Ants in citrus groves.
The chemical control of ants has been recommended for several years in Sicilian citrus groves because of their predatory activity on natural beneficial insects and their help in protecting honeydew-producing insect pests. The efficacy of chlorpyrifos-ethyl [chlorpyrifos] applied to the trunks of the trees to protect against ants was compared with that of insecticidal gum containing hexane, and pyrethrum in an orange grove (cv. Navelina) in Sicily in 1994-96. The encyrtid Leptomastix dactylopii was released in 1994-95 to control cotonello [the pseudococcid Planococcus citri], and the aphelinid Aphytis melinus was released in 1996 to control citrus red scale insect [the diaspidid Aonidiella aurantii]. The most common species of ants found in citrus groves in eastern Sicily were Linepithema humile, Camponotus nylanderi and Tapinoma erraticum. Chlorpyrifos gave the best control and was the least costly. Insecticidal gum applied to the trunk gave better results than pyrethrum, but is known to have a possible phytotoxic effect on trees less than 10 years old, and is also costly to apply. The study verified the negative effects on the crop caused by the presence of L. humile. It is concluded that in integrated control programmes, the best time to treat ants and release beneficial insects is between April and September.