Adult beetles are 10-12 mm long with red heads and black eyes. Their bodies are gray with lighter gray and red markings on the underside of the thorax. Adults have yellowish brown legs and long antennae. Larvae are longer (up to 20 mm), with clear segmentation and no legs. They are white with a near yellow head capsule.
Adult O. erythrocephala are very active and can often be seen flying above leafy spurge plants. Ringed grooves chewed around the stems of plants can also be indicative of their presence. Larvae can be found by cutting into stems and looking for burrows or the larvae themselves. Dead stems and tops of stems are also a good indication of the insects presence, larvae or adult.
Adult beetles emerge from soil in early to mid-summer. They must begin feeding for approximately two weeks before they reach sexual maturity. After mating females girdle the stems of leafy spurge plants and chew holes above the rings where a single egg is deposited in each hole. She can lay up to 40 eggs. Eggs take 7-10 days to hatch. Larvae then burrow down stems to root crowns where they continue to feed on plant tissue in crown and lateral roots. Larvae overwinter here until they pupate the following spring to emerge as adults later in the season. They typically have one generation per a year though there is a possibility that in some cases two years may be required for larvae to mature in colder areas of North America.
Leafy spurge vascular tissue is damaged by larval feeding resulting in reduced above ground tissue, flowering and root reserves. Adults also girdle stems but their impact is far less than larvae.
O. erythrocephala are readily available in Montana. If you are interested in obtaining these insects view the biocontrol vendor list for options.
This species may only be effective on certain biotypes of leafy spurge, limiting its efficacy in many areas. Despite this, it is well established in many areas of the Western U.S. It is best paired with Apthona spp. when using biocontrol agents to control leafy spurge.
Using the Agent
Adult stem borers can be collected in mid-summer at peak day time temperatures when leafy spurge flowers have emerged. Due to their ability to fly sweep netting is often less efficient than simply collecting them by hand or with forceps. 50-100 adults should be released per site for establishment. Successful redistribution can be assessed by looking for mined stems or larvae in the summer or next generation adults the following spring or summer.
The red-headed leafy spurge stem borer should not be a primary method of control for leafy spurge. As with other weeds an integrated approach should be employed. Due to its deep root system (3-7 m) and the ability to regenerate from very small root fragments (>1/2 in long), hand pulling and mowing are often unsuccessful on established plants and can even help spread the plant. Small infestations should be treated with a labeled herbicide as soon as possible. Some combination of chemical and biological control is preferred on sites with established plants.
Grazing with sheep and goats has been shown to weaken colonies of leafy spurge and can be paired with both Apthona spp. and O. erythrocephala. In these cases, herbicides can be used at the site perimeter to contain the weed. Leafy spurge is toxic to cattle so they should not be used to control the plant. Additionally, aggressive revegetation, particularly with grasses, should be employed to provide competition for weeds.
For more information on control methods and herbicide recommendations contact your local weed district or Extension Service.
Hansen, Rick. Agriculture and Life Sciences Cornell. “Hyles Euphorbiae.” Accessed January 18, 2017. https://biocontrol.entomology.cornell.edu/weedfeed/Oberea.php
Winston, R., C.B. Randall, R. D. Clerck-Floate, A. McClay, J. Andreas, M. Schwarzlander. May 2014. Field Guide for the Biological Control of Weeds in the Northwest. http://www.ibiocontrol.org/westernweeds.pdf
Washington State University Integrated Weed Control Project. Biological Control Agents. Accessed January 18,2017. http://invasives.wsu.edu/biological/obereaerythrocephala.htm