Conservation of natural enemies in brassica crops: comparative selectivity of insecticides in the management of Brevicoryne brassicae (Hemiptera: Sternorrhyncha: Aphididae)

In the present study, we evaluate the toxicity of six insecticides to Brevicoryne brassicae (L.) (Hemiptera: Sternorrhyncha: Aphididae), predatory coleopterans Cycloneda sanguinea (L.) (Coccinellidae) and Acanthinus sp. (Anthicidae), and the hymenopteran parasitoid Diaeretiella rapae (McIntosh) (Braconidae, Aphidiinae). Late-instar nymphs of B. brassicae and adults of C. sanguinea, Acanthinus sp. and D. rapae were exposed to nine concentrations of acephate, deltamethrin, dimethoate, methamidophos, methyl parathion and pirimicarb. Selectivity, toxicity, and tolerance ratios were calculated from LC50 values to determine insecticide toxicity to B. brassicae and natural enemies as well as insecticide tolerance of the natural enemies. Pirimicarb was highly selective to Acanthinus sp., C. sanguinea, and D. rapae. Dimethoate, methamidophos and methyl parathion also showed selectivity to C. sanguinea and Acanthinus sp., but not to D. rapae. Methamidophos was the least potent insecticide against B. brassicae exhibiting the highest LC50 amongst the products tested and was more toxic to the D. rapae relative to the aphid. Overall, the predators Acanthinus sp. and C sanguinea were more tolerant to the insecticides than was the parasitoid D. rapae. The role of insecticides in IPM systems of brassica crops is discussed based on the toxicity to B. brassicae and selectivity to natural enemies.