Issue 9, June 19, 2009

Pine False Webworm

There have been reports of pine false webworm, Acantholyda erythrocephala, attacking Eastern white pines in northern Illinois. Larvae are present at this time and susceptible to control. There are two webworms that attack pines in Illinois, using silk to web the needles together, and then feeding in the silk tent. These tents become brown as a result of brown needles within the tent and large amounts of brown larval feces hanging in the web.

Pine false webworm feeds heaviest on Eastern white pine and red pine, but also attacks mugo, Scotch, Austrian, Japanese red, and table mountain pine. Adult sawflies emerge from overwintering pupae in the soil in May, and lay eggs. The female’s saw-like ovipositor cuts slits in the needles, inserting the end of the eggs into the slits. The eggs hatch into brown larvae that feed for 18 to 20 days before dropping to the soil to pupate. Webbing is typically spun around needles below the branch tip, leaving the end of the shoot free of webbing and damage. There is one generation per year.

Pine webworm, Tetralopha robustella, also overwinters in the pupal stage, emerging as moths from cocoons in the soil through much of the summer from June into August. The caterpillars spin webbing around foliage on the ends of branches, and enter needles to feed as leafminers. When larger, they live outside of the needles, continuing to feed on them. Fully-grown caterpillars are yellowish brown with dark brown stripes and about five-eighths inch long. In late September, the caterpillars drop to the soil to pupate. In the Midwest, they feed on Eastern white, red, Scotch, jack, and mugo pine.

Control pine false webworm with high pressure sprays of pyrethroids such as cyfluthrin (Tempo), permethrin (Astro), or bifenthrin (Onyx, Talstar) to penetrate the webbing and reach the larvae. Carbaryl (Sevin), spinosad (Conserve), and acephate (Orthene) will also be effective. The same insecticides will control pine webworm as well as Bacillus thuringiensis kurstaki (Dipel, Thuricide). Because pine false webworm is a sawfly, not a caterpillar, B.t.k. will not be effective on it.--Phil Nixon

Phil Nixon

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