Pine sawfly?

Can't help you directly, but Texas has an *excellent* extension service. Submit a sample of the larvae for id. Talk to Harris Co. Extension to find out how:

Pine sawfly for sure. Four or five generations of this sawfly may occur each year. Adult females begin to lay eggs in slits cut in the needles during late March. The eggs hatch in 10-21 days, and the larvae feed for about five weeks. When mature the larvae usually crawl to the ground and spin a cocoon in the loose litter at the base of the tree. The peak adult emergence occurs in late summer. Larvae from this late summer generation are responsible for most of the damage which, although never directly responsible for mortality, may predispose the trees to attack by other insects.

Natural control factors generally bring outbreak populations under control after one season. As noted, sanitation under the stems through out the summer will reduce or destroy the population.

If they are caterpillers BT will get them and it is safe to use.

From Mel & Donnie in Bluebird Valley

That's common and natural on a maturing pine tree. Pines in our area have been shedding needles for over a month. That's not a problem. As trees mature such as pines, often, some branches cannot manufacture enough food for the branch and the branch becomes symplastless, sheds its needles and is then shed. Shedding woody and non-woody parts is common and good for the survival of the tree. Very common and natural. We do not spray anything on the pines we care for.

Also just because an organism injures a tree does not mean the organism is bad and requires to be killed. E.g,

What does that mean, sanitation under the stems? Keep clear of pine needles under the tree?

Kate

They pupate in the debris under the tree they were in, clean up the debris, or if your into nasty garden chemicals poison the debris, and it can reduce the populations from generation to generation.