Until now, the conventional wisdom governing biological pest control called for releasing as many different natural predators as possible to suppress as many pests as possible. In one of the first field studies of its kind, a UC Davis scientist recently found that a greater variety of predators may not always mean better pest control. "My results suggest that, in some circumstances, one species of predator may be better than two," says zoology researcher David A. Spiller. "In some circumstances, it might be better to remove some predators, rather than introduce them." At a salt marsh on the northern shore of the San Francisco Bay Area, Spiller studied two species of spiders. When Cyclosa turbinata spiders were the only spider species in a plot, they outnumbered the total spiders found when Cyclosa shared its plot with another spider species, Metepeira grinnelli. Spiller found that Metepeira frequently displaced and sometimes killed Cyclosa. Because Cyclosa consumed more small insects per capita than Metepeira, Spiller believes Cyclosa alone would control small insects better than both species together. "Before general predators are introduced into an agricultural system," Spiller says, "the system should be researched to predict whether a combination or a single predator would offer the best pest control." Spiller will present his paper at 8:35 p.m. on Monday, Dec. 9.