Cody Ray Groebner
June 3rd 2015
The Sawfly Insect
Sawflies are a group of insects related to wasps and bees. Their name is derived from the saw-like ovipositor the adult female uses to lay eggs. Adult sawflies are inconspicuous wasp-like insects that do not sting. The larval or immature stage of sawflies are plant feeders and look like hairless caterpillars (the immature stage of butterflies and moths). The most distinguishing character between sawflies and caterpillars is the number of prolegs (fleshy, leg-like projections) on the abdomen. Caterpillars have 2-5 prolegs on the abdomen (Fig. 1), while sawflies have 6 or more. Sawflies often feed in groups and can quickly defoliate portions of their host plant. There are many different species of sawflies and each prefers specific plants or groups of related plants. Some of the more common sawflies that feed on trees and shrubs in Minnesota are described in this publication.
Mugo, Scot's, red, and jack pines are preferred; eastern white, Austrian, and ponderosa pines may also be fed on if they occur near a preferred host.
Larvae feed in groups on the previous year's needles and eat all previous-season needles on a single branch before moving to another branch to continue feeding. They will vacate a tree for a new host once all previous-season needles have been eaten. Larvae never eat new needles, but may feed on the bark of new shoots. European pine sawfly seldom kills trees since new foliage is never eaten; however, repeated defoliation's can slow growth. Feeding on bark of new shoots may cause twig mortality but it is rarely serious.
Life history and habits
Overwinter as eggs in the previous season's needles. Larvae begin feeding around mid-May and continue through June. After feeding, larvae pupate in the soil or on the tree and adults begin appearing in early September through late fall. Adults lay eggs in the current season's needles near the ends of branches where they overwinter. There is one generation per year.
If it is determined that control measures are needed, use the following as a guide for selecting the best method:
- Mechanical control: Examples here include methods such as hand picking larvae from plants, physically dislodging them by using forceful water sprays, or other means of nonchemical control. Population size and distribution will determine the effectiveness or suitability of the chosen method.
- Biorational insecticides: Insecticidal soap-best for low populations of young larvae. A note here -Bacillus thuringiensis (BT) will not control sawflies. Strains of this biological insecticide are effective against various caterpillar pests (larvae of butterflies and moths), but will not control sawfly larvae.
- Conventional insecticides: Any of the insecticides listed in Table 1 will provide good control of sawflies. These products should be considered only after all other management tactics have been explored.
If it is determined that chemical control measures are needed, they should be directed toward the young larvae. Young larvae are much more susceptible to chemical applications than larger, more mature larvae. This is especially true when using biorational products such as insecticidal soap. If larvae are nearly full grown, control measures should not be attempted as chemicals will not be as effective, and most of the damage that the plant will sustain has already been done. Finally, because sawflies often feed in groups, chemical applications should be directed only to the areas they are feeding on; entire tree sprays are unnecessary unless populations are wide-spread throughout the plant. A list of some insecticide options for sawfly control is given below.
A final note on control. The best control for sawflies or any other pests is preventive measures related to plant health. Correct plant selection, proper site selection when planting, and then continued recommended cultural care will ensure that plants are in excellent health. The better condition a plant is in, the more damage it can tolerate without affecting its health status.
Some insecticide options for sawfly control:
- acephate (Orthene)
- carbaryl (Sevin
- )insecticidal soap (M-Pede)
- >malathion (Malathion)
Methods of Prevention and Control
Treating Pine Sawfly larvae can be done in two methods depending on how the groups are formed. Very small groups of the larvae can be pruned off the tree and disposed of. Larger groups; however, will require an insecticide treatment. Over the counter insecticides, such as Sevin, will work on Pine Sawflies, but be sure you’re familiar with the toxicity level of the product you buy.