Bark beetles are small insects that inhabit the inner bark of trees. While they play a role in decomposing dead or dying wood, some species can significantly impact forest health by attacking and killing healthy trees during outbreaks. Natural predators are important in managing bark beetle populations, contributing to the balance of forest environments.
Insect Predators
A variety of insect species prey on bark beetles, contributing to their natural control. Checkered beetles (family Cleridae) are prominent predators; both adult and larval checkered beetles consume bark beetle adults and their larvae. Species like Thanasimus undatulus and Thanasimus dubious are known to specifically target bark beetles, including the southern pine beetle and Ips beetles. These predatory beetles possess strong mandibles to grasp and consume their prey.
Parasitic wasps, including those from the Braconidae and Ichneumonidae families, also regulate bark beetle numbers. Female wasps locate bark beetle larvae and pupae within tree bark, laying eggs on or inside them. The developing wasp larvae then feed on the bark beetle host. Another insect predator is the long-legged fly, Medetera bistriata, whose larvae consume bark beetle eggs, larvae, and pupae. These diverse insect predators target different life stages of bark beetles, collectively helping to limit their populations.
Avian Predators
Woodpeckers are significant avian predators of bark beetles, using specialized adaptations to extract insects from infested trees. The Hairy Woodpecker frequently consumes bark beetle larvae, often appearing in large numbers in infested forests. Downy Woodpeckers also consume bark beetle eggs, larvae, and adults, making them a common sight in areas with these insects. These birds use long, sticky tongues to access prey hidden beneath the bark.
The Black-backed Woodpecker and the Three-toed Woodpecker specialize in feeding on wood-boring and bark beetles. Black-backed Woodpeckers are found in recently burned forests, where they find abundant wood-boring beetle larvae, and also utilize bark beetle outbreaks as a food source. Three-toed Woodpeckers predominantly prey on bark beetles, with studies estimating a single woodpecker can consume approximately 670,000 bark beetles per year across all life stages. These birds often strip bark from trees to expose and consume beetle broods.
Predator Hunting Strategies
Predators employ various strategies and adaptations to locate and capture bark beetles within tree bark. Chemical cues are a primary method for many insect predators. Predatory beetles like checkered beetles and certain parasitic wasps are attracted to the pheromones released by bark beetles, which serve as kairomones, signaling the presence of their prey. These predators can also detect volatile chemicals released by stressed or infested trees, further guiding them to areas with high bark beetle activity.
Woodpeckers utilize auditory cues to pinpoint hidden prey. They tap on tree trunks and listen for subtle sounds that indicate the presence of beetle larvae or tunnels beneath the bark. This auditory detection is complemented by their physical adaptations, such as strong chisel-like bills for excavating wood and stiff tail feathers that provide support while hammering. The Black-backed and Three-toed Woodpeckers possess a unique three-toed foot structure, with two toes forward and one back, which enhances their grip and allows for more forceful excavation.
Parasitic wasps have a long, needle-like ovipositor that they use to drill through tree bark and deposit eggs directly onto or into bark beetle larvae. This specialized appendage allows them to reach prey that is otherwise inaccessible. Predatory beetles, with their robust mandibles, are equipped to tear into bark or seize exposed bark beetles. These diverse and specialized hunting strategies enable predators to effectively target and control bark beetle populations.