Abstract
Entomopathogenic nematodes are generally considered beneficial organisms. However, they can affect beneficial insects such as parasitoids. The interaction between the entomopathogenic nematodes
Heterorhabditis bacteriophora
Poinar (Rhabditida: Heterorhabditidae) and
Steinernema carpocapsae
Weiser, and the parasitoid
Microplitis rufiventris
Kokujev (Hymenoptera: Braconidae) was investigated in the laboratory. In non-parasitized hosts,
Spodoptera littoralis
Boisduval (Lepidoptera: Noctuidae) larvae exposed to
H. bacteriophora
showed a higher percent mortality than those exposed to
S. carpocapsae
. Both nematodes were able to invade and propagate in non-parasitized
S. littoralis
larvae and those parasitized
by M. rufiventris
. Both nematode species reproduced in
Microplitis
-parasitized hosts, but there was a higher number of nematodes in non-parasitized larvae.
S. carpocapsae
yielded higher numbers of infective juveniles than
H. bacteriophora
. Generally, the number of nematodes harvested increased as their host's size increased. The interaction between the nematodes and parasitoid favored the nematodes when the nematodes were inoculated during the parasitoid egg stage or the young parasitoid larvae, thus giving the nematodes a better chance to grow and reproduce, resulting in the death of the parasitoid larvae. Conversely, when the nematodes were inoculated during the late larval instar of the parasitoid, the competition partially favored the wasp, thus giving approximately 50% of the wasps a better chance to develop, emerge, and reproduce, providing evidence that both nematodes and wasps could reproduce in the same host. Egg maturation of female wasps derived from nematode-infected hosts was not significantly different than those from control hosts. The combined application of nematodes and parasitoids may be beneficial if the detrimental effects of the nematodes on the parasitoid could be avoided by precisely timing the application strategies. It is clear that
Microplitis
larvae and the nematodes share the host larva and engage in a trophic interaction with each other. Intraguild predation is briefly discussed.