ABSTRACT. – Terrestrial isopods play a particularly important ecosystem function in mineralizing organic matter but, according to the species and the cultivated agroecosystem, their status of pest is yet to be confirmed. In this context, Porcellio laevis Latreille, 1804 is considered as a serious pest for some varieties of melon (Cucumis melo L.) in Tunisia. Monthly samples (March 2013 to December 2015) showed that the important variation in density of P. laevis depended both on season and melon variety: afamia, canary, cantaloupe and tziri. Furthermore, this density was positively correlated with maturity stage of melon (immature, ripe and overripe). In melon, analysis of total phenolic contents and hydrophilic antioxidant activity exhibited a significant difference between varieties and maturity stages (P < 0.01). Our results showed that the most damaged varieties afamia and cantaloupe, characterized by (i) thinner cortex, (ii) higher total phenolic contents, (iii) high concentration of internal ethylene and (iv) liberation of aromatic odor during mature and post mature stages, offered favorable conditions for fast growth, longer survival and higher fertility of P. laevis leading to an increase in population and turning it into a crop pest.