Horntails are non-stinging wasp relatives associated with the dying branches and trunks of common hardwood species. (They are secondary invaders and not the primary reason for tree death/dieback.) Adults are generally brown-reddish in color with wasp-like yellow markings. Their abdomens (waists) are wide/broad and not pinched. Adults may be active approximately from June to late September. Adult female horntails are striking in that they can insert their sharp ovipositors (egg laying devices/stingers) up to 13 mm into solid wood. She does this to deposit a single egg, which will hatch into a whitish and segmented larva with fleshy, poorly formed thoracic legs. On occasion, when egg laying, females become stuck and perish. Female horntails preferentially lay eggs in unhealthy or dying trees. Female horntails also vector a species of tree rotting fungus (Cerrena unicolor). This fungus is a requirement for the successful development of the insects and may accelerate the already begun decay of the tree. Larvae reach approximately 50 mm in length and will bore into the heartwood of trees, creating round tunnels that are approximately the width of a pencil. Pupation occurs and the life cycle is completed, roughly in one year. Adults emerge through round exit holes in the tree. Horntails are present in the northern US. Different species of horntails exist, and their hosts vary, including conifers.
Larvae are only found in previously dead or dying wood. The presence of this insect in live trees indicates dead wood and that the tree is a potential hazard. Damage may be seen on the trunks and main branches of maples and beech especially, other hardwoods as well. The most noticeable damage may be the irregularly round exit holes formed by the emerging adults. On certain hosts, especially maple, confirm that these exit holes are not caused by the Asian longhorned beetle (ALB; see information on ALB in this guide). Tunneling within dead wood will also be present.
Scout for irregular, round exit holes from emerging adults, particularly on dead branches or dying trees. If present, this indicates the presence of dead wood and the tree/limb may be hazardous. This information may be important if considering branch or tree removal.
Keep trees growing vigorously and healthy. Plant trees on the right sites and prioritize proper planting. Avoid tree stress or decline caused by other biotic and abiotic factors.
One of the coolest natural enemies out there is of the pigeon tremex. It is the parasitoid wasp Megarhyssa macrurus macrurus (long-tailed giant ichneumon wasp) which lays its eggs in horntail larval galleries. The females of this species have an even more impressive ovipositor than that of their hosts - it is approximately 8 cm in length, allowing her to drill deep into infested wood to paralyze and lay her egg on horntail larvae. As with the pigeon tremex, often the parasitoid's ovipositor gets stuck in the tree, and the female perishes where she is stuck.
Because this insect is a secondary invader, and not a primary pest causing tree mortality, no chemical management is necessary.
Chemical management is not necessary.
