Disclosed are pyrimidinium compounds as represented by the general formula (I), wherein: X is O； Y is O； R1 is phenyl, naphthalenyl or a heteroaromatic mono or bicyclic ring system, which may be further substituted； R2 is alkyl, haloalkyl or CR5R6CH2OR21； R3 and R4 are alkyl or haloalkyl, or R3 and R4 may be taken together to form an optionally substituted heterocyclic or heteroaryl ring system, such as a pyridine or thiazole ring system； and wherein the remaining substituents are as defined herein. Representative compounds include 3-(2,4-difluorophenyl)-2-hydroxy-4-oxo-1-(2,2,2-trifluoroethyl)-4H-pyrido[1,2-a]pyrimidinium inner salt； 3-(4-fluorophenyl)-2-hydroxy-4-oxo-1-(2,2,2-trifluoroethyl)-4H-pyrido[1,2-a]pyrimidinium inner salt； and 2-hydroxy-4-oxo-3-phenyl-1-(2,2,2-trifluoroethyl)-4H-pyrido[1,2-a]pyrimidinium inner salt. Further disclosed is a composition which comprises a parasiticidally effective amount of compound as defined above, and at least one carrier for protecting an animal from an invertebrate parasitic pest. Also disclosed is a seed which has been treated with a compound as defined above.
