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1. Agricultural land use threatens ecosystem services such as biological control by natural enemies because of simplification of habitat structure and intensification of disturbance and agrochemical inputs. Low parasitism rates of agricultural pests have typically been attributed to a lack of resources for parasitoids in highly simplified landscapes, but this could be confounded by the nearly ubiquitous correlation between landscape complexity and the cover of intensively farmed agricultural crops. 2. Here, we disentangle the mechanisms driving landscape-scale effects on host—parasitoid interactions by taking advantage of a landscape modification gradient in which the diversity of habitat types and annual crop cover in the landscape were uncorrelated. We quantified herbivore densities and parasitism and hyperparasitism rates on two important crop pests (aphids and Plutella xylostella) across 30 landscapes. We used structural equation modelling (SEM) to test whether land-use intensity (insecticide application and habitat disturbance) or resource availability for parasitoids (floral resources and alternative host plants) was mediating the effects of habitat diversity and annual crop cover on the landscape. 3. Rates of primary- and hyperparasitism of aphids and primary parasitism of P. xylostella decreased with increasing annual crop cover, whereas decreasing habitat diversity in the landscape had little effect on parasitism rates. These effects were mediated almost entirely by greater habitat disturbance and greater frequency of insecticide application, rather than by changes in resource availability. 4. Parasitoids were more sensitive to intensive farming practices than were their herbivore hosts, and in turn hyperparasitoids were more sensitive than were primary parasitoids. This supports the theoretical prediction that higher trophic levels should be increasingly sensitive to the disturbances associated with land-use change. 5. Synthesis and applications. Our work suggests that increased land-use intensity (e.g. higher insecticide inputs and greater levels of disturbance associated with increasing area of annual crops) has been underestimated as a driver of landscape effects on host—parasitoid interactions. These findings have important implications for the maintenance of ecosystem services such as biological control. The promotion of low-intensity farming practices that limit the extent and frequency of agrochemical inputs and habitat disturbances will be essential for the maintenance of effective biological control by parasitoids in agroecosystems.

Sustainable agricultural practices in conjunction with ecological restoration methods can reduce the detrimental effects of agriculture. The Society for Ecological Restoration International has produced generic guidelines for conceiving, organizing, conducting and assessing ecological restoration projects. Additionally, there are now good conceptual frameworks, guidelines and practical methods for developing ecological restoration programmes that are based on sound ecological principles and supported by empirical evidence and modelling approaches. Restoration methods must also be technically achievable and socially acceptable and spread over a range of locations. It is important to reconcile differences between methods that favour conservation and those that favour economic returns, to ensure that conservation efforts are beneficial for both landowners and biodiversity. One option for this type of mutual benefit is the use of agri-environmental schemes to provide financial incentives to landholders in exchange for providing conservation services and other benefits. However, further work is required to define and measure the effectiveness of agri-environmental schemes. The broader potential for ecological restoration to improve the sustainability of agricultural production while conserving biodiversity in farmscapes and reducing external costs is high, but there is still much to learn, particularly for the most efficient use of agri-environmental schemes to change land use practice.

