Disturbances associated with agricultural intensification reduce our ability to achieve sustainable crop production. These disturbances stem from crop-management tactics and can leave crop fields ...more vulnerable to insect outbreaks, in part because natural-enemy communities often tend to be more susceptible to disturbance than herbivorous pests. Recent research has explored practices that conserve natural-enemy communities and reduce pest outbreaks, revealing that different components of agroecosystems can influence natural-enemy populations. In this review, we consider a range of disturbances that influence pest control provided by natural enemies and how conservation practices can mitigate or counteract disturbance. We use four case studies to illustrate how conservation and disturbance mitigation increase the potential for biological control and provide co-benefits for the broader agroecosystem. To facilitate the adoption of conservation practices that improve top-down control across significant areas of the landscape, these practices will need to provide multifunctional benefits, but should be implemented with natural enemies explicitly in mind.
Conservation biological control (CBC) is a sustainable approach to pest management that can contribute to a reduction in pesticide use as part of an Integrated Pest Management (IPM) strategy. CBC is ...based on the premise that countering habitat loss and environmental disturbance associated with intensive crop production will conserve natural enemies, thus contributing to pest suppression. The abundance and diversity of natural enemies increases in response to a variety of conservation measures, including plant and habitat diversification, a reduction in cropping intensity, and increased landscape complexity. However, the response of natural enemy populations to conservation measures is not consistent; often it fails to translate into pest suppression or improved crop yield, and is seldom utilised in commercial crop production settings. CBC is a complex strategy drawing on a number of ecological and behavioural processes, operating at multiple scales, and mediated by management actions that are, potentially, targeted at a wide range of pest organisms. Given this inherent complexity, it is not surprising that the scientific understanding of CBC is incomplete, or that the design and adoption of reliable CBC prescriptions have proved elusive. To tackle this, we consolidate existing knowledge of CBC using a simple conceptual model that organises the functional elements of CBC into a common, unifying framework. We identify and integrate the key biological processes affecting natural enemies and their biological control function across local and regional scales, and consider the interactions, interdependencies and constraints that determine the outcome of CBC strategies. Conservation measures are often effective in supporting natural enemy populations but their success cannot be guaranteed; the greatest limitation to the development of effective CBC is due to a failure to adequately direct biological control services to achieve suppression of the target pests. By considering the performance of these and other components of CBC within the context of an integrated system, we believe that the limiting factors can be identified, and removed, allowing effective CBC strategies to be implemented.
•Conservation biological control aids natural pest management and sustainable farming.•A unifying framework outlines the functioning of conservation biological control.•Framework integrates conservation and biological control at local and landscape scale.•Routes to effective natural pest management are described.
Insects are among the most diverse and widespread animals across the biosphere and are well‐known for their contributions to ecosystem functioning and services. Recent increases in the frequency and ...magnitude of climatic extremes (CE), in particular temperature extremes (TE) owing to anthropogenic climate change, are exposing insect populations and communities to unprecedented stresses. However, a major problem in understanding insect responses to TE is that they are still highly unpredictable both spatially and temporally, which reduces frequency‐ or direction‐dependent selective responses by insects. Moreover, how species interactions and community structure may change in response to stresses imposed by TE is still poorly understood. Here we provide an overview of how terrestrial insects respond to TE by integrating their organismal physiology, multitrophic, and community‐level interactions, and building that up to explore scenarios for population explosions and crashes that have ecosystem‐level consequences. We argue that TE can push insect herbivores and their natural enemies to and even beyond their adaptive limits, which may differ among species intimately involved in trophic interactions, leading to phenological disruptions and the structural reorganization of food webs. TE may ultimately lead to outbreak–breakdown cycles in insect communities with detrimental consequences for ecosystem functioning and resilience. Lastly, we suggest new research lines that will help achieve a better understanding of insect and community responses to a wide range of CE.
Climate extremes including heatwaves are increasing in frequency, duration, and intensity. Exposure of ectothermic insects to temperature extremes will potentially impact their survival, development, reproduction, and other ecological aspects which are reviewed here. The outcomes (positive, negative, or neutral) may influence species interactions and create conditions that lead to breakouts, breakdowns, or both over time.
Primary consumers are under strong selection from resource (‘bottom‐up’) and consumer (‘top‐down’) controls, but the relative importance of these selective forces is unknown. We performed a ...meta‐analysis to compare the strength of top‐down and bottom‐up forces on consumer fitness, considering multiple predictors that can modulate these effects: diet breadth, feeding guild, habitat/environment, type of bottom‐up effects, type of top‐down effects and how consumer fitness effects are measured. We focused our analyses on the most diverse group of primary consumers, herbivorous insects, and found that in general top‐down forces were stronger than bottom‐up forces. Notably, chewing, sucking and gall‐making herbivores were more affected by top‐down than bottom‐up forces, top‐down forces were stronger than bottom‐up in both natural and controlled (cultivated) environments, and parasitoids and predators had equally strong top‐down effects on insect herbivores. Future studies should broaden the scope of focal consumers, particularly in understudied terrestrial systems, guilds, taxonomic groups and top‐down controls (e.g. pathogens), and test for more complex indirect community interactions. Our results demonstrate the surprising strength of forces exerted by natural enemies on herbivorous insects, and thus the necessity of using a tri‐trophic approach when studying insect‐plant interactions.
The evolution of land plants approximately 470 million years ago created a new adaptive zone for natural enemies (attackers) of plants. In response to attack, plants evolved highly effective, ...inducible defense systems. Two plant hormones modulating inducible defenses are salicylic acid (SA) and jasmonic acid (JA). Current thinking is that SA induces resistance against biotrophic pathogens and some phloem feeding insects and JA induces resistance against necrotrophic pathogens, some phloem feeding insects and chewing herbivores. Signaling crosstalk between SA and JA commonly manifests as a reciprocal antagonism and may be adaptive, but this remains speculative. We examine evidence for and against adaptive explanations for antagonistic crosstalk, trace its phylogenetic origins and provide a hypothesis-testing framework for future research on the adaptive significance of SA–JA crosstalk.
