Survey studies were carried out to determine the identity and bionomics of insect vectors of tristeza and greening diseases of citrus in citrus growing regions of Ethiopia between 1982 and 1985: Results of these studies revealed that three species of aphids:Aphis gossypiiGlover,Toxoptera aurantiiBoyer de Fonscolombe andT. citricidus(Kirkaldy), were implicated in tristeza, whereas the citrus psyllid,Trioza erytreaeDel Guercio, was solely responsible for greening; the Asiatic psyllid,DiaphorinacitriKuwayama, was not found in this country. Among the aphids,A. gossypiiwas least common on citrus whileT. aurantiiwas found in large numbers and was widely distributed throughout the country;T. citriciduswas confined mainly to the middle Awash areas.Trioza erytreawas widely spread in the country above 1500 m and was more severe at higher altitudes. Host range studies indicated thatA. gossypii, T. aurantiiandT. erytreaeare polyphagous whileT. citriciduswas found only on citrus. No parasitoid wasrearedfromA. gossypiiduring the study while five and six species were identified fromT. aurantiiandT. erytreaerespectively. The encyrtids,Psyllaephagus pulvinatus(Waterston) andPsyllaephagussp. were the dominant and widely distributed primary parasitoids ofT. erytreae.Eleven species of predators were recorded on one or more of the insect vectors.