11 May 2026

Native and Invaded-Range Surveys Provide Mixed Support for Enemy-Release of Nymphoides Peltata in the Invaded Range

Abstract: Natural or anthropogenic movement of plant species outside their historical ranges may result in exposure to new environmental conditions and a lack of natural enemies, thus promoting their establishment and spread into new areas. A biogeographical comparison of native and invasive populations can provide insight into the mechanisms of successful invasions and guide effective management strategies, such as biological control, by targeting plant traits that promote invasiveness. We studied the Eurasian aquatic plant, Nymphoides peltata, in situ in the native (China, Korea) and invaded (USA) ranges to determine whether there were differences in natural enemy attack rates (percent leaf damage, frequency of leaf herbivory or disease), productivity (plant cover, reproduction), and leaf traits (leaf elemental content, leaf toughness, dry matter content, specific leaf area) between areas. We also investigated whether there was evidence of a tradeoff between natural enemy attack and growth or reproduction, as would be predicted by invasion theory. Plant cover (23–29 % higher) and reproductive output (eight times more seeds / m2) were consistently higher in the invaded range. Leaf traits consistently differed between ranges, which we would expect if plants in the invaded range had fewer herbivores or other pests. The amount of leaf damage present was similar between ranges, but the frequency of herbivory was 50 % greater, on average, in the native than invaded range. Although we did not quantify suppression of N. peltata by natural enemies, we found evidence of more frequent herbivory in Asia and reduced reproduction and plant cover compared to the USA, which supports further investigation into viability of biological controls.

11 May 2026

High Temperatures will Likely Limit Establishment Success of the Brazilian Peppertree Thrips, Pseudophilothrips Ichini (Thysanoptera: Phlaeothripidae) in the USA, Despite Variation in Microhabitat Thermal Environments

Abstract: Biological control of the invasive tree, Schinus terebinthifolia Raddi, is under investigation to improve conservation and restoration of native plant communities in the continental USA. Release and monitoring of the Brazilian peppertree thrips, Pseudophilothrips ichini, is ongoing in multiple states and climate zones but establishment has been variable. In particular, establishment has not been confirmed in hot, southern Texas locations despite release of over 150,000 thrips across four locations since 2022. To understand whether thermal limitations may preclude use of P. ichini in some regions, we investigated upper and lower thermal limits of P. ichini. We measured upper limit of chill injury zone (ULCIZ) and lower limit of thermal injury zone (LLTIZ) in the laboratory under multiple combinations of temperature and exposure duration then modeled spatial variation in survival based on detailed weather data over 20 years. Additionally, we documented microhabitat variation in temperature extremes in three release sites in south Texas to evaluate whether thermal refugia exist due to variation in microhabitat conditions. Based on LLTIZ and ULCIZ, thermal injury accumulates rapidly at temperatures above 33.08 ± 0.15 ◦C and more slowly at decreasing temperatures below 7.85 ± 0.82 ◦C. Temperatures within the canopy of S. terebinthifolia in the field varied widely and produced a range of predicted mortality, with temperatures at the base of trees that were more moderate in both summer and winter. We determined that, based on the current distribution of S. terebinthifolia in the USA, climate suitability differs between states. Suitability of Florida locations was deemed highly to moderately suitable across seasons, but most Texas locations were unsuitable, including previous release locations in south Texas. These findings suggest releases should continue through most of Florida, in areas of southern California, and locations along the northern gulf coast of Texas. Additionally, augmentative releases of P. ichini during mild seasons may provide opportunities for use of this biological control agent to manage S. terebinthifolia in Texas.

24 Mar 2026

Intraspecific Variation in Rapid Cold Hardening and Acclimation of the Adventive Parrot’s Feather Weevil, Phytobius (=Parenthis) Vestitus, in the Southern USA

Abstract: Plasticity in thermal tolerance, expressed through acclimation or rapid cold hardening, for example, provides organisms with a mechanism to deal with unexpected and often rapid changes in the thermal environment. Spatial variation in response to high or low temperatures may occur due to evolutionary adaptation, particularly if a fitness increase coincides with the ability to respond quickly to environmental change. Thermal tolerances of beneficial insects used for biological control dictate where and under what thermal conditions the insects will provide value to management programs. We investigated two aspects of thermal phenotypic plasticity in response to thermal conditions using four populations of the adventive parrot’s feather weevil, Phytobius vestitus, from the southern USA. At low temperatures, we determined the presence and variation in rapid cold hardening in one of the four populations using two temperature ramping rates. In contrast, at high temperatures, all P. vestitus populations displayed a significant heat acclimation response, documented as elevated loss of motor control and motor function temperatures after acclimation. Thus, observed patterns of plasticity differed between high and low temperatures and among source populations. These results demonstrate the presence of geographic variation in phenotypic plasticity in response to thermal environments and emphasizes the need to consider plasticity when selecting climate-adapted populations of biological control agents.

23 Sep 2021

Field Site Analysis of Giant Salvinia Nitrogen Content and Salvinia Weevil Density

Abstract: In 2012, a giant salvinia (Salvinia molesta Mitchell) biological control project was initiated in Louisiana. Although similar quantities of salvinia weevils (Cyrtobagous salviniae Calder and Sands) were released at all sites, weevil densities were highly variable among sites. Additionally, signs of plant nitrogen depletion (yellowing plants) were observed at some sites. Because it is well known that plant nutrition can affect the success of a biocontrol agent because of slowed development and/or reduced fecundity, the correlation between giant salvinia nitrogen content and Salvinia weevil density was investigated during the growing seasons of the second and fourth years. During 2013, weevils were reintroduced to sites, and the magnitude of adult weevil density increase varied by site. Giant salvinia nitrogen content varied among sites and sampling dates. Upper Big Break plants had greater nitrogen than all other sites during 75% of sampling dates. Additionally, adult and larval densities were significantly correlated to plant nitrogen content. During 2015, trends were less distinct and weevil densities and nitrogen content varied based on the interaction between sampling date and site, but a significant correlation was not detected. Results confirmed published reports of the importance of plant nitrogen content to salvinia weevil productivity. Additional studies are warranted to evaluate and understand the role of nitrogen at giant salvinia biocontrol field sites.

24 Aug 2021

Geographic and Genetic Variation in Susceptibility of Butomus umbellatus to Foliar Fungal Pathogens

Abstract: Large-scale patterns of plant invasions may reflect regional heterogeneity in biotic and abiotic factors and genetic variation within and between invading populations. Having information on how effects of biotic resistance vary spatially can be especially important when implementing biological control because introduced agents may have different Impacts through interactions with host-plant genotype, local environment, or other novel enemies. We conducted a series of field surveys and laboratory studies to determine whether there was evidence of biotic resistance, as foliar fungal pathogens, in two introduced genotypes (triploid G1, diploid G4) of the Eurasian wetland weed, Butomus umbellatus L. in the USA. We tested whether genotypes differed in disease attack and whether spatial patterns in disease incidence were related to geographic location or climate for either genotype. After accounting for location (latitude, climate), G1 plants had lower disease incidence than G4 plants in the field (38% vs. 70%) but similar pathogen richness. In contrast, bioassays revealed G1 plants consistently received a higher damage score and had larger leaf lesions regardless of pathogen. These results demonstrate that two widespread B. umbellatus genotypes exhibit different susceptibility to pathogens and effectiveness of pathogen biological controls may depend on local conditions.