06-26-15 Field Note

Populations of defoliating insects have reached their summer peak. Beau Larkin shares observations about these insects, and includes a few wildflower images for good measure!

Posted on 6/26/2015 by Beau Larkin

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Populations of defoliating insects have reached their summer peak. Beau Larkin shares observations about these insects, and includes a few wildflower images for good measure!

Hawthorns fared poorly in spots; this shrub lost almost 100% of its leaf tissue. Western tent caterpillar populations increase and decrease over years based on forage availability, disease, parasitoids, and weather. Caterpillar populations have been strong for a few years in the Swan Valley.

Left of center, cottonwood leaf defoliation approaches 100%, but the caterpillars didn’t munch the cottonwood on the right at all.

Under the cottonwoods, I thought I heard raindrops falling on understory vegetation. Instead, a rain of fecal pellets excreted by the caterpillars had created this unusual soundscape. Wild sarsaparilla (Aralia nudicaulis, above) and cow parsnip (Heracleum maximum, inset) leaves filled with pellets.

A few western larch branch tips grew brown and deformed over the past few weeks. This is the work of western spruce budworm (Choristoneura occidentalis). Right now, budworm damage on larch appears to be widespread but light.

I disturbed a budworm’s ‘tent’ on an Engelmann spruce seedling and it backed out hind end first (above). It then dropped backward off the foliage and retreated down a silky thread (inset).

Many subalpine fir trees also showed budworm symptoms, but I found no caterpillars here. The pest for this tree species remains unknown for now.

Spittlebugs (Aphrophora sp.) also appeared on western larch. I dug a nymph out of the spittle and placed it back on the stem for a photo (upper right). Several other nymphs had already climbed higher in the tree and metamorphosed to their adult form (lower right).

In early May, we noticed Cooley spruce gall adelgids (Adelges cooleyi) in large numbers on Douglas-fir. The outbreak on Douglas-fir has subsided; only the dry wooly tufts remain (above). Defoliation was minor in most cases (inset). Most of the adelgids have flown to Engelmann spruce, their alternate host.

Back on the spruce trees, the adelgids have begun feeding. While feeding, they produce hormones that induce the formation of these galls that will soon house adelgid eggs.

Cow parsnip flowers appeared in multiple stages. Here, an umbel flushes with new flowers.

With all its flowers open, this plant is an insect magnet.

White bog orchid (Platanthera dilatata) blooms near Southwest Marsh.

With broad leaves and inconspicuous flowers (inset), water plantain (Alisma sp.) blooms have appeared with the seasonal drying of the Pothole.

About MPG North

Established in 2005, the property boundary at MPG North encloses 200 undeveloped acres in Western Montana’s Swan Valley. Researchers and field staff manage the property to improve habitat quality for wildlife, discover new ways to restore damaged landscapes and study forest ecology. We also create opportunities to share what we've learned with local conservation organizations, students of all ages, management agencies and volunteers. Through these education and outreach efforts, we seek to inspire others to work together and protect undeveloped landscapes.