The Southern Pine Beetle: The Tree Killer 

Written by Charlotte Hohman, NPS, and Sara Abbitt, AmeriCorps Cape Cod

The geographic range of damage from the southern pine beetle.

Map/United States Department of Agriculture and the United States Forest Service

Given that it’s smaller than a grain of rice, it might be hard to believe that the minuscule southern pine beetle (Dendroctonus frontalis) could cause massive damage to forests! These beetles have been a well-known foe of the southern United States for centuries, but they are a new enemy to the Northeast.

The southern pine beetle was first recorded in the southeastern United States in the late 1700s. Though they are originally native to the southeast, warming winter temperatures have allowed the beetle's range to expand up the east coast in recent decades.

Southern pine beetle from Pilgrim Heights, Truro under a microscope.

Photo/Felicia Hubacz, Massachusetts Bureau of Forest Fire Control and Forestry

When European settlers arrived in North America, they cut down many of the original forests that were primarily composed of trees like oak and hickory, which are naturally resistant to the southern pine beetle. With the soil quality altered from agricultural use by the settlers, pine species that are susceptible to the beetle grew back in the place of the oak and hickory. Infestations in New Jersey and New York started around a decade ago, and in 2023, there were outbreaks on Martha's Vineyard and Nantucket. Early this year, an infested tree was identified at Pilgrim Heights in the town of Truro within the bounds of Cape Cod National Seashore. 

Life cycle of the southern pine beetle.

Graphic/Ronald F. Billings, Texas A&M Forest Service

Unfortunately, it can be challenging to spot the beetles themselves, considering that they are smaller than half of a grain of rice in their adult form. The beetle looks different during each stage of its life:

• The egg is white.

• The larva is crescent-shaped with a dark red/brown head.

• The pupa is white.

• As an adult, they are light brown/black.  

Popcorn-like pitch tubes on an affected tree.

Photo/Jiri Hulcr, University of Florida

Luckily, the physical appearance of the beetle isn't the only way to identify their presence, as you can tell by the damage they cause. The presence of pitch tubes would be your first physical indicator. Pitch tubes look like popcorn sticking out of the bark; these are the tree's natural defense against predators. If you peel back the bark of an infested tree, you might also find S-shaped designs drilled into the wood called "galleries."

Southern pine beetle galleries drilled under the bark of the tree tend to look like complex mazes.

Photo/Jiri Hulcr, University of Florida

Female southern pine beetles will create these galleries to lay their eggs. The females also release pheromones to draw males to the trees. Once a tree becomes infested, it can die quickly. Often, the trees that the beetles choose are weakened ones, but that is not always the case. Southern pine beetles like to infest many trees in an area and have been known to kill acres of trees in very short periods of time. An outbreak can be very harmful for many reasons, but dangerous specifically for Cape Cod because of the Pitch Pine Barren habitat that many species rely on. 

A southern pine beetle (left) and a black turpentine beetle (right) compared to a grain of rice (middle) in someone’s palm.

Photo/ Southern Forest Insect Work Conference Archives

Southern pine beetles are often mistaken for the black turpentine beetle, a familiar insect to the northeastern United States. Black turpentine beetles are larger than southern pine beetles, measuring up to the size of a grain of rice. Their damage to trees is visually similar, but there are a few key differences. The pitch tubes they create tend to be located from the foot of the tree to about fifteen feet up, whereas southern pine beetles tend not to cause damage around the tree's base. Differences in the galleries made under the bark can also indicate which species is the culprit, with the galleries of black turpentine beetles tending to be less intricate. Black turpentine beetles also do not kill acres of trees at a time, but rather one to a few sickly trees in one area.

Lindegren funnel traps are an excellent way to monitor for the beetle, but must be checked regularly.

Photo/Mississippi Entomological Museum

Fortunately, we don't need to wait for an outbreak to happen to confirm the presence of southern pine beetles. Setting and monitoring traps on trees or poles are effective ways of identifying a small population of beetles before things get out of control. Lindegren funnel traps are used to monitor for the southern pine beetle. These traps consist of a series of funnels that contain a preservative like ethanol at the bottom. The funnels are strung between two trees and attract the beetles, who mistake the trap for a tree.

Aerial view of an outbreak, where large patches of trees are dying.

Photo/Ronald F. Billings, Texas A&M Forest Service, Bugwood.org

Aerial and ground surveys are another technique used to detect beetles in early and later stages. Sadly, many infestations of single or small groups of trees are caught too late, which leads to an outbreak, where larger swaths of forest are impacted.

Thinning of pine stands is a management technique used to combat the southern pine beetle throughout the United States. This sign indicating that the forest has been thinned to prevent southern pine beetles is located in Virginia.

Photo/ Katlin Dewitt, Virginia Department of Forestry

There are a few effective ways to treat a southern pine beetle outbreak. Prescribed burns, where planned fires are set and carefully managed, can combat an outbreak as well as strengthen the ecosystem in pitch pine forests.

Felling trees is another option, with a few different techniques available. The "cut and remove" technique consists of removing infected trees from the site to be processed, while "cut and leave" can be used when trees cannot be taken to a different location, so they are left where they are cut. Cutting down trees and thinning areas of forest creates more distance between trees, which makes it more difficult for the beetles to communicate via pheromones, find each other, and attack in large numbers.

The pitch pine habitat on Cape Cod will need to be protected from the destructive southern pine beetle to survive.

Photo/John N. Cullity, Sandwich Conservation Trust

The southern pine beetle will continue to be a threat to New England with the rise in average temperatures and warming weather. There are ways to combat and stop them from spreading further north, but people must be on the lookout for warning signs. Early detection is the best way to keep the beetles contained in a small area while determining a course of action for response and elimination. The southern pine beetle is a threat everyone should take seriously to protect Cape Cod's Pitch Pine Barrens for generations to come.

You can help keep our forests safe by following these guidelines:

• Be on the lookout! If you see a tree displaying symptoms of southern pine beetle infestation, like pitch tubes, contact the Massachusetts Department of Conservation Forestry Health program to report the tree. Massachusetts Southern Pine Beetle Reporting Form
• Make sure you are not bringing in firewood to campsites and bonfires from elsewhere. Use local firewood instead!