A pyrimidinone compound of formula (IIIA) or (VA): ##STR15## wherein R13 is hydrogen or halogen and R14 is trifluoromethyl or pentafluoroethyl, with the proviso that when R14 is trifluoromethyl, R13 is halogen; ##STR16## wherein R10 is hydrogen or C1-4 alkyl; R15 is cyano and R16 is trifluoromethyl, difluoromethyl or pentafluoroethyl or R15 is hydrogen or halogen other than fluorine and R16 is pen