Interspecific Competition between Steinernematid Nematodes within an Insect Host

Larvae of Galleria mellonella exposed to infective juveniles of Steinernema carpocapsae and Steinernema glaseri were coinfected by both nematode species. Infective juveniles of both species that penetrated and established in their insect hosts always developed into apparently normal adults. In both nematode species, the proportion of established females was reduced in cadavers that had been exposed to both species compared with cadavers exposed to one species. Although S. glaseri and S. carpocapsae produced progeny from the same cadavers, S. glaseri was less affected by mixed infection than S. carpocapsae. In the mixed infection at a rate of 8 infective juveniles of each species, the progeny production of S. glaseri was not reduced, whereas that of S. carpocapsae was significantly reduced by 79% compared with the respective single species treatments. At a rate of 25 infective juveniles of each species, progeny production of both S. glaseri and S. carpocapsae was significantly reduced by 38 and 94%, respectively, compared with the respective single species treatments. The ratio of inocula between the two species affected the progeny production. If S. glaseri and S. carpocapsae were combined at the rates of 8:16, 16:16, and 16:18 infective juveniles, respectively, S. glaseri had reductions in progeny production of 53, 9, and 30%, respectively, whereas S. carpocapsae had reductions of 35, 85, and 98%, respectively. The intrinsic superiority of S. glaseri can be ascribed to its faster development that deprives its slower competitor of food resources. In addition, the less specific association of S. glaseri to its bacterial symbiont, Xenorhabdus poinarii, allows it to develop in cadavers colonized by Xenorhabdus nematophilus, the symbiont of S. carpocapsae.