Efficacy of Steinernematid Nematodes Against Three Insect Pests of Crucifers in Quebec

Abstract

Steinernematid nematodes were evaluated against the three major cruciferous insect pests: the imported cabbageworm Artogeia rapae, the diamondback moth Plutella xylostella, and the cabbage looper Trichoplusia ni. LC₅₀ values of S. carpocapsae All, S. feltiae UK, S. feltiae 27, and S. riobrave 335 were 18.2, 3.6, 5.7, and 8.3 on A. rapae L₂; 24.5, 2.3, 6.0, and 15.5 on P. xylostella L₃; and 10.1, 4.7, 9.5, and 7.8 on T. ni L₂, respectively. Insect mortality from the nematode species and isolates was modulated by temperature. Maximum mortality (100%) was recorded for A. rapae L₂ from S. riobrave at 30 °C, 95.8% from S. feltiae, and 91.7% from S. feltiae 27 at 25 °C and 75.7% from S. carpocapsae at 30 °C. Mortality of A. rapae L₂ increased with contact time to nematode. Mortality of 76% and 78% was achieved for S. carpocapsae and S. feltiae, respectively, after 12-hour exposure. Susceptibility of A. rapae, P. xylostella, and T. ni larvae to entomopathogenic nematodes increased with larval age development. The addition of adjuvants - Corn Oil (0.9%, 1.8%, 3.6%), Leafshield (3.0%, 6.0%, 12.0%), Seaweed (0.1%) and Agral (0.05%) - significantly increased the density and survival rate of S. carpocapsae on cabbage leaves compared to water only. At 20 °C and 70% relative humidity (RH), survival rates of S. carpocapsae All, S. feltiae UK, and S. riobrave 335 on cabbage leaves were 43%, 2%, and 0% after 4 hours following application. Under field conditions, foliar applications of S. carpocapsae provided 35.3% and 33.0% control of A. rapae (L₃-L₅) on Brussels sprouts and broccoli in 1996 and 24.9%, 19.4% and 14.9% on Brussels sprouts, broccoli, and cauliflower, respectively, in 1999. Based on our field results, foliar applications of S. carpocapsae do not provide an acceptable level of A. rapae control under Quebec's environmental conditions.

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