Diseases & Pests
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European Pine Sawfly
by Don Janssen, UNL Extension Educator
The European pine sawfly (EPS), Neodiprion sertifer, is a common sight on certain pines in the spring. This accidentally introduced pest is, as the name implies, native to Europe and was first found in North America in 1925 in New Jersey. It is a problem primarily on Scotch and mugo pines (Pinus sylvestris and P. mugo), but will also affect red pine (P. resinosa), jack pine (P. banksiana), and Japanese red pine (P. densiflora). EPS will also infest other pines, such as eastern white pine (P. strobus) and Austrian pine (P. nigra) if they are adjacent to the more preferred pine species.
EPS overwinters as eggs on needles. The white or yellow eggs are partially inserted into a needle by the female the previous fall. They appear as evenly spaced yellow or light brown spots running the length of one or more needles, and are easily overlooked. The eggs hatch in the spring to produce caterpillar-like larvae with black heads and legs, and gray-green bodies. There is an off-white stripe down the middle of the back and slightly lighter stripes on either side.
As soon as they hatch, larvae begin feeding on the previous year's growth. The young larvae eat only the surface of the needle, which discolors the needles making it look like dried straw. Older larvae eat the entire needle from tip to base. The larvae feed in groups of 10-100. They tend to eat all the needles on one branch before moving on to the next one. The missing foliage is usually very obvious, so it's easy to spot an infestation once the larvae are halfway grown.
The larvae feed for 4 to 6 weeks, eventually growing to about one inch long. Once they have finished their development – usually about the time the current year's growth is emerging from the candles – they pupate inside tough, golden brown cocoons either in the soil, in litter beneath the tree, or in protected sites on the lower trunk.
Larval colonies can be removed by smashing, wiping or shaking the insects off the plants. Infested branches can also be clipped off and destroyed, but this can damage the tree's appearance as much or more than the insects will. Birds and rodents may feed on the larvae, but they rarely eliminate all the sawflies on a tree.
Although EPS larvae look like caterpillars, it is important to know that they actually belong to the insect order Hymenoptera, the group of insects that includes ants, bees and wasps. This means that insecticides labeled for control of caterpillars may not be effective. This is particularly true of the bacterial insecticide BT, or Bacillus thuringiensis, which only affects caterpillars. Make sure the insecticide you choose to use lists sawflies on the label! The best time to apply chemical controls is when the larvae are still young (less than Â½ inch long) because they are more susceptible than older, larger larvae.
EPS has only one generation per year. They often return year after year to the same location, so if you have problems this year, then you should be on the lookout for them next year about mid-May.
Photo Credit: Iowa State University
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