Battle of the Bugs : Growers Grapple With Infestation, Fear New Influx of Insects

An experiment in entomology is going on in Bob Tobias’ back yard.

Not an intentional experiment, actually. A swarm of perseae mites, a tiny insect that attacks the leaves of avocado trees, has moved into an avocado tree behind his house. And a nectarine tree. And a peach tree.

“It is really going to town on the peach,” said Tobias, general manager for Mission Produce.

Although the Medfly got more attention, mobilizing armies of government workers and squadrons of insecticide-spraying helicopters with its brief Camarillo appearance, the perseae is a serious threat. It devastated crops in San Diego before arriving in Fillmore two years ago and has already spread throughout the county.

Nor is it the only insect local farmers fear. Like any agricultural region, Ventura County is awash in crop-munching bugs. Some, like the perseae, are relatively new imports. Others have vexed growers for years.

Their presence has been very much on the minds of farmers lately as the federal government considers lifting a ban on Mexican avocados. Bringing the avocados north, local growers say, could introduce still more insects into the country.

“Any time we have a possibility of introducing a plant pest we don’t currently have in the area, there’s a great deal of concern,” said David Buettner, the county’s chief deputy agricultural commissioner. “We certainly don’t need any more introduced.”

Farmers have established a balance with most pests in the area. Forget eradication--keeping the bugs from multiplying to unmanageable levels is the best farmers can do. And that balance, achieved with pesticides and the use of predatory insects, constantly changes.

“We look at what we do as management,” said David Holden with AG RX, an Oxnard-based agricultural supplies and consulting firm. “We used to call it ‘pest control,’ but you don’t control anything.”

Of the many insects currently in the county, perseae causes the most alarm. The mites latch onto the undersides of leaves and drain them of chlorophyll, killing them. In avocado trees--the mite’s favorite target--the fruit is then left unsheltered from the sun. The avocados shrivel and fall from the trees, often before they mature.

Farmers have fought back by spraying trees with a fine oil to suffocate the mites. They’ve also purchased and released into orchards a different kind of mite that preys on perseae in hopes the good bugs will eat the bad ones.

But the infestation is still spreading, said Ben Faber, a University of California farm adviser for Ventura and Santa Barbara counties. Local growers probably won’t achieve equilibrium with the pest for another few years, he said.

The perseae infestation, Faber said, is an example of how a foreign insect can suddenly appear and throw the county’s insect balance out of whack. “Along comes the perseae mite, and wham!” he said. “‘We don’t have predators for it, because it’s a new beast.”

Back in the early 1920s, the insect invader was a small, flat and circular pest called red scale. The scale, which probably came from the Mediterranean area, attacks the leaves and fruit of citrus trees and can seriously harm the trees if left unchecked.

Farmers started an eradication program in 1922. The scales, however, proved impossible to destroy completely, and efforts turned from eradication to control.

Now, to keep the population down, farmers use tiny wasps that lay their eggs inside the scales, eventually killing them.

The Fillmore Insectary raises the wasps--about 20 million each month--said manager Stan Zervas. They also produce a different wasp to kill black scale, which feeds off citrus, olives and some ornamental plants.

The wasps are raised in six climate-controlled rooms, a production-line version of the cycle of eating that growers hope will happen in the field. Scales are grown on squash, then moved to another room and exposed to the wasps, which plant their eggs to create the next generation of scale-fighting insects.

“You have to keep three things alive to get one,” Zervas said.

Local farmers have come to depend on “beneficial insects,” like the wasps, enough to support three cooperative insectaries and several private ones in Ventura County. Last year, more than 3 billion beneficial insects, with a total value of about $2.5 million, were released in the county.

The use of predatory insects has its limits. Holden said pesticide remains the best way to deal with many vegetable pests. Although predator insects exist for the beet army worm and the cabbage looper--two species entrenched throughout the county--the pests can damage crops quickly, before the beneficial insects have multiplied enough to keep their prey in control.

Reliance on pesticides, however, also can upset the bug balance. Avocado growers in the Camarillo area this year are experiencing problems with the omnivorous looper, which chews holes in the leaves of avocado trees. Tobias said the infestations have been caused, in part, by malathion spraying to kill Medflies in the area.

Along with eradicating Medflies, the malathion killed the beneficial insects that normally help keep omnivorous loopers in check. “This was a bad looper year, which, coupled with the malathion spraying, made it a terrible looper year in Camarillo,” he said.

Even without changes caused by spraying campaigns or new trade policies, the insect balance changes with the weather. The heavy winter rains this year made for a bumper crop of fuller rose beetles in the spring, Faber said. The beetles, which thrive on tender green foliage, die as the weather dries out, usually before avocado trees start to produce new leaves. This year’s late rains, however, kept more beetles alive for a longer period of time.

Local farmers don’t know how the pests found in Mexican avocado growing areas would react to Ventura County’s climate or to the other insects already present. They also don’t know how they would fight the avocado seed weevil, the stem weevil or the Mexican fruit fly if those pests suddenly appeared in the county.

Zervas said the first line of defense against any bug you don’t already have is to prevent its arrival.

“From a bug standpoint, if you can keep it out, keep it out,” he said.