Corresponding author: Eric Darrouzet ( eric.darrouzet@univ-tours.fr ) Academic editor: Travis Glare
© 2018 Marie-Anne Wycke, Romaric Perrocheau, Eric Darrouzet.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Wycke M-A, Perrocheau R, Darrouzet E (2018) Sarracenia carnivorous plants cannot serve as efficient biological control of the invasive hornet Vespa velutina nigrithorax in Europe. Rethinking Ecology 3: 41-50. https://doi.org/10.3897/rethinkingecology.3.28516
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Vespavelutinanigrithorax, an invasive species, a direct result of increased trade and climate change, is spreading rapidly in Europe and endangering entomofauna in general and more alarmingly honeybee (Apismellifera) populations, and therefore their pollination services. All traps used now, to try to control this species, seem to be not efficient enough and non-selective. However, in the current context of massive disappearance of insects in general, it is urgent to find means of protection for the entomofauna. While no selective trapping is still occurring, we performed a pilot study to test a carnivorous plant as a potential biocontrol tool to trap V.velutina. In our study, we analyzed the hornet-capturing ability of two Sarracenia hybrids (S.juthatipsoper and S.evendine) on a 2-years period (2015 and 2016). Our results show that these plants trapped more dipterans than other taxa, and they do not attract many hornets. In such condition, both Sarracenia hybrids cannot therefore be used in a mass trapping system, because they are not selective, and too few hornets are trapped. To maximize captures of V.velutina while minimizing captures of non-target species, other systems need to be thus developed, as traps using hornet pheromone-based baiting.
Invasive species, yellow-legged hornet, selective trap, biocontrol, pest management, Sarracenia sp.
Biological invasions have occurred frequently around the world, especially in recent decades, mainly due to the increase in human travel and international trade (
Around 2004, the yellow-legged hornet, Vespavelutinanigrithorax, was accidentally introduced into France from China (
The use of baited traps is generally regarded as the best means to control wasps, although uncontrolled mass trapping induces side effects on non target species (
To replace classical traps which demonstrated their non-selectivity (
Our study focused on two Sarracenia hybrids: S.juthatipsoper and S.evendine. They were collected in the botanical garden of Nantes (GPS coordinates 47°13'10"N, 1°32'34'W). These hybrids produce new urns in autumn that will persist and remain active until the emergence of new urns in May. More than 50 plant stools were present in a peat bog of about 60 square meters. Samples were collected twice: 132 and 120 urns were randomly collected on the peat bog surface in October 2015 and 2016 respectively. Since the plants are cultivated in a relatively small numbers and are destined to recreate a bog habitat for the gardens’ visitors, it was problematic to sample a larger number of urns for our experiment. Thus, to maximize our sample size while limiting our impact on the bog, we pooled the samples from the two hybrids. Before being opened with a scalpel, urns were frozen at -20 °C for 24 hours to kill any insects inside. The insects inside urns were counted and identified to order.
Technicians from the city hall of Nantes and from Bionéo (sarl Prophy Végétal) located Vespavelutina nests in and around the botanical garden of Nantes. These data were useful to determinate if Sarracenia plants we collected could be present in the foraging area of hornet colonies. According to their flight capacities, workers can forage in an area of 2.000 m around their nest (
We performed data analyses with the software Rstudio (1.0.143 version – 2009–2016 RStudio, Inc.). Analyses were used to compare the relative abundances of the insect orders found in the urns (Diptera, Hymenoptera, Lepidoptera, Coleoptera and Heteroptera), and in Hymenoptera (Vespavelutina, V.crabro, Vespula sp., Apis sp. and Bombus sp.). To compare the abundances of the insect within each sampling year, we used a chi-squared test and a Wilcoxon signed-rank test for paired samples. We used a Bonferroni correction to reduce type I errors per year (corrected α = (0.05/10) = 0.005).
In 2015 and 2016, several Vespavelutina colonies were located in Nantes city, and particularly in the botanical garden (Figure
Heatmap of Vespavelutina’s nests observed in 2015 (A) and in 2016 (B). The green circle shows the location of the botanical garden where plants were collected.
Average number of insects per urns in 2015 (light grey) and 2016 (dark grey). Letters indicate the statistical differences at p=0.005 (Wilcoxon test with Bonferroni correction).
