Projecting pest population dynamics under global warming: the combined effect of inter- and intra-annual variations

Pest management facing warming and chemical stresses: Multi-stress effects on the biological agent Trichogramma oleae

Global change is affecting plant-insect interactions in agroecosystems and can have dramatic consequences on yields when causing non-targeted pest outbreaks and threatening the use of pest natural enemies for biocontrol. The vineyard agroecosystem is an interesting system to study multi-stress conditions: on the one hand, agricultural intensification comes with high inputs of copper-based fungicides and, on the other hand, temperatures are rising due to climate change. We investigated interactive and bottom-up effects of both temperature increase and copper-based fungicides exposure on the important Lepidopteran vineyard pest Lobesia botrana and its natural enemy, the oophagous parasitoid Trichogramma oleae. We exposed L. botrana larvae to three increasing copper sulfate concentrations under two fluctuating thermal regimes, one current and one future. Eggs produced by L. botrana were then exposed to T. oleae. Our results showed that the survival of L. botrana, was only reduced by the highest copper sulfate concentration and improved under the warmer regime. The development time of L. botrana was strongly reduced by the warmer regime but increased with increasing copper sulfate concentrations, whereas pupal mass was reduced by both thermal regime and copper sulfate. T. oleae F1 emergence rate was reduced and their development time increased by combined effects of the warmer regime and increasing copper sulfate concentrations. Size, longevity and fecundity of T. oleae F1 decreased with high copper sulfate concentrations. These effects on the moth pest and its natural enemy are probably the result of trade-offs between the survival and the development of L. botrana facing multi-stress conditions and implicate potential consequences for future biological pest control. Our study supplies valuable data on how the interaction between pests and biological control agents is affected by multi-stress conditions.

Functional and Behavioral Responses of the Natural Enemy Anthocoris nemoralis to Cacopsylla pyri, at Different Temperatures

Anthocoris nemoralis is the dominant predator of pear sucker (Cacopsylla pyri) in the UK. Anthocoris nemoralis migrates into orchards in spring or is introduced as a biocontrol agent, reaching peak population levels in July-August, contributing to effective control of summer pear sucker populations. However, due to temperature dependent development and metabolism there are concerns that C. pyri populations or feeding rates may increase due to changing climatic conditions. Thus, how A. nemoralis responds to temperature, impacts its ability as a biocontrol agent. Functional response assays, monitoring attack rate and handling time of A. nemoralis and behavioral assays, using Ethovision tracking software occurred, to assess the impact of temperature on predation. Experiments were conducted at current and future July-August mean temperatures, predicted using RCP4.5 and RCP8.5 (medium and high, representative concentration pathway) emissions scenarios, using 2018 UK Climate Projections (UKCP18). All treatments demonstrated a Type II functional response, with female anthocorids demonstrating shorter handling times and higher attack rates than males. Males showed longer prey handling times at 18 °C compared to 23 °C and more time was spent active at lower temperatures for both sexes. Females did not show significant differences in attack rate or handling time in response to temperature. Overall prey consumption was also not significantly affected by temperature for either sex. This study suggests that anthocorids are likely to remain effective natural enemies under future predicted temperatures, due to non-significant differences in prey consumption.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10905-023-09836-5.

Computational biogeographic distribution of the fall armyworm (Spodoptera frugiperda J.E. Smith) moth in eastern Africa

