Raspberry Horntail

The raspberry horntail larvae bears a spine on the tail end.
The raspberry horntail larva bears a spine on the tail end.

Raspberry horntail adult.
Raspberry horntail adult.

Wilted cane tip due to horntail larval injury.
Wilted cane tip due to horntail larval injury.

Wilted cane tip and cane tip with leaf dieback due to horntail larval injury.
Wilted cane tip and cane tip with leaf dieback due to horntail larval injury.

Ectoparasitoid larvae feeding on a raspberry horntail larva.
Ectoparasitoid larvae feeding on a raspberry horntail larva.

HOSTS

  • Raspberry
  • Rose
  • Other Brambles

DESCRIPTION

The mature larva has a cylindrical white body about 1 in long, a hardened brown head, and a short spine on the tail end. The pupa is tan and about 3/4 inch long. Adults are 1/2 inch to 3/4 inch long, iridescent black, narrow-bodied wasps with long antennae. Eggs are about 1/16 inch long, pearly white, oblong, with a curved point at one end.

BIOLOGY

There apears to be only one generation of raspberry horntail (Hartigia cressonii) per year in northern Utah. Egg-laying extends from early spring to early summer, so larvae of all sizes can be found in canes during the summer.

The horntail overwinters as a mature larva in a silk-lined cavity in the lower cane. Pupation occurs within the cane in early spring. Adults emerge through a small hole cut in the lower cane, beginning in early to mid spring. Females insert eggs singly under the epidermis of new canes, usually only one egg per cane, but multiple horntail larvae have been observed in a single cane. The young larva tunnels upward in a spiraling pattern within the growing cane, feeding primarily in the cambium just below the bark. When the larva reaches the cane tip it feeds heavily in the cambium and pith. The older larva then tunnels downward, primarily through the center pith of the cane, to form a cavity to spend the winter.

SYMPTOMS

  • Berry canes with terminal growth that softens, wilts, and dies back
  • Crooked and weakened canes
  • Reduced fruit yields of damaged canes
  • Reduced plant vigor
  • Greater susceptibility to winter injury

GENERAL MANAGEMENT

Cultural Practices: Healthy plants are less attractive to insect pests and better able to withstand environmental stresses. Good crop production practices include selection of suitable planting sites, selection of raspberry varieties adapted to a site, soil preparation before planting, maintaining optimal soil fertility, and prevention of nutrient deficiencies such as iron chlorosis, which is common to alkaline soils of Utah. Use of good production practices is important to reduce horntail infestation.

Pruning and Sanitation: Prune and destroy infested canes when tip-wilting becomes apparent; this will remove larvae and reduce the population for the next season. Wilting of cane tips is apparent from June to August. Cut the canes about 6 inches below the tip to ensure that larvae are removed. Cane tips with a larva feeding in the pith often become soft. In small plantings, or if infestation levels are low, larvae can be killed by squeezing the soft cane near the tip with gloved fingers. Prune or mechanically destroy horntail larvae one to two times per week to ensure that larvae do not tunnel down the canes and escape removal.