Effect of temperature and Lepidopteran host species on entomopathogenic nematode (Nematoda: Steinernematidae, Heterorhabditidae) infection

Experiments were conducted to determine the effect of temperature on entomopathogenic nematode infection of an insect host. Late instars of Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), Heliothis virescens (F.) (Lepidoptera: Noctuidae), Trichoplusia ni (Hubner) (Lepidoptera: Noctuidae), and Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) were incubated at 10 temperatures ranging between 9.9 and 40°C, and exposed to 150 infective juvenile entomopathogenic nematodes (Nematoda: Steinernematidae; Heterorhabditidae) per larva. The number of infecting Steinernema riobrave Cabanillas, Poinar and Raulston, S. carpocapsae (Weiser) (Kapow) and Heterorhabditis bacteriophora (Poinar) (Cruiser), nematodes was recorded. Temperature, nematode species, and target insect all significantly affected the number of infective juvenile nematodes invading host insects. The temperature supporting the highest levels of nematode infection varied depending on insect host species. Larvae of P. gossypiella were then incubated at the same range of temperatures, and exposed to 2 dose rates (100 and 200 infective juveniles per larva) of S. riobrave, S. carpocapsae (Guardian), H. bacteriophora (Cruiser), or H. bacteriophora (Lawn Patrol). Increasing nematode dosage had no effect on the temperature at which nematode infection of P. gossypiella was highest. Doubling the nematode dose rate did not result in a significant increase in the number of infective juveniles infecting larvae for the nematode species tested with the exception of S. riobrave. The optimum temperature for the control of insect targets by a nematode will vary among target species. Assuming existing nematode temperature optima and applying the same conditions to untested insect species may not result in maximum biocontrol efficacy.