Localized failure of a weed biological control agent attributed to insecticide drift

摘要: Abstract In South Africa, a bud-feeding apionid weevil, Trichapion lativentre (Beguin Billecocq), is one of three introduced insect herbivores that are responsible for the successful biological control Sesbania punicea (Cav.) Benth., leguminous weed American origin. With few exceptions, annual seed crop S. has declined by more than 98% since T. became established on during late 1970s. However, there several localized infestations in Olifants river valley where been much less elsewhere country, and pod production still prolific. this valley, often occurs close proximity to citrus orchards, many which sprayed with organophosphate insecticides spring early summer (August–October). vicinity populations remained low (the main period bud-burst ) weevil numbers only increased later, when insecticide treatments orchards had almost ceased. As result, incidence damaged flower-buds was lowest, highest, plants orchards. The negative effects insecticides, as measured higher levels weed, decreased exponentially increasing distance up 300 m from nearest orchard.