Effects of Atlas cedar (Cedrus atlantica) defoliation on performance of the pine processionary moth (Thaumetopoea pityocampa)

Abstract

The pine processionary moth (Thaumetopoea pityocampa) is an important defoliating insect of native cedar stands in Northern Africa. In 2002 and 2003, we studied the size of needles of Atlas cedar trees that had been defoliated or not in the previous year, and compared the oviposition preference and larval performance of processionary moth on these two types of trees in cedar stands of central Algeria. Needle length and their number per needle cluster were twice as high on non-defoliated trees than on defoliated trees. There were about ten times fewer egg batches on defoliated than on non-defoliated trees in both study years. Young larvae raised in the laboratory on the foliage of previously defoliated trees were smaller compared to those fed on the foliage from healthy trees. Larval colonies transferred to trees in the field showed two times higher mortality on defoliated trees. It was concluded that the decline in population density in defoliated stands often observed after outbreaks results both from the fact that the female moths avoid laying their eggs on defoliated trees and the lower performance of larvae which later feed on the new-grown needles.

Genetic differentiation of the pine processionary moth at the southern edge of its range: contrasting patterns between mitochondrial and nuclear markers

“…Finally, host plant range fragmentation could have influenced the genetic structure, as may be suggested by SAMOVA results, although more precise data about past host plant distribution would be needed to confirm this hypothesis. The recent finding of high population densities on C. atlantica in the Algerian mountains (Sbabdji and Kadik ) is likely the results of a shift to high elevation from the lower pine forests, although it may indicate that this conifer is highly suitable to the pine processionary moth and could have been used in the past in high‐elevation refugial areas, in the same manner that mountain pines played a role in the recent history of the species in Europe (Rousselet et al. ).…”

Climate change and insect pest distribution range.

“…Novel host tree species encountered during the expansion are suitable for larval development (Stastny et al, 2006), and thus it seems likely that range expansion will continue as long as temperature will increase. At the southern edge of the distribution range, in northern Africa, T. pityocampa is expanding in native mountain stands of cedar (Cedrus atlantica), threatening these endangered ecosystems (Sbabdji and Kadik, 2011), while it remains stable in the low-elevation stands of Aleppo pine (Pinus halepensis) facing the Sahara desert (Zamoum and Démolin, 2005). Bark beetles (Dendroctonus spp.)…”

Effect of periodic defoliations by Thaumetopoea pityocampa Schiff. on radial growth in cedar woodland in Chréa, Algeria

“…A small percentage of their pupae exhibit extended diapauses (Démolin, 1974;Carus, 2010). Females lay between 70 and 300 eggs (Huchon & Démolin, 1970) grouped in a single cylindrical batch on the base of one or two needles (pines) or on the bark of 1-2 cm diameter cedar branches (Sbabdji & Kadik, 2011). Larvae are gregarious throughout their development, which occurs during autumn and winter in five stages.…”

“…In Algeria, the cedar forest of Chrea national Park is one of the numerous cedar forests severely defoliated by this insect (Sbabdji et al, 2009). Although the trees grow new foliage after each defoliation (Sbabdji & Kadik, 2011), their health is not assured because their vigour can be decreased by repeated outbreak (Hartmann & Messier, 2008). The different control practices have not significantly reduced the defoliations, mainly due to the difficulty to access to the tree crowns.…”