(Beyond Pesticides, January 22, 2010) Gardeners have long turned to parasitic wasps and other beneficial insects to control unwanted insects, and new genetic research suggests even more ways to harness these species’ potential. Scientists, led by John H. Werren, Ph.D., professor of biology at the University of Rochester, and Stephen Richards, Ph.D., at the Genome Sequencing Center at the Baylor College of Medicine, have sequenced the genomes of three parasitoid wasp species, revealing many features that could be useful as a “natural” alternative to pesticides. The study, “Functional and Evolutionary Insights from the Genomes of Three Parasitoid Nasonia Species” was published in the January 15, 2010 issue of the journal Science.
Already, many of these parasitoid wasps are hard at work, but because they are so small, most people are unaware of their existence. “Parasitic wasps attack and kill pest insects, but many of them are smaller than the head of a pin, so people don’t even notice them or know of their important role in keeping pest numbers down,” says Dr. Werren. “There are over 600,000 species of these amazing critters, and we owe them a lot. If it weren’t for parasitoids and other natural enemies, we would be knee-deep in pest insects.”
According to Dr. Werren, parasitoid wasps are like “smart bombs” that seek out and kill only specific kinds of insects. “Therefore, if we can harness their full potential, they would be vastly preferable to chemical pesticides, which broadly kill or poison many organisms in the environment, including us.”
In addition to being useful for controlling insects and offering promising venoms, the wasps could act as a new genetic system with a number of unique advantages. According to researchers, their long term goal is to genetically modify parasitoids through selective breeding to improve their utility in pest control. The genome sequences provide tools and baseline information to advance toward this goal.
Three wasp genomes were sequenced for this study, all of which are in the wasp genus Nasonia. While fruit flies have been the standard model for genetic studies for decades, largely because they are small, can be grown easily in a laboratory, and reproduce quickly. Nasonia share these traits, but male Nasonia have only one set of chromosomes, instead of two sets like fruit flies and people. “A single set of chromosomes, which is more commonly found in lower single-celled organisms such as yeast, is a handy genetic tool, particularly for studying how genes interact with each other,” says Dr. Werren. Unlike fruit flies, these wasps also modify their DNA in ways similar to humans and other vertebrates””a process called “methylation,” which plays an important role in regulating how genes are turned on and off during development.
Among the future applications of the Nasonia genomes that scientists are hoping could be of use in pest control is identification of genes that determine which insects a parasitoid will attack, identification of dietary needs of parasitoids to assist in economical, large-scale rearing of parasitoids, and identification of parasitoid venoms that could be used in pest control. Because parasitoid venoms manipulate cell physiology in diverse ways, researchers are hoping they also may provide an unexpected source for new drug development.
While the prospect of utilizing parasitic wasps as a natural alternative to toxic pesticides is exciting, it is important that scientists proceed with caution. In some cases, introducing a new species to combat another can take a devastating toll on an ecosystem, especially if the beneficial insect itself has no predators. The article, “When Good Bugs Go Bad,” by Doug Stewart of the National Wildlife Federation explains that introduction of beneficial insects can essentially turn invasive in the absence of the enemies and competitors that kept it in check back home.
In Hawaii, for instance, parasitic wasps from China and the U.S. mainland were released at least 100 times before 1950 by the Hawaiian Sugar Planters’ Association to fight sugar-cane insects. In 1999 and 2000, ecologists collected more than 2,000 caterpillars of native moths and found exotic wasps developing from eggs in one in five native swamp caterpillars. And most of these, they discovered, were from just three species of parasitic wasps that were deliberately released in the cane fields. Without the native caterpillars that the wasps were using as hosts, insect-eating birds would starve.
Still, though, Mr. Stewart explains in his article that in classical biological control using exotic natural enemies to counter invasive insects examples of biocontrol insects that have themselves gone out of control are relatively few. When it does work, this method is far more benign, efficient, and precisely targeted than the usual method of controlling insect species: spraying their general whereabouts with toxic chemicals.
This has happened in the case of the Asian lady beetle, which was imported as early as 1916 in an attempt to naturally control certain insect pests aphids, scale and other soft-bodied arthropods. While they are sometimes considered a nuisance in the absence of predators, they are still considered to be a beneficial insect.
To attract parasitic wasps naturally, Gardeners.com recommends supplying food and moisture; adult wasps feed on nectar and pollen. Plant alyssum, herbs from the dill family, and flowers from the daisy family, because small and shallow-faced flowers provide easy access to these tiny beneficial insects. If you have a bird bath or pond in your garden, place stones in the water so wasps have a place to land and drink safely.
Many beneficial insects are also available through garden centers. The most available are ladybugs, preying mantises, trichogramma for gypsy moth control, lacewings, insect parasitic nematodes, and fly parasites for control of breeding flies in stables and kennels. Some of the less common but still available insects include predatory mites to control mite pests, aphid midge for woolly adelgid control, leaf miner parasites and many, many more. Ask your garden center manager if they can get what you want since many beneficial insects have a short shelf life and must be ordered when needed.
For more information on Nasonia and emerging studies, visit the Werren laboratory web site.