Do local enemies attack alien and native Impatiens alike?

Abstract

The enemy release hypothesis (ERH) attributes the invasive behavior of some alien species to decreased pressure from natural enemies, as they have been left behind in the hosts' native range. The majority of research supports this idea, but some studies confirm it only partially or even contradict it. Here, we present the results of ERH tests of three Impatiens species studied in southern Poland in 2010-2011. Two of them are alien and invasive in Europe (Impatiens glandulifera, I. parviflora) and one is native (I. noli-tangere). We compared the three species in terms of the percentage of all leaves showing symptoms of disease and/or damage, and also the number of pests recorded on the monitored plants.In 1071 individual plant controls, we assessed 17 180 leaves, 7552 of which showed symptoms of disease/damage, and we recorded 5721 invertebrates, 5220 of them were pests. Rusts and spots were the predominant symptoms and Aphidoidea were the dominant group of pests. Comparisons of the two alien and one native Impatiens did not confirm the ERH in 90% of the performed tests. Most of the differences between the species were not significant, and most of the significant ones contradicted the ERH. The only results confirming the ERH were found in comparisons between I. parviflora and I. noli-tangere. The tests between two alien species showed that I. parviflora was under higher pest pressure, while I. glandulifera had more disease and damage symptoms, thus, plant-enemy relations differed between the two balsams. In summary, the presented results add evidence that the success of some alien species may depend on factors related to biotic and/or abiotic conditions in ways that are not explained by the enemy release hypothesis.

Plant palatability and trait responses to experimental warming

“…We selected this plant group because it is a species-rich group with many species co-occurring in similar habitats along wide altitudinal ranges with a strong temperature gradient 24 . In addition, the interactions of several species from the genus Impatiens with herbivores have been previously intensively studied 25,26 . For example, Gruntman et al 25 recorded resistance to the generalist herbivore coupled with production of specific secondary defence compounds at I. glandulifera.…”

Biological flora of Central Europe: Impatiens glandulifera Royle

“…glandulifera experiences much lower levels of leaf damage by natural pests and invertebrate herbivory in invasive UK populations (<15% of leaves damaged) than in native Indian populations (up to 65% of leaves damaged) (Tanner et al, 2008(Tanner et al, , 2014b. Recent field studies in Poland, however, found similar levels of herbivore/pest damage of I. glandulifera leaves than of (native) I. noli-tangere leaves (Najberek et al, 2020a(Najberek et al, , 2017. The pressure of herbivores/pests varied across several Central European populations, with old populations (established 65-85 years ago) subject to higher levels of leaf damage and aphid pressure than recently established populations (5-25 years old) (Gruntman et al, 2017).…”

“…in the Polish Tatra Mountains nonetheless showed that respectively 58% and 45% of leaves showed at least one disease or damage symptom. Observed symptoms included spots, necrosis, mines, discoloration, deformation, wilting and herbivory damage (Najberek et al, 2020a(Najberek et al, , 2017. Experimental work using fungicide and insecticide treatments suggest that generalist invertebrate herbivores and pests have little negative effects on I. glandulifera's fitness in Switzerland (Burkhart and Nentwig, 2008).…”

Insect pests and their role as biocontrol agents&nbsp;on populations of Impatiens glandulifera in Bulgaria &ndash; a case study

“…Najberek et al (2017) provide evidence, that in the mountains in the Czech Republic, the invasive alien species I. glandulifera tended to be more attacked from pests than the native species Impatiens noli-tangere L. In another garden experiment by Kollmann et al (2007), for the first time a viral infection found by I. glandulifera in various European regions has been reported, which has led to reduce above-ground biomass of the invasive species. Based on the above statements, we tend to accept Najberek's (2017) claim, that the success of the ЕRH depends on various factors, the significance of which varies depending on the biotic and / or abiotic conditions of the place where the plant is introduced. The latter raises the question of establishing the role of local enemies on the Himalayan balsam populations in its invasion areas.…”