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Flat leaftiers on oak

The flat leaftier, Psilocorsis  reflexella, caused partial browning of leaves on many bur oaks in Crow Wing and northern Morrison Counties during August and September.  This forest insect is one of the most common leaftiers.  They use their sticky silk to tie together two or more leaves in a flat pattern, somewhat resembling a stack of pancakes.  As each caterpillar grows to about ½ inch, it scrapes away the epidermis and soft tissue of leaf blades without removing the opposing epidermis and without completely browning leaves before moving to fresh leaves. Since the caterpillars do not cause death of entire leaves, they place minor stress on trees. 

P. reflexella can be recognized by its pale green body, black head, dark brown thoracic shield and lighter brown end of its abdomen.  This leaf tier feeds on other trees and can be found throughout eastern North America and Ontario.  Leaf feeding continues until late September when caterpillars drop to ground, crawl under fallen leaves, change into pupae, overwinter. They emerge as small moths the following June.  Each moth has a wingspan of up to l inch, and its forewings have gray brown mottling over a yellow brown ground color. 

Basswood square blotch leaf miner

Reports of basswood square blotch miner, Phyllonorycter luceticila, is being reported from the Detroit Lakes Area in forest stands as of September 20th.   With two generations per year, caterpillars can be found mining leaves in July and again in September.  The mines are transparent and square-shaped (see its name above) and are found between the veins on the underside of the leaves.  They are also visible from the upper surface.  The pale colored caterpillars are about ? inch long when fully grown.  The pupae are found in a flat, oval cocoons at the center of the mines.  Adults are tiny strikingly colored moths, silvery white with gold and black markings.