A composition comprising an alkynyl phenoxy compound of Formula (I) as a synergist and a pesticidal active ingredient is described, wherein R and R, similar or different, are (C-C)alkyl or RO- and RO- together represent a group -O-CH-O-, -O- CH(CH)-O, -O-CH-CH-O-, -O-CH-CH-, R is (C-C)alkyl, (C-C)alkenyl or -B- (CH-CH-O)z-R where B is -CH-O- or -O-, z is 0, 1 or 2 and R is (C-C)alkylR is hydrogen or methylR is hydrogen or methylx is an integer from 1 to 2 y is 0, 1 or 2 with the proviso that when R is -B-(CH-CH-O)z-R, y is 1 and 5-(propargyloxy)- benzo[1,3]dioxole is excluded.
