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Marin IJ Articles

Pitting Bug Against Bug in the Landscape

  • Dave Phelps
  • The Eugenia shrub, also known as the Australian bush cherry, is a fantastic plant that makes quick, tall hedges that do well with little water. They are, after all, from Australia.

    At first, they were a big hit in California, a Mediterranean climate similar to their homeland. Walt Disney used them as topiary plants, turning the glossy plants into large hedged animals at his Orange County theme park. He also used them as large hedges, planting more than 2,400 feet of them around the park. They had few pests and were always beautiful plants — until their native adversary, psyllids, from Australia found their way here.

    First found in Los Angeles in 1988, the psyllids quickly spread, showing up in Northern California the next year, turning these perfect shrubs into ugly, puckered, black moldy deformities. It was awful.

    It would have stayed that way if it weren't for Disney. When his hedges and topiaries got infested with the psyllids, something had to be done.

    A team of entomologists was sent to Australia to find a natural predator for the pest. In New South Wales, they found a tiny parasitoid wasp called tamarixia. These wasps lay their eggs next to the young psyllid nymphs; the wasp larvae enter the psyllid and use them as incubators and develop into an adult inside the dead psyllid.

    The wasps were brought back, tested and released in 1992 at various locations throughout the state.

    Luckily, the wasps spread and psyllid populations along the coast showed a decrease of 10 percent to 20 percent a year.

    Finding natural predators for pests is now common and makes sense. Rather than applying toxic pesticides that harm the ecology, releasing predators (that have been tested for adverse affects) to hunt the pests is a much more sustainable solution. This is called biological control. After physical and cultural controls, it is the preferred control method in any Integrated Pest Management program.

    Other similar parasitoid wasps have been found to parasitize the smoke tree sharpshooter, the blue gum psyllid nymphs as well as the Asian citrus psyllid nymphs and many others. A more common wasp, encarsia formosa, otherwise known as the greenhouse whitefly parasitic wasp, can be purchased as eggs glued to a card or inside parasitized scale insects. This tiny wasp is an expert at controlling whitefly populations on tomatoes. Trichogramma wasps parasitize pest caterpillars.

    Recently California has been under attack from another Australian adversary — the myoporum thrip. It's a familiar tale: A wonderful large, fast-growing, glossy evergreen shrub or small tree from a Mediterranean climate made it's way into the California nursery trade in a big way. The plants were a huge success. I've even heard a town council proclaim, "We'll approve this addition so long as you plant a row of myoporums along the property to screen it from the neighbors." Little did they know that the natural adversary was on its way.

    Sure enough, the myoporum thrip (klambothrips myopori) found its way from Australia. What we have seen since is the devastation of one of the most dependable evergreen screen plants in coastal California. An emergency label was made for Safari insecticide to control the pest. Dinotefuran, however, is highly toxic to bees and shrimp, has been detected in ground water, and may be hazardous to aquatic organisms — not something that makes sense to use near the coast. We need another wasp. Unfortunately, there are not enough myoporum laetum plants used as priceless topiaries at world-class theme parks and at this time, no team of entomologists are out finding their natural predators or testing them.

    Until someone cares enough, or the myoporum thrip's predators find their way here themselves, we had best look to alternative screen plants in the landscape. Meanwhile, millions upon millions of tiny little wasps are hard at work around the clock parasitizing some of our most damaging pests without the use of toxic pesticides.