baptisia seed pod weevil

Baptisia seed pod weevil is a very small pear-shaped weevil. It occurs in the United States east of the Great Plains. It feeds exclusively on wild indigo plants in the genus Baptisia. The larvae feed on the developing seeds inside a seed pod. Adults are found on the foliage of host plants, especially on the seed pods.

Baptisia seed pod weevil is a tiny beetle, but it is one of the larger members of the subfamily Apionini. Adults are 1⁄16″ to ⅛″ (2.5 to 3.6 mm) in length, including the long snout. The body is stout and pear-shaped. It is entirely black, and it is sparsely covered with short, fine, pale hairs.

The head is very narrow between the eyes. The beak-like projection of the head (rostrum) is very long, slender, cylinder-shaped, and slightly curved. The surface is shallowly pitted (punctate). On the male, the rostrum is slightly longer than the first segment of the thorax (pronotum). On the female it is 1.5 to 2.0 times longer than the pronotum. The eyes are prominent. The antennae are attached to the sides of the rostrum near the base. The last three antennal segments are expanded, forming a club that is pointed at the tip.

The pronotum is slightly narrowed at the rear, rounded toward the middle, then narrowed to the front. When viewed from the side it is moderately convex. The surface is covered with moderately deep punctures.

The wing covers (elytra) are deeply grooved from the base to the tip. The spaces between the grooves are flat to slightly convex, and they have two rows of fine punctures. Each puncture bears a fine scale.

The legs are black. On the male, the fourth segment (tibia) on the middle and hind legs is armed with a long, blunt spine.

Total length: 1⁄16″ to ⅛″ (2.5 to 3.6 mm)

One generation per year: May to October

The female excavates a hole in a developing seed pod. She lays usually a single egg and pushes it through the hole into the seed pod. When the egg hatches, the larva feeds on the developing seeds. This usually causes the plant to abort the pod. The larva pupates inside the pod. The newly emerged adult either bores a hole to escape the pod or waits for the pod to dry and split. Sometimes adults overwinter in the pod.

Seeds of Baptisia plants

Sources

30, 82, 83.

Common and sometimes locally abundant

Trichapion rostrum

Trichapion rostrum, wild baptisia seed weevil, inside a white baptisia (white false indigo) seed pod. Photographed on 10/3/2023 at Barnes Prairie, Racine Co., WI. Several weevils were found inside this seed pod.

Babette Kis
10/6/2023

Location: Barnes Prairie, Racine Co., WI

Trichapion rostrum, wild baptisia seed weevil, inside a white baptisia (white false indigo) seed pod. Photographed on 10/3/2023 at Barnes Prairie, Racine Co., WI. Several weevils were found inside this seed pod.