Dusky birch sawfly, Croesus latitarsus

Appearance

Larvae are yellow-green with black blotches on their sides and have a black head; they are about 24 mm (1") long when full grown.

Hosts

Birch.

Damage

Larvae feed in groups around the edges of leaves. Heavy defoliation by this insect is rare.

Life history and habits

Overwinter as prepupae in the soil. First generation larvae feed from May to early July. A second, overlapping generation may occur and feed through September.

Use the following as a guide for selecting the best method for control:

1. 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.
2. 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.
3. 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)
• bifenthrin
• carbaryl (Sevin
• insecticidal soap (M-Pede)
• malathion (Malathion)
• permethrin