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What’s bugging plant lovers 

The future of SLO County’s rich agricultural harvest hinges on a tiny insect, squashed between two pieces of glass for a microscope slide mount.
 
Cal Poly’s entire greenhouse complex has been declared off-limits, under strict federal quarantine since county agriculture inspectors discovered an unusual pinhead-sized mealy bug sucking the vital juices of a tropical houseplant.
 

click to enlarge OFF LIMITS :  Agriculture officials are working to stop the spread of a small sucking insect found at Cal Poly that could have a devastating impact on local crops. - PHOTO BY CHRIS GARDNER
  • PHOTO BY CHRIS GARDNER
  • OFF LIMITS : Agriculture officials are working to stop the spread of a small sucking insect found at Cal Poly that could have a devastating impact on local crops.
# It’s the first time this insect pest has established a foothold in the continental U.S., and it has federal, state, and local experts worried. “We have a problem here,� says county deputy ag commissioner Richard Little. “This mealy bug has a very wide host range, 200 to 300 different plants in 80 families. If we like to eat it, so does the mealy bug.�
 
Known as the passion vine mealy bug, the little insect goes after grapes, citrus, avocados, corn, potatoes, soybeans, cabbage, peanuts, and many more commercially grown food crops. “Anytime anyone uses the word ‘grapes’ here, we definitely pay attention,� Little notes.
 
According to the U.S. Dept. of Agriculture, “the likelihood of this pest becoming established in the U.S. is high, and the consequences of its establishment would be severe.�
 
In other countries where these mealy bugs have become established, growers have had to buy and use more pesticides to try to control the sucking pest. The quality and quantity of their harvest has declined by up to 20 percent, says Little, adding that it’s difficult to predict what the impact would be in SLO County: “These numbers don’t exist for us. This pest has never been found here.�
 
It’s not easy to distinguish the threatening passion vine mealy bug from the common garden-variety citrus mealy bug, which is a native insect with natural local predators such as birds and wasps. It takes a highly trained specialist to tell the difference.
 
Mealy bug samples collected from throughout Cal Poly’s greenhouses and fields have been sent to state and federal specialists for identification, and officials are anxiously awaiting the results.
 
“It’s very intense, time-consuming work,� explains Little, who spent months identifying mealy bug species during his studies at the Museum of Systematic Entomology at the University of California at Riverside. First the cottony mass covering the bug “like an umbrella coated with wax� has to be dissolved, then the tiny balloon-like insect has to be softened on the inside and squeezed out with tiny probes before it’s dehydrated, stained, and baked in a microscope slide mount.
 
Then the fun begins for mealy bug specialists, who count various tubular ducts and measure appendages to distinguish between the 5000 species of mealy bugs, using a complex scoring system. “It can be counting hairs between fingernails,� Little says.
 
It’s much easier to stop the mealy bug pest in its tracks before it becomes well established. The quarantine on Cal Poly’s greenhouses is designed to prevent these insects from reaching other areas, especially since at one point in their lifecycle, they’re active crawlers. “They can get on your shoes or crawl up your jeans,� he explains. Students aren’t allowed entry to the greenhouses, plants cannot be removed, and maintenance crews dress in special protective suits that are then buried.
 
Because of the quarantine, last weekend’s planned “Tomatomania� plant sale was cancelled, along with sales of basil seedlings. However, student-grown Easter lilies were approved for delivery to area churches, since the flowers are not a host for these mealy bugs.
 
Depending what the lab work shows about the pest infestation, plants—or even the entire greenhouse—may have to be destroyed, according to Little.
 
Meanwhile, officials are working to trace the origin of the passion vine mealy bugs, which were found on a China doll houseplant in the tropical greenhouse. “Cal Poly has provided records on where the plant came from, and crews are checking around the state. Cal Poly is the middleman, and I need to find out where the beginning was. It will be extremely frustrating if we can’t find out where it came from,� he says.
 
For Cal Poly ornamental horticulture students, the mealy bug infestation is an educational experience, says Bob Rice, professor of integrated pest management at the Horticulture and Crop Science Dept.


 “We’re taking every advantage of this. It’s ‘learn by doing’—although I would have appreciated other opportunities for learning.� ∆


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