Raspberry Horntail Research Summary


6 Years of Raspberry Horntail Research, berry condensed

Recent research has defined horntail biology developed a degree-day model, identified wasp parasitoids for biocontrol, evaluated insecticides, and assessed raspberry cultivars for susceptibility. 

wilt caused by raspberry horntail
hole in canes from horntails Horntail larvae hollow out the pith of the tops of raspberry canes. 
wasp larvae feeding on horntail
Several small larvae of an ectoparasitic pteromalid wasp feeding on a single horntail larva inside a raspberry cane. 

The raspberry horntail, Hartigia cressonii, is a prevalent cane-borer in raspberries of northern Utah. The horntail is a stem sawfly that exclusively attacks first-year primocanes. It was first found in Utah in the 1980s, and is known from the Pacific Northwest, California, and Colorado. Infested canes have lower berry yield, vigor, and winter survival. Through a comprehensive research program covering 6 years, we have defined horntail biology and life history in Utah, developed a degree-day model to predict adult activity, assessed biological control by parasitoid wasps, evaluated insecticide efficacy, and evaluated summer- and fall-fruiting raspberry cultivars for susceptibility. This article provides an overview of the findings.

Horntail Biology

There is only one generation each year; horntails are active from late spring through summer. Adults chew their way out of overwintering chambers within canes beginning in late May. Female sawflies seek attractive raspberry primocanes on which to insert eggs under the soft epidermis or bark. After hatching, the young horntail larva tunnels upwards in the cambium as the new cane grows. At the cane tip, the larva feeds heavily in the center pith causing the tissue to soften and wilt, leading to the characteristic shepherd’s crook. Typically only one larva develops per cane; however, two larvae can develop in bifurcated canes. Wilted canes are evident from late June through early September. Larvae consume the succulent tissue in the cane tip, make a U-turn and tunnel downward through the cane pith. The mature larva overwinters within a silk-lined chamber, 1.5 to 2 feet above the base of the cane.

Predicting Horntail Activity

A degree-day (DD) model was developed to predict timing of adult egg-laying. In early spring, raspberry canes containing horntail larvae were collected from farms in five northern Utah counties across three years. They were placed in a constant 77°F chamber within mesh fabric cages, and checked 2 to 3 times per week for adult emergence. Using a lower developmental threshold of 50°F, and accumulating degree days from January 1 of each year, the adult emergence period was found to span 500 to 1800 DD. This timing corresponds to approximately late May to mid-August, but varies with location and year. The DD model provides a critical tool to improve the timing of horntail management.

Natural Enemies

We detected an abundance of biological control by parasitoid wasps; however, parasitism of the horntail larva takes place in the cane tip, after some injury has already occurred. We found three species of native parasitoid wasps attacking horntail larvae. One of the most common is an ichneumonid wasp with a long ovipositor. It is a solitary ecotoparasite; an individual parasitoid egg is laid upon the horntail larva within the cane tip, and the parasitoid larva consumes the horntail. Another common parasitoid we found is a gregarious pteromalid wasp whose larvae attack horntail larvae in groups of three to twenty. The least abundant parasitoid in our survey was a tiny eurytomid wasp that is known to parasitize gall midges and gall wasps. In our study, the majority of horntail parasitism occurred from late June to mid-August with peak rates of parasitism from 40-100% in late July and early August.

Cultivar Resistance

Since 2009, 21 cultivars of floricane-fruiting (summer-bearing) raspberries and 16 cultivars of primocane-fruiting (fall-bearing) raspberries have been evaluated at the USU Horticultural Research Farm in Kaysville. Horntail infestation was substantially lower in primocane- than floricane-fruiting plants. The main reasons are likely two-fold: primocane-fruiting canes were removed at ground level in the fall or spring, thus removing the overwintering horntail larvae; and horntails avoid thin canes which are more common in primocane-fruiting cultivars.

