Abstract
Effects of precedent infection of Steinernema carpocapsae and S. glaseri on subsequent nematode invasion were investigated at 25°C. Behavior of Galleria mellonella larvae infected through injection with ca. 50 S. carpocapsae infective juveniles did not change 6 hr post-infection, but invasion of both nematode species decreased by ca. 50%, compared to previously uninfected hosts. Precedent infection with S. glaseri promptly suppressed subsequent invasion of the two nematode species. Subsequent invasion was also significantly decreased by symbiotic Xenorhabdus bacteria: invasion rates to insects killed by X. nemato-philus injection, X. poinarii injection, and by hot water treatments were 1.8, 0, and 5.4% for S. carpocapsae and 1.8, 5.0 and 7.8% for S. glaseri, respectively, while invasion rates to the non-treated live insects were 16.5% for S. carpocapsae and 15.1% for S. glaseri. At the early stage of the subsequent invasion, the sex ratio (% male) of the invading S. carpocapsae in the hosts with and without the precedent infections were 5.3% and 12.3%, respectively. These results indicated that insects infected with a Steinernema/Xenorhabdus complex may emanate suppressive substance (s) against subsequent nematode invaders.
