**Abstract**

The date palm is one of the most economically important perennial plants of the North Africa and in Morocco, where it is extensively cultivated for food and many other commercial purposes. Palm trees are threatened by many pests such as *Potosia opaca* newly identified in Morocco, especially in Marrakesh and Errachidia regions. In addition, olive mill wastewaters (OMW) are an environmental problem in olive oil producing countries such as Morocco. Generally, these effluents are drained into ecosystems without any pre-treatment. To reduce their negative impact and to get benefits in particular from their high phenolic content, OMW were used as bio-insecticides in crude form. The results showed that crude OMW were effective to control this pest causing a weight loss similar to Cordus insecticide (17% *vs.* 15%) and mortality almost similar to Kemaban insecticide. OMW's biocide potential was related principally to their high phenolic content. Based on HPLC analysis, ten phenolic molecules were identified, including two which were revealed as the major monomeric phenolic compounds in OMW, 0.248 g/L of hydroxytyrosol and 0.201 g/L of tyrosol. In this chapter, the potential use of OMW as bio-insecticides for the control of *P. opaca* in date palm is discussed.

**Keywords:** olive mill wastewaters, *Potosia opaca*, date palm trees, insecticidal activity, biological control