Horntail population pressure was higher in the 2009-2011 cultivar trial than in the 2013-2014 trial, likely because of successive years of removal of infested canes at the site as part of the sampling process. Of the summer-bearing cultivars, ‘Royalty’, ‘Moutere’, ‘Octavia’, and ‘Cascade Gold’ were the least attractive to horntail while ‘Cascade Bounty’, ‘Nova’, ‘Titan’, ‘Willamette’ and ‘Saanich’ had the highest infestations.

Cultivars with the greatest winter hardiness, cane vigor, and yields tended to have fewer horntails. For fall-bearing cultivars, horntail infestation did not exceed one larva per row-foot of plants, and there were no differences among cultivars.

IPM for raspberry horntail utilizes a comprehensive approach to reduce horntail populations, use resistant cultivars, and optimize timing of insecticide applications to protect natural enemies. By gaining a better understanding of horntail biology and its life cycle, we have tailored an IPM program for Utah raspberry production systems, shown at right.

Fact sheets on raspberry horntail and suitability of raspberry cultivars for Utah are available on the USU Extension website at utahpests.usu.edu and fruit.usu.edu.


Floricane-fruiting (summer-bearing) cultivar susceptibility to raspberry horntail (RHT):
mean number of larvae per row-foot of plants, Kaysville, UT.

Cultivar # RHT Cultivar # RHT
2009 - 2011 Trial
Royalty 0.25 a Reveille 2.85 abc
Moutere 0.80 a Chemainus 2.95 abc
Cascade Dawn 1.25 ab Canby 3.25 bc
Cowichan 1.55 abc Georgia 3.62 c
Coho 1.60 abc Cascade Bounty 3.75 cd
Cascade Delight 1.75 abc Titan 4.10 cd
Lauren 1.85 abc Willamette 5.10 cd
Tulameen 2.20 abc Saanich 5.95 d


2013 - 2014 Trial
Octavia 0.01 a Prelude 0.26 ab
Cascade Gold 0.05 a Cascade Bounty 0.68 ab
1142 - 1 0.12 a Nova 1.07 b
Chemainus 0.18 a 3.62 c


Primocane-fruiting (fall-bearing) cultivar susceptibility to raspberry horntail (RHT):
mean number of larvae per row-foot of plants, Kaysville, UT.

Cultivar # RHT Cultivar # RHT
2009 - 2011 Trial
Polana 0.40 Joan J 0.70
Caroline 0.60 Ruby 0.70
Polka 0.60 Himbo Top 0.80
Summit 0.60 Heritage 0.90
Jaclyn 0.60 Anne 1.00


2013 - 2014 Trial
Autumn Treasure 0.03 Polana 0.23
Josephine 0.06 Autumn Bliss 0.30
Brice 0.08 Joan J 0.34
Vintage 0.14 Dinkum 0.50
Autumn Britten 0.18


The USU-Recommended IPM Program for Raspberries

  • Select more resistant raspberry cultivars.
    • Fall-bearing are less susceptible than summer-bearing cultivars.
  • Prune out infested canes before adults begin to emerge in May.
    • Remove fall-bearing canes at ground level.
    • Remove floricane-fruiting canes with horntail tunnels in the pith.
  • If warranted, apply effective insecticides beginning at 500 DD to kill adults before eggs are laid; repeat based on protection interval of insecticide through 1800 DD.
    • Carbamate: carbaryl (Sevin)
    • Pyrethroid: bifenthrin (Bigrade, Capture), esfenvalerate (Asana), fenpropathrin (Danitol), zeta-cypermethrin (Mustang Max)
    • Organophosphate: malathion, diazinon
  • Prune out infested cane tips all summer to lower horntail populations and prevent further cane injury.
  • Conserve natural parasitoid wasps by avoiding unnecessary insecticide applications.

- Diane Alston, Entomologist


Acknowledgements: Thank you to Dr. Brent Black and Thor Lindstrom for provision of raspberry cultivar plots, and to all the students who helped with this research, including undergraduate research fellows.