Nursery, Greenhouse, and Landscape News

New Beetle Predator of Euonymus Scale

Cybocephalid beetles, closely related to picnic beetles, are important predators of armored scales. A species similar to Cybocephalus nipponicus was introduced into the United States in the late 1980's as part of a biological control project against euonymus scale. Because so little was known about the biology of this beetle, it was examined in lab experiments to learn more about its development, reproduction and prey consumption. San Jose scales were used in many of the tests because euonymus scale was difficult to grow indoors.

The hemispherical adults are about 1 mm long. The females are all black, while the males have a large beige-colored head and pronotum. Four days after mating, the females lay an average of 3 tiny eggs each day under scale covers, and can lay more than 500 eggs if they live long enough (there was extreme variability in longevity in these tests). The eggs are transparent ovoids when laid, and turn grayish or purple before hatching. The yellowish larvae bite into scales to feed on them, resulting in distinctive broken areas on the scale covers. The larvae hide under scale covers as they eat the liquid content of the scale body. They ate an average of 20 San Jose scales during their developmental period. They are cannibalistic when scales are not available, eating other beetle larvae or eggs. After about 12 days the larvae complete their development and build a pupal chamber from the armor coverings of 3 or more adjacent scales.

Adults also attack scales, chewing a hole in the scale cover and then feeding on the body contents. The number of San Jose scales eaten increased with scale density (some scales were only partially consumed, but they still were killed), and the beetles preferred older, larger scales. Each pair of adult beetles killed an average of 92 scales in a 2 day period. However, predation rates in the field need to be determined to assess the value of these beetles as biocontrol agents.

Source:

Alvarez, J. M. and R. van Driesche. 1998. Biology of Cybocephalus sp. nr. nipponicus (Coleoptera: Cybocephalidae), a natural enemy of euonymus scale (Homoptera: Diaspididae). Environ. Entomol. 27(1): 130-136.


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