New Zealand pastures largely comprising Lolium ryegrass species (Poales: Poaceae) are worth $19.6B and are subject to major pest impacts. A very severe pest is the Argentine stem weevil Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). This has been previously suppressed by the importation biological control agent, Microctonus hyperodae Loan (Hymenoptera: Braconidae). However, this suppression has recently declined and is subject to investigation. It has been hypothesised that grass type influences the parasitism avoidance behaviour by the weevil and thus parasitism rates. This study explored the hypothesis using three common pasture grasses: a diploid Lolium perenne x Lolium multiflorum hybrid ryegrass (cv. Manawa), a tetraploid Italian ryegrass L. multiflorum Lam. (cv. Tama), and a diploid perennial ryegrass L. perenne L. (cv. Samson). The described laboratory-based microcosm methodology determined the extent of weevil avoidance behaviour on each of these three grasses when subjected to the parasitoid. Such reaction was gauged by the extent of reduced weevil on-plant presence and feeding compared to the control populations. In the absence of the parasitoid, the hybrid cv. Manawa ryegrass is as highly favoured by the weevil as the tetraploid cv. Tama. On diploid cv. Samson, feeding is considerably less. In the presence of the parasitoid, weevils on the tetraploid cv. Tama plants showed little avoidance activity in response to the parasitoid and it can be argued that the benefits of staying on this plant outweighed the possibility of parasitism. Conversely and surprisingly, in the parasitoid’s presence, weevils on diploid cv. Manawa showed very strong avoidance behaviour leading to levels of exposure similar to those found on the less-preferred diploid cv. Samson. These findings reflect how weevil parasitism rates have declined in most Lolium grasses, particularly diploids, since the 1990s, but not in the tetraploid L. multiflorum . This contribution supports the hypothesis that the decline in weevil parasitism rates has been the result of rapid evolution arising from parasitoid-induced selection pressure and the countervailing effect of the nutritional quality of the host plants.

1. An increase in pesticide resistance in many pest species is promoting interest in biological control. Much remains to be learned about natural enemy immigration into and persistence within crops at specific times and how to maximize suppression of pest populations. Therefore this study was conducted to test a novel biological control approach, 'attract and reward' which combines two aspects of applied insect ecology: synthetic herbivore-induced plant volatiles (HIPVs) to improve immigration of beneficial taxa into crops and nectar plants to maintain their populations. 2. The 'attract and reward' approach was tested in sweetcorn, broccoli and wine-grapes with several HIPV formulations at 1·0% (v/v) as attractants and buckwheat (Fagopyrum esculentum Moench) as reward. Abundance of insects was assessed with non-attractive sticky traps for up to 22 days after the HIPV spray application. 3. In sweetcorn, Eulophidae were more numerous in the attract treatments: methyl anthranilate, methyl jasmonate (MeJA), methyl salicylate (MeSA) and HIPV mix. Encyrtidae were more abundant near MeJA-treated plants. In broccoli, Scelionidae were more abundant in MeSA treatments with reward and near cis-3-hexenyl acetate-treated plants without reward whilst Ceraphronidae were more numerous near MeSA and predators were more abundant near HIPV mix-treated plants. Nectar plant reward increased catches of parasitoids from several families in all three tested crop species and increased predators in sweet corn and broccoli. 4. Increases in natural enemy numbers were correlated with effects at the first and second trophic levels. Significantly fewer larvae of the sweetcorn pest Helicoverpa spp. were found on sweetcorn plants from plots with reward and significantly less Helicoverpa spp. damage was evident to cobs for one of the HIPV treatments. 5. Synthesis and applications. Results suggest that applications of synthetic HIPVs can enhance recruitment of natural enemies and buckwheat was a suitable resource subsidy plant for increasing abundance and residency. Whilst both of these approaches offer potential to enhance biological control, further work is required to realize fully synergistic effects from their combination as an 'attract and reward' approach.

Climate change affects agriculture through a range of direct and indirect pathways. These include direct changes to impacts of pests and diseases on crops and indirect effects produced by interactions between organisms. It remains unclear whether the net effects of these biotic influences will be beneficial or detrimental to crop yield because few studies consider multiple interactions within communities and the net effects of these on community structure and yield. In this study, we created two experimental grapevine communities in field cages, and quantified direct and indirect effects of key pest and disease species under simulated climate change conditions (elevated temperature and reduced humidity). We found that the net impact of simulated climate change on total yield differed for the two communities, with increased yield in one community and no effect in the other. These effects, and the interactions between pests and pathogens, may also have been affected by the prevailing abiotic conditions, and we discuss how these may contribute to our findings. These results demonstrate that future research should consider more of the interactions between key organisms affecting crops under varying abiotic conditions to help generate future recommendations for adapting to the effects of climate change.

