Weakening density dependence from climate change and agricultural intensification triggers pest outbreaks: a 37-year observation of cotton bollworms

Population dynamics of the glacial relict amphipods in a subarctic lake: role of density-dependent and density-independent factors

Relative role of intrinsic density-dependent factors (such as inter- and intraspecific competition, predation) and extrinsic density-independent factors (environmental changes) in population dynamics is a key issue in ecology. Density-dependent mechanisms are considered as important drivers of population dynamics in many vertebrate and insect species; however, their influence on the population dynamics of freshwater invertebrates is not clearly understood. In this study, I examined interannual variations in the abundance of the glacial relict amphipod Monoporeia affinis in a small subarctic lake based on long-term (2002-2019) monitoring data. The results suggest that the population dynamics of amphipods in the lake is influenced by the combined effects of both intrinsic and extrinsic factors. The reproductive success of amphipod cohorts was inversely related to its initial abundance, indicating it is influenced by density-dependent factors. M. affinis recruitment was negatively correlated with population density and near-bottom temperature but positively correlated with food availability, which is defined as the concentration of chlorophyll a. Multiple regression with chlorophyll, temperature, and abundance of parent cohort as independent factors explained about 80% of the variation in the reproductive success of amphipods. The negative correlation between amphipod recruitment and water temperature indicates that the current climate conditions adversely affect the populations of glacial relict amphipods even in cold-water lakes of the subarctic zone. Results of this study can be useful in environmental assessments to separate population oscillations connected with density-dependent mechanisms from human-mediated changes.

One Biosecurity: a unified concept to integrate human, animal, plant, and environmental health

In the wake of the SARS-CoV-2 pandemic, the world has woken up to the importance of biosecurity and the need to manage international borders. Yet strong sectorial identities exist within biosecurity that are associated with specific international standards, individual economic interests, specific research communities, and unique stakeholder involvement. Despite considerable research addressing human, animal, plant, and environmental health, the science connections between these sectors remain quite limited. One Biosecurity aims to address these limitations at global, national, and local scales. It is an interdisciplinary approach to biosecurity policy and research that builds on the interconnections between human, animal, plant, and environmental health to effectively prevent and mitigate the impacts of invasive alien species. It provides an integrated perspective to address the many biosecurity risks that transcend the traditional boundaries of health, agriculture, and the environment. Individual invasive alien plant and animal species often have multiple impacts across sectors: as hosts of zoonotic parasites, vectors of pathogens, pests of agriculture or forestry, as well as threats to biodiversity and ecosystem function. It is time these risks were addressed in a systematic way. One Biosecurity is essential to address several major sociological and environmental challenges to biosecurity: climate change, increasing urbanisation, agricultural intensification, human global mobility, loss of technical capability as well as public resistance to pesticides and vaccines. One Biosecurity will require the bringing together of taxonomists, population biologists, modellers, economists, chemists, engineers, and social scientists to engage in a new agenda that is shaped by politics, legislation, and public perceptions.

Olive Production Threatened by a Resurgent Pest Liothrips oleae (Costa, 1857) (Thysanoptera: Phlaeothripidae) in Southern Italy

Simple Summary

Liothrips oleae (Costa, 1857) (Thysanoptera: Phlaeothripidae) is widespread in the Mediterranean area, and in all regions, it is reputed to be a secondary pest in olive crops, mainly associated with damage to leaves and secondarily with damage to drupes, for which this thrips pest has a marginal impact on olive production. Taking into account the increase in the frequency of extreme damage by this species in Southern Italy in the last decade, this research aimed to elucidate the real impact (i.e., damage to leaves and drupes) by feeding thrips’ activity in olive orchards. Our results revealed that the impact of thrips was significant in all monitored olive orchards and the estimated damage level on drupes and leaves was higher in organic olive than in integrated olive management. A detailed morphological description of the Italian specimens and their molecular characterization are also provided.

