The open bar is closed: restructuration of a native parasitoid community following successful control of an invasive pest

Abstract

When an invasive species establishes in a new area and reaches high densities, some antagonists may benefit from this bonanza situation. How such a newly formed community may then be challenged after the regulation of the invaders by external outputs -e.g. the deliberate introduction of specialized natural enemies -remains however poorly documented. To investigate this issue, we used the case study of the invasion of the Asian chestnut gall-wasp Dryocosmus kuriphilus Yasumatsu in France and its subsequent control by the exotic parasitoid Torymus sinensis. From the survey of 26 locations during 5 years after the T. sinensis introduction, we analyzed how the patterns of co-occurrence between the different native parasitoid species changed through time. Our results demonstrate that native parasitoid communities experienced increased competition as the D. kuriphilus levels of infestation decreased. During the last year of the survey, two alternative patterns were observed: either native parasitoid communities were almost inexistent, or they were finally dominated by one main parasitoid: Mesopolobus sericeus. We observe that the two patterns correlate with the habitat and that they may be explained by environmental features such as differences in the initial states of the native community structure. These results highlight how the "boom-and-bust" dynamics of an invasive pest followed by successful biological control can deeply alter the structure of native communities of natural enemies.

Raise and fall of an invasive pest and consequences for native parasitoid communities

“…This is encouraging considering the growing impact of biological invasions and insect pest outbreaks, but also the need to implement efficient, yet sustainable strategies for crop protection. Future studies would show at what extent observations by Muru et al [5] are generalizable over longer time periods or other model systems. Noticeably, better understanding about population dynamics and interactions with the broader community of hosts available across habitats should allow to fine-tune predictions about parasitoids' response to fluctuating resources.…”

“…To view a copy of this license, visit http://creativecommons.org/licen ses/by-nd/4.0/ communities, immediately before, and up to five years following the introduction of its natural enemy T. sinensis. Using co-occurrence and clustering analyses, Muru et al [5] demonstrate that the invasion and the consecutive (efficient) control of the Asian chestnut gall wasp by the parasitoid T. sinensis have a significant impact on the structure of local parasitoid food webs. In particular, following decline in the Asian chestnut gall wasp's populations, native parasitoids markedly switched to alternative hosts, most likely due to their respectively higher relative abundances.…”

“…Despite their capacity to adaptively switch their foraging behaviour, the response of the native parasitoid communities to the new, unfamiliar resource was not fast enough in order to contain the primary outbreak under an appropriate damage threshold, thus requiring the introduction of the more specialized parasitoid T. sinensis. Nevertheless, based on current ecological theory, results presented by Muru et al [5] suggest that the response of native parasitoid community to fluctuating host dynamics -i.e. shifts in parasitoid foraging behaviour based on their traits -could be predictable.…”

“…[4]). In their study, Muru et al [5] took advantage of an existing biological control program focusing on the Asian chestnut gall wasp Dryocosmus kuriphilus, an invasive (and highly damaging) pest of chestnut trees. The species is currently a successful invader in many geographic regions, including southern France, where local parasitoid communities failed to provide an adequate control since its widespread establishment in 2010 [6].…”