Willow Sawfly – Nematus ventralis

Willow Sawfly – Nematus ventralis Scientific Name: Nematus ventralis Common Name: Willow Sawfly Distribution: Australia, Europe, South America, and North America. Host plants: Most species are willows, such as Salix spp. and Populus spp., however they seem to favor Salix eriocephala, Miyabeana, sachalinensis, and purpurea, as well as their hybrids. Identification: The common sawfly species known as Nematus ventralis, or the willow sawfly, belongs to the Tenthredinidae family. This non-native European sawfly may also feed on poplars (Populus spp.), despite their popular name.  While sawflies are thought to be rather uncommon, on both poplars and willows, population explosions have been seen on occasion.  up to 3/4 of an inch in length. Large yellow patches down the sides, black heads, and bodies that are either black or green-black. Life Cycle: After maturing, mature larvae descend to the ground, pupate, and then either reproduce in July or overwinter in the ground until emerging again in the spring. As a result, there are either one or two generations produced year. Damage: Larvae feed in bunches, devouring whole leaves ultimately after starting out as tiny holes in them. Heavy defoliation occurs occasionally, especially on young or tiny trees. When adults lay their eggs inside the leaves, the damage they do is usually little in comparison to the harm the larvae do. Throughout a growing season, a leaf sawfly epidemic can significantly hinder willow development, particularly in the establishing year. If there is no alternative food available, the larvae will swiftly remove the young leaves off a shrub and migrate to the older leaves. Since sawfly larvae frequently hatch in clusters, it is not unusual to see a large number of them eating next to each other on the leaf’s margin. If the weather is favorable for growth, the second generation might grow to be far larger than the first and ought to be managed. Willow sawfly pupae overwinter in the soil, and if left unchecked, small populations may grow over the course of several years. Larval populations should be observed to prevent significant, regional epidemics. Management: Physical removal of larvae is an option if populations are small. Spritzing insecticidal soap directly onto larvae has good results. Spinosad (Conserve), acephate (Orthene), and carbaryl (Sevin) have all proven successful in lowering larval numbers during significant outbreaks. Although none of these three products are particularly labeled for use on willow bioenergy crops, they are all intended for use on ornamental shrubs.