Population dynamics and biological control of the citrus thrips,Scirtothrips citri(Moulton), was studied over a 3-year peiod on ‘Washington’ navel orange, ‘Lisbon’ lemon, and ‘Marsh’ grapefruit near Corona (Riverside County), Calif. The native phytoseiid predator,Euseius hibisci(Chant), was excluded from experimental plots in citrus groves by spraying a residue of malathion on plot trees and those surrounding the plots. Subsequent mass release of this predator into these plots suppressed the citrus thrips below economic levels. In plots that had been sprayed with malathion, the disappearance of the insecticide from the leaves was monitored. The leaf residues did not stimulate fecundity of the citrus thrips by early summer. Early spring populations of>0.50E. hibisciper leaf on inland valley citrus groves of southern California responded numerically and functionally to second- and third-generation increases ofS. citri. These responses byE. hibiscioccurred before citrus thrips could irreparably damage the rind of fruit of ≤4 cm diameter. Field trials on lemon were designed to assess the effect of five citrus pesticides on the Corona Foothill strain ofE. hibisci. Dimethoate, methomyl, and parathion were extremely toxic toE. hibisci; residual toxicity of chlorobenzilate and carbaryl to the predator 26 days posttreatment was comparable to the water control.