Feeding rates (mm2/h per larva) of larval Colorado potato beetles,Leptinotarsa decemlineata(Say), were measured in 2- to 2.5-h trials on excised ‘Russet Burbank’ potato (Solanum tuberosumL.) leaflets at constant temperatures from 14 to 42°C. In all instars, feeding rate was greatest at ≈29°C and decreased symmetrically at higher and lower temperatures. Second, third, and fourth instars fed at 42°C. In 24-h trials consisting of repeated 2- to 2.5-h measures at ≈6-h intervals, feeding rates at 23 and 29°C varied among and within groups of larvae, but no consistent diel pattern was detected.