Bicyclo-[2,2,1]-heptanes, bicyclo-[2,2,2]-­octanes and bicyclo-[2,2,3]-nonanes, having 2 or 3 ring hetero atoms selected from O, S and N substituted at the 1-position by a carbocyclic group other than an alkynylphenyl group, and substituted at the 4-position and optionally substituted at the 3 and/or 5 position, are valuable pesticides, particularly insecticides and acaracides. Various cyclisation processes are disclosed to form the various bicyclo ring systems.