Karl Foord - Extension Educator, Horticulture
I have a Meyer lemon (Citrus × meyeri) which goes outside in the summer and struggles through the long Minnesota winter. This is a wonderful plant with fragrant blossoms and nice fruit. I noticed a lot of very small white cottony blobs on the stems and leaves as well as some scale insects. I believe I have California red scale (Aonidiella aurantii). According to Whitney Cranshaw in his Garden Insects of North America this scale affects many ornamental plants and can be a serious pest of citrus. The adult females are round, reddish orange, and have concentric rings on the cover. Young stages produce some cottony filaments of wax around their body; later stages form the more solid cover.
This scale insect has a fascinating life cycle that features a sessile female and a winged male (Exhibit 1).
I clipped a citrus leaf and examined it under the dissecting scope. I found a sessile female (photo 1) and when I turned her over several crawlers exited (photos 2 & 3). I also found
white caps (photos 4 & 5), late first instars (photo 6) and an individual in first molt.
Photo 2: California red scale (Aonidiella aurantii) overturned female with exiting crawler
Photo 3: California red scale (Aonidiella aurantii) overturned female with exiting crawler
Such a lifestyle made me curious as to how such species mate (Exhibit 2).
To eliminate the scale, I put the pot in the shower and try to hose off the scale. This knocks them down but does not eliminate them. This is probably an excellent time to consider the use of imidacloprid as a systemic insecticide. The plant is showing some flowers now and no pollinators will have access to these flowers. In addition the material will only be in the pot in a plant holder box in the house and so no chance of contamination of our water systems.
For more information see the excellent publication from the University of California Division of Agriculture and Natural Resources.