The fall armyworm (FAW), Spodoptera frugiperda J.E. Smith, has caused massive maize losses since its attack on the African continent in 2016, particularly in east Africa. In this study, we predicted the spatial distribution (established habitat) of FAW in five east African countries viz., Kenya, Tanzania, Rwanda, Uganda, and Ethiopia. We used FAW occurrence observations for three years i.e., 2018, 2019, and 2020, the maximum entropy (MaxEnt) model, and bioclimatic, land surface temperature (LST), solar radiation, wind speed, elevation, and landscape structure data (i.e., land use and land cover and maize harvested area) as explanatory variables. The explanatory variables were used as inputs into a variable selection experiment to select the least correlated ones that were then used to predict FAW establishment, i.e., suitability areas (very low suitability - very high suitability). The shared socio-economic pathways, SSP2-4.5 and SSP5-8.5 for the years 2030 and 2050 were used to predict the effect of future climate scenarios on FAW establishment. The results demonstrated that FAW establishment areas in eastern Africa were based on the model strength and true performance (area under the curve: AUC = 0.87), but not randomly. Moreover, ∼27% of eastern Africa is currently at risk of FAW establishment. Predicted FAW risk areas are expected to increase to ∼29% (using each of the SSP2-4.5 and SSP5-8.5 scenarios) in the year 2030, and to ∼38% (using SSP2-4.5) and ∼35% (using SSP5-8.5) in the year 2050 climate scenarios. The LULC, particularly croplands and maize harvested area, together with temperature and precipitation bioclimatic variables provided the highest permutation importance in determining the occurrence and establishment of the pest in eastern Africa. Specifically, the study revealed that FAW was sensitive to isothermality (Bio3) rather than being sensitive to a single temperature value in the year. FAW preference ranges of temperature, precipitation, elevation, and maize harvested area were observed, implying the establishment of a once exotic pest in critical maize production regions in eastern Africa. It is recommended that future studies should thus embed the present study's modeling results into a dynamic platform that provides near-real-time predictions of FAW spatial occurrence and risk at the farm scale.

Pest scenario of Helicoverpa armigera (Hub.) on pigeonpea during future climate change periods under RCP based projections in India

Gram pod borer, Helicoverpa armigera (Hub.) is the major insect pest of pigeonpea and prediction of number of generations (no. of gen.) and generation time (gen. time) using growing degree days (GDD) approach during three future climate change periods viz., Near (NP), Distant (DP) and Far Distant (FDP) periods at eleven major pigeonpea growing locations of India was attempted. Multi-model ensemble of Maximum (Tmax) and Minimum (Tmin) temperature data of four Representative Concentration Pathways viz., RCP 2.6, 4.5, 6.0 and 8.5 of Coupled Model Inter comparison Project 5 (CMIP5) models was adopted here. The increase in projected Tmax and Tmin are significant during 3 climate change periods (CCPs) viz., the NP, DP and FDP over base line (BL) period under four RCP scenarios at all locations and would be higher (4.7-5.1 °C) in RCP 8.5 and in FDP. More number of annual (10-17) and seasonal (5-8) gens. are expected to occur with greater percent increase in FDP (8 to 38%) over base line followed by DP (7 to 22%) and NP (5to 10%) periods with shortened annual gen. time (4 to 27%) across 4 RCPs. The reduction of crop duration was substantial in short, medium and long duration pigeonpeas at all locations across 4 RCPs and 3 CCPs. The seasonal no.of gen. is expected to increase (5 to 35%) with shortened gen. time (4 to 26%) even with reduced crop duration across DP and FDP climate periods of 6.0 and 8.5 RCPs in LD pigeonpea. More no. of gen. of H. armigera with reduced gen. time are expected to occur at Ludhiana, Coimbatore, Mohanpur, Warangal and Akola locations over BL period in 4 RCPs when normal duration of pigeonpeas is considered. Geographical location (66 to 72%), climate period (11 to 19%), RCPs (5-7%) and their interaction (0.04-1%) is vital and together explained more than 90% of the total variation in future pest scenario. The findings indicate that the incidence of H. armigera would be higher on pigeonpea during ensuing CCPs in India under global warming context.

Molecular epidemiology on seasonal variation of yellow mosaic disease incidence in blackgram (Vigna mungo L. Hepper) with its vector Bemisia tabaci

