The cucumber beetle is a common insect found in gardens and agricultural settings, targeting plants in the cucurbit family, such as cucumbers, squash, and melons. Identifying this pest correctly is important because it causes damage through direct feeding and by transmitting plant diseases like bacterial wilt. Visual identification relies on recognizing the insect’s size, shape, and the distinct color patterns found on its wing covers. These features help distinguish the adult beetle from other insects.
The Two Primary Forms
The cucumber beetle is commonly observed in two main types that are visually distinct. The Spotted Cucumber Beetle (Diabrotica undecimpunctata howardi) features a bright, yellowish-green body color. Its most recognizable characteristic is the arrangement of 12 distinct black spots distributed across its hard wing covers, known as the elytra. This pattern gives the beetle a speckled appearance against its pale green background.
The second type is the Striped Cucumber Beetle (Acalymma vittatum), which is generally a brighter yellow or greenish-yellow color. Instead of spots, this species has three prominent, longitudinal black stripes running down the length of its wing covers. These stripes extend almost to the tip of the abdomen, providing a clear visual contrast with the yellow body. Both species have a black head and feed on the same types of host plants.
Identifying Features of the Adult Beetle
The adult cucumber beetle possesses a physical structure for identification. The insect is small, typically measuring about one-quarter of an inch (approximately 6 to 7 millimeters) in length. Its body shape is elongated and oval, giving it a slender profile.
The head is characteristically black in both the spotted and striped varieties. A defining feature is the antennae, which are long and slender, often appearing nearly as long as the entire body of the beetle. The hard outer wings, or elytra, cover the abdomen and serve as the canvas for the distinctive spots or stripes.
Appearance of Larvae and Eggs
The immature life stages of the cucumber beetle are typically found in the soil around the base of host plants. The eggs are tiny, oval-shaped structures that are a pale yellow to orange-yellow color. A female beetle deposits these eggs in small clusters on the soil surface or within crevices near the plant stem.
Once hatched, the larvae are slender with soft, creamy white or yellowish-white bodies. They possess a prominent dark-colored head capsule and a dark plate at the tip of the abdomen. Larvae grow up to about one-half inch long and have three pairs of small legs located close to the head. This subterranean stage feeds on the plant roots.
Distinguishing from Look-Alikes
The most common case of mistaken identity involves the beneficial Lady Beetle. While the spotted cucumber beetle may share a similar color scheme with some yellow lady beetles, the body shape is a strong distinguishing factor. Lady beetles are typically much smaller and have a rounded, dome-like shape, unlike the elongated oval of the cucumber beetle.
Antennae provide the most reliable separation; the Lady Beetle has short, stubby antennae, whereas the cucumber beetle’s antennae are long and thin. Another similar-looking insect is the Western Corn Rootworm, which can be confused with the striped cucumber beetle due to its parallel striping. The Striped Cucumber Beetle has three black stripes that run the full length of the wing covers and a black abdomen. In contrast, the Western Corn Rootworm’s stripes may fade before reaching the tip of the wings, and its abdomen is generally yellow-green.