Robert C. Venette

Spotted lanternfly, Lycorma delicatula (White) is a planthopper (Hemiptera: Fulgoridae) that is native to China and invasive elsewhere in Asia and North America. The insect feeds on several plants and is an emerging pest of apples, grapes, walnuts, and other hardwoods. Forecasts of the ultimate geographic distribution for L. delicatula in Asia and North America, particularly its northern latitudinal limits, are uncertain because of limited information about the cold tolerance of this insect. Cooling rate can affect supercooling point, the temperature at which bodily fluids begin to freeze and a common reference point for insect cold tolerance studies. This study measures changes in supercooling point of overwintering L. delicatula eggs in response to different cooling rates. Overwintering egg masses were collected from two field locations in Virginia, USA in November and December 2024. Supercooling points of individual eggs were measured with contact thermocouple thermometry at cooling rates of 0.033, 0.5, and 1 °C/min. The distribution of supercooling points changed with different cooling rates and were negatively related to the cooling rate. At a cooling rate of 0.033 °C/min, SCPs ranged from -28.4 to -22.9 °C and, at 1 °C/min, from -29.2 to -24.7 °C. If supercooling points reflect lethal temperatures for L. delicatula , relatively rapid cooling may slightly overestimate the cold tolerance of the insect and inflate the estimated geographic area where overwintering might be successful. Such risk-averse forecasts may be useful for biosecurity efforts.

Soybean gall midge, Resseliella maxima Gagné, was first described in 2019 following widespread outbreaks in soybean across the midwestern United States. Larval feeding inside stems causes lesions, lodging, and yield loss. Third instars overwinter in the soil within silken cocoons, but their cold tolerance, an important factor for survival in the temperate midwestern United States, is unknown. In 2022 and 2023, late-season soybean stems with R. maxima were collected from southwestern Minnesota. Third instars were retrieved and transferred to vials of sand, where they successfully burrowed and formed cocoons. Vials with cocoons were stored at 13 and 3 °C, and larval supercooling points and lower lethal temperatures (LTs) were measured after 1 and 2 months. All individuals remained larvae by the time of measurements, suggesting they were in diapause. Supercooling points and lower LTs were primarily between −20 and −25 °C. Alignment between these measurements suggests that R. maxima is freeze-intolerant. There were no consistent effects of storage time or temperature, indicating a lack of further acclimation. The temperature causing 50% mortality (LT50) was −19.8 °C in both 2022 (95% CI: −26.4 to −13.2 °C) and 2023 (95% CI: −26.6 to −13.0 °C). Historical soil temperature data reveal the coldest temperature recorded from 2015 to 2024 near the northern portion of R. maxima’s known range (−17.7 °C) would cause <50% mortality to R. maxima populations, while average coldest temperatures were substantially warmer (−3.1 to −8.5 °C). Short-term exposures to winter soil temperatures may not cause significant mortality to overwintering R. maxima in the midwestern United States.

Elongate hemlock scale, Fiorinia externa Ferris (Hemiptera: Diaspididae), is an invasive pest of eastern hemlock, Tsuga canadensis, and other Pinaceae such as Fraser fir, Abies fraseri. Cut Fraser firs (ie for Christmas trees and other holiday greenery) with F. externa have been intercepted in US states beyond where the insect is known to be established and, in some cases, where exposure to freezing temperatures might be prolonged. This study measures the effect of constant low temperatures (3, −10, or −20 °C) on survival of overwintering F. externa females from eastern hemlock in Michigan and from eastern hemlock and Fraser fir in North Carolina. Survival was determined with biochemical viability testing, which assesses the presence of metabolically active cells, and changes in survivorship through time were quantified with Kaplan–Meier methods and beta regression. Collection date and host occasionally affected survival rate but not in a consistent pattern. Survival rates generally decreased as temperature decreased. At 3 °C, F. externa maintained high survival (>75%). At −10 °C, survival was projected to fall to 50% within 22 to 92 d and 10% by 45 to 195 d. At −20 °C, survival typically declined to 50% by 1 to 27 d and 10% by 6 to 52 d. We used survival durations at −20 °C to map how often F. externa might experience 50 or 90% mortality from prolonged cold exposure. Temperatures in recent winters have not been below −20 °C for long enough to stop F. externa from spreading throughout the ranges of eastern hemlock or other hosts in Canada and the continental United States.

