EXPOSURE OF THE GROUND DWELLING SPIDER OEDOTHORAX-APICATUS (BLACKWALL) (ERIGONIDAE) TO SPRAY AND RESIDUES OF DELTAMETHRIN

Experiments were carried out with deltamethrin using the epigeal erigonid spider Oedothorax apicatus. The spiders were exposed to spray, residues and contaminated food. Exposure in the field, of spiders and their major prey items (collembolans) to the spray, was measured by means of a fluorescent tracer. The quantities of spray fluid recovered from these organisms was lower than the quantity measured on surfaces exposed to the spray on the soil. The availability of residues on soil was assessed by exposing individuals to sprayed soils of varying moisture content, to a soil showered after spraying and by exposing topically treated spiders to unsprayed soils. The effects of the residues were strongly related to the water content of the soil. On sprayed soils at field capacity, the toxic effects were highest. A shower shortly after spraying reduced the effect of residues considerably. On very dry soils (12.5% of field capacity) high effects were also observed both on sprayed and unsprayed soils. This effect could be attributed to unfavorable air humidity conditions near the soil surface. The relative contribution of the three routes of uptake, i.e. exposure to spray and to residues and consumption of contaminated prey, was studied with radio-labelled deltamethrin. Spiders were exposed to sprayed soil surfaces (moisture content 75% of field capacity), topically treated and fed with topically treated fruit flies. The latter route contributed little to the body burden. The amount of deltamethrin absorbed from the soil was twice the amount absorbed after topical treatment.