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Red pine shoot moth

Red (Norway) pines at scattered locations in central and east central Minnesota have had up to twenty percent of their shoots killed by Dioryctria resinosella, commonly known as the red pine shoot moth. Caterpillars of this insect bore into shoots in late May and feed there until July in central Minnesota (the second week of July in l997) when they transform into nonfeeding pupae and then moths. Caterpillars have brown to black heads, and their bodies range in color from brown to purple on their backs and whitish to gray to green on their under sides. Single hairs extend from rows of black spots on their backs. Pupae are brown and can be 3/4 inch in length, and there are six, often slightly twisted hooks on the posterior ends of their bodies (seen only with a larger magnifier). Moths resemble the Zimmerman pine moth which have forewings of gray blended with reddish brown, and transverse zigzag white and black lines. Their hind wings are yellowish white.

Emergence of the moths from their pupal cases occurs as early as mid July and as late as early September. Eggs are laid on the undersides of bark scales along the main stem and at the bases of branches. Young caterpillars from these eggs overwinter in silken coverings and move to the shoots the next May. Older larvae may bore into more than one shoot or move to and infest cones. Other older caterpillars wander about and pupate among the needles or under bark scales on branches or trunks, but bored shoots are the most common location for pupation, and this pest appears to infest only red or Norway pines.

Parasites often reduce their numbers, but control on ornamental red pines could involve removing infested (browned) shoots and/or spraying the young shoots in the spring with a systemic insecticide such as acephate twice at l4 day intervals. CAUTION: Spraying may also eliminate some natural enemies of this pest.

There are several other species of shoot moths that feed on red and other pines. Since their life cycles may differ from that of the red pine shoot moth, identification is important for best treatment. Parasites often keep these pests in check, but dry weather and poor soil conditions reportedly encourage buildup and damage by tip moths.