Parasiticidal compound

Parasiticidal pyrazole derivatives of formula (I) wherein: R1 represents CN, C1-6 alkoxycarbonyl, NO2, CHO, C1-6 alkanoyl, phenyl optionally substituted by one or more halogen, or C1-6 alkyl optionally substituted by one or more halogen; R2 represents a group of formula (II), (III) or (IV) in which: R7 represents H, halogen, carbamoyl, cyano, tri(C1-6 alkyl)silyl, C1-6 alkyl (optionally substituted by one or more halogen, OH or C1-6 alkoxy), C1-6 alkoxycarbonyl, phenyl, or a 5- or 6-membered ring heterocycle which is saturated or partially or fully unsaturated and contains up to 4 hetero-atoms independently selected from up to 4 N atoms, up to 2 O atoms and up to 2 S atoms and which is attached to the alkynyl moiety by an available C, S or N atom where the valence allows; and R8, R9 and R10 each independently represents H, halogen, phenyl optionally substituted by one or more halogen, CN or C1-6 alkyl optionally substituted by one or more halogen; R3 represents H, C1-6 alkyl, halogen, NH2, NH(C1-6 alkanoyl), NH(C1-6 alkoxycarbonyl), N(C1-6 alkoxycarbony)2, NH(C1-6 alkyl), N(C1-6 alkyl)2, NHCONH(C1-6 alkyl), N-pyrrolyl, NHCONH(phenyl optionally substituted by one or more halogen), N-CH(phenyl), OH, C1-6 alkoxy, SH or S(O)n(C1-6 alkyl optionally substituted by one or more halogen) where n is 0, 1 or 2; and R4, R5 and R6 each independently represents H, halogen, C1-6 alkyl optionally substituted by one or more halogen, C1-6 alkoxy optionally substituted by one or more halogen, S(O)n(C1-6 alkyl optionally substituted by one or more halogen) where n is 0, 1 or 2, or CH3CO, CN, CONH2, CSNH2, OCF3, SCF3 or SF5; or a pharmaceutically or veterinarily acceptable salt thereof.