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New to gardening, many species are unknown to me. This one (and many of its friends) with nice metallic colored stripes just apppear on my lavender, rosemary and slightly less on honeysuckle.
It is Rosemary beetle, certainly. How much of a pest it is depends on how many there are; if there are a lot, they can reduce a lavender or rosemary plant to virtually woody stumps by eating it all, so if you were a professional grower, this pest would be taken very seriously. However, in the average garden, they may not be too much of a pest and can be controlled with simple physical intervention. Given they like rosemary, a culinary plant, it's not a great idea to use most pesticides, so some sort of organic control or spray would be best. You can hand pick them off, or take a bag or large sheet of plastic and shake individual branches over it, disposing of the fallen beetles afterwards. Pyrethrum sprays should be okay to use, and there may be other organic treatments in your area, designed for use on food crops, that will likely deal with a heavy infestation. There is information about this pest in the link below, also describing its life cycle and when is the best time to treat with a pesticide if you need to, though its primarily talking about rosemary beetle in the UK, so some of the treatments listed may be unavailable to you
