Changes in plant architecture in Brazilian peppertree damaged by the biological control agent, Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae)

Authors: Halbritter, Dale; KARIUKI, EUTYCHUS - University Of Florida; Wheeler, Gregory; RAYAMAJHI, MIN - Former ARS Employee; MINTEER, CAREY - University Of Florida; Read, Quentin

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2023
Publication Date: 12/23/2023
Citation: Halbritter, D.A., Kariuki, E., Wheeler, G.S., Rayamajhi, M.B., Minteer, C., Read, Q.D. 2023. Changes in plant architecture in Brazilian peppertree damaged by the biological control agent, Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae). Biological Control. 188.Article c105434. https://doi.org/10.1016/j.biocontrol.2023.105434.
DOI: https://doi.org/10.1016/j.biocontrol.2023.105434

Interpretive Summary: Plants can react to insect feeding damage by changing how they grow to try to recover lost vegetation, and this may vary depending on how fertile the soil is. The problem arises in biological control where the invasive target plant grows in the wild in a variety of different soil conditions. We need to understand how this may impact the plant's ability to resist the biological control agents we release to combat them. We aimed to understand this dynamic between Brazilian peppertree and its thrips agent. A garden plot experiment was set up in which saplings received different levels of supplemental fertilizer on top of what was already naturally present in the soil. One plot was at a research station that already had high soil nitrogen and the other at a station that had 1/4 the soil nitrogen. Plant growth data were collected approximately monthly for 2 years before and 2 years after releasing the thrips. The size of the saplings increased steadily at both plots as expected, but the rate of increase was only greater for plants receiving greater supplemental fertilizer at the low nitrogen site. The thrips did not impact any of the plants at the high nitrogen site, regardless of supplemental fertilizer. In contrast, the density of stem tips at the low nitrogen site increased dramatically following thrips release and was greatest for plants with greater supplemental fertilizer. Additionally, the percentage of dead stem tips quadrupled during the second year of thrips releases, but tip mortality did not differ between supplemental fertilizer levels. Our accomplishment was confirming that soil fertility can impact agent performance on Brazilian peppertree, but that more fertility isn't always better. This will contribute to understanding and predicting how agents may perform at wild field sites in the invaded range with differing soil conditions.

Technical Abstract: Plants may compensate for herbivory damage by reallocating resources and altering growth patterns, which may be further influenced by environmental variables like nutrient availability. We compared the impacts of fertilizer applications on the growth attributes of Brazilian peppertree before and after releasing Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae), an approved biological control agent. A garden plot containing 96-103 saplings was established at each of two research sites in Florida: one site with high background soil nitrogen and one with 1/4 the background soil nitrogen. Each plant was randomly assigned a permanent fertilizer supplement (24N-8P-16K) administered bimonthly: no fertilizer n=69 (0g/L), medium fertilizer n=66 (0.8g/L), or high fertilizer n=66 (3.6g/L). Thrips were released after 22 mo and releases continued every 1-3 mo. Plant growth attributes were collected approximately monthly from October 2017 to April 2021. Crown volume and height steadily increased at both plots, but greater rates of increase were observed for plants with higher supplemental fertilizer at the lower nitrogen site. Thrips had negligible impact on plant attributes at the high nitrogen site. In contrast, the density of stem tips at the low nitrogen site increased dramatically following thrips release and was greatest for plants with high supplemental fertilizer. Additionally, the percentage of dead tips quadrupled during the second year of thrips releases, but tip mortality was greatest for plants with medium supplemental fertilizer. Fertilized plants produced more unseasonal lateral vegetative buds after thrips attack, providing new resources to sustain thrips numbers. Soil nitrogen levels at natural field sites may therefore impact thrips performance.