First thank you for thinking about our butterflies. Different species of butterfly larvae need very specific host plants for their larvae. According to the Xerces Society a good host plant for the giant swallowtail in your zone would be Citrus and for the pale swallowtail ceanothus or wild lilacs. As for nectar the blooming plants that delight butterflies are members of the Aster, daisy, euphorbias, lily, prickly pear and many more. I have never gardened in your climate zone so I suggest you contact a local master gardeners to see what specific flowers would do best. The good news is that the harmful pesticides you were concerned about (neonicotinoides) are rarely used anymore on flowering plants sold to consumers. You should feel confident buying plants at a local garden center or nursery for your butterfly garden. Keep growing, Marianne Binetti