Defoliation of wild native box trees (Buxus sempervirens): Does box rust (Puccinia buxi) infection influence herbivory, survival and growth of the invasive Cydalima perspectalis?

Abstract

The invasive box‐tree moth Cydalima perspectalis causes damage to horticultural box trees (Buxus spp.) in private gardens and parks in Europe and defoliation of large areas of European native box trees Buxus sempervirens, which grow in the understorey of deciduous forests. In some parts of their distribution area, wild native box trees are infected by the box rust Puccinia buxi, a fungus which does not occur in the native range of C. perspectalis. We examined whether the infection of P. buxi deters grazing by C. perspectalis in 31 wild box‐tree stands in forests in north‐western Switzerland and south‐western Germany. On average, 82.4% of the box trees were infested by P. buxi (among‐site variation 20%–100%), or 18.5% of their leaves. Linear mixed‐effect (LME) models revealed that the percentage of rust‐infected leaves was influenced by the local box‐tree density and the slope aspect of the forest site. 9.5% of the leaves showed grazing damage by C. perspectalis. LME showed that the percentage of leaves with grazing damage was affected by the elevation of the site and the percentage of rust‐infected leaves. The effect of box rust infection on food choice and larval performance (survival and growth rate) was examined in two experiments. In food‐choice tests, larvae of C. perspectalis did not show any preference for uninfected or rust‐infected box‐tree leaves and consumed similar amounts of leaf tissue of either type. However, when larvae were reared on leaves with three different degrees of P. buxi‐infection (and uninfected leaves as control), both survival and growth rate decreased with increasing degree of rust infection. This indicates that larval performance of C. perspectalis is reduced by the box rust. In the case of an outbreak of C. perspectalis, however, larvae may indiscriminately defoliate wild box trees.

Diapause and biological cycle of Cydalima perspectalis (Walker) in the eastern Pyrenees

“…In areas with higher altitudes than those in this study, decreased temperatures in July or August will limit the larval population by increasing the diapause induction of the offspring of the first generation of adults. This first generation will depend on winter mortality factors affecting the diapausing larvae, little known so far as could be entomopathogenic fungi‐ or plant‐associated microorganisms (Baur et al, ). The survival of natural boxwood in the studied area will depend on its ability to regrow one to two years after defoliation and on the adaptation of several indigenous natural enemies of the region to feed on C. perspectalis .…”

“…Zamani, Farahani, Farashiani, Salehi, and Samavat () found larvae infected by Beauveria bassiana (Balsamo) in Iran. Recently, Baur, Jung, and Rusterholz () found that the performance of the C, perspectalis larvae decreased when they fed on box leaves infected with the box rust, Puccinia buxi (DC). Finally, Peterlin, Rodic, and Trdan () mention predation by birds in Slovenia.…”

Host-mediated, cross-generational intraspecific competition in a herbivore species

“…Even if prior herbivory induced the production of chemical defenses, it is possible that this did not exert any particular pressure upon females for choosing undefended leaves or plants on which to oviposit, as their offspring would have been able to cope with it. Last, BTM larvae proved to be unable to distinguish between box tree leaves infected or not by the box rust Puccinia buxi, while their growth is reduced in the presence of the pathogenic fungus (Baur et al, 2019). Altogether, these results suggest that BTM female moths are not influenced by the amount of intact leaves and probably not either by their chemical quality when choosing the host plant, perhaps because of their strong ability to develop on toxic plants.…”

Host-mediated, cross-generational intraspecific competition in a herbivore species

“…Even if prior herbivory induced the production of chemical defenses, it is possible they this did not exert any particular pressure upon females for choosing undefended leaves or plants on which to oviposit, as their offspring would have been able to cope with it. Last, BTM larvae proved to be unable to distinguish between box tree leaves infected or not by the box rust Puccinia buxi , while their growth is reduced in the presence of the pathogenic fungus (Baur et al, 2019). Altogether, these results suggest that BTM female moths are not influenced by the amount of intact leaves and probably not either by their chemical quality when choosing the host plant, perhaps because of their strong ability to develop on toxic plants.…”