Abstract: 【Objective】 To provide the fundamental dat a of controlling the flea species of media of plague and to probe insecticidal m echanisms of fenoxycarb to the early third instar larvae and the newly emerged a dults of Xenopsylla cheopis (Rothschild, 1903) through histological observations. 【Methods】 The early third instar larvae and the newly emerged adults of X. cheopis were treated with fenoxycarb by microliter syringes. The changes of tissues were determined by the methods of histology, microphotographics and statistics. 【Results】 The cuticula of the third instar larvae of X. cheopis treated with fenoxycarb were thicker, the reproductive cells of ovarial rudiments became atrophied, and interstitial tissues of sperma gonia became less. The testicular plug of the newly emerged adults of X. cheopis treated with fenoxycarb disappeared faster than treated with a cetone, the salivary gland cells were damaged seriously, and the midgut epitheli a become atrophied. 【Conclusions】 (1) Fenoxycarb caused the death of X. cheopis larvae by disturbance of metamorphosis and changes in cuticula, ovarial rudiments and testicular rudiments. (2) Fenoxycarb escalated disappearance of testicular plug in the newly emerged male adults.   (3) Fenoxycarb caused the death of the newly emerged adults of X. cheopis by damage of salivary gland cells and atrophy of midgut epithelia.10 Refs. In Chinese

Key words: Fenoxycarb, Xenopsylla cheopis, histology, insect growth regulator, insecticidal mechanism