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

Abstract

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 LC 50 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 LC 50 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.

Side effects of pesticides on the larvae of the hoverfly Episyrphus balteatus in the laboratory

“…Despite the broad spectrum toxicity of carbamates, many authors have demonstrated the selectivity of pirimicarb to several predatory insects such as Anthicidae, Chrysopidae and Coccinellidae (Angeli et al 2005;Bacci et al 2009;Cabral et al 2008). However, laboratory as well as field studies have proven the high toxicity of pirimicarb to syrphid larvae (Colignon et al 2003;Jansen 1998Jansen , 2000Niehoff and Poehling 1995).…”

“…The cabbage aphid, Brevicoryne brassicae (Homoptera: Aphididae), in particular causes serious yield loss in cabbage crops, not only because of the severe feeding damage (Bacci et al 2009), but also because of the high population densities they may reach on cabbage plants (Costello and Altieri 1995;Liu et al 1994). Several natural enemies of the cabbage aphid are reported to occur in brassica crops, which can play an important role in the suppression of the aphid population.…”

Insecticidal Activity of Dienamides on Cabbage Caterpillar and Beneficial Insects

“…This difference is due to greater penetration of these molecules into the insect's cuticle. [27][28][29] However, this has not been noted here as the solubility and molecular weight of the amides were not related to their insecticidal activities.…”

Toxicity and residual effects of insecticides on Ascia monuste and predator Solenopsis saevissima

“…The mortality of pest and predator determined in the insecticide selection and physiological selectivity bioassays, respectively, were analyzed using Student's t ‐test ( P < 0.05). We considered the insecticides that showed physiological selectivity to the predator to be those that caused higher mortality to the pest than to the predator . The mortalities from insecticides and insecticide + synergist combinations were analyzed using Student's t ‐test ( P < 0.05)…”

“…The insecticides that are used in pest management programs must be effective in controlling pests and have a low impact on non‐target organisms, such as natural enemies. Determining the residual period of control for an insecticide is essential to plan insect management strategies, which will influence the spraying frequency and, in turn, affect pest control costs . In addition to being efficient in controlling pests, each insecticide must possess a different mechanism of action to avoid the pressure of pest population selection for insecticide resistance …”