NONTARGET EFFECTS OF REPEATED METHIOCARB SLUG PELLET APPLICATION ON CARABID BEETLE (COLEOPTERA, CARABIDAE) ACTIVITY IN WINTER-SOWN CEREALS

The effects of repeated annual application of methiocarb-based slug pe llets, broadcast on the soil surface and drilled into the seed bed, on carabid beetle activity were investigated over a four year period on a winter-sown cereal field using pitfall traps in barriered plots. Fol lowing applications in late autumn all winter-active carabid populatio ns were severely depressed; total carabid activity falling to less tha n 5% and 10-15% following broadcast and drilled applications, respecti vely, compared with untreated plots. Spring and summer-active species, not active at the time of application, were largely unaffected by app lications and were responsible for a gradual recovery of total activit y from early spring onwards. Activity of all affected winter species r emained demonstrably depressed on treated areas for the remainder of t heir seasonal incidence. However, all except one species, Bembidion ob tusum, recovered to normal activity levels in the following season pri or to reapplication. Recovery patterns are discussed in terms of the k nown biology of the species involved. Evidence that a minority of summ er-active species were also affected by treatments, sometimes positive ly and sometimes negatively, were attributed to indirect effects possi bly involving prey availability and foraging behaviour. The long-term ecological and short-term agronomic implications of methiocarb effects on carabid populations in winter-sown cereals are discussed.