Spring returned to the Washington area in abundance this week with the flowering of some of our most beautiful plants such as forsythia, Bradford pears, and Yoshino cherries. One of my favorite trees, the weeping willow, blooms in late March and early April. The showy yellow blossoms of the males and downy white flowers of the females create a delicate contrast with light green leaves arrayed on drooping branches.
A willow leaf turned upside down reveals a clutch of willow beetle eggs.
As sure as the willow is a harbinger of spring, so too is the gorgeous imported willow leaf beetle that makes the willow its home. This alien came to America in the early 1900's from the Mediterranean region probably on ornamental willows imported for use in landscapes. Adult willow leaf beetles spend the months of winter chilling out beneath the bark of willow trees or in protected locations in the leaf litter. With the return of spring's warmth and a bonanza of willow leaves, beetles return to the tree to resume the circle of life. Adult beetles feast on the tender young willow leaves. Nutrients from the leaves are converted to hundreds of small yellow eggs deposited on the lower surfaces of leaves in clutches of a few to more than thirty. The eggs hatch in a few days into small larvae that graze across the surface of the leaf like a herd on miniature cows. Their tiny jaws remove only the soft tissues of the leaf leaving behind the tough veins and cuticle. This type of feeding results in damage called skeletonization.
A small herd of willow beetle larvae skelotonize the undersurface of a leaf.
Larvae of the imported willow leaf beetle are a favorite food of many predators including lady bugs and assassin bugs. However, the larvae evolved a clever defense to dissuade attacks by hungry predators. A series of glands line the sides of the thorax and abdomen of the beetle larvae. When enemies approach, the larvae secrete a droplet from each gland. These droplets line the vulnerable margins of the larvae and contain an aromatic blend of chemicals. To my nose these odors are quite pleasant; however, would-be predators find them repellent and scurry away. When danger has passed, larvae withdraw their secretions into the glands and store them for future use. These beetles are not wasteful. During the months of April and May, take a few moments to stop by a willow and try to catch a glimpse of the remarkable imported willow leaf beetle. It is one of spring's delights.