Efficacy of Steinernematid Nematodes Against Three Insect Pests of Crucifers in Quebec
AbstractSteinernematid 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. LC[sub5][sub0] 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 L[sub2]; 24.5, 2.3, 6.0, and 15.5 on P. xylostella L[sub3]; and 10.1, 4.7, 9.5, and 7.8 on T. ni L[sub2], respectively. Insect mortality from the nematode species and isolates was modulated by temperature. Maximum mortality (100%) was recorded for A. rapae L[sub2] from S. riobrave at 30 ºC, 95.8% from S. feltiae, and 91.7% from S. feltiae 27 at 25 ºC and 75.7% from S. carpocapsae at 30 ºC. Mortality of A. rapae L[sub2] 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 ºC 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 (L[sub3]-L[sub5]) 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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