Combining photoperiod and thermal responses to predict phenological mismatch for introduced insects

Phenological Mapping of Invasive Insects: Decision Support for Surveillance and Management

Readily accessible and easily understood forecasts of the phenology of invasive insects have the potential to support and improve strategic and tactical decisions for insect surveillance and management. However, most phenological modeling tools developed to date are site-based, meaning that they use data from a weather station to produce forecasts for that single site. Spatial forecasts of phenology, or phenological maps, are more useful for decision-making at area-wide scales, such as counties, states, or entire nations. In this review, we provide a brief history on the development of phenological mapping technologies with a focus on degree-day models and their use as decision support tools for invasive insect species. We compare three different types of phenological maps and provide examples using outputs of web-based platforms that are presently available for real-time mapping of invasive insects for the contiguous United States. Next, we summarize sources of climate data available for real-time mapping, applications of phenological maps, strategies for balancing model complexity and simplicity, data sources and methods for validating spatial phenology models, and potential sources of model error and uncertainty. Lastly, we make suggestions for future research that may improve the quality and utility of phenological maps for invasive insects.

Climate suitability analyses compare the distributions of invasive knotweeds in Europe and North America with the source localities of their introduced biological control agents

Climate suitability analyses based on ecological niche modeling provide a powerful tool for biological control practitioners to assess the likelihood of establishment of different candidate agents prior to their introduction in the field. These same analyses could also be performed to understand why some agents establish more easily than others. The release of three strains of Aphalara itadori (Shinji) (Hemiptera: Pysllidae), each from a different source locality in Japan, for the biological control of invasive knotweed species, Reynoutria spp. Houtt. (Caryophyllales: Polygonaceae), provides an important opportunity to compare the utility of climate suitability analyses for identifying potential climate-based limitations for successful biological control introductions. Here, we predict climate suitability envelopes for three target species of knotweed in Europe and two target species of knotweed in North America and compare these suitability estimates for each of these species to the source localities of each A. itadori strain. We find that source locality of one strain, the Kyushu strain, has little-to-no suitability compared to other locations in Japan based on knotweed records from Europe, supporting an earlier study based on North American Japanese knotweed records. The source locality of a second strain, the Murakami strain, was predicted to have medium-to-high suitability based on records of knotweeds from North America. In contrast, European records of Reynoutria × bohemica Chrtek & Chrtková and Reynoutria sachalinensis (F. Schmidt) Nakai predicted no suitability for this locality compared to other locations in Japan, while European records for Reynoutria japonica Houtt. predicted low suitability. The source locality of the final strain, the Hokkaido strain, was predicted as having medium-to-high suitability based on knotweed records of all examined species from both North America and Europe.

An integrative phenology and climatic suitability model for emerald ash borer

Introduction

Decision support models that predict both when and where to expect emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), are needed for the development and implementation of effective management strategies against this major invasive pest of ash (Fraxinus species) in North America and other regions such as Europe. We present a spatialized model of phenology and climatic suitability for EAB for use in the Degree-Days, Risk, and Phenological event mapping (DDRP) platform, which is an open-source decision support tool to help detect, monitor, and manage invasive threats.

Methods

We evaluated the model using presence records from three geographic regions (China, North America, and Europe) and a phenological dataset consisting primarily of observations from the northeastern and midwestern United States. To demonstrate the model, we produced phenological event maps for a recent year and tested for trends in EAB's phenology and potential distribution over a recent 20-year period.

Results

Overall, the model exhibited strong performance. Presence was correctly estimated for over 99% of presence records and predicted dates of adult phenological events corresponded closely with observed dates, with a mean absolute error of ca. 7 days and low estimates of bias. Climate stresses were insufficient to exclude EAB from areas with native Fraxinus species in North America and Europe; however, extreme weather events, climate warming, and an inability for EAB to complete its life cycle may reduce suitability for some areas. Significant trends toward earlier adult emergence over 20 years occurred in only some areas.

Discussion

Near real-time model forecasts for the conterminous United States are available at two websites to provide end-users with decision-support for surveillance and management of this invasive pest. Forecasts of adult emergence and egg hatch are particularly relevant for surveillance and for managing existing populations with pesticide treatments and parasitoid introductions.

