Pyridine compound and use thereof

The present invention provides a compound which is represented by formula (I-1) (wherein R 4 represents a hydrogen atom, a C 1-6 alkyl group or the like; Ar 1 represents a C 6-10 aryl group, a 3-6 membered heterocyclyl group or the like; A represents a C 1 -C 6 alkylene group, a C 2 -C 6 alkenylene group or the like; R a represents a hydrogen atom, a C 1-6 alkyl group, C 6-10 aryl group or an amino group; and Ar 1 and R a may combine with each other to form a 5- or 6-membered ring together with a carbon atom to which Ar 1 and R a are bonded) or the like, or a tautomer or salt of the compound. The present invention also provides a bactericide for agricultural and horticultural use, a pest control agent, and an insecticidal or acaricidal agent, each of which contains, as an active ingredient, at least one substance selected from the group consisting of the compound, and a tautomer and salt of the compound.