Grout, T.G., & Richards, G.I. 1992 Organophosphate resistance in California red scale (Homoptera: Diaspididae) on citrus in the eastern Cape and the effect of oil as an organophosphate synergist.. Journal of the Entomological Society of Southern Africa 55(1): 1-7.

Notes: Abstract: A bio-assay comparing the efficacies of chlorpyrifos, methidathion, prothiofos, parathion and phenthoate at 0,053 of their field dosages was conducted using resistant red scale crawlers; results showed that the crawlers were resistant to all these organophosphates as had been found previously in the Transvaal.