Biocontrol agent impacts on Tradescantia fluminensis.

Abstract

The aims of my study were to measure the impact of four biological control agents (Neolema ogloblini - leaf beetle, Neolema abbreviata - tip beetle, Lema basicostata - stem beetle, and the fungus Kordyana brasiliensis) on the growth of Tradescantia fluminensis, a weed of conservation areas in New Zealand. I also aimed to measure the interactions among biological agents, in order to understand whether having multiple species agents would cause additional impact on the target weed. I did this by running a glasshouse experiment with combinations of agents applied to potted plants, a similar outdoor experiment, and field releases to measure agent impacts on the weed. From September 2020 to March 2021 I ran the glasshouse experiment with 139 tradescantia plants (control group + ten treatments) and the outdoor experiment with 43 plants (control group + five treatments). The potted tradescantia with biological agents were enclosed in mesh bags to prevent escape and cross-contamination. After about eight weeks I counted the surviving beetles, harvested the plant shoots, measured the leaf area with a leaf area machine, and dried the shoots for 48 hours in ovens at 65 C in order to obtain final shoot dry weight. I also took pictures of the plants before treatment which were used to estimate the starting leaf area and starting dry weight of each plant. These data were used to calculate the relative growth rates (RGR) for leaf area and dry weight (in cm²/cm²/day and g/g/day).

The results showed that treatments leaf, tip, stem and leaf*stem caused a significant reduction in tradescantia relative growth rates. I did not find any additional damage for treatments with multiple biological agents. In this study the biological agent Kordyana brasiliensis did not affect tradescantia growth. The releases done around Christchurch showed that the beetles had established at many of the sites but were not yet causing obvious reductions in tradescantia growth.

The results found in this thesis are promising that these biocontrol agents may eventually be effective in controlling tradescantia.