The yellow mosaic disease (YMD) of blackgram caused by Mungbean yellow mosaic virus has emerged as a serious threat to grain legume production, especially in Southeastern Asia. Seasonal incidence of YMD with its vector population was assessed in three different agroclimatic zones of Tamil Nadu in India for three consecutive cropping seasons namely, Rabi 2018 (October-December), Summer 2019 (March-May), and Kharif 2019 (June-August) at three different time intervals viz., 20, 40, and 60 days after sowing (DAS). For all three seasons, disease incidence and whitefly count were recorded for a resistant and susceptible variety of blackgram in fields without any vector control intervention. The highest disease incidence (87%) was observed in the Panpozhi location during the summer season followed by Vamban and Coimbatore locations. The whitefly count was made through both visual count and yellow sticky traps. The whitefly population was highest at 20 DAS and decreased with the increasing age of crop for all the three locations assessed. Molecular epidemiology was analyzed by determining latent infection of mungbean yellow mosaic virus (MYMV) using molecular diagnosis. Latent infection was found to be well pronounced in the Coimbatore location during the Kharif season, where the crop was asymptomatic in both the resistant and susceptible varieties for all the three time periods assessed. The latent infection of MYMV observed in Coimbatore and Vamban ranged from 16.6 to 83.3% in both resistant and susceptible varieties for all three seasons. In Panpozhi, the latent infection of MYMV ranged from 16.6 to 66.6% for the susceptible variety (CO-5) for all three seasons observed. However, in the Panpozhi location, the resistant variety (VBN-8) failed to record any latent infection.

Evolved transcriptional responses and their trade-offs after long-term adaptation of Bemisia tabaci to a marginally-suitable host

Although generalist insect herbivores can migrate and rapidly adapt to a broad range of host plants, they can face significant difficulties when accidentally migrating to novel and marginally-suitable hosts. What happens, both in performance and gene expression regulation, if these marginally-suitable hosts must be used for multiple generations before migration to a suitable host can take place, largely remains unknown. In this study, we established multigenerational colonies of the whitefly Bemisia tabaci, a generalist phloem-feeding species, adapted to a marginally-suitable host (habanero pepper) or an optimal host (cotton). We used reciprocal host tests to estimate the differences in performance of the populations on both hosts under optimal (30 oC) and mild-stressful (24 oC) temperature conditions, and documented the associated transcriptomic changes. The habanero pepper-adapted population greatly improved its performance on habanero pepper but did not reach its performance level on cotton, the original host. It also showed reduced performance on cotton, relative to the non-adapted population, and an antagonistic effect of the lower-temperature stressor. The transcriptomic data revealed that most of the expression changes, associated with long-term adaptation to habanero pepper, can be categorized as "evolved" with no initial plastic response. Three molecular functions dominated: enhanced formation of cuticle structural constituents, enhanced activity of oxidation-reduction processes involved in neutralization of phytotoxins and reduced production of proteins from the cathepsin B family. Taken together, these findings indicate that generalist insects can adapt to novel host plants by modifying the expression of a relatively small set of specific molecular functions.

Size, not temperature, drives cyclopoid copepod predation of invasive mosquito larvae

During range expansion, invasive species can experience new thermal regimes. Differences between the thermal performance of local and invasive species can alter species interactions, including predator-prey interactions. The Asian tiger mosquito, Aedes albopictus, is a known vector of several viral diseases of public health importance. It has successfully invaded many regions across the globe and currently threatens to invade regions of the UK where conditions would support seasonal activity. We assessed the functional response and predation efficiency (percentage of prey consumed) of the cyclopoid copepods Macrocyclops albidus and Megacyclops viridis from South East England, UK against newly-hatched French Ae. albopictus larvae across a relevant temperature range (15, 20, and 25°C). Predator-absent controls were included in all experiments to account for background prey mortality. We found that both M. albidus and M. viridis display type II functional response curves, and that both would therefore be suitable biocontrol agents in the event of an Ae. albopictus invasion in the UK. No significant effect of temperature on the predation interaction was detected by either type of analysis. However, the predation efficiency analysis did show differences due to predator species. The results suggest that M. viridis would be a superior predator against invasive Ae. albopictus larvae due to the larger size of this copepod species, relative to M. albidus. Our work highlights the importance of size relationships in predicting interactions between invading prey and local predators.

