Warming Alters Prey Density and Biological Control in Conventional and Organic Agricultural Systems

Microplastics accumulation in leaf litter: Field evidence for microplastic ingestion and transfer through prey-predatory relationships

Microplastics (MP) contamination of the terrestrial environment is a global concern. The contamination level of MPs in leaf litter and soil fauna that feed on it has not been reported. Moreover, the interspecific relationships among field soil fauna at different trophic levels and their effects on MP loads remain unclear. Thus, we selected a model food chain including a prey-isopod and predatory-spider relationship to evaluate the role of this relationship in the MPs body burden. The results showed that MP concentrations in the fallen leaf litter ranged from 5340 ± 336.15 particles/kg to 10920 ± 432.43 particles/kg dry weight during different seasons of the monitoring year. However, we found MP particles ranged from 1.17 ± 0.25 to 10.11 ± 1.02 particles/ind in isopods and 2.25 ± 0.35 to 4.25 ± 0.35 particles/ind in spiders. All extracted MPs were colored and blue was the most prevalent one. Fiber-shaped polyester (≤500 μm) and (501-1000 μm) were the most common MPs size in tested fauna and leaf litter, respectively. Our findings indicate that MP ingestion by isopods pose a significant risk for higher trophic levels in the terrestrial food chain. Magnification of MPs was observed in the predatory spider with MP concentration increasing from 46.45 ± 16.68 particles/gm wet weight in isopod to 147.51 ± 54.4 particles/gm wet weight in spider, annually. Furthermore, the results indicate that these soil invertebrates may represent a source of MPs to other organisms in the environment.

Seasonal variations and risk assessment of microplastic contamination in agricultural soil and associated macroinvertebrates in Egypt

Contamination by microplastics (MPs) has the potential to rank among the world's most significant environmental issues. Despite the fact that MP contamination is a global problem, little is known about the time variation of MPs in agricultural soil and its faunal communities which represent a key role to risk assessment. This study represents a first field investigation regarding the MP concentrations in agricultural ecosystem in Egypt. Our study investigates the seasonal fluctuations of MPs in soil and its common fauna in a citrus orchard (Citrus sinensis) in Egypt's Sohag Governorate. Moreover, this work aimed to identify how feeding strategies and body size of the selected fauna affect the no. of MPs ingested. The greatest mean concentration of MPs in soil was observed in summer (664 ± 90.20 items/kg) dry weight. However the lowest was recorded in autumn (354 ± 70.92 items/kg). Aporrectodea caliginosa (earthworms) was more contaminated with MPs (6.84 ± 2.5 item/individual annually) than Anisolabis maritima (earwigs) (2.06 ± 0.86 item/individual annually). When comparing between taxa without considering the size of the organisms, earwigs showed higher MPs concentrations (ranged from 117.93 ± 5.23 to 244.38 ± 4.57 items/gm wet weight) than the earthworms (ranged from 25.62 ± 2.43 to 51.66 ± 4.05 items/gm wet weight). Our results found that blue and red colors were the predominant colors in the soil and the selected fauna. Also, polyester fibers (PES) were the most popular type of microplastics, followed by fractions of polyethylene (PE) and polypropylene (PP). Interestingly, the reduction in the MP particles in the present taxa was observed compared to those in the soil. Pollution load index (PLI) value varied across seasons, with the lowest recorded in autumn due to reduced MPs abundance. The Hazard (H) index indicates a moderate risk (level III) due to high polyester abundance and a low hazard score (4) across all seasons. Our results represent a starting point for further studies on the impact of MPs on soil organisms in various agricultural soils.

How modularity and heterotrophy complicate the understanding of the causes of thermal performance curves: the case of feeding rate in a filter-feeding animal

Warming global temperatures have consequences for biological rates. Feeding rates reflect the intake of energy that fuels survival, growth and reproduction. However, temperature can also affect food abundance and quality, as well as feeding behavior, which all affect feeding rate, making it challenging to understand the pathways by which temperature affects the intake of energy. Therefore, we experimentally assessed how clearance rate varied across a thermal gradient in a filter-feeding colonial marine invertebrate (the bryozoan Bugula neritina). We also assessed how temperature affects phytoplankton as a food source, and zooid states within a colony that affect energy budgets and feeding behavior. Clearance rate increased linearly from 18°C to 32°C, a temperature range that the population experiences most of the year. However, temperature increased algal cell size, and decreased the proportion of feeding zooids, suggesting indirect effects of temperature on clearance rates. Temperature increased polypide regression, possibly as a stress response because satiation occurred quicker, or because phytoplankton quality declined. Temperature had a greater effect on clearance rate per feeding zooid than it did per total zooids. Together, these results suggest that the effect of temperature on clearance rate at the colony level is not just the outcome of individual zooids feeding more in direct response to temperature but also emerges from temperature increasing polypide regression and the remaining zooids increasing their feeding rates in response. Our study highlights some of the challenges for understanding why temperature affects feeding rates, especially for understudied, yet ecologically important, marine colonial organisms.

