Toxicity and persistence of five organophosphorus insecticides following one summer spray in 1975 and two in 1976 at 0·05% conc. (400 gm a.i./ha) on apple cv ‘red delicious’ were evaluated againstQuadraspidiotus perniciosus Comstock at Solan, Himachal Pradesh. Fenitrothion was found to be highly toxic to the crawlers of the scale; methyl-parathion and diazinon proved to be intermediate in toxicity while phosalone and malathion respectively were less toxic compounds. Phosalone was highly persistent (ca 2 weeks) but did not provide enough protection to the fruits against the pest insect owing to its low intrinsic toxicity. The deposits formed on apple by fenitrothion, methyl-parathion and diazinon were relatively less persistent but provided 23 to 27, 14 to 18 and 10 to 15 days protection respectively to the fruits. The fruits were found safe for consumers use after 20–22 days following the application of fenitrothion, 14–16 days of phosalone, 12–13 days of diazinon, 9–11 days of methyl-parathion and less than 1 day when malathion was sprayed. All the insecticide residues were within the acceptable limits at the time of harvest.