Foliar pests of watermelon in Hawaii includeLiriomyza sativaeBlanchard andLiriomyza trifolii(Burgess) (Diptera: Agromyzidae),Thrips palmiKarny (Thysanoptera: Thripidae),Aphis gossypiiGlover (Homoptera: Aphididae),Tetranychus cinnabarinus(Boisduval) (Acari; Tetranychidae) andTrialeurodes vaporariorumWestwood (Homoptera: Aleurodidae). In studies in 43 commercial plantings arthropod pest densities remained below density treatment levels (DTLs) without weekly pesticide applications.T. palmiandA. gossypiiwere the major foliar pests on Oahu (1984–1985) and Molokai (1986) because DTLs were surpassed between 12 and 41 % of the survey dates. The occasionsT. palmiandA. gossypiisurpassed DTLs varied with locality and in the latter species with the presence of non‐persistent transmitted viruses.Liriomyzaspp.,T. cinnabarinusandT. vaporariorumdensities surpassed DTLs less than 11 % of the survey dates.