Discovery of Spider Early Warning System Could Help Farmers Defend Crops
A species of small wolf spider has been found to possess "an early warning system" to detect danger-a system triggered by traces of silk and excrement left by predators-which reduces the spiders' desire to eat and reproduce.
Since some insects also have been found to possess a similar warning system, scientists might eventually gain access to the chemical cues and be able to regulate both insect and spider populations among farmers' crops.
The research, by Matt Persons, assistant professor of biology at Susquehanna University in Selinsgrove, Pa., and three Ohio researchers is in the February 2001 issue of Animal Behaviour, an academic journal. Co-authors of the paper, titled "Wolf spider predator avoidance tactics and survival in the presence of diet-associated predator cues," are Sean Walker, a graduate student at Miami University (Ohio), Ann Rypstra, professor of zoology at Miami University (Ohio), and Samuel Marshall, biology field manager at Hiram College.
The researchers tested activity level and avoidance behavior of the small wolf spider, when it came in contact with silk traces and excrement from the larger predatory wolf spider. They found that the tested spiders were able to perceive and discriminate between predators and non-predators just by detecting their silk and excreta. Spiders are able to tell what predators were eating just by chemical cues alone. They show more defensive behavior when the predator's silk and excreta indicate that they have been feeding on the spider prey, and less when they have been feeding on something else. These chemical cues serve as an "early warning system" to the prey - producing elevated levels of antipredator behavior.
"This antipredator behavior is effective at minimizing getting eaten, but it is costly behavior - interfering with both eating and reproduction. It is the costs that are most interesting from a biocontrol perspective," says Persons. "For example, the presence of chemical cues from a larger species of predatory wolf spider causes reduced feeding, and the production of fewer eggs by another species of wolf spider. This is true even when the predator isn't around - as long as the silk and excreta are present."
Persons and his students have extended their research to see if a similar "early warning system" is also present in insects. He's collaborating with Susquehanna senior biology student J.C. Owens on research indicating that cricket species in the same neighborhood with one particular species of wolf spider also show strong antipredator responses, while cricket species that are not found in the same habitat do not. The antipredator response is primarily in the form of avoidance and reduced movement.
"It is difficult to eat and find mates if you don't move around. Given that most habitats are littered with silk and excreta from spiders, this may be a powerful deterrent to inhibit feeding for many species of insects," says Persons. "They may also avoid areas with these cues entirely. We are still at the early stages of testing these ideas, but the potential is enormous."
This could be used as an added weapon in the integrated pest management arsenal for farmers. Persons reports that spider silk and excreta are non-toxic, non-polluting substances that have the potential to have large behavioral effects on their insect prey. Unlike pesticides, it is also difficult for insects to evolve resistance to spider chemical cues.
"This is true because insects that ignore spider silk and excreta are likely to be more prone to being eaten by spiders, because they won't exhibit appropriate defensive maneuvers," says Persons. "My colleagues have also started some preliminary studies examining responses by some crop pests to spider excreta and silk. It looks like many insects respond to this predator cue, but the full implications of these responses still need to be worked out."
He believes that a synthetic compound containing elements of the spider silk and excrement could eventually be produced, giving farmers a new weapon in their fight to protect crops against potentially harmful insects.
Persons may be reached by calling his office at (570) 372-4526, or his home at (570) 568-1067. His e-mail is [email protected].
If you're interested in a copy of the paper, or have additional needs, feel free to call me at (814) 867-1963, or e-mail me at [email protected]. Dick Jones Communications assists Susquehanna with its public affairs work.
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