The springtail, Protaphorura fimata Gisin (Onychiuridae), was recently identified as a serious subterranean pest of lettuce (Lactuca sativa L. [Asteraceae]) in the Salinas Valley of California and little is known about efficacy of insecticides to control it. The efficacy of 15 insecticides was determined against P. fimata individuals by evaluating their feeding injury on germinating lettuce seeds in three laboratory experiments. In two experiments, a low density of P. fimata (50 individuals) was exposed to insecticide-treated substrates (filter paper and soil); a high density of P. fimata (100 individuals) was exposed to insecticide-treated soil in the third experiment. In all three experiments, 25 uncoated, untreated lettuce seeds were placed on the surface of treated substrate and exposed to P. fimata for 7 d. Significantly more P. fimata individuals and their feeding injury were found in the distilled water (control) treatment than any insecticide treatments. Overall, percentage of injured seedlings and number of feeding sites per seedling were significantly reduced in all the insecticide treatments particularly with pyrethroid (zeta-cypermethrin, bifenthrin, and lambda-cyhalothrin) and neonicotinoid (dinotefuran, thiamethoxam, and clothianidin) insecticides, as well as tolfenpyrad, chlorpyrifos, and spinetoram (0 to ∼3% injured seedlings) compared with distilled water (up to ∼85% injured seedlings). Although cyantraniliprole, novaluron, flonicamid, and flupyradifurone insecticides reduced P. fimata feeding on germinating lettuce seeds relative to distilled water, their efficacy against P. fimata was inferior to other insecticides, especially in the high P. fimata density experiment.