Thesis Defence: Revisiting Canada’s oldest invasive plant biological control system
July 21 at 9:00 am - 1:00 pm
Andres Mancera Barreto, supervised by Dr. Jason Pither, will defend their thesis titled “Revisiting Canada’s oldest invasive plant biological control system – Exploring ecological relationships influencing physical and metabolic characteristics of the invasive Hypericum perforatum” in partial fulfillment of the requirements for the degree of Master of Science in Biology.
An abstract for Andres Mancera Barreto’s is included below.
Defences are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.
Abstract
Hypericum perforatum is an invasive plant introduced to North America in the 1700s. H. perforatum thrives in open, sunny areas, and produces toxic metabolites, hypericins and hyperforin, that cause health problems in herbivores. The plant’s toxicity has resulted in considerable expenses to ranchers. In response, Canada developed its first biological control program in the 1950s, introducing seven specialized insect herbivores from H. perforatum’s native range, of which five established successfully. Several decades after the successful control of H. perforatum across Canada’s grasslands, there are rising questions regarding the effectiveness of the insects in British Columbia as new reports claim observing persistent plant populations, especially at higher elevations. To identify factors causing possible variation in biocontrol effectiveness we quantified the phenology, abundance and morphology of 30 plants and the secondary metabolic profiles at the flowering stage of 5 individuals per site, across 17 populations exposed to different geo-climatic conditions weekly from April to December 2024. We also measured the abundance, phenology, identity and herbivory of the released insects on the plants and across all sites to identify variations in plant responses to biological pressures. H. perforatum presents phenological differences associated with growing season length, aspect and latitude. Increased insect presence and herbivory are associated with earlier plant sexual reproduction and senescence. Plants in populations facing east and west present greater metabolite concentrations than other populations and biological control abundance is associated with lower hyperforin concentration. We observed a trade-off between hyperforin and hypericin in H. perforatum, with plants showing higher concentrations of one over the other. Our results flag candidate variables that may contribute to variation in biocontrol effectiveness, particularly abundance and herbivory, highlighting the need to investigate insects’ preferences to ensure future effective control. Although our results explore associations and are observational, biocontrol appears to remain effective as plant coverage was low across all of our sites, with no site averaging more than 25% coverage, and plant absence was positively associated with increasing herbivory.
