Defense of Host Plants against Orgyia trigotephras in Northeast of Tunisia

Abstract

The egg-larval stage of Orgyia trigotephras were observed in shrubs maquis of Jebel Abderrahmane in north-east Tunisia, mainly on Quercus coccifera and Pistacia lentiscus, while only eggs were noticed on Phillyrea media. This kind of observation suggest us to study tree defense against O. trigotephras which will be explored by chemical analysis of P. lentiscus, Q. coccifera and P. media. Two types of analyses were the focus of this study to understand plant defense (i) primary metabolites and (ii) components of essential oils of these tested plants. Kjeldhal method was used for nitrogen and Mrssorr method for potassium, sodium and phosphorus extraction. Essential oils were extracted with the hexane solvent; chemical composition was determined using (GC/MS) methods. Oil compounds were identified by comparison to their retention time. Results of mineral extraction showed that percentage of potassium, sodium, phosphorus and nitrogen were more important in P. lentiscus and P. media than in Q. coccifera. Five major compounds were identified from essential oils of Q. coccifera, four from P. media and four from P. lentiscus. Nitrogen, which is a source of protein for insects, is produced in low concentrations in the foliage, decreasing nitrogen levels strategy for defending the plant against insect larvae. The absence of monoterpens in the foliage at P. media could explain the choice of larvae not to feed upon this host which probably confers resistance against this defoliator.