Abstract

This study investigated a resurgence of Liothrips oleae Costa (Thysanoptera: Phlaeothripidae), an insect pest of olive crops, in a focal Southern Italian olive-producing area (Calabria Region). The young and adult olive thrips feed on the leaves and fruits of wild and cultivated olive trees, producing distortions, necrosis, and premature dropping of fruit. In our study, organic and integrated olive groves were compared for two years in order to establish the relationship between leaf and fruit damage among olive groves managed under different phytosanitary conditions. Sampling techniques were used in order to collect and count leaves and fruits (on plants and dropped premature drupes) presenting symptoms of thrips’ feeding activity. The impact of the thrips was significant in all orchards, and the estimated damage level on drupes and leaves was higher in organic olive management in each year. A morphological description of the adult females of the species is provided, and the first molecular characterization of the Calabrian olive thrips population was performed by using three different genetic regions (cytochrome c oxidase subunit I (COI), 28S ribosomal subunit (28S), and internal transcribed spacer 2 (ITS2)).

Response of a rice insect pest, Scirpophaga incertulas (Lepidoptera: Pyralidae) in warmer world

Background

Increases in global mean temperature, changes in rainfall patterns, and extreme climatic events are expected results of climate change. The individual effects of elevated temperature and precipitation on insect pests due to the impact of climate change have been widely modeled individually but their combined effects are poorly understood.

Results

Ten years of monthly abundance of an important economic rice insect pest, the rice yellow stem borer (YSB), Scirpophaga incertulas Walker (Lepidoptera: Pyralidae), was modeled in relation to temperature and rainfall using cross-correlation functions, general linear models, ARIMA models and simple linear regressions. The results suggested that increasing temperature and rainfall separately had a positive effect on growth rate of YSB. However, the combined effect of high temperature and rainfall was negative Temperature affected abundance of YSB negatively at high rainfall, but positively at intermediate to low rainfall level. The growth rate of YSB was found to be high at relatively low temperature and abundant rainfall.

Conclusion

The combined effects of temperature and rainfall showed a quadratic response of YSB abundance, which indicated that outbreak risk of YSB may be reduced if climate change results in increasing temperature and rainfall. It should be noted that we could address only a few of the important factors which could influence our model prediction.

Evolutionary tracking is determined by differential selection on demographic rates and density dependence

Recent ecological forecasts predict that ~25% of species worldwide will go extinct by 2050. However, these estimates are primarily based on environmental changes alone and fail to incorporate important biological mechanisms such as genetic adaptation via evolution. Thus, environmental change can affect population dynamics in ways that classical frameworks can neither describe nor predict. Furthermore, often due to a lack of data, forecasting models commonly describe changes in population demography by summarizing changes in fecundity and survival concurrently with the intrinsic growth rate (r). This has been shown to be an oversimplification as the environment may impose selective pressure on specific demographic rates (birth and death) rather than directly on r (the difference between the birth and death rates). This differential pressure may alter population response to density, in each demographic rate, further diluting the information combined to produce r. Thus, when we consider the potential for persistence via adaptive evolution, populations with the same r can have different abilities to persist amidst environmental change. Therefore, we cannot adequately forecast population response to climate change without accounting for demography and selection on density dependence. Using a continuous-time Markov chain model to describe the stochastic dynamics of the logistic model of population growth and allow for trait evolution via mutations arising during birth events, we find persistence via evolutionary tracking more likely when environmental change alters birth rather than the death rate. Furthermore, species that evolve responses to changes in the strength of density dependence due to environmental change are less vulnerable to extinction than species that undergo selection independent of population density. By incorporating these key demographic considerations into our predictive models, we can better understand how species will respond to climate change.

Phenological responses in a sycamore-aphid-parasitoid system and consequences for aphid population dynamics: A 20 year case study

