Tree of Heaven Project

Lead scientist: RFH Sforza

Presentation & context

Tree of heaven, Ailanthus altissima (Mill.) Swingle, is one of five known species of the genus Ailanthus belonging to the family Simaroubaceae.

 

Young Ailanthus altissima in southern France (Photo by RFH Sforza)

This deciduous tree is a serious threat to ecosystems in introduced areas and is listed as one of the forty most invasive woody angiosperms from 40 different genera worldwide. Tree of heaven is native to northern and central China. It was introduced to Europe in 1740 for decorative purposes, as the tree was pest and disease free, and into North America in 1781 by accident where it is now considered the second most abundant non-native tree species. It has been detected in 48 states and occupies over 86,000 ha in southern USA. Recently, the attention has been focused on eriophyid mites (Trombidiformes: Eriophyoidea), well known for their high specificity and for the impact they can due to the associated host, despite to their extremely small size. One of the promising biocontrol candidate is an eriophyid mite species associated with Ailanthus spp.: Aculus taihangensis Hong & Xue, 2005. It is originating from Asia but has been found in several European countries.

Research components

According to the impact that Aculus taihangensis is doing on Tree of heaven (See photo), it is considered very promising and a screening of it host range and impact started to release it in an area-wide biological control program in North America.

 

Leaf symptoms (rolling and yellowing) induced by eriophyid mite colony on its host, Ailanthus altissima (Photo by RFH Sforza)

We focused our research at EBCL, in partnership with BBCA Rome (www.bbcaonlus.org), on the host specificity of the eriophyid mite candidate. In 2019-20, we first explored its host range of by exposing 13 plant species, selected either for their phylogenetic and ecological similarity to the target weed or their economic importance. Shortly after inoculation with the mite, we recorded a quick decrease in mite number on all nontarget species and no sign of mite reproduction. Whereas, after just one month, the population of mites on tree of heaven numbered in the thousands, irrespective of the starting population, and included both adults and juveniles. Significantly, we observed evidence of damage due to the mite only on target plants. Due to the specificity, strong impact on the target, and the ability to increase its population to high levels in a relatively short amount of time, we find A. taihangensis to be a very promising candidate for the biological control of tree of heaven. In 2022, we added four non-target species to the test, which revealed not attacked by the mite.

 

Outdoor Host specificity testing with the eriophyid mite and a series of non target plants (Photo by RFH Sforza) 

In 2023, about ten new species will be also tested. In addition to host specificity testing, we will investigate in 2023/24 an integrative management of Tree of heaven by combining biocontrol and mechanical control.

Student involved

Chebance (Master2, 2023) 

Recent publications

Marini et al. 2021 Insects