Effect of fungal isolates and imidacloprid on cabbage aphid brevicoryne brassicae and its parasitoid diaeretiella rapae

Abstract

Diaeretiella rapae (McIntosh) is a primary parasite of the cabbage aphid Brevicoryne brassicae (L.); both species are widely distributed throughout the world. In this research, the efficacy of imidacloprid and five entomopathogenic fungi: Acremonium sclerotigenum, Beauveria bassiana, Paecilomyces variotii, Simplicillium sp. and Lecanicillium muscarium, against cabbage aphid and its parasitoid was evaluated. Concentration-mortality and time-mortality data were subjected to Probit analyses to estimate LC50 (lethal concentration) and LT50 (lethal time) values for each isolate and imidacloprid for adults of B. brassicae and D. rapae. The LC50 values for A. sclerotigenum, B. bassiana, P. variotii, Simplicillium sp., L. muscarium and imidacloprid were 2.7 × 103, 3.7 × 103, 8.1 × 106, 4.7 × 105 and 2.5 × 103 conidia ml-1 and 13.56 ppm, respectively. Cumulative mortality of B. brassicae and D. rapae 7 days after treatments was 98.56% and 99.99% by L. muscarium at high concentration (108 conidia ml-1), respectively. The highest mortality of B. brassicae and D. rapae after 48 and 72 hours was observed in combinations of sublethal mixed treatments: LC25 (imidacloprid + A. sclerotigenum), LC25 (imidacloprid + B. bassiana), LC25 (imidacloprid + L. muscarium), and LC25 (imidacloprid + A. sclerotigenum), LC25 (imidacloprid + B. bassiana), LC25 (imidacloprid + P. variotii), LC25 (imidacloprid + Simplicillium sp.), LC25 (imidacloprid + L. muscarium), respectively. The LT50 values for B. brassicae and D. rapae at concentration 108 conidia ml-1 were obtained 0.26 and 2.16 days by A. sclerotigenum, and 7.4 and 6.22 days – by P. variotii isolate, respectively. This study showed that imidacloprid had harmful effect on the pest and parasitoid; however, fungal isolates were safer than imidacloprid to the parasitoid. The results of this study show that entomopathogenic fungi can be effectively used alone and mixed with sublethal concentration (LC25 = 9.23 ppm) of imidacloprid in integrated pest management of B. brassicae.