From Ambrosia trifida branchlet galls.

Neolasioptera ambrosiae

N. ambrosiae is hard to find because there is usually no apparent gall or only the slightest swelling; occasionally, it causes a noticeable fusiform swelling on the small side branchlets. One to several larvae occur in a stem where they crawl up and down silken tubes where the pith would normally be. Before pupation, the larva cuts a hole almost all the way through the twig and retracts into the pith, where it overwinters. In spring the larva pupates, and the adult emerges a short time later.

Tapered stem swelling...Neolasioptera ambrosiae Felt

This species is based on a New York series from giant ragweed, A. trifida. Specimens from Maryland on A. artemisiifolia differ somewhat, so more than one species may be involved...Single larvae do not always cause a swelling of the stem. Hosts: A. artemisiifolia, A. confertiflora, A. dumosa, A. trifida. Distr.: New York to South Carolina, Nebraska to Texas, and California.