Locust Borer: All You Need to Know for Effective Management

The Locust Borer is a fascinating type of long-horned beetle that has piqued the interest of entomologists and nature lovers alike. Known by its scientific name, Megacyllene robiniae, this beetle’s appearance mimics a wasp or hornet, with its black body adorned by bright yellow markings and a distinctive “W” shape across the wing covers ([1]). At about an inch in length, these beetles also have reddish legs, adding to their intimidating and striking presence.

Significant damage can be caused by the Locust Borer to black locust trees (Robinia pseudoacacia) as their larvae burrow into the trunks ([2]). Although these infestations often weaken or kill damaged trees, the adult beetles contribute to pollination, feeding on the pollen of goldenrod and other flowers ([3]). This beetle’s deceptive appearance may serve as a form of protection, as it closely resembles stinging insects, thereby deterring potential predators.

Identification and Description

Adult Locust Borer

The Adult Locust Borer (Megacyllene robiniae) is a type of longhorn beetle. They are approximately 3/4 inch in length with striking black and yellow markings on their thorax and wing covers, known as elytra ¹.

• Color: black with brilliant yellow markings
• Distinctive “W” mark on elytra
• Reddish legs
• Moderately long and black antennae

These beetles are part of the longhorned beetle family and can often be seen feeding on the pollen of goldenrod plants^[2^], providing them with natural camouflage.

Larval Stage

During the larval stage, these insects can reach up to 1 inch in length and are white, legless grubs².

• Color: white
• Legless grubs
• Up to 1 inch long

The larvae feed on the xylem of host trees, such as black locust and its cultivars (e.g. purple robe locust)^[3^]. Extensive tunneling in the wood can result in structural weakness of branches or trunks.

Comparison between adult and larval stages:

Life Cycle and Behavior

Egg Development

• Locust borer eggs are laid by adult beetles on the bark of black locust trees (Robinia pseudoacacia) in late summer, usually around August¹.
• The female beetle deposits eggs in crevices, knots, or bark injuries to protect them from predators and harsh environmental conditions³.

Larval Feeding and Tunneling

• Once the eggs hatch, white, legless larvae begin feeding on the tree’s xylem and creating tunnel-like galleries within the tree².
• Larvae primarily target stressed or drought-affected black locust trees, limiting their growth and overall health⁴.
• As larvae grow larger, they move deeper into the tree’s heartwood, causing significant damage to the tree⁵.
• Larval feeding creates visible holes and frass (a combination of sawdust and droppings) on the tree bark⁶.

Comparison Table: Locust Borer vs. Hickory Borer

Pupation and Adult Emergence

• In the late winter or early spring, locust borer larvae create pupal chambers within the tree and undergo pupation¹⁵.
• Adult beetles emerge from the pupal chambers in the fall, usually with one generation per year¹⁶.
• They resemble wasps or hornets due to their similar coloration and markings¹⁷.

Pros and cons of locust borer attack on black locust trees

Pros:

• None (locust borer is a destructive pest for black locust trees)

Cons:

• Reduces tree growth and overall health¹⁸
• Causes structural damage to infested trees¹⁹
• Facilitates the entry of pathogens and other pests²⁰

Damage and Impact

Effects on Black Locust Trees

The Locust Borer (Megacyllene robiniae) is a type of long-horned beetle that mainly targets Black Locust trees (Robinia pseudoacacia). Adult beetles lay eggs in the fall, and the larvae burrow into the tree’s bark, creating tunnels. These tunnels weaken the tree’s trunk and branches, making them more susceptible to breakage.

Black Locust trees that are already stressed or damaged (for example, from drought or cracks in the bark) are more likely to be attacked by Locust Borers. The damage can be severe, and in some cases, lead to the death of the tree.

Economic and Ecological Impact

Locust Borers can have both economic and ecological consequences due to their impact on Black Locust trees. Black Locust trees are valuable for their timber, as they are resistant to rot and are used for posts, fences, and other outdoor structures. The damage caused by Locust Borers can significantly reduce the quality and yield of this timber.

Ecologically, Black Locust trees provide habitat and food for various species of animals. As the trees are weakened or killed by Locust Borer infestations, their ability to provide these benefits is compromised. In addition, fallen or weakened branches can pose a hazard to both humans and animals.

Example:

Affected trees may attract both Locust Borers and Painted Hickory Borers, but Painted Hickory Borers are active in the spring, while Locust Borers are active from late summer to early fall, usually around September.

Comparison Table: Locust Borer vs. Painted Hickory Borer

Management methods for Locust Borer infestations include improving tree health, pruning infested branches, and applying insecticide to the bark in late July or early August before eggs are laid. These measures can help mitigate the damage and impact of Locust Borers on Black Locust trees and the surrounding ecosystems.

Relationship with Goldenrod and Pollination

The Locust Borer (Megacyllene robiniae) is a longhorned beetle known for its relationship with goldenrod and pollination. This beetle belongs to the order Coleoptera. They are distinctly black and yellow, often mimicking the color pattern of stinging insects like bees¹.

Adult locust borers are typically observed in late summer, feeding on the pollen of goldenrod¹ and other flowers. Goldenrods are part of the Solidago genus and thrive in full to partial sun with dry to average soil moisture⁴.

Key features of locust borers and goldenrods:

• Locust Borers:
  • Black and yellow in color
  • Feed on pollen of goldenrod and other flowers
  • Help in pollination of flowers
  • Mimic bees
• Goldenrods:
  • Grow in full to partial sun
  • Dry to average soil moisture requirements
  • Attract pollinators like locust borers and bees

Beetles like locust borers play an essential role in pollination, ensuring the survival of plant species such as goldenrods³. However, their larvae are known to tunnel into the trunks of black locust trees and may cause damage or death¹.

Prevention and Management Strategies

Cultural Control Methods

To minimize locust borer damage to trees, promoting overall tree health is essential. Locust borers are more likely to attack weakened or stressed black locust trees. It is advisable to:

• Remove and destroy infested branches promptly
• Keep trees well-watered and properly fertilized
• Monitor the habitat and location of black locust trees
• Avoid planting new black locust trees in high-risk areas

Chemical Control Options

In cases where locust borers are causing significant damage, chemical control methods can be used. Examples include:

• Carbamates: A group of insecticides proven effective against locust borers
• Pyrethroids: Another class of insecticides known for their efficacy against locust borer infestations

Pros and Cons:

When using insecticides, it’s crucial to follow label instructions and apply them during late July or early August to target the adult locust borers before they lay eggs.

In conclusion, locust borer management involves a combination of cultural and chemical control methods. By maintaining tree health, monitoring infestations, and applying insecticides when needed, you can protect your black locust trees from these destructive pests.