Cestrum (Solanaceae) species have become invasive in conservation and agricultural areas in South Africa, resulting in the initiation of a biological control (biocontrol) programme against these ...species in 2007. Of the four Cestrum species recorded in South Africa, Cestrum laevigatum Schltdl. and C. parqui L’Herit., which are both commonly referred to as inkberries, have become invasive while C. aurantiacum Lindl. and C. elegans (Brongn.) Schltdl. are still isolated at a few sites in the country. The biocontrol programme against Cestrum species (commonly called cestrum) was initially focussed on pathogens associated with these plants. Although the fungus Uromyces cestri Bertero ex Mont. (Pucciniales: Pucciniaceae) was found to be a promising agent for cestrum, the pathogen project was shelved due to lack of capacity. Field surveys conducted in Argentina from 2012 to 2020 revealed a total of eight phytophagous insects that could be candidate agents. Among these is a leaf-feeding flea beetle Epitrix sp. (Coleoptera: Chrysomelidae) that has been tested for host specificity. Out of 47 plant species tested to date, Epitrix sp. has only fed and developed on three Cestrum species, suggesting that it is suitable for release against cestrum in South Africa. Permission to release Epitrix sp. will be sought once it has been identified to the species level or it has been described as a new species. Two chrysomelid beetle species, a root-feeding flea beetle (Diphaulaca sp.) and an unidentified leaf-feeding flea beetle, were also collected on C. parqui, but attempts to rear the former were unsuccessful. Three other leaf-miners collected from C. parqui include: Acrocercops leucographa Clark (Lepidoptera: Gracillariidae), an unidentified moth (Lepidoptera: Argyresthiidae) and Liriomyza sp. nr. schlingerii (Diptera: Agromyzidae). A glass-winged butterfly (Lepidoptera: Nymphalidae) was the only herbivore that may be of biocontrol value on C. laevigatum. Whilst it is essential to extend the surveys to other regions of the native range, it is also important to prioritize the most promising potential biocontrol agents for further testing in South Africa. Given the suite of potential biocontrol agents in the native range, there are good prospects for the biocontrol of cestrum species in South Africa.
The farming practices adopted since the end of the Second World War, based on large areas of monocultures and chemical use, have adversely affected the health of farmers and consumers and ...dramatically reduced farmland biodiversity. As a consequence, many studies over more than twenty years have stated that agriculture is facing three main challenges: (1) feeding the growing world population (2) with more environmentally friendly products (3) at a reasonable return for the producer. Increasing the efficacy of biocontrol could be one lever for agriculture to meet these expectations. In this study we propose implementation of a relatively under-researched system based on the management of landscape level crop diversity that would reduce demand for pesticide use and increase conservation biocontrol. The principle of manipulating crop diversity over space and time at a landscape scale is to optimize resource continuity, such as food and shelter for natural enemies to increase biocontrol services, reduce pest outbreaks and crop losses. The feasibility of such management options is discussed in relation to environmental, social and economic aspects. The operational and institutional inputs and conditions needed to make the system work are explored, as well as the potential added values of such a system for different stakeholders.
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•Agriculture needs to be economically, socially and environmentally sustainable.•Increasing crop diversity at the landscape scale could improve biocontrol.•Complementary skills need to be gathered for optimal decision making.•The landscape biocontrol management has to be established in a win-win process.•More technical studies are needed before broadening this promising practice.
This study aims to apply an integrated pest control model (IPC) of brown planthoppers (bph) on rice against the presence of natural enemies in maintaining rice productivity. The research was ...conducted in Sentul Village, Tanggulangin District, Sidoarjo, East Java Province from September 2020 to December 2020. The research was conducted using a survey method. The research location was selected using the purposive sampling method, namely the area with the highest percentage of attacks, having been attacked at least 3 times the planting season, planting Inpari-4 rice varieties, and reported as brown planthoppers endemic areas in Sentul Village, Tanggulangin District, Sidoarjo. The results showed population abundance, percentage level of attack, lowest brown planthoppers attack intensity with IPC treatment and the highest with conventional control pedals, while the composition and abundance of brown planthoppers natural enemies was dominated by the family, Tetragnathidae and Coccinellidae (Coccinela repanda).
The fall armyworm (FAW), Spodoptera frugiperda, is a major pest of maize in North and South America. It was first reported from Africa in 2016 and currently established as a major invasive pest of ...maize. A survey was conducted to explore for natural enemies of the fall armyworm in Ethiopia, Kenya and Tanzania in 2017. Smallholder maize farms were randomly selected and surveyed in the three countries. Five different species of parasitoids were recovered from fall armyworm eggs and larvae, including four within the Hymenoptera and one Dipteran. These species are new associations with FAW and were never reported before from Africa, North and South America. In Ethiopia, Cotesia icipe was the dominant larval parasitoid with parasitism ranging from 33.8% to 45.3%, while in Kenya, the tachinid fly, Palexorista zonata, was the primary parasitoid with 12.5% parasitism. Charops ater and Coccygidium luteum were the most common parasitoids in Kenya and Tanzania with parasitism ranging from 6 to 12%, and 4 to 8.3%, respectively. Although fall armyworm has rapidly spread throughout these three countries, we were encouraged to see a reasonable level of biological control in place. This study is of paramount importance in designing a biological control program for fall armyworm, either through conservation of native natural enemies or augmentative release.
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