Biopesticides and Biocontrol Agents Used in Vineyards
Azadirachtin (C35H44016) is a chemical compound belonging to the limonoid group and is a secondary metabolite present in neem seeds. It was initially found to be active as a feeding inhibitor towards the desert locust (Schistocerca gregaria); it is now known to affect over 200 species of insects by acting mainly as an antifeedant and growth disruptor, and as such it possesses considerable toxicity towards insects (LD50 in littoralis is 15 μg/g). It fulfils many of the criteria needed for a natural insecticide if it is to replace synthetic compounds. Azadirachtin is biodegradable (it degrades within 100 h when exposed to light and water) and shows very low toxicity to mammals (the LD50 in rats is >3,540 mg/kg, making it practically non-toxic). This compound is found in the seeds (0.2–0.8 % by weight) of the neem tree, Azadirachta indica (hence the prefix aza does not imply an aza compound, but refers to the scientific species’ name). Many more compounds related to azadirachtin are present in the seeds as well as in the leaves and the bark of the neem tree, which also show strong biological activities among various pest insects. Effects of these preparations on beneficial arthropods are generally considered to be minimal. Some laboratory and field studies have found neem extracts to be compatible with biological control. Because pure neem oil contains other insecticidal and fungicidal compounds in addition to azadirachtin, it is generally mixed at a rate of 2–5 mL/L of water when used as a pesticide, depending on the requirement. It is extracted from the kernels of the neem tree, Azadirachta indica, as a yellow green powder with a strong garlic-/sulphur-like odour. Neem extract concentrate generally contains azadirachtin 10 % w/w and is formulated as an emulsifiable concentrate containing 0.15 % w/w or 0.30 % w/w azadirachtin.