Species interactions have a spatiotemporal component driven by environmental cues, which if altered by climate change can drive shifts in community dynamics. There is insufficient understanding of the precise time windows during which inter-annual variation in weather drives phenological shifts and the consequences for mismatches between interacting species and resultant population dynamics-particularly for insects. We use a 20 year study on a tri-trophic system: sycamore Acer pseudoplatanus, two associated aphid species Drepanosiphum platanoidis and Periphyllus testudinaceus and their hymenopteran parasitoids. Using a sliding window approach, we assess climatic drivers of phenology in all three trophic levels. We quantify the magnitude of resultant trophic mismatches between aphids and their plant hosts and parasitoids, and then model the impacts of these mismatches, direct weather effects and density dependence on local-scale aphid population dynamics. Warmer temperatures in mid-March to late-April were associated with advanced sycamore budburst, parasitoid attack and (marginally) D. platanoidis emergence. The precise time window during which spring weather advances phenology varies considerably across each species. Crucially, warmer temperatures in late winter delayed the emergence of both aphid species. Seasonal variation in warming rates thus generates marked shifts in the relative timing of spring events across trophic levels and mismatches in the phenology of interacting species. Despite this, we found no evidence that aphid population growth rates were adversely impacted by the magnitude of mismatch with their host plants or parasitoids, or direct impacts of temperature and precipitation. Strong density dependence effects occurred in both aphid species and probably buffered populations, through density-dependent compensation, from adverse impacts of the marked inter-annual climatic variation that occurred during the study period. These findings explain the resilience of aphid populations to climate change and uncover a key mechanism, warmer winter temperatures delaying insect phenology, by which climate change drives asynchronous shifts between interacting species.

Effects of climate change and crop planting structure on the abundance of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

The interactions between plants and insects play an important role in ecosystems. Climate change and cropping patterns can affect herbivorous pest insect dynamics. Understanding the reasons for population fluctuations can help improve integrated pest management strategies. Here, a 25-year dataset on climate, cropping planting structure, and the population dynamics of cotton bollworms (Helicoverpa armigera) from Bachu County, south Xinjiang, China, was analyzed to assess the effects of changes in climate and crop planting structure on the population dynamics of H. armigera. The three generations of H. armigera showed increasing trends in population size with climate warming, especially in the third generation. The relative abundances of the first and second generations decreased, but that of the third generation increased. Rising temperature and precipitation produced different impacts on the development of different generations. The population numbers of H. armigera increased with the increase in the non-Bacillus thuringiensis (Bt) cotton-planted area. Asynchrony of abrupt changes existed among climate change, crop flowering dates, and the phenology of H. armigera moths. The asynchronous responses in crop flowering dates and phenology of H. armigera to climate warming would expand in the future. The primary factors affecting the first, second, and third generations of moths were T mean in June, the last appearance date of the second generation of moths, and the duration of the third generation of moths, respectively. To reduce the harm to crops caused by H. armigera, Bt cotton should be widely planted.

Relative importance of long-term changes in climate and land-use on the phenology and abundance of legume crop specialist and generalist aphids

Insect populations are prone to respond to global changes through shifts in phenology, distribution and abundance. However, global changes cover several factors such as climate and land-use, the relative importance of these being largely unknown. Here, we aim at disentangling the effects of climate, land-use, and geographical drivers on aphid abundance and phenology in France, at a regional scale and over the last 40 years. We used aerial data obtained from suction traps between 1978 and 2015 on five aphid species varying in their degree of specialization to legumes, along with climate, legume crop area and geographical data. Effects of environmental and geographical variables on aphid annual abundance and spring migration dates were analyzed using generalized linear mixed models. We found that within the last four decades, aphids have advanced their spring migration by a month, mostly due to the increase in temperature early in the year, and their abundance decreased by half on average, presumably in response to a combination of factors. The influence of legume crop area decreased with the degree of specialization of the aphid species to such crops. The effect of geographical variation was high even when controlling for environmental variables, suggesting that many other spatially structured processes act on aphid population characteristics. Multifactorial analyses helped to partition the effects of different global change drivers. Climate and land-use changes have strong effects on aphid populations, with important implications for future agriculture. Additionally, trait-based response variation could have major consequences at the community scale.

