Is this planted related to an alchol drink? Poison oak and sumac are also common to your area. I don't know about the insecticide question though.

No, I think you're thinking of wormwood-Artemesia absinthium.

A friend of the family in Montana always brought over some of his Elderberry Wine or Brandy during cold/flu season - which was used as Cough Syrup in our house in winter. A sick kid would sleep really well and sweat off a fever in one night, after having just a small bit. (I understand it to be a oldtime tonic for Norwegians and other indigenous nordic peoples)

The White Flower clusters are also reputed to be medicinal.

My mom would make a great summer drink by soaking the White Flower clusters in water with other added
ingredients and putting it in the fridge for three weeks. talk about a healthy drink that you couldn't get enough of ! Old family recipe...

All elderberries have some toxic chemicals in them, if you eat them raw. sambucus mexicana is the worst, do a search on CA ag website and you will come across reported deaths from this plant. sambucus can. (american elder) and sambucus nigra (black elder) are much less toxic and are the one's to use for wine and eating just cook them first.
the leaves contain a chemical that produces cyanide after digestion, so I would guess it's use as an insecticide would be limited at best.

I've never seen a mexican elderberry though I read they are edible in jellies et cetera in which the seeds are filtered out. Here in Florida the southern elderberry is the Sambucus Canadensis with dark blue berries and it is definitely edible. I have several in my yard and I make pies from them every year. The wood of all elderberries is toxic, however, so don't chew a twig of it.