Obscure Mealybug Found on Almond Trees for First Time in California

By Jhalendra Rijal

Pseudococcus viburni  has been found for the first time in almond crops in California. This insect is not just an obscure mealybug, it is THE obscure mealybug — that’s the official common name assigned to it by the Entomological Society of America.

Previously known to be a pest of grapes in coastal California, the mealybug was found in an almond orchard in Modesto, CA. There were adult females, egg masses, and a few crawlers in a tree trunk, branches, and even in fruit clusters. Female adults were collected and sent to the California Department of Food and Agriculture (CDFA) for identification. To our knowledge, this is the first detection of this mealybug species in almonds. However, another mealybug species, Ferrisia gilli, is commonly found in pistachios, and occasionally in almonds in San Joaquin Valley.

The obscure mealybug is a polyphagous and cosmopolitan pest. The origin of this species is believed to be South America, although there are some reports that mention Australia as its place of origin. This species might have been introduced in California in the late 1800s, and it has often been confused with the grape mealybug (Pseudococcus maritimus).

More than 295 host plants, ranging from evergreen to deciduous and perennial to annual plants, have been reported. While this mealybug species was found just in one orchard so far, it may be present in others as well, and we have no clue about its potential to cause bigger problems for almond growers. When I looked at the specimen under the microscope, there was evidence of natural parasitism, a common phenomenon for many mealybug species infesting a range of host plants.

Identification:

The body of the female adult varies from pink to light purple, and the body size is about 3 mm long with many side (lateral) whitish filaments. Two long anal filaments arise from the abdomen, and there is no stripe on the top surface of body. The eggs are light colored, gray to yellow, and an egg case (ovisac) is present.

As mentioned earlier, the obscure mealybug is often misidentified as the closely related species, grape mealybug. A good way to differentiate these two species in the field is to prod the female mealybug with a sharp object and look for the color of the exuded fluid, which is red for the grape mealybug, bute white to opaque for the obscure mealybug

Since this is a new species for almonds, we don’t know about its phenology for that host plant, although there have been some studies from the vineyard system in California. It is important to carry out further studies on this pest and to monitor its spread in other almond orchards in the area. A pheromone trap is available for this pest, and we’ll be conducting some trapping work in orchards in north San Joaquin valley in the near future.

Read more at:

– Mealybugs & Mealybug Look-Alikes of the Southeastern United States

– Mealybugs in California Vineyards

– Biology and Management of Mealybugs in Vineyards

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Jhalendra Rijal is an area IPM Advisor for northern San Joaquin Valley in the UC Statewide IPM Program of the University of California Cooperative Extension. Follow him on Twitter at @IPMadvisorNSJV.