Surviving drought: a framework for understanding animal responses to small rain events in the arid zone

Large rain events drive dramatic resource pulses and the complex pulse-reserve dynamics of arid ecosystems change between high-rain years and drought. However, arid-zone animal responses to short-term changes in climate are unknown, particularly smaller rain events that briefly interrupt longer-term drought. Using arthropods as model animals, we determined the effects of a small rain event on arthropod abundance in western New South Wales, Australia during a longer-term shift toward drought. Arthropod abundance decreased over 2 yr, but captures of 10 out of 15 ordinal taxa increased dramatically after the small rain event (<40 mm). The magnitude of increases ranged from 10.4 million% (collembolans) to 81% (spiders). After 3 months, most taxa returned to prerain abundance. However, small soil-dwelling beetles, mites, spiders, and collembolans retained high abundances despite the onset of winter temperatures and lack of subsequent rain. As predicted by pulse-reserve models, most arid-zone arthropod populations declined during drought. However, small rain events may play a role in buffering some taxa from declines during longer-term drought or other xenobiotic influences. We outline the framework for a new model of animal responses to environmental conditions in the arid zone, as some species clearly benefit from rain inputs that do not dramatically influence primary productivity.

Detecting mismatches in the phenology of cotton bollworm larvae and cotton flowering in response to climate change

Current evidence suggests that climate change has directly affected the phenology of many invertebrate species associated with agriculture. Such changes in phenology have the potential to cause temporal mismatches between predators and prey and may lead to a disruption in natural pest control ecosystem. Understanding the synchrony between pest insects and host plant responses to climate change is a key step to improve integrated pest management strategies. Cotton bollworm larvae damage cotton, and thus, data from Magaiti County, China, collected during the period of 1990-2015 were analyzed to assess the effects of climate change on cotton bollworm larvae and cotton flowering. The results showed that a warming climate advanced the phenology of cotton bollworm larvae and cotton flowering. However, the phenological rate of change was faster in cotton bollworm larvae than that in cotton flowering, and the larval period was prolonged, resulting in a great increase of the larval population. The abrupt phenological changes in cotton bollworm larvae occurred earlier than that in cotton, and the abrupt phenological changes in cotton flowering occurred earlier than that in larval abundance. However, the timing of abrupt changes in larval abundance all occurred later than that in temperature. Thus, the abrupt changes that occurred in larvae, cotton flowering and climate were asynchronous. The interval days between the cotton flowering date (CFD) and the half-amount larvae date (HLD) expanded by 3.41 and 4.41 days with a 1 °C increase of T_mean in May and June, respectively. The asynchrony between cotton bollworm larvae and cotton flowering will likely broaden as the climate changes. The effective temperature in March and April and the end date of larvae (ED) were the primary factors affecting asynchrony.

Presence of snow coverage and its thickness affected the mortality of overwintering pupae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Helicoverpa armigera causes serious damage to most crops around the world. However, the impacts of snow thickness on the H. armigera overwintering pupae are little known. A field experiment was employed in 2012-2015 at Urumqi, China. At soil depths of 5, 10, and 15 cm, overwintering pupae were embedded with four treatments: no snow cover (NSC), snow cover (SC), increasing snow thickness to 1.5 times the thickness of SC (ISSC-1), and to two times the thickness of SC (ISSC-2). Results suggested that snow cover and increasing snow thickness both significantly increased soil temperatures, which helped to decrease the mortality of overwintering pupae (MOP) of H. armigera. However, the MOP did not always decrease with increases in snow thickness. The MOPs in NSC and ISSC-1 were the highest and the lowest, respectively, though ISSC-2 had much thicker snow thickness than ISSC-1. A maximum snow thickness of 60 cm might lead to the lowest MOP. The longer the snow cover duration (SCD) at a soil depth of 10 cm in March and April was, the higher the MOP was. A thicker snow cover layer led to a higher soil moisture content (SMC) and a lower diurnal soil temperature range (DSTR). The highest and the lowest MOP were at a depth of 15 and 10 cm, respectively. The SMC at the depths of 10 and 15 cm had significant effects on MOP. A lower accumulated temperature (≤0 °C) led to a higher MOP. The DSTR in March of approximately 4.5 °C might cause the lowest MOP. The largest influence factor for the MOPs at depths of 5 and 10 cm and the combined data were the SCDs during the whole experimental period, and for the MOPs at a depth of 15 cm was the soil temperature in November.

