The brown prionid beetle (Orthosoma brunneum) belongs to the family Cerambycidae, commonly known as longhorn beetles. These beetles are known for their elongated bodies and long antennae, which can be as long as or longer than their bodies in some species.
They are typically wood-boring insects, with larvae that develop in living or decaying wood. A homeowner in Wayne County, Ohio found this brown prionid beetle and brought it to the Plant Pest Diagnostic Clinic at The Ohio State University for identification.
Taxonomy and identification
There are more than 36,000 cerambycid species described in the world, belonging to 8 subfamilies in more than 5000 genera. In North America, about 1000 species in 300 genera have been reported so far.
This particular beetle is Orthosoma brunneum, and it is monotypic, meaning it is the only species reported in this genus in the world. O. brunneum is native to the United States.
The name "Orthosoma" refers to the perfectly parallel margins and parallel lines of the beetle's elytra, which is a distinctive feature of this genus. "Brunneum" is derived from the Latin word for "brown," reflecting the typical coloration of the brown prionid beetle.
Ecology and life cycle
Females lay eggs from June to late summer on decaying wood with high moisture content and fungal colonization. Larvae develop within the wood, feeding and creating tunnels with coarse fibrous frass for 2-3 years before pupating and emerging as adults.
The larvae of O. brunneum typically feed on moist decaying wood. They are often found in various types of wood substrates, including decaying trees, utility poles, and even railway logs. This behavior is crucial in ecosystems as it contributes to the decomposition and nutrient cycling of woody tissues in dead trees, which is important for forest health.
In terms of their diet, larvae of O. brunneum are known to feed on both hardwoods and conifers. Host tree species include Cercis canadensis (eastern redbud-Caesalpiniaceae), Juglans nigra (eastern American black walnut-Juglandaceae), Juniperus virginiana (eastern redcedar-Cupressaceae), Ostrya virginiana (American hophornbeam-Betulaceae), Pinus rigida (pitch pine- Pinaceae), Pinus strobus (eastern white pine- Pinaceae), Pinus virginiana (Virginia pine), Robinia pseudoacacia (black locust-Fabaceae), and Tsuga canadensis (eastern hemlock-Pinaceae).
The larvae also have been reported feeding on other tree genera, including Carya (hickory- Juglandaceae), Castanea (chestnut- Fagaceae), Quercus (oak- Fagaceae), Tilia (lime trees- Malvaceae), Acer (maple- Sapindaceae), Abies (fir- Pinaceae) (Lingafelter, 2007), and Fraxinus (ash-Oleaceae) (Heffern et. Al., 2018).
Adult O. brunneum are reported to feed on fruits, flowers, and leaves. They are attracted to light, so the adult beetles can end up indoors sometimes. Adults are active from May to November.
Do you know?
When threatened, this beetle can produce a squeaking sound. The sound is derived from rubbing the hairs and the serrated margin on the hind femur against the edge of the elytra.
Larvae of any longhorn beetle are a great protein source for vertebrates. The use of larvae of O. brunneum and a few other longhorn beetles as food for humans has been reported in different parts of Asia and Africa (Kiewhuo et. al., 2024; Thomas, 2018).
Pest status and management
While O. brunneum is not generally considered a primary agricultural pest in the United States, it can cause considerable damage to various wooden structures and crops under certain conditions. The beetle larvae can bore into utility poles, railway sleepers, timber, firewood piles, and other wooden structures. Their activity can weaken the wood and compromise the integrity of these materials over time (Baker, 1972).
Although their primary habitat is decaying wood, there are unverified reports that larvae of O. brunneum have been known to occasionally damage fruit crops and healthy trees. Further studies are needed to confirm the statement.
Since these beetles prefer moist wood for egg-laying, keeping wood dry can deter them. This includes ensuring that wooden structures are well-maintained and not exposed to excessive moisture.
Treating logs and wooden structures with preservatives before they come into contact with the ground can prevent larvae from infesting them. These treatments create a barrier that discourages egg-laying and reduces the likelihood of damage.
Regular inspection of wooden structures and orchards for signs of beetle activity, such as exit holes can help identify infestations early, thereby controlling potential damage.