Average number of Hymenoptera per urns in 2015 (light grey) and 2016 (dark grey). Letters indicate the statistical differences at p=0.005 (Wilcoxon test with Bonferroni correction).
The relative abundance of insect orders was analyzed for both experimental years (chi-squared test): in 2015, with Heteroptera (one individual), X-squared = 2915.5, df = 4, p-value < 2.2e-16, and without the heteropteran individual, X-squared = 2056.2, df = 3, p-value < 2.2e-16; in 2016, X-squared = 2328, df = 4, p-value < 2.2e-16 and X-squared = 1641.3, df = 3, p-value < 2.2e-16 with or without the heteropteran individual respectively. The comparison of the relative abundance of insect orders for both years combined without heteropteran individuals (one individual per year) showed differences (X-squared = 169.44, df = 3, p-value < 2.2e-16). In 2015 and 2016, dipterans trapped by Sarracenia plants were significantly more common than any other taxa (Table
Comparison (Wilcoxon test) of relative abundances of some insect orders (Diptera, Hymenoptera, Lepidoptera, Coleoptera and Heteroptera) trapped by Sarracenia hybrids in 2015 and 2016.
2015 / 2016 | Diptera | Hymenoptera | Lepidoptera | Coleoptera |
---|---|---|---|---|
Hymenoptera | Z=672, P<0.001 for both year | |||
Lepidoptera | Z=16924, P<0.001 for both year | NS / Z=9678.5, P<0.001 | ||
Coleoptera | Z=16968, P<0.001 for both year | NS / NS | NS / NS | |
Heteroptera | Z=17290, P<0.001 for both year | NS / NS | NS / NS | NS / NS |
Comparison (Wilcoxon test) of relative abundances of Hymenoptera trapped by Sarracenia hybrids in 2015 and 2016.
2015 / 2016 | Vespa velutina | Vespa crabro | Vespula sp. | Apis sp. |
---|---|---|---|---|
Vespa crabro | Z=10810, P<0.001 / Z=7620, p=0.007 | |||
Vespula sp. | Z=9571, p=0.07 / Z=7560, p=0.03 | Z=7488, p=0.002 / NS | ||
Apis sp. | Z=10230, P<0.001 / NS | NS / NS | NS / NS | |
Bombus sp. | Z=11365, P<0.001 / NS | NS / NS | Z=10503, P<0.001 / NS | Z=9903, P<0.001 / NS |
Our results show that the carnivorous Sarracenia hybrids we analyzed do not attract a lot of V.velutina hornets, in spite of the presence of several hornet colonies at proximity. Indeed, V.velutina represented just a small percentage of the large numbers of insects captured in the plant urns. In 2015 and 2016, only 4.3% and 0.7% of all the insects captured were V.velutina, respectively. Hymenopterans were infrequent; flies were the main prey. Indeed, this result is classical, as ants and flies are the two main prey groups in insectivorous plants (
Other species of Sarracenia or Nepenthes for example should be investigated to determine if these species can trap more hornets than the Sarracenia hybrids S.juthatipsoper and S.evendine. The quantification of their attractiveness and the identification of visual and/or olfactory cues they used need to be performed. The aim will be to develop a specific biomimetic trap for V.velutina. However, the genus Nepenthes uses highly diverse means to attract and capture many different types of insects (Moran et al. 1999
In seeking control solutions, it is difficult to strike the right balance between controlling the invasive hornet, its effects on native pollinators, and limiting the deleterious effects of traps on entomofauna. None of the traps currently used seem to show specificity for V.velutina. Baited traps are generally regarded as the best means for controlling wasps and are commonly used, although concerns about their use have been raised because they can have significant effects on non-target species (
MAW analyzed insects traped by plants and wrote the manuscript, RP collected plant samples, ED developed the concept, designed the manuscript and reviewed it. MAW: 45%, RP: 10%, ED: 45%.
Authors | Contribution | ACI |
---|---|---|
MAW | 0.45 | 1.636 |
RP | 0.10 | 0.222 |
ED | 0.45 | 1.636 |
We gratefully acknowledge J. Pearce for her English editing services, P. Gacel from Bioneo and R. Salvador from Nantes city hall for the V.velutina nests location data in Nantes. This study was supported by funding from the Centre-Val de Loire region (a French regional grant) for our FRELON 2 project. M-A. Wycke received support from Vetopharma.