"I figured if the insects didn't work, we could always fall back to the insecticide program," Rosenbrand explains. The insect-release program began in 2006. "We released everything that would eat a mealybug," he recalls.

They released predators, which consume all VMB stages from egg to adults, and parasitoids, which lay eggs inside the VMB and eat it from the inside out.

"The two strategies are complementary, not contradictory," Rosenbrand says. "The difference is that some of the predators tend to work best in high-density populations, while parasitoids can work well at both high and low density populations, and they are not as likely to disperse."

Although the insecticide sprays (Lorsban, Lannate,Dimethoate, Provado, and Applaud) were not successful in eradicating the mealybugs, they did serve a useful purpose. First, they kept the VMB population below damaging levels. Second, although they weren't the target at the time, Argentine ants, were also victims of some of the insecticides.

"The sprays killed everything except the mealybugs beneath the bark. But it did kill the ants," Rosenbrand recalls. "That meant we could start with a clean slate."

"The Argentine ants may directly kill some beneficials," explains Cooper, "but mainly the ants protect the mealybugs by disrupting the behavior of the beneficials (parasites are unable to lay eggs and predators are unable to consume their prey).

The UC Berkeley team began releasing insects one month after bud break in 2006 — 18,000 Coccidoxenoides perminutus (a small, black parasitic wasp), on April 19. One day later 30,000 ladybugs were released, 50,000 green lacewings, and 2,000 minute pirate bugs. On April 25, 5,000 Cryptolaemus montrouzieri (beetles appropriately named the "mealybug destroyer") were released, and one week later, 80,000 more ladybugs. On May 17, the parasite Anagyrus pseudococci (a brown parasitic wasp with white-tipped antennae) was released, with 50 females and 25 males.

"In the beginning, my strategy was eradication," recalls Rosenbrand. "We released everything we could obtain.

Now things have changed somewhat to a more refined approach using insects that have proved their success."

During the months that followed, various quantities of those insects were released. All predators were purchased by Rosenbrand through a commercial insectary. The
Closeup of vine mealybug female.

"The C. perminutus were imported from South Africa and the A. pseudococci were brought in from northern Italy, both were collected on VMB and may perform better than the native parasites," Daane explains.

By the end of the season, Rosenbrand and the UC Berkeley team had released 1,765 Anagyrus, 94,650 Coccidoxenoides, 35,000 Cryptolaemus, 670,000 ladybugs, 10,000 minute pirate bugs, and 700 cards each containing 500 green lacewing eggs for a total of 350,000 lacewings.

The scientists sampled mealybug populations between April and October, and monitored parasitism rates and economic damage to grape clusters before harvest. From these mealybug samples, both A. pseudococci and C. perminutus were recovered, thus confirming their ability to reproduce under field conditions.