Soil surface applications of chemicals for the control of neonate Diaprepes abbreviatus (Coleoptera : Curculionidae) and their effect on ant predators

The root weevil, Diaprepes abbreviatus, as a larva, inflicts feeding injury to the bark of all root parts of a citrus tree, thereby impairing root fun ction and supplying infection courts for soil-borne root rot diseases. Idea lly, larvae should be controlled at the soil surface before they reach the root zone. In screenhouse and field experiments conducted in central Florid a from 1996-99, the synthetic pyrethroid, bifenthrin, at 0.54 g/m(2) (0.554 kg ai/ha) and RPA107382, an analog of fipronil, at 0.156 and 0.312 ml/m(2) (0.242-0.466 kg ai/ha), were applied uniformly to the soil surface beneath the tree to form a chemical barrier against neonates of D. abbreviatus. By comparison to the control, larval populations were reduced by 80-100% with in one week and these reductions persisted for 4-8 weeks. In an open screen house, bifenthrin gave excellent root protection of container-grown trees d uring a 22 week period when neonates were added to containers weekly for 12 weeks, RPA107382 was highly effective for about 2 weeks but lacked residua l effect. The accumulation of leaf litter beneath the tree impaired coverag e of the soil by bifenthrin resulting in reduced control. According to week ly baited trap counts, both chemicals reduced non-target foraging ants, par ticularly Solenopsis invicta Buren. The reduction in S. invicta was tempora ry however, but it did allow time for other foraging ants to re-establish a nd increase.