Field investigations on the effects of an organophosphorus pesticide, thionazin, on predacious Carabidae (Coleoptera)

Abstract

The effects of soil-applied thionazin on field populations of Carabidae were assessed in two fields of potatoes in Berkshire, England. Broadcast at 11·2 or 44·8 kg/ha in a light sandy loam soil, thionazin considerably reduced numbers of Carabids for up to eight weeks after application. Lower catches occurred again six months later when treated soils were rotavated after lifting of the potato crop; these were attributed to the exposure of Carabidae to thionazin residues which had leached into deeper layers of the soil. Dosages of 2·24 or 8·96 kg/ha applied in rows sometimes increased numbers of Carabidae trapped, possibly because of sublethal effects increasing locomotor activity. Carabidae affected most by the treatments were the small diurnally active species such as Bembidion lampros (Hbst), B. quadrimaculatum (L.), and Trechus quadristriatus (Schr.) which were also abundant at the time when the treatments were applied. Larger species such as Harpalus rufipes (Deg.), Pterostichus vulgaris (L.), P. madidus (F.) and Calathus fuscipes (Goeze) were also affected but were generally less susceptible partly because they appeared later in the season when the pesticide had partly disappeared. The rapid disappearance of thionazin from the surface 1·3 cm of soil could account for the low susceptibilities of non-burrowing species; Asaphidion flavipes (L.) which rarely burrowed was less susceptible and Harpalus aeneus (F.) which readily burrowed was more susceptible than other species of similar size.