Soil Population Studies. I.—The Effects of Cultivation and Treatment with Insecticides

Abstract

The effects of cultivation and treatments with DDT and BHC on soil Collembola and Acarina were, investigated. Cultivation resulted initially in a drastic reduction of the micro-arthropod population and in the fallow plots this reduction persisted. Re-seeding resulted in rapid recolonisation by Collembola, but the populations of Oribatei and Mesostigmata remained at a low level over a period of 17 months after sowing. Treatment with BHC caused a heavy reduction of most micro-arthropoda. DDT caused reductions of mites, particularly Mesostigmata, but there was a marked increase of Collembola in the plots so treated. Significant increases of Collembola and significant reductions of predacious Mesostigmata were also noted in the comparison of plots treated with a DDT plus BHC mixture with those receiving BHC alone. The increase of Collembola was thus associated with a reduction of predatory pressure. In most cases, the effects of the treatments that included BHC were apparent 17 months later, but a temporary recovery of near-surface dwelling Collembola occurred in the BHC-treated plots in February 1952. Of the groups and species significantly affected by insecticide treatments in October 1951, only in one case did the data of October 1952 produce significant evidence of recolonisation. This recovery was noted in the DDT-treated population of Punctoribates punctum (Koch).