Impact of Aceria alhagi (Acari: Eriophyidae) as a potential biological control agent on the invasive weed Alhagi maurorum (Fabaceae) in its native range.

Camelthorn, Alhagi maurorum Medik. (Fabaceae, Leguminosae), a native component of the Asian flora, is invasive in Australia, South Africa and the USA where it is considered a noxious weed in several states. To date there is no biological control program against this weed; however, initial investigations into potential biocontrol agents revealed an eriophyid mite, Aceria alhagi Vidovic & Kamali, causing considerable damage in the native range. The mite attacks the growing tips as well as the flowers of the plants, not only reducing height and plant vigor but also reducing seed set. To assess the host range and impact of this potential biological control agent, on the target weed, no-choice tests as well as an open-field impact experiment were conducted at the research farm of the School of Agriculture, Shiraz University, Shiraz, Iran, over 2 years (2018 and 2019). Results from the no-choice tests suggest that A. alhagi poses negligible risk to the non-target plants tested in this study. In the first year of the open field impact test, plants did not flower; however, plant height was significantly reduced by mite attack. In the second year, significant reductions in plant biomass (26%), seed production (95%) and photosynthesis (53%) were observed in response to mite attack that would potentially limit the competitiveness of camelthorn as well as long-distance dispersal through seed in the invaded range. These results suggest that A. alhagi is a promising candidate for the biological control of camelthorn and should be prioritized for any future studies, expanding on the host range testing and safety.

Unraveling the biogeographic origins of the Eurasian watermilfoil (Myriophyllum spicatum) invasion in North America.

PREMISE OF THE STUDY: Using phylogeographic analyses to determine the geographic origins of biological invaders is important for identifying environmental adaptations and genetic composition in their native range as well as biocontrol agents among indigenous herbivores. Eurasian watermilfoil (Myriophyllum spicatum) and its hybrid with northern watermilfoil (M. sibiricum) are found throughout the contiguous United States and southern Canada, forming one of the most economically costly aquatic plant invasions in North America, yet the geographic origin of the invasion remains unknown. The objectives of our study included determining the geographic origin of Eurasian watermilfoil in North America as well as the maternal lineage of the hybrids. METHODS: DNA sequence data from a cpDNA intron and the nrDNA ITS region were compiled for accessions from 110 populations of Eurasian watermilfoil and hybrids from North America and the native range (including Europe, Asia, and Africa). Datasets were analyzed using statistical parsimony and Bayesian phylogenetics to assess the geographic origin of the invasion. KEY RESULTS: The two Eurasian watermilfoil cpDNA haplotypes in North America are also found from China and Korea, but not elsewhere in the native range. These haplotypes did not overlap and were limited in native geographic range. The ovule parent for hybrids can come from either parental lineage, and multiple haplotypes from both parental species were found. CONCLUSIONS: The geographic origin of this prolific aquatic plant invasion of North America is in Asia. This provides critical information to better understand the invasion pathway and inform management into the future.