1. Habitat manipulation is important for enhancing biological control of arthropod pests, but identification of selective food plants that benefit only natural enemies is required in order to avoid inadvertently exacerbating pest damage. 2. Greenhouse experiments were conducted to identify potential ground-cover plant species that would improve performance of the egg parasitoid Trichogramma carverae when mass released in vineyards to control the leafroller pest Epiphyas postvittana. Further experiments determined which plants increased immature survival and adult longevity of E. postvittana and a field experiment investigated field enhancement of biological control. 3. Greenhouse survival of T. carverae was greater in the presence of flowering shoots of Lobularia maritima than with flowering shoots of either Brassica juncea or Coriandrum sativum, or with shoots of any species from which flowers had been removed or a control with no shoots. Similar experiments with Fagopyrum esculentum and Borage officinalis showed survival was higher in the presence of shoots with flowers than in without-flower and control treatments. 4. Daily fecundity of T. carverae was greater in the presence of flowering shoots of L. maritima than F. esculentum and with treatments without flowers. There was no significant enhancement of fecundity with Brassica juncea and Borage officinalis flowers. 5. Adult longevity of male and female E. postvittana was as long in the presence of Borage officinalis and F. esculentum flowers as when fed a honey-based artificial diet but longevity was significantly lower than in the artificial diet treatment when caged with C. sativum and L. maritima, irrespective of whether flowers were present or not. 6. Larval development of E. postvittana on intact potted plants was lower on C. sativum and L. maritima than on Brassica juncea, Borage officinalis, F. esculentum and Trifolium repens (a known host of E. postvittana). 7. In the first and second 48-h periods after release of T. carverae in a field experiment, parasitism was significantly higher in pooled treatments with flowers (C. sativum, F. esculentum and L. maritima) than in pooled treatments without flowers (conventional ground-cover or bare earth). 8. Lobularia maritima provided clear benefit to T. carverae but was not used by adult and larval E. postvittana. 9. Synthesis and applications. Lobularia maritima is recommended as the selective food plant best suited to this system and its use beneath vines offers the additional advantage of suppressing weeds, so avoiding the need for herbicide applications and mechanical control.

Honeybees ( L.) are frequently used in agriculture for pollination services because of their abundance, generalist floral preferences, ease of management and hive transport. However, their populations are declining in many countries. Agri-Environment Schemes (AES) are being implemented in agricultural systems to combat the decline in populations of pollinators and other insects. Despite AES being increasingly embedded in policy and budgets, scientific assessments of many of these schemes still are lacking, and only a few studies have examined the extent to which insect pollinators use the floral enhancements that are part of AES and on which floral components they feed (i.e., pollen and/or nectar). In the present work, we used a combination of observations on honeybee foraging for nectar/pollen from the Californian annual plant in the field, collection of pollen pellets from hives, and pollen identification, to assess the value of adding phacelia to an agro-ecosystem to benefit honeybees. It was found that phacelia pollen was almost never taken by honeybees. The work here demonstrates that honeybees may not use the floral enhancements added to a landscape as expected and points to the need for more careful assessments of what resources are used by honeybees in AES and understanding the role, if any, which AES play in enhancing pollinator fitness. We recommend using the methodology in this paper to explore the efficacy of AES before particular flowering species are adopted more widely to give a more complete illustration of the actual efficacy of AES.

