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Columbine Sawfly (06/11/20)

My department chair recently texted me a photo of a heavily defoliated columbine and a closeup of the critter causing the damage, and asked “What are these little green worms eating my wife’s columbine leaves?”

My department chair recently texted me a photo of a heavily defoliated columbine and a closeup of the critter causing the damage, and asked “What are these little green worms eating my wife’s columbine leaves?” After responding, I promptly checked our columbines and sure enough, I found the same culprit – columbine sawfly larvae. Columbine sawfly (Pristiphora rufipes) is native to Europe but is adventive and widespread in North America. Adults (not pictured) are small, stingless wasps with dark wings and orange legs. Larvae (Figures 1 and 2) resemble small green caterpillars, and reach a length of just over 10 mm when mature. Note the fleshy prolegs on the abdomen – sawfly larvae have six or more pairs, while true caterpillars have five or fewer.

The larvae begin feeding along leaf margins, and eventually consume the leaves except for the midribs. A heavily defoliated plant (Figure 3) has a characteristic skeleton look to it. Fortunately, the damage is only aesthetic and plants will recover fully unless drought stressed. Larvae do not feed on the flowers. Adults emerge in early May and lay eggs on the leaves. Larvae begin hatching in late May and can continue to feed through mid-June or later, depending on the year. When mature, larvae drop to the soil to pupate, and remain as pupae until the next spring when they finish development and emerge as adults. There is only one generation per year.

Control is aimed at the larvae. For light infestations, larvae simply can be picked off or shaken off and drowned in a cup of soapy water. Insecticidal soap is effective on small larvae, but the larvae must be completely covered by the soap spray. Bt spray, while effective on young true caterpillars, DOES NOT work in controlling sawfly larvae. Ready-to-use pyrethroid insecticides labeled for use on ornamental plants can be used, but only as a last resort because birds will consume the larvae, and pollinators such as bees, butterflies and hummingbirds visit the flowers for nectar. Look for the active ingredients cyfluthrin or esfenvalerate. Cover the flowers and apply only to the leaves and stems according to the label instructions. Once the spray dries, uncover the flowers. If you decide to use an insecticide, be sure to read, understand and follow the directions on the product label.

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Patrick Beauzay

State IPM Coordinator

Research Specialist, Extension Entomology

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