Bottom-Up Forces in Agroecosystems and Their Potential Impact on Arthropod Pest Management

Bottom-up effects are major ecological forces in crop-arthropod pest-natural enemy multitrophic interactions. Over the past two decades, bottom-up effects have been considered key levers for optimizing integrated pest management (IPM). Irrigation, fertilization, crop resistance, habitat manipulation, organic management practices, and landscape characteristics have all been shown to trigger marked bottom-up effects and thus impact pest management. In this review, we summarize current knowledge on the role of bottom-up effects in pest management and the associated mechanisms, and discuss several key study cases showing how bottom-up effects practically promote natural pest control. Bottom-up effects on IPM also contribute to sustainable intensification of agriculture in the context of agricultural transition and climate change. Finally, we highlight new research priorities in this important area. Together with top-down forces (biological control), future advances in understanding ecological mechanisms underlying key bottom-up forces could pave the way for developing novel pest management strategies and new optimized IPM programs.

Functional response of Harmonia axyridis preying on Acyrthosiphon pisum nymphs: the effect of temperature

In the current study, we investigated the functional response of Harmonia axyridis adults and larvae foraging on Acyrthosiphon pisum nymphs at temperatures between 15 and 35 °C. Logistic regression and Roger’s random predator models were employed to determine the type and parameters of the functional response. Harmonia axyridis larvae and adults exhibited Type II functional responses to A. pisum, and warming increased both the predation activity and host aphid control mortality. Female and 4th instar H. axyridis consumed the most aphids. For fourth instar larvae and female H. axyridis adults, the successful attack rates were 0.23 ± 0.014 h⁻¹ and 0.25 ± 0.015 h⁻¹; the handling times were 0.13 ± 0.005 h and 0.16 ± 0.004 h; and the estimated maximum predation rates were 181.28 ± 14.54 and 153.85 ± 4.06, respectively. These findings accentuate the high performance of 4th instar and female H. axyridis and the role of temperature in their efficiency. Further, we discussed such temperature-driven shifts in predation and prey mortality concerning prey-predator foraging interactions towards biological control.

Climate change and land use induce functional shifts in soil nematode communities

Land-use intensification represents one major threat to the diversity and functioning of terrestrial ecosystems. In the face of concurrent climate change, concerns are growing about the ability of intensively managed agroecosystems to ensure stable food provisioning, as they may be particularly vulnerable to climate extreme-induced harvest losses and pest outbreaks. Extensively managed systems, in contrast, were shown to mitigate climate change based on plant diversity-mediated effects, such as higher functional redundancy or asynchrony of species. In this context, the maintenance of soils is essential to sustain key ecosystem functions such as nutrient cycling, pest control, and crop yield. Within the highly diverse soil fauna, nematodes represent an important group as their trophic spectrum ranges from detritivores to predators and they allow inferences to the overall state of the ecosystem (bioindicators). Here, we investigated the effects of simulated climate change and land-use intensity on the diversity and abundance of soil nematode functional groups and functional indices in two consecutive years. We revealed that especially land use induced complex shifts in the nematode community with strong seasonal dynamics, while future climate led to weaker effects. Strikingly, the high nematode densities associated with altered climatic conditions and intensive land use were a consequence of increased densities of opportunists and potential pest species (i.e., plant feeders). This coincided with a less diverse and less structured community with presumably reduced capabilities to withstand environmental stress. These degraded soil food web conditions represent a potential threat to ecosystem functioning and underline the importance of management practices that preserve belowground organisms.

Combined effects of night warming and light pollution on predator-prey interactions

Interactions between multiple anthropogenic environmental changes can drive non-additive effects in ecological systems, and the non-additive effects can in turn be amplified or dampened by spatial covariation among environmental changes. We investigated the combined effects of night-time warming and light pollution on pea aphids and two predatory ladybeetle species. As expected, neither night-time warming nor light pollution changed the suppression of aphids by the ladybeetle species that forages effectively in darkness. However, for the more-visual predator, warming and light had non-additive effects in which together they caused much lower aphid abundances. These results are particularly relevant for agriculture near urban areas that experience both light pollution and warming from urban heat islands. Because warming and light pollution can have non-additive effects, predicting their possible combined consequences over broad spatial scales requires knowing how they co-occur. We found that night-time temperature change since 1949 covaried positively with light pollution, which has the potential to increase their non-additive effects on pea aphid control by 70% in US alfalfa. Our results highlight the importance of non-additive effects of multiple environmental factors on species and food webs, especially when these factors co-occur.

Can agricultural practices that mitigate or improve crop resilience to climate change also manage crop pests?

Sustainable agricultural practices that are promoted for mitigating climate change have the potential to also improve pest management. The author highlights recent studies that demonstrate effects of climate-mitigating agricultural practices on arthropod pests and predators in agronomic cropping systems. Promising practices for suppressing pests and/or improving biological control include: plant species diversification, especially via the addition of perennial species; cover cropping; tillage practices that retain crop residue; application of organic fertilizers such as compost and manure; and water management practices such as irrigation and sustainable rice intensification. More research is needed that explicitly tests pest and predator responses to agricultural practices under climate change conditions, if these practices are to be effectively promoted and implemented as agricultural pest management strategies.