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California Root Borer (Prionus californicus)

California root borer, mostly found in the United States’ western parts, is a part of the longhorn beetle family (Cerambycidae). The larva of this species bore into the roots of deciduous trees, hence the name.

California Root Borer Beetle

Scientific Classification

  • Family: Cerambycidae
  • Genus: Prionus
  • Scientific name: Prionus californicus

Physical Description and Identification

Adult

Size:  25.4 – 76.2 mm (1 – 3 inches)

Color: They have a reddish-brown body, while some could even be completely black. Their wing cases possess a smooth and shiny texture.

Other Characteristic Features: Sexual dimorphism remains visible in the adult beetle species. The males appear smaller than the females, with more serrated antennae.

Prionus californicus

Larva

The larva is cream or brown, growing to about 6.35 – 76.2 mm (0.25 – 3 inches) in 3 – 5 years. The body segmentation is prominently visible in the larva that also has large mandibles. They are voracious eaters of roots furrowing through them, consuming the tissues initially and then moving deep within, upwards, and eventually attacking the apex.

California Root Borer Beetle Larvae

Pupa

The pupae are pale cream, being a complete replica of the adult species. They reach a length of about 25.4 – 50.8 mm (1 – 2 inches) with their legs and other appendages not being glued to their body. The entire pupation stage takes place on the surface of the soil within a cell made up of root material and soil.

Egg

The eggs are cream or yellowish-brown, 4.8 mm (0.18 inches) long. The female lays about 200 eggs during her lifetime.

California Root Borer Beetle Eggs

Quick Facts

Other NamesGiant root borer, round-headed borer (the larva is called by this name)
Lifespan10 – 20 days
DistributionThroughout Western North America, from Mexico and California up to Alaska
HabitatLarvae: Near the roots of deciduous trees and shrubs Adults: Mostly in fields around crops like grapevines and hops
Common PredatorsGround beetles, rodents, and ground-dwelling fungi
Seasons active fromJune – September
Host PlantsDeciduous trees, shrubs, conifer, brambles, crops like hops and grapevines, fruit trees (cherries, cranberries) 
Diet  of larvae and adultsLarvae: Roots
Adults: Agricultural crops, leaves of fruit trees
California Root Borer

Identifying the Damage Caused by Them

Being an orchard pest, they mainly cause intense damage to the roots by removing the tissues completely through constant digging. In this manner, the entire tree eventually gets prone to infection and could wither and die. The adults also cause a significant amount of harm to the crops though at a lesser intensity.

Did You Know

  • The larva’s cylindrical body earns them the name round-headed borers.
Giant Root Borer

Image Source: i.pinimg.com, bugguide.net, lh6.ggpht.com, lh3.googleusercontent.com

California root borer, mostly found in the United States’ western parts, is a part of the longhorn beetle family (Cerambycidae). The larva of this species bore into the roots of deciduous trees, hence the name.

California Root Borer Beetle

Physical Description and Identification

Adult

Size:  25.4 – 76.2 mm (1 – 3 inches)

Color: They have a reddish-brown body, while some could even be completely black. Their wing cases possess a smooth and shiny texture.

Other Characteristic Features: Sexual dimorphism remains visible in the adult beetle species. The males appear smaller than the females, with more serrated antennae.

Prionus californicus

Larva

The larva is cream or brown, growing to about 6.35 – 76.2 mm (0.25 – 3 inches) in 3 – 5 years. The body segmentation is prominently visible in the larva that also has large mandibles. They are voracious eaters of roots furrowing through them, consuming the tissues initially and then moving deep within, upwards, and eventually attacking the apex.

California Root Borer Beetle Larvae

Pupa

The pupae are pale cream, being a complete replica of the adult species. They reach a length of about 25.4 – 50.8 mm (1 – 2 inches) with their legs and other appendages not being glued to their body. The entire pupation stage takes place on the surface of the soil within a cell made up of root material and soil.

Egg

The eggs are cream or yellowish-brown, 4.8 mm (0.18 inches) long. The female lays about 200 eggs during her lifetime.

California Root Borer Beetle Eggs

Quick Facts

Other NamesGiant root borer, round-headed borer (the larva is called by this name)
Lifespan10 – 20 days
DistributionThroughout Western North America, from Mexico and California up to Alaska
HabitatLarvae: Near the roots of deciduous trees and shrubs Adults: Mostly in fields around crops like grapevines and hops
Common PredatorsGround beetles, rodents, and ground-dwelling fungi
Seasons active fromJune – September
Host PlantsDeciduous trees, shrubs, conifer, brambles, crops like hops and grapevines, fruit trees (cherries, cranberries) 
Diet  of larvae and adultsLarvae: Roots
Adults: Agricultural crops, leaves of fruit trees
California Root Borer

Identifying the Damage Caused by Them

Being an orchard pest, they mainly cause intense damage to the roots by removing the tissues completely through constant digging. In this manner, the entire tree eventually gets prone to infection and could wither and die. The adults also cause a significant amount of harm to the crops though at a lesser intensity.

Did You Know

  • The larva’s cylindrical body earns them the name round-headed borers.
Giant Root Borer

Image Source: i.pinimg.com, bugguide.net, lh6.ggpht.com, lh3.googleusercontent.com

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