Efficacy of a dehydrated steinernematid nematode against black cutworm (Lepidoptera: Noctuidae) and diamondback moth (Lepidoptera: Plutellidae)

We compared the ability of in vitro-produced, commercially formulated with in vivo-produced, nonformulated Steinernema carpocapsae (Weiser) Poinar. All strain to infect and kill larvae of black cutworm, Agrotis ipsilon (Hufnagel), and diamondback moth, Plutella xylostella (L.). In vitro-produced nematodes formulated in wettable dispersible granules, which were stored dry, were rehydrated in water for 0-72 h before application. Against black cutworms, the efficacy of nematodes was (from most to least effective): in vivo > in vitro rehydrated for 72 h > in vitro rehydrated for 48 h > in vitro rehydrated for 24 h > dehydrated (0 h). Nematodes rehydrated for 72 h in water or moist soil were equally effective against black cutworm larvae, and both were significantly more effective than nematodes without rehydration. These results indicated that nematodes in the wettable dispersible granule formulation required time to rehydrate in the soil before infecting black cutworm larvae. Nematode treatments described above were applied to radish plants held at 100 or 75% RH and tested against diamondback moth larvae. At 100% RH, nematode efficacy was (from most to least effective): in vitro rehydrated for 72 h > in vivo > in vitro rehydrated 48 h > in vitro rehydrated 24 h > dehydrated (0 h). The efficacy of all treatments was lower at 75% than at 100% RH, and the ranking of in vivo and in vitro nematodes rehydrated for 72 h was reversed. The nematodes in the wettable dispersible granule formulation were effective for foliar treatments when humidity was high and nematodes were rehydrated for at least 48 h before application. The data show that nematode infectivity was reduced unless nematodes were rehydrated.