wedge-shaped beetle

not listed

not listed

not listed

Macrosiagon flavipennis is a parasitic, wedge-shaped beetle. It occurs in the United States east of the Great Plains and in California, in southern Ontario Canada, and in Mexico.

Adults are robust, ¼″ to 7⁄16″ (7 to 11 mm) in length, and mostly dull black.

The head and thorax are entirely black. The head is elongated, directed downward, and strongly constricted behind the eyes, creating a “neck”. The upper surface (vertex) is hairless, rounded, and distinctly elevated above the front margin of the upper thoracic plate (pronotum). The upper part of the face (frons), corresponding to the forehead, is smooth and has a distinct concavity or dimple. The upper part of the mouth (labrum), corresponding to the upper lip, is elongated, rounded at the tip, and hairy. The pair of chewing structures on the mouth (mandibles) are very little curved. There are two oval, small but prominent compound eyes and no simple eyes (ocelli). The antennae have 11 segments. The base of each antenna is near the middle of the inner margin of the eye. On the female the antennae are black except for the first two segments, which are orange, and they have a single, short, forward-pointing projection on each segment (pectinate). On the male they are entirely orange and comb-like, with dense, thick, long projections on both sides of each antennal segment (biflabellate). The projections on both sides are usually pointed forward, making the antennae appear one-sided (flabellate). On both sexes there are no projections on the first two segments.

The pronotum is bell-shaped, longer than the base is wide and narrowest behind the head. The rear corners are acutely angled and a large triangular lobe in the middle covers the plate between the wing bases (scutellum). It does not have a sharp lateral ridge on each side. At the base there is a distinct, raised, fin-like projection (tubercle).

The abdomen on the male is entirely black. On the female the abdomen is mostly orange, black on the last one-and-a-half segments. The hardened forewings (elytra) are strongly pointed and long, as long as the abdomen but not as long as the hindwings. For most of their length they do not touch each other but are separated like an inverted V, exposing the hindwings. On the female they are yellow on the basal half, black on the rear half. The line separating the black from the yellow is semicircular. On the male they are entirely yellow. The hindwings are yellowish-brown.

The legs are long and slender. On the front legs the third segment (femur) is indented at the tip. On the hind legs the femur is distinctly compressed. On the front and middle legs, the last part of the leg (tarsus), corresponding to the foot, has five segments. On the hind leg it has only four segments. The inner surface is smooth and hairless. The second tarsal segment on the hind leg is not flat above, and is as long as the third segment. There is a pair of claws at the end of each tarsus. Each claw is split in two.

Total length: ¼″ to 7⁄16″ (7 to 11 mm)

June and July

The female lays eggs on flowers. When an egg hatches, the first stage larva (triungulin) attaches itself to the underside of a solitary bee or wasp. After it is carried back to the host’s nest, the triungulin invades the cell of a host larva and enters into the body of the larva. It then delays further development while the host matures. When the host larva is completely developed, the triungulin exits the larva’s body and consumes it and its stored food.

Larvae of wasps and bees

Flower nectar

Sources

24, 29, 30.

No species in this genus has a common name, nor does the genus itself. The common name for the family Ripiphoridae is wedge-shaped beetles, and it is applied here for convenience.

I found these after the rain today just west of Houston.

Location: Houston County, MN

Location: west of Houston, MN

I found these after the rain today just west of Houston.