Spring phenology of cotton bollworm affects wheat yield

Climate change has changed numerous species phenologies. Understanding the asynchronous responses between pest insects and host plants to climate change is helpful in improving integrated pest management. It is necessary to use long-term data to analyze the effects of climate change on cotton bollworm and wheat anthesis. Data for cotton bollworm, wheat yield, and wheat anthesis collected since 1990 were analyzed using linear regression and partial least-squares regression, as well as the Mann-Kendall test. The results showed that warmer temperatures in the spring advanced the phenologies of cotton bollworm and wheat anthesis, but the phenology changes in overwintering cotton bollworm were faster than those in wheat anthesis, and the eclosion period of overwintering was prolonged, resulting in an increase in overwintering adult abundance. This might lead to more first-generation larvae and subsequent wheat damage. An early or late first-appearance date significantly affected the eclosion days. The abrupt changes of phenologies in cotton bollworm, wheat anthesis, and climate were asynchronous, but the abrupt phenology changes occurred after or around the climate abrupt change, especially after or around the abrupt changes of temperature in March and April. The expansion of asynchronous responses in the change rate of wheat anthesis and overwintering cotton bollworm would likely decrease wheat yield due to climate warming in the future. Accumulated temperature was the major affecting factor on the first eclosion date (t1), adult abundance, and eclosion days. Temperatures in March and April and precipitation in the winter mainly affected the prepeak date (t2), peak date (t3), and postpeak date (t4), respectively, and these factors indirectly affected wheat yield. Thus, the change in the spring phenology of the cotton bollworm and wheat anthesis, and hence wheat yield, was affected by climate warming.

The fingerprints of global climate change on insect populations

Synthesizing papers from the last two years, I examined generalizations about the fingerprints of climate change on insects' population dynamics and phenology. Recent work shows that populations can differ in response to changes in climate means and variances. The part of the thermal niche occupied by an insect population, voltinism, plasticity and adaptation to weather perturbations, and interactions with other species can all exacerbate or mitigate responses to climate change. Likewise, land use change or agricultural practices can affect responses to climate change. Nonetheless, our knowledge of effects of climate change is still biased by organism and geographic region, and to some extent by scale of climate parameter.

Capturing the interaction types of two Bt toxins Cry1Ac and Cry2Ab on suppressing the cotton bollworm by using multi-exponential equations

Transgenic crops are increasingly promoted for their practical effects on suppressing certain insect pests, but all transgenic crops are not equally successful. The insect pests can easily develop resistance against single Bacillus thuringiensis (Bt) toxin transgenic crops. Therefore, transgenic crops including two or more mixed Bt-toxins can solve this problem by delaying the resistance development and killing the majority of targeted pests before the evolution of resistance. It is important to test the controlling effects of transgenic crops including multiple mixed toxins on a particular insect pest. Previous research has checked the cross-resistance and interactions between Bt toxins Cry1Ac and Cry2Ab against one susceptible and four resistant strains of cotton bollworm. The results showed that independence was the main interaction type between two toxins for the susceptible strain, whereas synergism was the main interaction type for any one resistant strain. However, the optimal combinations of two toxins were not obtained. In the present study, we developed two multi-exponential equations (namely bi- and tri-exponential equations) to describe the combination effects of two Bt toxins. Importantly, the equations can provide predictions of combination effects of different continuous concentrations of two toxins. We compared these two multi-exponential equations with the generalized linear model (GLM) in describing the combination effects, and found that the bi- and tri-exponential equations are better than GLM. Moreover, the bi-exponential equation can also provide the optimal dose combinations for two toxins.

