The present invention is directed to novel pyrazole derivatives and their use as pesticidal agents. The pyrazole derivatives have Formula I: or a salt thereof, where R1 represents R5O, R5SO2, R5SO or R5S in which R5 is as defined herein; X is halo, cyano, C1-6 alkoxycarbonyl, C2-6 alkynyl, optionally substituted C6-14 aryl or an optionally substituted 5- to 7-membered heteroaromatic ring linked to thiazole via a carbon-carbon bond; R2 is hydrogen, amino, chloro, bromo, iodo, cyano, C1-6 alkoxy, C1-6 alkyl or C6-10 aryl; and R3-R7 each represent hydrogen, halogen, straight- or branched-chain C1-4 alkyl or C1-4 alkoxy, either of which is unsubstituted or substituted by one or more halogen atoms, straight- or branched-chain C1-4 alkylthio or C1-4 alkylsulphinyl, either of which is substituted by one or more halogen atoms, nitro, cyano, or straight- or branched-chain C1-4 alkylsulphonyl group which is unsubstituted or substituted by one or more halogen atoms.