Lethal effects of two reduced risk insecticides on Harmonia axyridis and Coleomegilla maculata (Col., Coccinellidae) following two routes of exposure
Abstract: Reduced-risk pesticides are new compounds noted for their lower impact on human health and environment, and lower toxicity onto non-target organisms than traditional products. Novaluron (Rimon® EC 10) and chlorantraniliprole (Altacor® 35 WG), two reduced-risk insecticides, have been registered to control the codling moth, Cydia pomonella (L.) (Lep., Tortricidae), in Canada in 2008. Novaluron inhibits the chitin synthesis and belongs to the benzoylphenyl urea chemical class. Chlorantraniliprole, part of a new class of selective insecticides, the anthranilic diamides, causes paralysis of the muscle cells by interfering with the ryanodine insect receptors. Both compounds act by ingestion and contact, exhibiting ovicidal and larvicidal activities. Due to the high toxicity to codling moth and their low negative impact on the environment, novaluron and chlorantraniliprole are recommended for use in IPM programs. However, several studies have shown negative effects on beneficial arthropods. The aim of this study was to evaluate the effects of novaluron and chlorantraniliprole on two aphidophagous predators commonly found in apple orchards in south eastern Canada, Harmonia axyridis (Pallas) and Coleomegilla maculata (De Geer) (Col., Coccinellidae). We studied specifically the lethal effects of novaluron and chlorantraniliprole on larvae of H. axyridis and C. maculata following ingestion of treated prey and exposure to residues. Insecticide field rates (100 g a.i./ha novaluron and 50.75 g a.i./ha chlorantraniliprole) were tested against the predators in laboratory conditions. To evaluate the lethal effect of exposure to insecticides via ingestion, 1st instar larvae were fed with treated aphids for 24 hours. In a second bioassay, larvae were placed individually in dry Petri dishes previously dipped in insecticide solutions. Mortality was assessed at 24 h, 72 h and 6 d after start of exposure. Following ingestion of treated prey, novaluron was highly toxic for H. axyridis causing 96.7% mortality after 6 days. C. maculata was not sensitive to novaluron and none of the species were sensitive to chlorantraniliprole. Both insecticides were toxic to H. axyridis and C. maculata via contact with residues. At 6 d, Chlorantraniliprole caused 100% mortality of both species, and exposure to novaluron resulted in 100% mortality for H. axyridis and 98.9% for C. maculata.