By Nate Royalty, Ph.D.
What does it look like?
The adult eucalyptus tortoise beetle is hemispherical in shape and about 3/8-inch long, the same shape and slightly larger than a common
ladybird beetle. The adult is reddish-brown to gray in color, with mottled spots. Larvae are pale red to greenish-gray with a black head and three pairs of black legs on the thorax. The beetle’s eggs are orange and elliptically shaped, and are laid in clusters underneath the bark of the tree.
Host material and range
Eucalyptus tortoise beetles are found in California. They are most prevalent in the southern coastal counties (San Diego, Orange and Los Angeles Counties), the Central Valley and the San Francisco Bay area. Although capable of feeding on many varieties of eucalyptus, it is most commonly found on the blue gum, manna, river red, lemon and flooded species.
This type of tortoise beetle produces multiple generations of insects per year. Female beetles can lay more than 40 eggs on the tree; these eggs are usually concentrated high up in the canopy where they are difficult to detect. The adults are more active at night than in the daytime, and damage to the leaves often is the best indicator of an infestation. Feeding damage is characterized by irregular or semicircular notches along the edges of leaves. Feeding beetles can consume most of the leafy tissue, leaving little more than the midvein. The beetles can also stunt growth by biting off the terminal buds from leaves.
Like many insect pests, tortoise beetles feed preferentially on stressed trees. Proper fertilization and occasional heavy irrigation during periods of drought will help prevent infestation. There are no native natural enemies in California that prey specifically on tortoise beetle, although research on the effectiveness of parasitoids from Australia is ongoing. Larvae secrete irritants, making them an undesirable food source for generalist predators.
Soil-applied systemic insecticides are effective for control of eucalyptus tortoise beetle. Foliar sprays are impractical because the pest can hide under loose bark, and because most trees are too large to effectively treat. Applications can be made in the fall, or in early spring, just before the new leaves emerge.
What can you do?
Eucalyptus tortoise beetles can be difficult to detect because they tend to dwell in the upper canopy of the tree. However, the distinctive damage to foliage is easy to spot on even tall eucalyptus trees. Inspecting loose bark for eggs, larvae and adults during the day may also help spot an infestation before the defoliation becomes serious.
When the infestation is somewhat sparse, handpicking the pest and destroying it is an option for control. Despite being tedious, this method is very effective. Also, remember to keep up with good cultural practices to minimize tree stress.
Nate Royalty, Ph.D. is product development manager — insecticides, Bayer Environmental Science.