Cold Tolerance of Megacopta cribraria (Hemiptera: Plataspidae): An Invasive Pest of Soybeans

Susceptibility of Different Life Stages of Kudzu Bug Megacopta cribraria (F.) (Hemiptera: Plataspidae) to Two Different Native Strains of Beauveria bassiana

This is the first study that examined and compared the survival, LC50, and RR50 estimates of Megacopta cribraria F. (Hemiptera: Plataspidae) nymphs and adults that were exposed to two native Beauveria bassiana isolates (Previously codified as NI8 and KUDSC strains) at four concentrations. The greatest reduction in survival and mortality was observed primarily on or after 10 d post-exposure to B. bassiana isolates. Survival of early instars (2nd, 3rd) were not affected by either strains or concentration at 3 d and 5 d post-exposure. Survival of later instars (5th) and adults was significantly reduced when exposed to the KUDSC strain at all concentrations. Comparison of dose−mortality values (LC50) using resistance ratios (RR50) were significantly different between life stages of the kudzu bug for both strains of B. bassiana. The LC50 values showed that kudzu bug adults are more susceptible than any other life stage when exposed to either strain. The KUDSC strain was more pathogenic than NI8 10 d after exposure, but NI8 exhibited significantly higher pathogenicity than KUDSC 20 d after exposure. Our results suggest potential field application of B. bassiana for kudzu bug control and their integration into pest management strategies to suppress them before they cause economic damage to soybean crops.

Climate Mismatch between Introduced Biological Control Agents and Their Invasive Host Plants: Improving Biological Control of Tropical Weeds in Temperate Regions

Simple Summary

Mismatched distributions between biological control agents and their host plants occur for a variety of reasons but are often linked to climate, specifically differences in their low-temperature tolerances. How to measure and use low-temperature tolerances of control agents to inform agent prioritization, selection for redistribution, or predict efficacy is vitally important, but has not been previously synthesized in a single source. We discuss causes of climate mismatches between agents and target weeds, the traditional and non-traditional approaches that could be used to decrease the degree of mismatch and improve control, and regulatory issues to consider when taking such approaches. We also discuss the variety of cold tolerance metrics, their measurement and ecological value, and the types of modeling that can be carried out to improve predictions about potential distributions of agents. We also briefly touch on molecular bases for cold tolerance and opportunities for improving cold tolerance of agents using modern molecular tools.

Abstract

Many weed biological control programs suffer from large-scale spatial variation in success due to restricted distributions or abundances of agents in temperate climates. For some of the world’s worst aquatic weeds, agents are established but overwintering conditions limit their survival in higher latitudes or elevations. The resulting need is for new or improved site- or region-specific biological control tools. Here, we review this challenge with a focus on low-temperature limitations of agents and propose a roadmap for improving success. Investigations across spatial scales, from global (e.g., foreign exploration), to local (selective breeding), to individual organisms (molecular modification), are discussed. A combination of traditional (foreign) and non-traditional (introduced range) exploration may lead to the discovery and development of better-adapted agent genotypes. A multivariate approach using ecologically relevant metrics to quantify and compare cold tolerance among agent populations is likely required. These data can be used to inform environmental niche modeling combined with mechanistic modeling of species’ fundamental climate niches and life histories to predict where, when, and at what abundance agents will occur. Finally, synthetic and systems biology approaches in conjunction with advanced modern genomics, gene silencing and gene editing technologies may be used to identify and alter the expression of genes enhancing cold tolerance, but this technology in the context of weed biological control has not been fully explored.

Determining Spread Rate of Kudzu Bug (Hemiptera: Plataspidae) and Its Associations With Environmental Factors in a Heterogeneous Landscape

By the end of 2017, kudzu bug was reported in 652 counties in the United States since it was first observed in Georgia in 2009. Modeling its invasion dynamics is valuable to guide management through early detection and prevention of further invasion. Herein, we initially estimated the spread rate of kudzu bug with county-level invasion records and then determined important spatial factors affecting its spread during years 2010-2016. As kudzu bug infests a large heterogeneous area and shows asymmetric spread, we first utilized spatially constrained clustering (SCC), an unsupervised machine learning method, to divide the infested area into eight spatially contiguous and environmentally homogenous neighborhoods. We then used distance regression and boundary displacement methods to estimate the spread rates in all neighborhoods. Finally, we applied multiple regression to determine spatial factors influencing the spread of kudzu bug. The average spread rate reached 76 km/yr by boundary displacement method; however, the rate varied largely among eight neighborhoods (45-144 km/yr). In the southern region of the infested area, host plant density and wind speed were positively associated with the spread rate, whereas mean annual temperature, precipitation in the fall, and elevation had inverse relationships. In the northern region, January minimum temperature, wind speed, and human population density showed positive relationships. This study increases the knowledge on the spread dynamics of kudzu bug. Our research highlights the utility of SCC to determine natural clustering in a large heterogeneous region for better modeling of local spread patterns and determining important factors affecting the invasions.

Degree Day Requirements for Kudzu Bug (Hemiptera: Plataspidae), a Pest of Soybeans

Understanding the phenology of a new potential pest is fundamental for the development of a management program. Megacopta cribraria Fabricius (Hemiptera: Plataspidae), kudzu bug, is a pest of soybeans first detected in the United States in 2009 and in Maryland in 2013. We observed the phenology of kudzu bug life stages in Maryland, created a Celsius degree-day (CDD) model for development, and characterized the difference between microhabitat and ambient temperatures of both kudzu, Pueraria montana (Lour.) Merr. (Fabales: Fabaceae) and soybeans, Glycine max (L.) Merrill (Fabales: Fabaceae). In 2014, low population numbers yielded limited resolution from field phenology observations. We observed kudzu bug populations persisting within Maryland; but between 2013 and 2016, populations were low compared to populations in the southeastern United States. Based on the degree-day model, kudzu bug eggs require 80 CDD at a minimum temperature of 14°C to hatch. Nymphs require 545 CDD with a minimum temperature of 16°C for development. The CDD model matches field observations when factoring a biofix date of April 1 and a minimum preoviposition period of 17 d. The model suggests two full generations per year in Maryland. Standard air temperature monitors do not affect model predictions for pest management, as microhabitat temperature differences did not show a clear trend between kudzu and soybeans. Ultimately, producers can predict the timing of kudzu bug life stages with the CDD model for the use of timing management plans in soybean fields.