goldenrod leaf beetle

not listed

NNR - Unranked

not listed

Goldenrod leaf beetle is a medium-sized skeletonizing leaf beetle. It occurs across northern United States and southern Canada from the East Coast to the Midwest, and in the Rocky Mountain states and provinces. It is found in old fields from early July to mid-September.

Adults are oblong, ¼″ to ⅜″ (7 to 10 mm) long, and yellow with black markings. The black markings are not metallic or iridescent.

The head and mouthparts are directed downwards. The head is broad and partly visible from above, partly covered by the pronotum. It is not constricted neck-like at the rear. It is yellow with a small black spot on each side, and a larger spot at the rear (occipital spot). The occipital spot is small and oblong. It does not form a band or extend down the front. The compound eyes are oval and black. They are not notched. The space between the eyes is more than half the width of the head. The antennae are slender and thread-like (filiform). and are yellow near the base grading to black near the tip. They are shorter than the body and have 11 segments, including the scape and pedicel, the two basal segments. They are inserted into the head between the eyes moderately close to each other. The third segment is shorter than the fourth.

The thorax is much wider than long. The exoskeletal plate covering the thorax (pronotum) is nearly as wide as the base of the hardened forewings (elytra). It is yellow with three black spots, one in the middle (middorsal) and one on each side. The base of the pronotum is straight, not strongly wavy.

The elytra are yellow, parallel sided, and broadly rounded at the rear. They have a distinct flat margin that extends all of the way to the tip. They are finely pitted and densely covered with minute hairs. There are three black longitudinal stripes, one at the inner margin (sutural stripe) and one on each side (lateral stripes), leaving one yellow stripes on each elytron. The lateral black stripes are narrower or about as wide as the yellow stripes. They continue to the rear and join the sutural stripe at the wingtip. The plate between the wing bases (scutellum) is short, blunt, and black. When carrying eggs, the abdomen of the female is often greatly distended.

The legs are moderately long and slender. The third segment (femur) and forth segment (tibia) of each leg are yellow. The upper side of each tibia is shallowly grooved. The groove is black on the front tibia only. On the male there is a broad, curved spur at the tip of the middle tibia only. On the female none of the tibia have a spur at the tip. The last part of each leg (tarsus), corresponding to the foot, has five segments. Each segment is mostly yellow, black just at the tip. The third segment is broadened and has two lobes at the tip, appearing heart-shaped. The fourth segment is extremely small and is concealed between the lobes of the third segment, making it appear that there are only four segments. Each tarsus ends with a claw. Each claw has two teeth.

The larvae are black and look like caterpillars, but have six legs on the thorax and no prolegs on the abdomen.

Total length: ¼″ to ⅜″ (7 to 10 mm)

Weedy fields

One generation per year: Early July to mid-September

Larvae feed on top of leaves.

Goldenrods, including Canada goldenrod, giant goldenrod, and Missouri goldenrod.

Pollen and leaves of goldenrods

Sources

24, 27, 29, 30, 82.

Scattered but locally common to abundant

Trirhabda canadensis goldenrod leaf beetle

Trirhabda canadensis goldenrod leaf beetle, on Canada goldenrod leaf, Barnes Prairie, Racine Co., WI. Photo taken on July 16, 2021.

Location: Barnes Prairie, Racine Co., WI

Trirhabda canadensis goldenrod leaf beetle, on Canada goldenrod leaf, Barnes Prairie, Racine Co., WI. Photo taken on July 16, 2021.

Location: Woodbury, Minnesota