An international team of researchers has sequenced the genomes of three species of tiny parasitic wasps that kill agricultural pests.

A female Nasonia wasp stinging a fly pupa and laying its eggs inside it. (Peter Koomen and Mathijs Zwier)

The consortium of scientists, led by biologist John Werren of the University of Rochester in New York mapped the complete genetic sequences of three types of Nasonia wasps, insects less than two millimetres long.

"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," said Werren, in a statement.

Parasitic wasps reproduce by a laying their eggs inside other insects, such as house flies and flesh flies, in their pupal stage. The wasps lay 40 to 50 eggs in each pupa.

When the eggs hatch, the wasp larvae consume the insect from the inside out, all the while making sure the host insect remains alive as long as possible.

Warren calls the wasps "smart bombs" that seek out and kill only certain types of insect. The information from the wasp genome could make the insect a tool for agricultural pest control, the scientists say.

"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," he said.

Parasitic wasp pupae developing inside a host fly pupa. The developing wasps have eaten the fly that was originally inside the pupal case. (Michael Clark) "Many people may not realize how dependent humans are on these tiny wasps which protect our food crops and save the U.S. billions of dollars each year by reducing crop loss," said Chris Smith of San Francisco State University, one of the study's authors.

Besides their importance as a predator of insect pests, the Nasonia wasps are interesting because of their unusual genetics.

Male wasps develop from unfertilized eggs and have only one copy of their genetic code in each of their cells. Because they carry only one copy, any mutation in their DNA is immediately visible, while it would be hidden in most species that carry two copies of each gene.

"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 Werren.

Nasonia is also considered a model organism — a "lab rat" — for other insect in the order Hymenoptera, which includes all wasps, bees and ants. Research on parasitic wasps could be applied to pollinating bumblebees or pesky carpenter ants.

In their decoding of the Nasomia genomes, the research team has already identified genes responsible for the wasps' venom. They also found that the wasp shares genes in common with bacteria and pox viruses, suggesting some transfer of genes between the species.

The research appears this week in the journal Science.