Threat to local crops posed by guava fruit flies triggers eradication plan

SAN JOSE — Citing a need for “immediate emergency eradication,” the California Department of Foods and Agriculture has declared war on the guava fruit fly. Three male flies were found in traps in the city’s Mayfair neighborhood two weeks ago, so beginning Wednesday, state and county crews will begin spreading a deadly “male attractant” insecticide on trees and telephone poles in the area.

Unlike eradication programs meant to eliminate mosquitoes that carry West Nile Virus, this one will require no aerial spraying. Though the pest is put to rest, according to Santa Clara County Agricultural Commissioner Joe Deviney, human exposure to the treatment is “negligible.”

“It’s a tropical fly with huge reproductive potential,” Deviney said, adding that males are targeted to disrupt the breeding cycle. “Basically, the population collapses when they don’t have males to mate with.”

According to fruit fly experts, the adult guava is about the size of a housefly, with a thorax that is black with yellow patches and a yellow-orange abdomen with a dark T-shaped mark.

And that T stands for trouble, especially for anyone growing guava, peach, cherry, citrus or melon crops. Alone, the male guava fruit fly is relatively harmless. But when a male and a female fruit fly meet, mate and have a brood of little larvae, that’s when the trouble begins. When the female lays her eggs in fruit, they hatch and become — to use what seems like a fairly harsh term for babies of any genus — maggots, which then tunnel through the fruit’s flesh, making it inedible.

Though guava fruit flies are not among the pests most feared by state agricultural authorities, the threat they pose to crops is significant. The total value of what are referred to as “host fruit and vegetables” during an infestation in California five years ago was $3 billion. Allowed to spread, a statewide infestation could result in control costs of $3.5 million a year and up to 252,000 additional pounds of pesticide used.

It is the male’s feckless fecundity that brings about its undoing. To end the reproductive cycle before it can begin, utility poles, street trees and other unpainted surfaces are treated with small amounts of a poison perfume that plays upon the male’s sexual yearnings with deadly results.

The sticky traps will be checked in two weeks, then monitored for up to three months, or until authorities are sure there are no more bouncing baby maggots in San Jose.

Contact Bruce Newman at 408-920-5004. Follow him on Twitter at BruceNewmanTwit.