Some wood-boring beetles tunnel through twigs during their period of larval (immature) development. These include the twig pruner, Anelaphus (formerly Elaphidionoides) villosus. Twigs of their hosts become partially severed during larval development, and as a result break easily. They may drop to the ground beneath the host plant, or remain hanging on the tree. The larvae of the twig pruner are white cream colored roundheaded borer larvae with long, lemon yellow hairs found on the prothorax. The life cycle of this insect is not fully understood at this time (Johnson and Lyon, 1991). Some references suggest the following: in North Carolina, adult twig pruners were caught in light traps starting in late April. Adults are slender, grayish longhorned beetles that are approximately 1/2 inch in length. By the late spring, the female chews a small niche in the bark of a twig at a leaf axil and there lays its eggs. One egg is inserted in each individual niche. Larvae hatch from their eggs and create an entrance hole in the twig, where they begin feeding in the center of the small branch, tunneling toward the base of the twig. The branch may remain attached to the host plant throughout the summer, but by the fall the larva begins to feed from the center of the twig out to the sapwood in circles, leaving behind a thin layer of bark holding the twig to the tree. The larva then moves to the center of the branch (the end that is to be cut off the tree) and creates a plug filled with fibrous or sawdust-like frass. Eventually the branch breaks free from the tree and falls to the ground. The larva may continue to feed inside the broken branch until temperatures begin to cool in the fall. It is thought that the insect overwinters as a pupa, so pupation occurs within the broken branch. If branches are left in place on the ground, the adult beetles will emerge again in the spring (by late April) from the hollow branch. A single generation occurs per year in New England. Additional species of twig pruners are known from similar hosts. Anelaphus (formerly Elaphidionoides) parallelus is an additional twig pruning species known in southern Ontario and New England which may be found on oak and hickory.
Twig pruning by these insects (or managers) causes more latent buds to grow on the host plant and can increase the density of the canopy of the tree. However, if this pruning happens excessively, the shape of the tree can be greatly altered. If the twig pruner is involved, often an abundance of pruned out twigs and small branches may be found beneath the tree late in the growing season. This species will leave clean-cut ends to the pruned out twigs. Twigs and small branches 0.24 - 1.97 inches in diameter are often preferred by this insect. A small, oval-shaped hole is created at the end of the severed branch. Twig pruners are considered secondary pests of previously stressed trees and shrubs. As such, they are not the primary cause of concern for host tree health.
Clean-cut twigs found beneath the base of susceptible host plants can be examined for creamy white colored roundheaded borer larvae within. Carefully split open the twigs to observe. Research has shown that multiple-funnel traps baited with ethanol and syn-2,3-hexanediol were attractive to Anelaphus villosus (Miller et al., 2015).
Rake up and destroy fallen branches/severed twigs if this insect is suspected. Do not leave the fallen twigs and branches in a nearby brush pile. This will remove the overwintering pupae, and prevent a new generation of adults from emerging from the removed twigs and branches the following spring. Maintain proper tree maintenance and practices that encourage the overall health of the host plant. Drought stressed trees may be more susceptible to twig pruners, so proper supplemental watering should be practiced if there are no local watering restrictions. Some sources suggest that trees growing too fast (fertilized) may also be attractive to twig pruners, so keep this in mind when making nutrient management decisions.
Natural enemies of the oak twig pruner (A. parallelus), a related species, are known in the scientific literature. These include but are not limited to: Atanycolus spp. (Hymenoptera: Braconidae), Eubazus denticulatus (Hymenoptera: Braconidae), and a potentially new genus of wasp (Hymenoptera: Braconidae, Hormiinae near Pambolus spp.) (Brown et al., 2016). Presumably, natural enemies of A. villosus also exist. In a survey of native longhorned beetles and their associated parasitoids (looking for a biocontrol option for invasive longhorned beetles) at least 15 species of Braconidae (parasitoid wasp) were collected in association with all of the native longhorned beetles sampled for, a combination that included the twig pruner (A. villosus) (Golec et al., 2020).
Acetamiprid (L)
Azadirachtin (NL)
Beauveria bassiana (NL)
Cyantraniliprole (NL)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Imidacloprid (L)
Isaria (paecilomyces) fumosoroseus (NL)
Permethrin (L)
Pyrethrins + piperonyl butoxide (L)
Zeta-cypermethrin (L)
Chemical management of this insect may be very difficult and is often unnecessary. Select cultural/mechanical management options instead.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
