MESOIONIC PESTICIDES

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.