Diapause of the Western cherry fruit fly, Rhagoletis indifferens (Diptera: Tephritidae): metabolic rate and overwintering adaptations

The Western cherry fruit fly, Rhagoletis indifferens (Curran), is a Tephritid fly in the Pacific Northwest and is known to infest native bitter cherry, Prunus emarginata (Douglas ex Hooker), which is distributed throughout the Cascade Mountain range. This species occupies temperate to alpine climates and exhibits overwintering adaptations of diapause and supercooling. Isothermal and differential scanning calorimetry were used to determine the effects of diapause chilling duration and post-chilling warm rearing on the metabolic rate and supercooling point of R. indifferens. Previous studies have included the effects of chilling duration on post-diapause development and emergence as well as on the levels of metabolic reserves. Metabolic rate of R. indifferens, was used to calculate the ability of this species to remain in diapause for more than 1 yr as well as predicting the potential effects of climate change on the future abundance and distribution. It was determined that R. indifferens could diapause for more than 1 yr based on the levels of metabolic reserves and metabolic rate.

Predation and Climate Limit Establishment Success of the Kyushu Strain of the Biological Control Agent Aphalara itadori (Hemiptera: Aphalaridae) in the Northeastern United States

Species of knotweeds, Reynoutria spp. Houtt. (Caryophyllales: Polygonaceae), including Japanese knotweed (R. japonica Houtt.), are among the most invasive and ecologically destructive plant species introduced to North America and Europe. The Kyushu strain of the psyllid Aphalara itadori Shinji (Hemiptera: Aphalaridae) has been approved as a biological control agent for release against Japanese knotweed in the United Kingdom, Canada, and the United States. However, recent reports from Canada suggest that both biotic and abiotic factors may limit its establishment. Therefore, we examined the potential role of predation by comparing open- versus closed-sleeve treatments, and climate mis-matches by collecting temperature data from release sites and performing climate suitability analyses using MaxEnt. Our results indicated that populations of the Kyushu strain could only be maintained in the field in closed-sleeve treatments, suggesting that predation is likely limiting the establishment success of this strain. In addition, we noted that daily maximum temperatures at our field sites might exceed documented developmental thresholds for this strain, and that MaxEnt species distribution modeling indicates no climate similarities between locations in eastern North America and Kyushu. Combined with previous results, our study suggests that the establishment of the Kyushu strain of A. itadori as a biological control agent for Japanese knotweed may be limited in eastern North America. We suggest that one strategy to increase the probability of establishment of the Kyushu strain could be to increase the number of release sites in an effort to find a more optimal niche with predator-free space.

Combining photoperiod and thermal responses to predict phenological mismatch for introduced insects

A wide variety of organisms use the regular seasonal changes in photoperiod as a cue to align their life cycles with favorable conditions. Yet the phenological consequences of photoperiodism for organisms exposed to new climates are often overlooked. We present a conceptual approach and phenology model that maps voltinism (generations per year) and the degree of phenological mismatch that can arise when organisms with a short-day diapause response are introduced to new regions or are otherwise exposed to new climates. Our degree-day-based model combines continent-wide spatialized daily climate data, calculated date-specific and latitude-specific day lengths, and experimentally determined developmental responses to both photoperiod and temperature. Using the case of the knotweed psyllid Aphalara itadori, a new biological control agent being introduced from Japan to North America and Europe to control an invasive weed, we show how incorporating a short-day diapause response will result in geographic patterns of attempted voltinism that are strikingly different from the potential number of generations based on degree-days alone. The difference between the attempted and potential generations represents a quantitative measure of phenological mismatch between diapause timing and the end of the growing season. We conclude that insects moved from lower to higher latitudes (or to cooler climates) will tend to diapause too late, potentially resulting in high mortality from inclement weather, and those moved from higher to lower latitude (to warmer climates) may be prone to diapausing too early, therefore not fully exploiting the growing season and/or suffering from insufficient reserves for the longer duration in diapause. Mapped output reveals a central region with good phenology match that shifts north or south depending on the geographic source of the insect and its corresponding critical photoperiod for diapause. These results have direct relevance for efforts to establish populations of classical biocontrol agents. More generally, our approach and model could be applied to a wide variety of photoperiod- and temperature-sensitive organisms that are exposed to changes in climate, including resident and invasive agricultural pests and species of conservation concern.