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June bugsJune 29, 2001

Large aspen tortrix

large aspen tortrix larvae

In addition to the defoliation by the forest tent caterpillar, large aspen tortrix was also present defoliating aspen trees near Duluth and along the north shore of Lake Superior. It has been present for the past two or three years. The presence of tortrix is often overlooked when it occurs along with the much more obvious forest tent caterpillar. Tortrix larvae are dark green to black and grow to only about 3/4 of an inch long. The larvae had already pupated by the 3rd week in June near Duluth.

Larch casebearer

Feeding damage from larch casebearer, an introduced pest, was visible by the first week of June in northeastern and north central Minnesota. This insect overwinters as a larvae in a case made out of a hollowed out needle which it cements to the base of a bud. In early spring the larvae begins mining more needles, often damaging only the outer end of the needle, the base of the needle staying green at least for a time. The larva lives in a hollowed out needle or case that it uses as a portable shelter during the entire larval stage. Damaged stands look off color tan or brown very similar to flooding damage. Needles have to be examined carefully to see the entrance hole in the mined out needles or to find the cases containing the larvae. In the western US, it is reported that each larva needs to feed on 24 to 76 needles to complete its development. Moths were observed on June 27th near McGregor in Aitkin County.

Larch casebearer occurs almost every where tamarack occurs in northwestern Minnesota and where FTC hasn't already feasted on them. Going north from Bemidji, defoliation tends to disappear about 15 miles south of Baudette. This is where FTC is also the heaviest. Going south from Bemidji, casebearer defoliation extends as far south as Park Rapids, southern Hubbard and northern Cass Cos.

Casebearer damage was common across northern Minnesota in 2000 and appears to have increased in 2001 in the northwestern counties.

Larch beetles

Larch beetle galleries were found in two tamarack stands last week in Beltrami Island: one (old-growth tamarack) in Hayes Lake State Park and another (younger tamarack) in a stressed site south of Faunce. Some trees with normal crowns were infested with larch beetles as well as those with sloughed bark and /or fading crowns.

In northeastern Minnesota, adults of the larch beetle have been captured weekly in pheromone traps since the traps were set out in three locations on May 4th. The first adults to emerge had overwintered under the bark as adults. It's likely that the most recently captured beetles overwintered as larvae.

Adult beetles have been attacking live trees and forming long egg galleries which run vertically up the trees. As of June 21st, eggs were found in the galleries and, as of June 25th, new larvae were present. In some locations, larch beetle pockets have expanded and the trees are suffering heavy attack by the larch beetle and are likely to be killed by them. Mortality of tamarack occurred last year on trees growing on upland as well as on lowland sites.

Spruce beetle

Spruce beetles, Dendroctonus rufipennis, continue to attack and kill white spruce trees along the North Shore in Cook and Lake Counties. The beetles prefer spruce fourteen inches and larger in diameter, but can occasionally be found on smaller trees as well. Many of the trees being attacked appear healthy with full crowns and healthy looking needles. The most obvious signs of recent attack are pitch tubes.

We are still interested in getting a better idea of the distribution of the spruce beetle in Minnesota. If you have any white spruce trees that you suspect have been attacked by the spruce beetle please contact one of the Forest Health Specialists.

Spruce budworm

Spruce budworm populations continue to decline in northeastern counties. Moderate to heavy defoliation occurred in St. Louis County in townships: T60, 61 62 of 18W and T 26,63 of 19W and was very obvious along Hwy 53. On June 12th and 13th , about 25% of the budworm were pupating. The remainder were mostly 6th instar larvae with a few 5th and 4th instars also present. On June 17th, abundant moths were observed north of Nashwauk in Itasca County.

In northwestern counties, spruce budworm larval surveys indicate a low-level population exists but there is only a trace of defoliation.

Yellow headed spruce sawfly

Sawfly larvae were actively eating the needles of ornamental white spruce near Burnt Shanty Lake in northern Itasca County on June 20th. Larvae averaged 3/4 of an inch long with some still only 1/4 inch long. Larvae were also reported in Beltrami County on June 18th.

Jack pine budworm

Jack pine budworm is almost nonexistent both in larval numbers and defoliation in Regions 1 and 3.

Two-lined chestnut borer

Oaks weakened by drought, defoliation, or other factors are targets of the two-lined chestnut borer, Agrilus bilineatus. After chewing their way through the bark these beetles lay eggs which hatch into very slender, flattened white larvae that have two spines at the end of their abdomens. As these larvae feed and tunnel through the live tissues of the inner bark and outer sapwood, they girdle the infested branches and eventually infest the trunk. Leaves wilt, turn a uniform brown, and usually remain attached for several months before dropping.

Rose chafer beetles

rosechafer beetle

Rose chafers were first observed in central Minnesota on June l4th. Roses, peonies, raspberries, grapes, shrubs and trees can have their leaves and flowers skeletonized or shredded by the rose chafer beetle, Macrodactylus subspinosus. These tan beetles have reddish-brown heads and orange or dark brown, slender legs. As adults, they live about three weeks. Their eggs are deposited just below the soil surface in grass, alfalfa, or clover-sod on sandy, well-drained soils. The larval stages, grubs, feed on roots of grasses and other plants until next June when they change into beetles, crawl out of the soil, disperse by flight, and congregate in great numbers as females emit sex attractant chemicals into the air.


Blister beetles

blister beetle image

Aggregations of blister beetles are a rare sight to see although there are more than 300 species of them in North America. 'Lucky' observers in Crow Wing, Itasca and Carlton Counties found Say's blister beetle, Lytta sayi, in the act of shredding leaves of lupines, peonies and some shade trees. This species is a dark, shiny, metallic green insect with black antennae and orange legs. Grubs of this beetle search out and feed on the wild bee larvae in the soil.

Blister beetles earned their name because they secrete a fluid that raises blisters on humans and, more importantly, deters their predators. When disturbed, blister beetles exhibit "reflex-bleeding". That is, they emit blood from their knee joints and other areas which can raise blisters. In the past, the active ingredient in their blood was extracted and used medicinally in poultices to raise blisters.


Pale green weevils

The first of the pale green weevils emerged June 8th near Grand Rapids and they have become quite numerous by the end of June. A collection of green weevils from near Grand Rapids was identified by Dr. Bill Mattson, a USFS research entomologist, as Polydrusus sericeus. The adults feed on the edges of the leaves of many trees and shrubs.