Western webspinning sawfly
Cephalcia spp.
16 host plants
Last updated
Western webspinning sawfly larvae feed gregariously within loose, grayish webbing on spruce branch tips and branch crotches. Foliage inside the web browns and becomes skeletonized as larvae feed. Picea species show damage from June through August. The sawfly creates noticeable aesthetic damage on landscape spruce but rarely threatens tree survival.
Prune branch tips with webbing and larvae intact before adult emergence in late summer. This pruning also improves tree form and removes visual damage. Do not apply pesticides into the webs; parasitoid wasps and predatory insects naturally suppress the sawfly. Trees recover rapidly the following season even after significant defoliation.
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Two types of sawfly are pestiferous in caneberry crops and cause two distinct types of damage. Onycholyda sitkensis larvae roll leaves and feed within the rolled leaves, which is inconsequential; the main concern is that they can be a contaminant in harvested fruit especially in mechanically harvested fields. Monophadnoides rubi larvae do not roll leaves but feed on leaves, leaving holes on leaf edges or between the leaf veins. Extensive feeding by Monophanoides larvae may skeletonize the...