Citricola Scale: Appearance, Territory, Damage and Life Cycle

Latin Name: Coccus Pseudomagnoliarum

Appearance: The citricola scale is a major pest. This pest is especially bothersome in the San Joaquin Valley when broad-spectrum pesticides are used sparingly, as these insecticides normally keep this pest under control. It was also a major pest in southern California’s inland areas until 1935, when Metaphycus luteolus was employed to control it. Citricola scale was brought to California from Asia and is currently found in Japan, California, Australia, the Mediterranean basin, and Russia’s Caucasus area.

The Citricola scale is a gentle scale. Citricola scale crawlers are active from June to August. They settle predominantly on the underside of leaves, but in severe infestations, they also rest on the top leaf surface and on twigs, and very rarely on fruit. Young scales are flat and virtually transparent; they develop slowly during the summer and fall, molting just once. Second-instar scales develop a mottled dark brown hue by November and start moving to twigs; this migration peaks in February and March. They develop faster on twigs than on leaves, and they become a gray tint.

Hosts Plants:

• Territory: United States: Arizona, California, Maryland.
• Worldwide: Australia, Azerbaijan, Europe, France, Georgia, Greece, Iran, Israel, Italy, Japan, Russia, Sicily, South Korea, Spain, Turkey, and Turkmenistan.

Damage Insect Cause: Citricola scale infests leaves when it is young, but develops on young branches in late fall or early winter. It sucks the sap from the leaves and branches and generates honeydew, a sugary fluid that drops onto the leaves and fruit. Honeydew stimulates fungal development (black sooty mold) at intermediate scale concentrations, which degrades or results in fruit culling in the packinghouse. Citricola scaling reduces fruit size and significantly reduces fruit yield the next season at greater concentrations.

Life History and Habits: Only female citricola scale insects exist. They reproduce in an asexual manner. During the summer, each female may lay between 1,000 and 5,000 eggs. From June through August, she will keep her eggs secure under her body until they hatch into crawlers. Citricola scale eggs hatch in two or three days. Crawlers are the babies that hatch from the eggs. The word crawlers seem a little deceiving because they don’t appear to be capable of doing anything. These crawlers go to a good feeding location, attach, becoming sessile, and feed until they molt into second instar nymphs, which happens around November. Ants frequently guard and farm these nymphs, which generate a lot of honeydew.