Biological control, a globally-important ecosystem service, can provide long-term and broad-scale suppression of invasive pests, weeds and pathogens in natural, urban and agricultural environments. Following (few) historic cases that led to sizeable environmental up-sets, the discipline of arthropod biological control has—over the past decades—evolved and matured. Now, by deliberately taking into account the ecological risks associated with the planned introduction of insect natural enemies, immense environmental and societal benefits can be gained. In this study, we document and analyze a successful case of biological control against the cassava mealybug, Phenacoccus manihoti (Hemiptera: Pseudococcidae) which invaded Southeast Asia in 2008, where it caused substantial crop losses and triggered two- to three-fold surges in agricultural commodity prices. In 2009, the host-specific parasitoid Anagyrus lopezi (Hymenoptera: Encyrtidae) was released in Thailand and subsequently introduced into neighboring Asian countries. Drawing upon continental-scale insect surveys, multi-year population studies and (field-level) experimental assays, we show how A. lopezi attained intermediate to high parasitism rates across diverse agro-ecological contexts. Driving mealybug populations below non-damaging levels over a broad geographical area, A. lopezi allowed yield recoveries up to 10.0 t/ha and provided biological control services worth several hundred dollars per ha (at local farm-gate prices) in Asia’s four-million ha cassava crop. Our work provides lessons to invasion science and crop protection worldwide. Furthermore, it accentuates the importance of scientifically-guided biological control for insect pest management, and highlights its potentially large socio-economic benefits to agricultural sustainability in the face of a debilitating invasive pest. In times of unrelenting insect invasions, surging pesticide use and accelerating biodiversity loss across the globe, this study demonstrates how biological control—as a pure public good endeavor—constitutes a powerful, cost-effective and environmentally-responsible solution for invasive species mitigation.

Global food security requires increased crop productivity to meet escalating demand 1–3 . Current food production systems are heavily dependent on synthetic inputs that threaten the environment and human well-being 2,4,5 . Biodiversity, for instance, is key to the provision of ecosystem services such as pest control 6,7 , but is eroded in conventional agricultural systems. Yet the conservation and reinstatement of biodiversity is challenging 5 , 8 , 9 , and it remains unclear whether the promotion of biodiversity can reduce reliance on inputs without penalizing yields on a regional scale. Here we present results from multi-site field studies replicated in Thailand, China and Vietnam over a period of four years, in which we grew nectar-producing plants around rice fields, and monitored levels of pest infestation, insecticide use and yields. Compiling the data from all sites, we report that this inexpensive intervention significantly reduced populations of two key pests, reduced insecticide applications by 70%, increased grain yields by 5% and delivered an economic advantage of 7.5%. Additional field studies showed that predators and parasitoids of the main rice pests, together with detritivores, were more abundant in the presence of nectar-producing plants. We conclude that a simple diversification approach, in this case the growth of nectar-producing plants, can contribute to the ecological intensification of agricultural systems. Current food production systems are heavily dependent on synthetic inputs that threaten the environment and human wellbeing. Results from multi-site field experiments in Thailand, China and Vietnam reveal that surrounding rice fields with nectar-producing plants significantly reduces pest numbers and the need for insecticide applications, while increasing yields.

The expansion of intensive agricultural practices is a major threat to biodiversity and to the delivery of ecosystem services on which humans depend. Local‐scale conservation management strategies, such as agri‐environment schemes to preserve biodiversity, have been widely adopted to reduce the negative impacts of agricultural intensification. However, it is likely that the effectiveness of these local‐scale management actions depend on the structure and composition of the surrounding landscape. We experimentally tested the utility of floral resource strips to improve local‐scale biological control of crop pests, when placed within a gradient of moderately simple through to highly complex landscapes. We found that experimental provision of floral resources enhanced parasitism rates of two globally important crop pests in moderately simple landscapes but not in highly complex ones, and this translated into reduced pest abundances and increased crop yield. Synthesis and applications. Our results lend experimental support for the ‘intermediate landscape complexity hypothesis’, which predicts that local conservation management will be most effective in moderately simple agricultural landscapes, and less effective in either very simple landscapes where there is no capacity for response, or in highly complex landscapes where response potential is already saturated. This knowledge will allow more targeted and cost‐effective implementation of conservation biological control programs based on an improved understanding of landscape‐dependent processes, which will reduce the negative impacts of agricultural intensification.