A Comprehensive Analysis of Wheat Resistance to Rhopalosiphum padi (Hemiptera: Aphididae) in Brazilian Wheat Cultivars

Rhopalosiphum padi L. is one of the predominant aphids affecting wheat crops worldwide. Therefore, the identification of resistant genotypes and the understanding of molecular response mechanisms involved in wheat resistance to this aphid may contribute to the development of new breeding strategies. In this study, we evaluated the resistance of 15 wheat cultivars to R. padi and performed morpho-histological and gene expression analyses of two wheat cultivars (BRS Timbaúva, resistant and Embrapa 16, susceptible) challenged and unchallenged by R. padi. The main findings of our work are as follows: 1) most Brazilian wheat cultivars recently released are resistant to R. padi; 2) Green leaf volatiles are probably involved in the resistance of the BRS Timbaúva cultivar to the aphid; 3) trichomes were more abundant and larger in the resistant cultivar; 4) the internal morphology did not show differences between cultivars; 5) the lipoxygenase-encoding gene was downregulated in the susceptible cultivar and basal expression remained level in the resistant cultivar; and 6) the expression of resistance-related proteins was induced in the resistant but not in the susceptible cultivar. Lipoxygenase is the first enzyme in the octadecanoic pathway, a well-known route for the synthesis of signaling molecules involved in the activation of plant defense. The overall analyses suggest that the key steps in BRS Timbaúva resistance to R. padi may be presence or absence of green leaf volatiles decreasing the aphid preference and the action of nonglandular trichome as a physical barrier, which allows continuous lipoxygenase-encoding gene expression.

Effects of simulated climate warming on the population dynamics of Sitobion avenae (Fabricius) and its parasitoids in wheat fields

BACKGROUND

Climate warming has considerable effects on crop development and pest population dynamics. Crucially, the tri-trophic responses of plants, herbivores and their natural enemies to warming are poorly understood. To delineate these interactive properties, a three-system approach and integrating life table methodology were used to examine the responses of wheat plants, English grain aphid and parasitoids under open-field infrared heating to simulate warming.

RESULTS

Warming significantly increased wheat biomass and grain weight, causing a phenological shift in plant growth. Importantly, warming significantly increased the number of aphids and the reproductive period, coupled with a higher net reproductive rate and intrinsic growth rate. Otherwise, duration of development, generation span, and population doubling time all decreased significantly. Warming had no effect on parasitoid abundance but resulted in a significant decrease in the rate of parasitism.

CONCLUSION

Warming may strengthen bottom-up effects on aphids by increasing wheat biomass, resulting in reduced regulation of aphid populations. Warming had a different effect on parasitoids between 2015 and 2016. These findings provide an important characterization of ecological mechanisms in plant-herbivore-parasitoid systems and give a theoretical foundation for improved forecasting of aphid population dynamics under climate change. © 2019 Society of Chemical Industry.

Climate model for seasonal variation in Bemisia tabaci using CLIMEX in tomato crops

The whitefly, Bemisia tabaci, is considered one of the most important pests for tomato Solanum lycopersicum. The population density of this pest varies throughout the year in response to seasonal variation. Studies of seasonality are important to understand the ecological dynamics and insect population in crops and help to identify which seasons have the best climatic conditions for the growth and development of this insect species. In this research, we used CLIMEX to estimate the seasonal abundance of a species in relation to climate over time and species geographical distribution. Therefore, this research is designed to infer the mechanisms affecting population processes, rather than simply provide an empirical description of field observations based on matching patterns of meteorological data. In this research, we identified monthly suitability for Bemisia tabaci, with the climate models, for 12 commercial tomato crop locations through CLIMEX (version 4.0). We observed that B. tabaci displays seasonality with increased abundance in tomato crops during March, April, May, June, October and November (first year) and during March, April, May, September and October (second year) in all monitored areas. During this period, our model demonstrated a strong agreement between B. tabaci density and CLIMEX weekly growth index (GIw), which indicates significant reliability of our model results. Our results may be useful to design sampling and control strategies, in periods and locations when there is high suitability for B. tabaci.

Spatially Differentiated Trends between Forest Pest-Induced Losses and Measures for Their Control in China

Historically, China has exhibited spatial differentiation in issues ranging from population distribution to ecological or economic development; forest pest-control work exemplifies this tendency. In recent times, global warming, man-made monoculture tree-plantations, increasing human population density, and intensified international trade aggravate forest pest outbreaks. Although the Chinese government has complied with internationally recommended practices, some aspects of pest management remain unaddressed due to existing differential regional imbalance in forest pest distribution and control capacities. Evidence shows that the high-income provinces in the south have taken advantage of economic and technological superiority, resulting in the adoption of more efficient pest-control measures. In contrast, the economically underdeveloped provinces of the northwest continue to experience a paucity of financial support that has led to serious threats of pest damage that almost mirror the demarcations of the Hu Huanyong Line. In this paper, we propose the introduction of a Public–Private–Partnership (PPP) model into forest pest control and the combination of the national strategies to enact regional prevention measures to break away from current spatially differentiated trends in China.

