with the number of papillae in the terminal group of bursal papillae variable. Scale bar (in C1) = 20 μm.

Bursa of Heterorhabditis mexicana is somewhat different from bursas of the above species and is presented in Figure 2 below:

Figure 2: Bursa of Heterorhabditis mexicana. The terminal group usually has 2 pairs of papillae.