REPRODUCTION OF THE ENTOMOPATHOGENIC NEMATODE HETERORHABDITIS-BACTERIOPHORA POINAR, 1976 - HERMAPHRODITISM VS AMPHIMIXIS

The present study was aimed at elucidating the mode of fertilization (self vs cross) in 2nd generation non-male adults of the entomopathogenic nematode Heterorhabditis bacteriophora strain HP88. For this purpose dumpy mutants (Hbdpy-1 and Hbdpy-2) were used as genetic markers. Forty hours after eggs hatching two types of juveniles were evident in the 2nd generation of either the wild-type or the mutant populations cultured in vitro: half of the 2nd generation individuals developed to the 4th developmental stage (J4) with discernible reproductive systems. The other individuals were, on average 1.4-2 times shorter and 1.6-3 times thinner (p < 0.05, t test) than the above described ''normal'' J4. They were less developed then the J4 type and had no identifiable reproductive system. Among 550 of the J4 type juveniles (either wild-type of dumpy) that had been individually transferred to culture plates, only 9 (i.e. 1.8%) gave rise to progeny. However, when dumpy non-male adults, originating from J4 type juveniles were crossed to wild-type males, 30-71% of them gave rise to progeny all of which were wild-type, indicating that reproduction occurred solely by cross-fertilization. These non-male adults were termed ''females''. Among 105 smaller-type juveniles which had been individually transferred to culture plates, 80% reproduced indicating a high rate of self-fertilization i.e. a high proportion of hermaphrodites. The smaller type juveniles were termed ''HJ'' (H for hermaphrodite). When dumpy HJ type juveniles were crossed with wild-type males, 70% (n = 30) gave rise to progeny. Each successful cross yielded both dumpy (46%-69%) and wild-type (31%-54%) progeny, indicating reproduction by self as well as cross-fertilization, respectively. The importance of the co-existence of these two reproductive strategies and their implication to genetic studies are discussed.