walnut lace bug

Walnut lace bug is a common, small, true bug. It occurs in the United States and southern Canada anywhere that its plant hosts are found. That is mostly east of the Great Plains, but also the Pacific Northwest, and there are a handful of scattered records elsewhere.

Most lace bugs (Corythucha spp.) have restricted food preferences and will feed on a single plant species or just a few species, often in the same plant family. In Minnesota, walnut lace bug feeds mostly on black walnut, but also on butternut and American Basswood. A single leaflet may have more than 100 nymphs and adults on it. The feeding causes small, dark-colored patches on the leaflet. The upper leaf surface appears whitish due to a peppering of tiny white spots. Heavily infested leaves may turn brown and fall off.

Adults are ⅛″ (3.3 to 3.8 mm) long and 1⁄16″ to 3⁄32″ (2.0 to 2.3 mm) wide. That is small for a true bug but medium-sized for a lace bug. The body is black. The upper parts all have a conspicuous network of ridges that creates small cells with yellowish, yellowish brown, or milky white (pale) rings (areolae) around transparent (hyaline) centers. An areola sometimes fills most or all of the cell. Viewed from above, the overall color is pale with brown or dark brown (dark) markings. The markings are formed by broad, dark, areolae around margins of cells.

The head is small and triangular. At the front of the head there is a rounded lobe (tylus) that projects forward. There are two compound eyes and no simple eyes (ocelli). The antennae are long and slender, and they are covered with bristly hairs. They have four segments. The first segment is at least twice as long as the second segment, the second segment is very short, and the third segment is much longer than the first two segments taken together. The fourth segment is shorter than the third and is slightly swollen. The mouth parts are optimized for piercing and sucking. They take the form of a 4-segmented beak (rostrum).

The exoskeletal plate covering the first segment of the thorax (pronotum) is highly modified. The front of the pronotum is inflated in the middle into a large hood that completely covers and extends slightly forward of the head. The hood is narrowed in front and bulbous behind. There are three longitudinal ridges (carinas). The hood is twice as high as the middle (median) carina, and it is not noticeably longer than the middle carina. A triangular, ridged extension in the rear of the pronotum projects backward and covers the small plate between the wing bases (scutellum). A broad, flat, lateral extension (paranotum) on each side of the pronotum projects well beyond the side of the body. The paranota are transparent or lightly tinged yellowish or brownish. The cells on the paranota are small, less than half the size of those on the hood. The veins separating the cells are pale or white. Usually, two or more few adjacent cells have an areola, creating a single, small, dark spot on the front half of the paranota. There is sometimes a faint second spot near the rear. The margins of the paranota have a fringe of numerous, small, closely spaced spines.

The wing covers (hemelytra) are narrow at the base then abruptly widened for most of their length. The sides of the widened portion are nearly straight, not concave, and they are the same width at the base and at the rear. The basal third is slightly elevated. The lateral margins are also armed with a fringe of short spines, but just on the basal half. The leading edge (costal margin) of the hemelytra are not entirely darkened. There is a pair of large dark spots near the base and a pair near the rear. The rear spots are narrowly connected at the top to the inner margin, giving the appearance (to this viewer) of a pair of saddlebags.

The legs are yellowish.

Total length: ⅛″ (3.3 to 3.8 mm)

Wherever black walnut is found

Adults overwinter in a state of reduced activity (diapause). They become active in April or May.

Adults and nymphs feed together on the underside of leaflets.

Sources

27, 29, 30, 82, 83.

Exploring Lace Bug - (Corythucha juglandis) under a Microscope
MicroSpectacle

Lace Bugs pooping, almost mating, and other behaviors of adults and nymphs (Corythucha juglandis)
Nature in Motion

Alfredo Colon
8/6/2022

Location: Albany, NY