Abstract: The vapours of ten volatile oils (citronella, eucalyptus, clove, lemon grass, dill, geranium, celery, lemon, cardamon and coriander) were used to study their effect on total protein, albumin and alkaline phosphatase, which are thought to be related to reproductive capacity of potato tuber moth Phthorimaea operculella. The results showed, clearly, that the biochemical responses were variable according to the type of oil and sex. Lemon had no effect in most cases. It only decreased females` total protein and alkaline phosphatase activity. All the remaining oils exerted effects, particularly six oils (clover, eucalyptus, citronella, dill, lemon grass and celery), generally, reduced the majority of the tested biochemical parameters in both males and females. Total proteins and albumin were reduced more by the tested oils than alkaline phosphatase, which increased in some cases, especially in males