Here are a couple of pictures of the puncture vine weevils (Microlarinus lareynii) I found on a healthy puncture vine (Tribulus terrestris) in the Central Valley near Fresno, California this last week. They were most easily seen by turning the plant over and looking closely on the ground just beneath the sprawling plant. I've been watching them fairly closely for several days. Two weeks ago when I first noticed them, the goatheads (or the thorn-covered seeds) looked healthy and were beginning to harden to the point of becoming very annoying. A few days ago I looked again and noticed that many of them were being hollowed-out by the growing puncture vine weevils. The
picture of the mature larva is a bit staged. I had
to remove it from the hole (seen below it) in order
to take the picture.
The weevils were introduced to the United States
over 40 years ago to control this weed. But, since
the weed is still a problem, the weevils have been
pretty much ignored. This is too bad. The weevils
are effective in at least reducing the puncture vine
problem; and, importantly, they haven't jumped
onto other useful plants. Many of our intoroduced biological control organisms have done just that.