Hot and hungry: Climate warming increases overwintering survival and enhances herbivory of alligator weed flea beetles.
Lu, X., Siemann, E., Shao, X., Wei, H., & Ding, J. (2013). Climate warming affects biological invasions by shifting interactions of plants and herbivores. Global change biology, 19(8), 2339-2347. PDF.
Summary
Alligator weed (Alternanthera philoxeroides) is a worldwide noxious weed that forms dense mats of floating vegetation that choke out waterways and natural areas. Alligator weed is projected to expand into the mid-Atlantic United States (U.S.) with climate change. Alligator weed can be effectively controlled by the alligator weed flea beetle, Agasicles hygrophilia, a biocontrol agent that feeds exclusively on its leaves and stems. Where the species co-occur, biocontrol beetles can successfully suppress alligator weed populations. However, the biocontrol beetle is more sensitive to cold winter temperatures than alligator weed, suggesting that climate change could affect biocontrol efficacy.
Lu et al. (2013) used field experiments in China, where alligator weed is also invasive, to examine how warming temperatures may affect the performance of alligator weed and its biocontrol beetle. As expected based on physiological tolerance, alligator weed has a broader geographic range than its biocontrol beetle, resulting in weaker biocontrol efficacy in colder climates (higher latitudes). Warming experiments increased the abundance of biocontrol beetles but had no effect on the performance of alligator weed.
Overall, warming enhanced the impact of herbivory by biocontrol beetles, increasing alligator weed mortality by 147% compared to ambient temperature conditions. This suggests that warming may improve the efficacy of biocontrol beetles, decreasing current populations of alligator weed at higher latitudes. However, if alligator weed is also able to shift its range with climate change, the current spatial mismatch between alligator weed and its biocontrol agent may remain.
Take home points
Warming increased overwintering survival, population sizes, and enhanced herbivory in the biocontrol agent but had no effect on the performance of alligator weed.
Herbivory by biocontrol beetles was much greater under warming conditions, significantly reducing the total, root, and shoot mass of alligator weed.
Warming conditions may improve overall biocontrol efficacy, although current spatial mismatches between biocontrol agent and host may still persist with climate change.
Management implications
Biocontrol efficacy may benefit from climate warming if warming allows for higher biocontrol beetle overwintering survival and enhanced herbivory.
Warming may allow biocontrol agents to expand their range, potentially reducing spatial mismatches between biocontrol and host - particularly if the biocontrol agents are cold temperature limited.
However, spatial mismatches may still occur as hosts also can shift their ranges with climate change. In these areas, alternative management strategies may still be necessary to manage target host populations.
Future biocontrol efforts should focus on how climate change may impact both biological control agents and their target hosts as trophic relationships are important for determining the outcome of biocontrol as a management strategy.
Read more about this topic: Diaz et al. 2012, Sun et al. 2020
Keywords
Alligator weed, Alligator weed flea beetle, Biocontrol, Climate warming, Field experiment, Management efficacy, Noxious weed, Changing biotic interactions (competitiveness)