Toxicity of pesticides to Halmus chalybeus (Coleoptera: Coccinellidae) and the effect of three fungicides on their densities in a citrus orchard

Abstract

The effect of three fungicides in five programmes on densities of Halmus chalybeus (steelblue ladybird) was tested in a citrus orchard. Programmes of five and nine applications of cupric hydroxide or chlorothalonil reduced densities by c. 35% and 70% respectively, compared with unsprayed plots. One application of copper sulphate and lime (Bordeaux mixture) reduced ladybird density by 81%, similar to the two nine‐application programmes. These reductions in numbers were probably due to a repellent effect since the fungicides had a relatively low toxicity. Ten fungicides, nine insecticides, and a miticide were screened for toxicity to adult H. chalybeus by a dip method. Copper‐based fungicides were more toxic than non‐copper fungicides at 3 times label rates, but not at label rates. The insecticides taufluvalinate, permethrin/pirimphos‐methyl, diazinon, and potassium salt were highly toxic at label rates. Two mineral oils, chlorpyrifos, and the miticide azocyclotin were moderately toxic, whereas buprofezin and one mineral oil were not toxic. H. chalybeus is an important predator of wax scales and the implications of these pesticide effects for biological control of these pests are discussed.

Keywords:

• Halmus chalybeus
• Coccinellidae
• fungicides
• insecticides
• toxicity
• biological control
• citrus