Large-Scale Climate Effects Meet an Amazonian Butterfly: Which Population Parameters Respond to El Niño?

One of the most tangible outcomes of climate change is change in the frequency of El Niño/La Niña events. They have a large impact on rainfall in the Western hemisphere, but their impact on tropical fauna is largely unknown. A decade long capture-mark-recapture study of the widespread Ecuadorian butterfly Nessaea hewitsoni (Felder & Felder) from an intact forest allowed us to analyze patterns of monthly and seasonal population dynamics before, during, and after an El Niño event. El Niño events did not affect long-term population size, but a 5-month delayed El Niño led to temporary emigration of females, with their subsequent return. Increased rainfall correlated with reduced survival in both sexes, but this effect was twice as strong in females. This investigation is the longest, continuous population study on any Neotropical insect species. Though we sampled on a modest scale, the magnitude of El Niño events suggests that our findings likely reflect insect population responses across a much larger portion of Amazonian forests. This study underscores the importance of analyzing multiple, interacting population parameters beyond local abundance in order to understand the biotic responses to El Niño and climate change in tropical systems. Had our analyses not included temporary emigration, no effect would have been detected because El Niño did not affect local population abundance.

A landscape genetic analysis of important agricultural pest species in Tunisia: The whitefly Bemisia tabaci

Combining landscape ecology and genetics provides an excellent framework to appreciate pest population dynamics and dispersal. The genetic architectures of many species are always shaped by environmental constraints. Because little is known about the ecological and genetic traits of Tunisian whitefly populations, the main objective of this work is to highlight patterns of biodiversity, genetic structure and migration routes of this pest. We used nuclear microsatellite loci to analyze B. tabaci populations collected from various agricultural areas across the country and we determine their biotype status. Molecular data were subsequently interpreted in an ecological context supplied from a species distribution model to infer habitat suitability and hereafter the potential connection paths between sampling localities. An analysis of landscape resistance to B. tabaci genetic flow was thus applied to take into account habitat suitability, genetic relatedness and functional connectivity of habitats within a varied landscape matrix. We shed light on the occurrence of three geographically delineated genetic groups with high levels of genetic differentiation within each of them. Potential migration corridors of this pest were then established providing significant advances toward the understanding of genetic features and the dynamic dispersal of this pest. This study supports the hypothesis of a long-distance dispersal of B. tabaci followed by infrequent long-term isolations. The Inference of population sources and colonization routes is critical for the design and implementation of accurate management strategies against this pest.

Warming impact on herbivore population composition affects top-down control by predators

Understanding warming impact on herbivores facilitates predicting plant/crop dynamics in natural/agricultural systems. However, it remains unclear how warming will affect herbivore population size and population composition, consequently altering herbivore colonization in a tri-trophic system (plant-herbivore-predator or crop-pest-biocontrol agent). We studied a soybean-aphid-lady beetle system, by conducting (1) a laboratory warming experiment to examine warming impact (+2 °C or +4 °C) on the aphid population size and composition (alate proportion), and (2) a field colonization experiment to examine whether the warming-induced effect subsequently interacts with predators (lady beetles) in affecting aphid colonization. The results showed that warming affected the initial aphid population composition (reduced alate proportion) but not population size; this warming-induced effect strengthened the top-down control by lady beetles and slowing aphid colonization. In other words, biocontrol on crop pests by predators could improve under 2-4 °C warming. Furthermore, aphid colonization was affected by an interaction between the alate proportion and predator (lady beetle) presence. This study suggests that warming affects herbivore population composition and likely mediates top-down control on herbivore colonization by predators. This mechanism may be crucial but underappreciated in climate change ecology because population composition (wing form, sex ratio, age/body size structure) shifts in many species under environmental change.