Toxicity of insecticides used in Tunisian citrus orchards on the introduced mealybug parasitoid Leptomastix dactylopii (Hymenoptera: Encyrtidae)

Abstract: Adults of Leptomastix dactylopii Howard (Hymenoptera: Encyrtidae), parasitoid of the mealybug Planococcus citri Risso (Hemiptera: Pseudococcidae), were exposed under laboratory conditions to the direct spraying and leaf treated disks using malathion, spinosad, acetamiprid, cyhexatin + tetradifon and methidathion to assess mortality rates after the exposure periods of 4 h, 24 h, 48 h and 72 h. We found that acetamiprid and methidathion showed significant differences compared to spinosad and cyhexatin + tetradifon 4 hours after their direct spray on adults with mortality rates of 66.25% for malathion, 73.75% for acetamiprid and 72.5% for methidathion. Spinosad and cyhexatin + tetradifon did not cause a shock effect four hours after their direct spray on adults with respective mortality rates of 20% and 28.75%. 72 hours after application, all active substances were highly toxic to L. dactylopii adults with mortality rates reaching 91.25%, 92.5%, 97.5% and 82.5%, respectively, for malathion, acetamiprid, methidathion and cyhexatin + tetradifon, except spinosad which proved to be moderately toxic with 57.5% mortality. On 4 h-aged residues on treated leaf disks, all tested insecticides were moderately toxic to adults of L. dactylopii, except spinosad which was not toxic. Nevertheless, spinosad became moderately toxic causing mortality rate of 45% on 24 hours aged residue. The group represented by malathion, acetamiprid, cyhexatin + tetradifon and methidathion were classified as toxic to adults of L. dactylopii while the spinosad was moderately toxic. Implications on integrated pest management of citrus pests were discussed.