Learn About Whitehall Bio Control: 7/12/2023

We were not able to fill all our requests for Dalmatian toadflax insects. The adult weevils are now about finished laying eggs and are dying of insect old age. Part of the reason was the wet, cool weather. Another major factor was the damage the stem-boring weevil Mecinus janthiniformis has been doing to our collection sites! They are really hammering the toadflax along the I-90 corridor from Missoula east past Clinton and along the I-15 corridor from Helena south to Boulder. It is very gratifying to see but makes it hard for us to collect because there are fewer, sicker toadflax plants thus fewer insects. The shorter deformed plants are also harder to collect from as we tap the insects into shallow plastic kitty litter trays from the top of the plants. This collection method is called pan-tapping. My back is definitely a bit stiff from all that bending and tapping!

We also have been calling some of the 100s of landowners who have received releases from us in the past and many are saying that their knapweed, spurge, and toadflax is decreasing. Keep up the good work, insects!! If the landowners are saying this on a "good" weed year like this where the weather is allowing the weed seeds to sprout and get ahead of the insects, then the insects are really working well on those sites.

We went to collect leafy spurge flea beetles in the Missoula area with about 20 other folks and it was, unfortunately, a bust. That site is crashing also... We were only able to collect six releases. We have requests for over 100 releases. We will try to collect them on smaller local sites and over the next two weeks hope to meet most or all the demand for these fine little spurge killers. Wish us luck!

An invasive weed that we hope you will destroy when you see it is musk thistle. Its scientific name is Carduus nutans. Some of its common names include musk thistle, nodding thistle, and nodding plumeless thistle. It is a biennial plant meaning it only lives two years and is in the daisy and sunflower family Asteraceae. It is native to Eurasia. The plant can grow up to 6 feet (2 meters), has red-purple flowers from 1 ¼ - 2 inches (3-5 cm), and the leaves, stems and flowers are sharply spined. It is considered a noxious weed in North America, South Africa, New Zealand, and Australia.

Musk thistle is somewhat controlled by an insect that was released in 1969 before many of the biocontrol safety measures were put in place. It would not be approved for release today as it sometimes damages some native thistles. We do not move this insect to new sites. This insect is called Rhinocyllus conicus, the musk thistle seedhead weevil. It lays its eggs on the back of musk thistle flowers and the larvae hatch and eat their way into the seedhead. They feed on the seeds within the flower and often kill most of the seeds. The larvae develop and pupate within the flower. The adults emerge in late summer and overwinter as adults. Next spring/summer they lay their eggs and the cycle starts over again. The weevils are strong flyers and usually find new stands of musk thistle in just a few years in Montana. Then within just a few more years, their population builds up enough to mostly control musk thistle.

Rhinocyllus conicus is a quiet "success." We do not celebrate much because they do damage some native thistles. You yourself will have to decide if you feel the damage they cause is worth the pretty good job they do to keep the nasty noxious weed musk thistle in check.

Again, we will be collecting leafy spurge insects for the next few weeks and will then do knapweed root boring weevils in late July into August to end the summer. Wash the undercarriage of your vehicles to prevent the spread of weed seeds. Make a weed control plan for your land and implement it! Keep at it!!