The results from two series of control experiments against the voles, Microtus agrestis and Arvicola terrestris, are reported. In a series of field experiments in the 1970s, three acute toxicants (zinc phosphide, crimidine, and difluorpropanol) were tested against Microtus. Oifluorpropanol (Gliftor) was found to be the most effective, but no ready-made bait containing it was available. The performance of the crimidine bait (Kastrix) was good enough to fulfill the registration requirements, while the zinc phosphide bait (Myrax) failed to give acceptable results. In the second series (early 1980s) a brodifacoum bait (Klerat) was found to be as efficacious as the crimidine bait (Kastrix) against Microtus, and sufficiently effective against Arvicola, on which the crimidine bait does not work. The experiments with bromadiolone (Arvicolon) and flupropadine (M & B 36,892) against Microtus were discouraging; against Arvicola they were promising, though not yet conclusive. In future research, special attention should be paid not only to the screening of potential toxicants and bait formulations, but also to the study of the basic differences in the reactions of even closely related species to the baits and their active ingredients, as well as to the compensatory demographic responses of the target pest populations in cases of suboptimal performance of the bait in the field
