|Twig girdler, Oncideres cingulata - Dave Rintoul|
In the summer after mating, the female straddles a small branch and chews a V-shaped groove in the outer portion around the twig, leaving the center portion intact. Her feet grip the tender bark, leaving a series of horizontal grooves in the distal branch.
|Hole for egg - Chris Barnhart (CB)|
The eggs are long and narrow, fitting into a tiny hole usually at the site of a side branch.
|Egg in its chamber - CB Click to enlarge|
The number of eggs per twig normally ranges from 3 to 8 but may range up to 40. Adults live 6 to 10 weeks.
Each female deposits 50 to 200 eggs which hatch in about 3 weeks. OKstate.edu
|Larva writhing around in its frass chamber - (CB)|
This will be her offspring's home until next summer, slowly enlarging its chamber while living in its woody poop (frass for insect connoisseurs). Her larvae require dead wood to develop and the cut effectively cuts off the twig's circulation. They cannot fully develop in green twigs with high moisture content.
The legless grub will live in the twig all winter whether it falls to the ground or occasionally dangles from the tree. The chamber hollows to provide a winter home as the grub rests. It starts feeding again in the spring and grows up to an inch long, living in a world of its frass which provides some insulation. Eventually it chews an exit hole for the future, then pupates in the frass before emerging as an adult beetle in late summer.
You can see some of the action in Dr. Chris Barnhart's video here. Meanwhile a couple of beautiful final portraits from Chris of the emerged adult, Oncideres cingulata.
Note: 2013 blog updated with video.