Field Assessment of the Host Range of Aculus mosoniensis (Acari: Eriophyidae), a Biological Control Agent of the Tree of Heaven (Ailanthus altissima)

Abstract

Tree of heaven (Ailanthus altissima) is a fast-growing deciduous tree native to China, considered a serious invasive species worldwide, with several socio-economic and ecological impacts attributed to it. Chemical and mechanical methods have limited efficacy in its management, and biological controls may offer a suitable and sustainable option. Aculus mosoniensis (Ripka) is an eriophyid mite that has been recorded to attack tree of heaven in 13 European countries. This study aims to explore the host range of this mite 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. mosoniensis to be a very promising candidate for the biological control of tree of heaven.

Keywords: Aculus mosoniensis; Ailanthus altissima; biological control; eriophyid mite; host range; invasive species; tree of heaven.

Figure 1

Map of the garden plot setup for target, Ailanthus altissima and nontarget plants inoculated with Aculus mosoniensis during host-specificity tests performed in 2019 and 2020, respectively. The number of replicates for each species is reported in brackets.

Figure 2

Number of live Aculus mosoniensis per gram of plant biomass collected from the plant species tested at 34, 47, and 61 days post-inoculation, respectively, in the field experiment performed 2019.The boxes represent the first to third quartile range with the median indicated by a line across the box and the mean by crosses. Bars flanked by different letters differ significantly at p = 0.05.

Figure 3

Number of live Aculus mosoniensis per gram of plant biomass collected from the plant species tested at 36 and 63 days post-inoculation, respectively, in the field experiment performed 2020. The boxes represent the first to third quartile range with the median indicated by a line across the box, and the mean by crosses. Outliers are indicated by empty dot. Bars flanked by different letters differ significantly at p = 0.05.

Figure 4

Symptoms of Aculus mosoniensis on Ailanthus altissima: (a) leaves strongly deformed 47 days post-inoculation in 2019; (b) dried and necrotic apical part 63 days after inoculation in 2020.

Figure 5

Number of live Aculus mosoniensis per gram of plant biomass collected from Ailanthus altissima (mean ± SE) through the season in field experiments performed in 2019 and 2020, respectively. The arrows represent the inoculation day (inoc.), whereas days after inoculation are indicated in brackets flanking the bars (34, 47 and 61 days in 2019; and 36 and 63 days in 2020).