Two Entomopathogenic Nematode Species with Different Search Strategies for Insect Suppression

Combining two species of entomopathogenic nematodes with different search strategies suppressed two pest species of soil insects when they occurred in the same habitat. The majority of individuals of Steinernema carpocapsae (Weiser) have a sit and wait (ambusher) strategy and tend to be near the soil surface. This species was effective against larvae of the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), which feeds near or at the soil surface. Heterorhabditis bacteriophora Poinar has an active foraging (cruiser) strategy and occurs deeper in the soil profile. It was effective against larvae of the black vine weevil, Otiorhynchus sulcatus (F.) (Coleoptera: Curculionidae), which occurs near roots. Soil temperature influenced the results. At 22°C, both nematode species killed their respective target insect within 1 wk. At 16°C, S. carpocapsae killed black cutworm larvae, but H. bacteriophora was not effective against black vine weevil larvae 2 wk after treatment. A few black vine weevil larvae were infected with H. bacteriophora at that temperature, and a longer exposure of the black vine weevil larvae to the nematode may have increased efficacy. In addition to search strategies, the susceptibility of the insects to the nematode species plays an important role in pest suppression.