Effects of soil temperature and snow cover on the mortality of overwintering pupae of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is one of the most damaging insect pests in the world. However, little is known about the effects of snow cover and soil temperature on the overwintering pupae of H. armigera. A field experiment was conducted from November 2, 2012 to April 24, 2013 at the agrometeorological experimental station in Wulanwusu, China. Overwintering pupae were embedded into the soil at depths of 5, 10, and 15 cm in the following four treatments: without snow cover, snow cover, and increased temperatures from 600 and 1200 W infrared lights. The results showed that snow cover and rising temperatures could all markedly increase soil temperatures, which was helpful in improving the survival of the overwintering pupae of H. armigera. The mortality of overwintering pupae (MOP) at a depth of 15 cm was the highest, and the MOP at a depth of 5 cm followed. The lower accumulated temperature (≤0 °C) (AT ≤ °C) led to the higher MOP, and the lower diurnal soil temperature range (DSTR) likely led to the lower MOP. After snowmelt, the MOPs at the depths of 5 and 10 cm increased as the soil temperature increased, especially in April. The AT of the soil (≤0 °C) was the factor with the strongest effect on MOP. The soil moisture content was not a major factor affecting the MOP in this semiarid region because precipitation was 45 mm over the entire experimental period. With climate warming, the MOP will likely decrease, and the overwintering boundary air temperatures of H. armigera should be expanded due to higher soil temperatures and increased snow cover.

Formulating spread of species with habitat dependent growth and dispersal in heterogeneous landscapes

Habitat heterogeneity can have profound effects on the spreading dynamics of invasive species. Using integro-difference equations, we investigate the spreading dynamics in a one-dimensional heterogeneous landscape comprising alternating favourable and unfavourable habitat patches or randomly generated habitat patches with given spatial autocorrelation. We assume that population growth and dispersal (including emigration probability and dispersal distance) are dependent on habitat quality. We derived an approximation of the rate of spread in such heterogeneous landscapes, suggesting the sensitivity of spread to the periodic length of the alternating favourable and unfavourable patches, as well as their spatial autocorrelation. A dispersal-limited population tends to spread faster in landscapes with shorter periodic length. The spreading dynamics in a heterogeneous landscape was found to be not only dependent on the availability of favourable habitats, but also the dispersal strategy. Estimates of time lag before detection and the condition for boom-and-bust spreading dynamics were explained. Furthermore, rates of spread in heterogeneous landscapes and corresponding homogeneous landscapes were compared, using weighted sums of vital rates.

The seesaw effect of winter temperature change on the recruitment of cotton bollworms Helicoverpa armigera through mismatched phenology

Knowing how climate change affects the population dynamics of insect pests is critical for the future of integrated pest management. Rising winter temperatures from global warming can drive increases in outbreaks of some agricultural pests. In contrast, here we propose an alternative hypothesis that both extremely cold and warm winters can mismatch the timing between the eclosion of overwintering pests and the flowering of key host plants. As host plants normally need higher effective cumulative temperatures for flowering than insects need for eclosion, changes in flowering time will be less dramatic than changes in eclosion time, leading to a mismatch of phenology on either side of the optimal winter temperature. We term this the "seesaw effect." Using a long-term dataset of the Old World cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in northern China, we tested this seesaw hypothesis by running a generalized additive model for the effects of the third generation moth in the preceding year, the winter air temperature, the number of winter days below a critical temperature and cumulative precipitation during winter on the demography of the overwintering moth. Results confirmed the existence of the seesaw effect of winter temperature change on overwintering populations. Pest management should therefore consider the indirect effect of changing crop phenology (whether due to greenhouse cultivation or to climate change) on pest outbreaks. As arthropods from mid- and high latitudes are actually living in a cooler thermal environment than their physiological optimum in contrast to species from lower latitudes, the effects of rising winter temperatures on the population dynamics of arthropods in the different latitudinal zones should be considered separately. The seesaw effect makes it more difficult to predict the average long-term population dynamics of insect pests at high latitudes due to the potential sharp changes in annual growth rates from fluctuating minimum winter temperatures.

Insect responses to interacting global change drivers in managed ecosystems

Insects are facing an increasingly stressful combination of global change drivers such as habitat fragmentation, agricultural intensification, pollution, or climatic changes. While single-factor studies have yielded considerable insights, multi-factor manipulations have gained momentum recently. Nevertheless, most work to date has remained within particular domains of research, such as 'habitat destruction' or 'climate change', and linkages among subdisciplines within the ecological literature have remained scarce. Here, I provide an overview of the most recent developments in the field, with a focus on main functional groups of insects, but also their interactions with other organisms. All major global change drivers (landscape modification, climate change, agricultural management) are covered both singly and in interaction. The manuscript concludes with concepts on how to statistically and conceptually deal with interactions in experimental and observational work.