INTERSPECIFIC COMPETITION BETWEEN STEINERNEMATID NEMATODES WITHIN AN INSECT HOST

Larvae of Galleria mellonella exposed to infective juveniles of Steine rnema carpocapsae and Steinernema glaseri were coinfected by both nema tode species. Infective juveniles of both species that penetrated and established in their insect hosts always developed into apparently nor mal adults. In both nematode species, the proportion of established fe males was reduced in cadavers that had been exposed to both species co mpared 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 inf ection at a rate of 8 infective juveniles of each species, the progeny production of S. glaseri was not reduced, whereas that of S. carpocap sae was significantly reduced by 79% compared with the respective sing le species treatments. At a rate of 25 infective juveniles of each spe cies, progeny production of both S. glaseri and S. carpocapsae was sig nificantly reduced by 38 and 94%, respectively, compared with the resp ective single species treatments. The ratio of inocula between the two species affected the progeny production. If S. glaseri and S. carpoca psae were combined at the rates of 8:16, 16:16, and 16:18 infective ju veniles, respectively, S. glaseri had reductions in progeny production of 53, 9, and 30%, respectively, whereas S. carpocapsae had reduction s of 35, 85, and 98%, respectively. The intrinsic superiority of S. gl aseri can be ascribed to its faster development that deprives its slow er competitor of food resources. In addition, the less specific associ ation of S. glaseri to its bacterial symbiont, Xenorhabdus poinarii, a llows it to develop in cadavers colonized by Xenorhabdus nematophilus, the symbiont of S. carpocapsae. (C) 1995 Academic Press, Inc.