Conifer Seed Bugs

Western conifer seed bugs look (and smell) like stinkbugs, but they are a type of leaf-footed bug.

Western conifer seed bug (Didier Descouens) CC BY-SA 4.0

Native to North America west of the Rocky Mountains, Western conifer seed bugs (Leptoglossus occidentalis) have recently expanded their range to the East Coast and are occasionally found in Europe.

Western conifer seed bug description

These narrow, shield-shaped insects are brown and average 3/4 to 1” in length. They have the classic tags seen on the rear legs of all leaf-footed bugs and their antennae tend to stick out on either side. Eggs are brown. Nymphs have light-colored legs and look much like assassin bigs, until they start filling out.

Conifer seed bug lifecycle

Adult female conifer seed bugs lay 200 eggs in rows, usually along needles, leaf midribs, or stems of host plants. In spring, the eggs hatch and nymphs go through five developmental stages, or instars, before reaching adulthood. In North America, there is only one generation a year, but two or more generations have been seen in Mexico and southern Europe.

Western conifer seed bug as seen through a window (BMRR) CC BY-SA 3.0

Conifer seed bug damage

These pests generally feed on the sap of developing conifer cones, causing the seeds within to distort and wither. Favored trees include lodgepole pine, white spruce, and Douglas-firs, though red pine, mountain pine, European black pine, Scots pine, and even pistachios are sometimes chosen. They can also vomit up digestive juices that soften hard seeds. I just hope they never find my stone pine!

Even worse, conifer seed bugs have been found to use their piercing mouthparts to damage PEX tubing. PEX tubing is similar to PVC and is used to insulate high voltage electrical wires, and to transport offshore oil and natural gas, sewage, and chemicals.

Western conifer seed bug found on summery savory (Kate Russell)

Insecticides are not recommended, though they can be used as a last resort against heavy nymph infestations. It is better to avoid using broad spectrum insecticides. Provide pollen and water for natural predators. Some tachinid flies have been known to parasitize conifer seed bug eggs. Spiders, assassin bugs, and birds also feed on conifer seed bugs.