Crop Pests and Predators Exhibit Inconsistent Responses to Surrounding Landscape Composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies

Predicting bee community responses to land-use changes: Effects of geographic and taxonomic biases

Land-use change and intensification threaten bee populations worldwide, imperilling pollination services. Global models are needed to better characterise, project, and mitigate bees' responses to these human impacts. The available data are, however, geographically and taxonomically unrepresentative; most data are from North America and Western Europe, overrepresenting bumblebees and raising concerns that model results may not be generalizable to other regions and taxa. To assess whether the geographic and taxonomic biases of data could undermine effectiveness of models for conservation policy, we have collated from the published literature a global dataset of bee diversity at sites facing land-use change and intensification, and assess whether bee responses to these pressures vary across 11 regions (Western, Northern, Eastern and Southern Europe; North, Central and South America; Australia and New Zealand; South East Asia; Middle and Southern Africa) and between bumblebees and other bees. Our analyses highlight strong regionally-based responses of total abundance, species richness and Simpson's diversity to land use, caused by variation in the sensitivity of species and potentially in the nature of threats. These results suggest that global extrapolation of models based on geographically and taxonomically restricted data may underestimate the true uncertainty, increasing the risk of ecological surprises

Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies

Polyphagy in the Australian population of South African citrus thrips (Scirtothrips aurantii Faure)

The South African citrus thrips, Scirtothrips aurantiiFaure, 1929, is highly polyphagous in its country of origin. Introduced to Australia in about 2002, populations of this thrips have been found only on the pasture weed Mother of Millions, Bryophyllum

Fresh, frozen or fake: a comparison of predation rates measured by various types of sentinel prey

Arthropod predators and parasitoids support the health and functioning of the world's ecosystems, most notably by supplying biological control services to agricultural landscapes. Quantifying the impact that these organisms have on their prey can be challenging, as direct observation and measurement of arthropod predation is difficult. The use of sentinel prey is one method to measure predator impact; however, despite widespread use, few studies have compared predation on different prey types within a single experiment. This study evaluated the predation rates on four sentinel prey items in grass and wheat fields in south-east Queensland, Australia. Attack rates on live and dead Helicoverpa armigera eggs, and dead H.\ua0armigera larvae and artificial plasticine larvae, were compared and the predators that were attracted to each prey type were documented with the use of field cameras. There was no significant difference in predation rates between sentinel eggs, while dead larvae were significantly more attacked than artificial larvae. Prey were attacked by a diverse range of predators, including ants, beetles, various nymph and juvenile insects and small mammals. Different predators were active in grass and crop fields, with predator activity peaking around dawn and dusk. The same trends were observed within and between the two habitats studied, providing a measure of confidence in the sentinel prey method. A range of different sentinel prey types could be suitable for use in most comparative studies; however, each prey type has its own benefits and limitations, and these should be carefully evaluated to determine which is most suitable to address the research questions

Landscape-scale mass-action of spiders explains early-season immigration rates in crops

Context Early-season immigration into arable fields by natural enemies is key for effective biocontrol, but little is known about the mechanisms underlying immigration processes. Objectives Here we test the mass action hypothesis for ballooning spiders, stating that local immigration rates are positively related to the amount of spiders in the surrounding landscape. Methods Immigration rates of spiders were assessed by sticky traps in remnant vegetation, in arable land 25–125 m from remnant vegetation, and in arable land further than 400 m from remnant vegetation. The experiment was conducted at 18 locations across two landscapes and repeated three times in a 2-week period in 2007 and 2008. Spider densities in crop and noncrop habitats were assessed by beat sheet sampling and used to calculate spider loads in landscape sectors around the experimental locations at five spatial scales. Results Regression analysis indicated that immigration rates were influenced by meteorological variables and landscape context at 2 km and possibly beyond. Regression models that included spider load at relevant spatial scales received more statistical support from the data than models with the proportion of remnant vegetation and crops. Regression analysis further indicated that wheat and—to a lesser extent— remnant vegetation are important habitats for the recruitment of ballooning spiders. Conclusions Our study provides support for the mass action hypothesis by showing that a combination of land-use variables with habitat specific spider densities allows the generation of functional cover types with greatly improved explanatory power

Measuring what matters: Actionable information for conservation biocontrol in multifunctional landscapes

Despite decades of study, conservation biocontrol via manipulation of landscape elements has not become a mainstream strategy for pest control. Meanwhile, conservation groups and governments rarely consider the impacts of land management on pest control, and growers can even fear that conservation biocontrol strategies may exacerbate pest problems. By finding leverage points among these actors, there may be opportunities to align them to promote more widespread adoption of conservation biological control at the landscape-scale. But are ecologists measuring the right things and presenting the right evidence to enable such alignment? We articulate key concerns of growers, conservation groups, and governments with regards to implementing conservation biological control at the landscape scale and argue that if ecologists want to gain more traction, we need to reconsider what we measure, for what goals, and for which audiences. A wider set of landscape objectives that ecologists should consider in our measurements include risk management for growers and co-benefits of multifunctional landscapes for public actors. Ecologists need to shift our paradigm toward longer-term, dynamic measurements, and build cross-disciplinary understanding with socioeconomic and behavioral sciences, to enable better integration of the objectives of these diverse actors that will be necessary for landscape management for conservation biocontrol to achieve its full potential

Role of grasslands in pest suppressive landscapes: how green are my pastures?

Grasslands are valuable non-crop habitats in the world's agricultural regions, providing more than simply forage for grazing domestic and wild animals. They provide refuge and resources that support high levels of arthropod biodiversity, most importantly for natural enemies that provide vital biological control services to the surrounding cropped landscape. Ideally, farmers could manage and manipulate grasslands to boost their biocontrol services, although to achieve this, knowledge of the ecological function of these habitats is essential. Unfortunately, grasslands are often bundled together with other habitat types, such as scrubland and forest, under the label 'non-crop habitats', and little is known about the contribution that these specific habitats make towards landscape pest suppression. While recent research has been investigating the importance of other non-crop habitat such as native vegetation remnants, the contribution that grassland habitats may make towards landscape pest suppression remains a significant knowledge gap in biocontrol research. Here, the current understanding of grassland habitats as biological control service providers in the world's mixed farming systems is reviewed. Limited research into whether grassland habitats support natural enemies, and thus contribute biological control services to the adjacent surrounding cropped landscape, has returned inconclusive, even conflicting, results. Potential explanations for this inconsistency are explored, including the lack of studies, inadequate estimates of predator impact and the variety of different grassland habitat types studied, including their diversity in composition and management practices. Conclusions drawn from these studies are discussed, and suggestions for management are recommended, including increasing grassland floristic diversity, limiting intensive management practices and implementing weed control. Future research directions are proposed, along with the need to develop a universal grassland classification system for research, management and conservation purposes, using grassland type, floristic diversity and management practices as key axes for classification