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Parasitic Wasps May Aid Pest Control Efforts

Parasitoid wasps kill pest insects, but their existence is largely unknown to the public. Now, scientists have sequenced the genomes of three parasitoid wasp species, revealing many features that could be useful in pest control and medicine, and in the enhancement of our understanding of genetics and evolution. "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," said Dr. John Werren, from the University of Rochester, a co-leader of the study along with Dr. Stephen Richards of the Baylor College of Medicine. "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.” Parasitoid wasp females are like "smart bombs" that seek out and kill only specific kinds of insects, said Dr. Werren. "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." Parasitoid wasps are four times smaller than the common fruit fly. The females seek out specific insect, tick, or mite hosts, inject venom and lay their eggs, with the wasp young emerging to devour the host insect; traits that make the wasps valuable assets as agents for biological control. Although their size is insignificant, the importance of parasitoid wasps in the control of populations of agricultural pests is crucial. Thanks to these insects billions of dollars’ worth of crops is saved each year.

The three wasp genomes sequenced by Dr. Werren, Dr. Richards, and an international team of over 150 colleagues (the Nasonia Genome Working Group), are in the wasp genus Nasonia, which is considered the "lab rat" of parasitoid insects. Among the future applications of the Nasonia genomes that could be of use in pest control are 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, they also may provide an unexpected source for new drug development. The scientists have identified 79 different proteins in this venom, 23 of which had never been observed before. This information could be very useful in the development of new drugs, because these proteins have important physiological effects on the cells of their hosts.

In addition to being useful for controlling pests and offering promising venoms, the wasps could act as a new genetic system with a number of unique advantages. 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," said Dr. Werren. Unlike fruit flies, these wasps also modify their DNA in ways similar to humans and other vertebrates in a process called "methylation," which plays an important role in regulating how genes are turned on and off during development.

The wasps have an additional advantage in that closely related species of Nasonia can be cross-bred, facilitating the identification of genes involved in species' differences. "Nasonia is currently the best genomic model system for understanding the genetic architecture of early speciation and complex phenotypes like behavior," said working group member Dr. Juergen Gadau from Arizona State University.

A startling discovery in the work was that Nasonia has been picking up and using genes from bacteria and Pox viruses (e.g., relatives of the human smallpox virus). "We don't yet know what these genes are doing in Nasonia," said Dr. Werren, "but the acquisition of genes from bacteria and viruses could be an important mechanism for evolutionary innovation in animals, and this is a striking potential example.”

Because of the rapid evolution of their mitochondria, these wasps may also prove useful as models for understanding mitochondrial diseases of humans, the authors noted.

"Emerging from these genome studies are a lot of opportunities for exploiting Nasonia in topics ranging from pest control to medicine, genetics, and evolution," said Dr. Werren. "However, the community of scientists working on Nasonia is still relatively small. That is why we are hoping that more scientists will see the utility of these insects, and join in efforts to exploit their potential."

The article on this work was published in the January 15, 2010 issue of Science. [Press release 1] [Press release 2] [Press release 3] [Science news focus] [Science abstract]