Fiorinia externa Ferris, elongate hemlock scale, was inadvertently introduced to North America from Japan. This insect is particularly problematic on hemlock, Tsuga spp., though it has been reported in association with several other conifers. The evidence that other conifers might be hosts, capable of supporting growing populations of the insect, has not been previously reviewed. Our review confirms that F. externa is an oligophagous pest of members of Pinaceae. Although species of Cupressaceae and Taxaceae have been reported as hosts of F. externa, they seem unable to support population growth of this pest. Evidence of the tree-killing potential of the insect, even on suitable hosts, is remarkably scant. The degree of pest risk posed by F. externa with respect to tree mortality in areas beyond the geographic range of hemlock seems modest, but uncertain.

Nonnative insects and pathogens pose major threats to forest ecosystems worldwide, greatly diminishing the ecosystem services trees provide. Given the high global diversity of arthropod and microbial species, their often unknown biological features or even identities, and their ease of accidental transport, there is an urgent need to better forecast the most likely species to cause damage. Several risk assessment approaches have been proposed or implemented to guide preventative measures. However, the underlying assumptions of each approach have rarely been explicitly identified or critically evaluated. We propose that evaluating the implicit assumptions, optimal usages, and advantages and limitations of each approach could help improve their combined utility. We consider four general categories: using prior pest status in native and previously invaded regions; evaluating statistical patterns of traits and gene sequences associated with a high impact; sentinel and other plantings to expose trees to insects and pathogens in native, nonnative, or experimental settings; and laboratory assays using detached plant parts or seedlings under controlled conditions. We evaluate how and under what conditions the assumptions of each approach are best met and propose methods for integrating multiple approaches to improve our forecasting ability and prevent losses from invasive pests.

Overwintering success is an important determinant of arthropod populations that must be considered as climate change continues to influence the spatiotemporal population dynamics of agricultural pests. Using a long-term monitoring database and biologically relevant overwintering zones, we modeled the annual and seasonal population dynamics of a common pest, Helicoverpa zea (Boddie), based on three overwintering suitability zones throughout North America using four decades of soil temperatures: the southern range (able to persist through winter), transitional zone (uncertain overwintering survivorship), and northern limits (unable to survive winter). Our model indicates H. zea population dynamics are hierarchically structured with continental-level effects that are partitioned into three geographic zones. Seasonal populations were initially detected in the southern range, where they experienced multiple large population peaks. All three zones experienced a final peak between late July (southern range) and mid-August to mid-September (transitional zone and northern limits). The southern range expanded by 3% since 1981 and is projected to increase by twofold by 2099 but the areas of other zones are expected to decrease in the future. These changes suggest larger populations may persist at higher latitudes in the future due to reduced low-temperature lethal events during winter. Because H. zea is a highly migratory pest, predicting when populations accumulate in one region can inform synchronous or lagged population development in other regions. We show the value of combining long-term datasets, remotely sensed data, and laboratory findings to inform forecasting of insect pests.

Tenuisvalvae notata (Mulsant) (Coccinellidae) is a predatory ladybird beetle native to South America. It specializes in mealybugs prey (Pseudococcidae), but relatively little is known about its ecology. In contrast, the ladybird beetle Cryptolaemus montrouzieri Mulsant (Coccinellidae) is indigenous to Australia and has been introduced to many countries worldwide including Brazil for biological control of mealybugs. The potential impacts of these introductions to native coccinellids have rarely been considered. The software CLIMEX estimated the climate suitability for both species as reflected in the Ecoclimatic Index (EI). Much of South America, Africa, and Australia can be considered climatically suitable for both species, but in most cases, the climate is considerably more favorable for C. montrouzieri than T. notata, especially in South America. The CLIMEX model also suggests seasonal differences in growth conditions (e.g. rainfall and temperature) that could affect the phenology of both species. These models suggest that few locations in South America would be expected to provide T. notata climatic refugia from C. montrouzieri. Although other ecological factors will also be important, such as prey availability, this analysis suggests a strong potential for displacement of a native coccinellid throughout most of its range as a consequence of the invasion by an alien competitor.