"We study these nematodes - which are actually insect killers - not only to understand how diverse they are, but also to use them as biological control alternatives," says Patricia Stock, a nematomologist in the University of Arizona College of Agriculture and Life Sciences.

"We want to see how they interact with the local insects. Using native biological control alternatives is more environmentally friendly than importing other pest control agents."

Known as entomopathogenic nematodes (EPN), the juvenile stage of these tiny worms travels with bacteria in its intestine that specifically kill certain insect species. Nematodes in the family Steinernematidae are associated with Xenorhabdus bacteria; those in the family Heterorhabditidae harbor Photorhabdus bacteria. Both types of EPN operate in similar ways.

In the soil or in encrypted habitats such as the pockets behind the bark of trees, the juvenile nematode waits for (or sometimes actively seeks) an unsuspecting host - a grub or a larva - to jump on it and penetrate it through the insect's natural openings - mouth, anus, spiracles. Or the nematode may enter the host directly by using a dorsal tooth.

Once inside the insect, the nematode vomits the pathogen, which kills the host within 24 to 48 hours and even digests its tissues, creating a perfect environment for the EPN to grow and multiply. One or more adult generations live entirely inside the decaying insect. The third stage infective juvenile is the only one that can live outside the insect host. Numbering about 150,000 strong or more, these juveniles exit the dead larva, carrying the bacteria, and look for other hosts to begin the cycle again. These juveniles also can survive dr
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4-Mar-2005