Survey of the 2006-2007 egg mass generation and the défoliation induced in 2007 bythe gypsy moth, Lymantria dispar L., in the cork oak forest of Bellif (Nefza, Tunisia)

Abstract: Mapping the defoliation caused in 2006 and 2007 by the gypsy moth Lymantria disparin the cork-oak forest of Bellif showed that the infestation mainly spread eastward. The localtopology and the direction of the wind, blowing predominantly from north-west, induced thespreading of the defoliation toward the inside of the forest, on the opposite of the egg massdistribution gradient. An average of 15 egg-masses per tree was enough to induce a completedefoliation of the study site in 2007, notably due to a good phenological concordance betweencaterpillar hatching and oak leaf bud opening. The size of the egg masses (29.25 ± 12.70mm inaverage) related to a high number of eggs (560 ± 242 eggs per cluster in average) as well as theabsence of any oophagous parasioid were characteristic factors of a population in progradation.