When Hollywood needs a creature for a film, directors often look to nature for ideas. Take, for example, the giant alien that chased Sigourney Weaver through three Aliens flicks. According to University of Wisconsin entomologist Michael Strand, that huge creature was modeled after a tiny insect.

“What that big intergalactic space monster was, was a parasitic wasp,” Strand says. The much smaller non-Hollywood version of the creature is just as determined to survive as its celluloid counterpart. Strand hopes that a better understanding of these wasps will lead to their use in biological pest control.

Parasitic wasps lay their eggs inside the caterpillar-like larval stage of other insects. The larva acts as an incubator for the wasp egg and then supports the growing wasp after it hatches. After supporting a growing parasite, the host insect rarely survives to adulthood.

Strand says there are many instances in nature where parasitic wasps provide natural pest control. Alfalfa weevils in Wisconsin and citrus scale insects in California are examples of naturally balanced pest control systems that function without any help from humans. Strand hopes that by learning more about the parasite/host relationship, other parasites could be developed to control a variety of crop pests.

Some wasp species have a little microbial help in carrying out their reproductive missions. Describing them as “flying hypodermics,” Strand says when a wasp lays her egg in a larvae, she injects a bit of insurance as well ? a virus that compromises the insect”s immune system so that it can”t attack the wasp egg.

The virus in question is a type of polydnavirus, a group of insect viruses discovered in the mid-1970s. Scientists found the virus particles hiding out in calyx fluid, which Strand describes as bright blue goop, in the wasps” ovaries. He says the calyx fluid is almost entirely made up of virus particles.

Strand says in this arrangement, both the wasp and the virus benefit. The wasp needs the virus to keep the host insect”s immune system in check and the virus needs the wasp in order to survive. The only loser in the arrangement is the hapless caterpillar.

The virus doesn”t multiply in the host larva, and is only spread when the wasp lays its eggs. Consequently, it might appear that the virus has backed itself into a biological dead end. Not so, says Strand. In addition to hanging around in the calyx fluid, the virus incorporates itself into the wasp”s genetic material.

As part of the wasp”s genome, the virus ends up in the egg and is passed on to the new wasp generation. So, by neutralizing the host”s immune system to protect the egg, the virus also ensures its own survival.

Strand wants to discover why some wasp species carry the virus and some don”t, and whether this could be used to increase the effectiveness of the wasps as biological control agents. In the broader view, learning why only some species within an insect group carry viruses or other organisms could also lead to a better understanding of insect-borne diseases like malaria.

Biological control is a relatively inexpensive technology compared with developing and testing chemical pesticides. Strand says its biggest problem is that it isn”t always a sure thing. There”s no guarantee the biocontrol agent will establish itself sufficiently to control a pest.

Because of this, “You can end up with either spectacular successes or spectacular failures,” Strand says. He says some past biocontrol campaigns went awry because the biological control agent was not well understood beforehand. He hopes that thorough study of the systems involving parasitic wasps will increase the chances of their being a successful pest control. “We want to make biocontrol a more predictable science,” he says.