Consumptive and non‐consumptive effects of wolf spiders on cucumber beetles and cucumber plant damage

Biological control research often focuses on the ability of predators to reduce pest densities and protect crops through consumption. Less studied is their ability to protect crops by altering pest behaviour (non‐consumptive effects). Lab experiments were conducted to test predation rates of striped cucumber beetles (Acalymma vittatum; Coleoptera: Chrysomelidae) and spotted cucumber beetles (Diabrotica undecimpunctata howardi; Coleoptera: Chrysomelidae) by large (>10 mm) wolf spiders (Araneae: Lycosidae). Field experiments were conducted to examine how the physical presence and/or cues of spiders impact the behaviour and mortality of A. vittatum (specialist) and D. undecimpunctata (generalist) cucumber beetles as well as growth and damage of cucumber plants (Cucumis sativus; Cucurbitaceae). A. vittatum and D. undecimpunctata adults were added to caged cucumber plants without a spider, with spider cues only (spider removed before beetle inclusion), with spider only (spider introduced to plants immediately before beetle inclusion), and with spiders and their cues present (spiders introduced 24 hr in advance of beetle inclusion). A. vittatum responded to spider cues primarily by emigrating from plants. Contrarily, D. undecimpunctata did not display obvious responses, such as reduced feeding or increased emigration, to spider foraging and/or cues. Actively foraging lycosids increased A. vittatum mortality and reduced densities of D. undecimpunctata in the field when cucumber plants were flowering. This study highlights how non‐consumptive and consumptive effects can play a role in modifying pest populations, and how these effects can vary across species and plant growth stages.     

Cycles in voles and small game in relation to variations in plant production indices in Northern Sweden

Population dynamics for voles (Cricetidae), Tengmalm's owl (Aegolius funereus (L.)), red fox (Vulpes vulpes (L.)) willow grouse (Lagopus lagopus (L.)), black grouse (Lyrurus tetrix (L.)), capercaillie (Tetrao urogallus L.), hazel hen (Tetrastes bonasia (L.)), mountain hare (Lepus timidus L.) and tularemia (Francisella tularensis (McCoy & Chapin)) and game bird recruitment were studied by index methods in northern Sweden. In addition contemporary temperature records and spruce (Picea abies (L.) Karst.) and pine (Pinus silvestris L.) cone crops (as indices for plant production) and the occurrence of forest damage, caused by voles eating bark, were studied.During 1970–80 two synchronous 4-year cycles were observed for voles, predators (Tengmalm's owl and red fox) and their alternative prey species (grouse and mountain hare). In grouse the change of numbers was correlated with that of recruitment. Autumn vole numbers peaked about a year before the other species and extensive forest damage occurred at winter peak densities of voles. These population fluctuations are consistent with a predator-prey model for their regulation. In short the model suggests that vole-food plant interactions trigger the cycle of voles, that voles generate the cycle of predators and that these in turn synchronize alternative prey populations to the others at vole declines.For voles, grouse and red fox the amplitude was higher in the first cycle compared to the second one whilst the opposite was true for the mountain hare. Although temperature and cone crops showed large interannual variations they still implied that herbivore food conditions were better during the former cycle. Hence, the reduction of the amplitude of the vole cycle may be explained by inter-cyclic differences in plant food conditions, implying food shortage (as indicated by bark-eating) at different population levels. The similar decrease of grouse and red fox populations may also be explained by deteriorated food conditions and/or for the fox by an outbreak of sarcoptic mange (Sarcoptes scabiae var. vulpes). The increased amplitude of the mountain hare cycle was part of a long-term rise in numbers after a tularemia epidemic in 1967. This is interpreted as a recovery, probably towards the generally higher pre-epidemic population level.     

Epigeic spiders are not affected by the genetically modified maize MON 88017

The genetically modified (GM) maize MON 88017 facilitates weed management owing to its tolerance to glyphosate, and resists western corn rootworm (WCR), Diabrotica virgifera virgifera, owing to the expression of Cry3Bb1 toxin. MON 88017 could therefore contribute to the solution of two major problems of European agriculture: continuous WCR spreading and high use of herbicides. To assess possible unwanted environmental impacts of MON 88017, we compared communities of spiders in plots planted in three successive years with this maize, its near isogenic non‐GM cultivar treated or not treated with an insecticide and two unrelated maize cultivars. Each of the five treatments was applied on five 0.5 ha plots in a 14 ha field. Spiders were collected in five pitfall traps per plot five times per year. Upon reaching the waxy ripening stage, all plants of first‐year cultivation were shredded to small pieces and ploughed into the soil in the respective plot, whereas in the 2nd and 3rd year the harvest was used for biogas production and only digestate was returned to the field. Out of 79 spider species, Pardosa agrestis, Pachygnatha degeeri and Oedothorax apicatus made up 28%, 25% and 23% of the total spider count in the 1st year of study; 2%, 8% and 84% in the 2nd; and 40%, 8% and 35% in the 3rd year. Statistical analysis did not reveal any influence of GM maize on the spider abundance and biodiversity. The abundance, and in two years also the species diversity, was insignificantly higher on the plots with GM maize than on plots with the insecticide‐treated non‐GM maize. The composition and size of spider community varied year to year, probably reflecting weather conditions and differences in field fertilization with organic matter.     

Landscape context of sheetweb spider (Araneae: Linyphiidae) abundance in cereal fields

Aim Sheetweb spiders (Araneae: Linyphiidae, subfamily Linyphiinae) exemplify a highly mobile group of farmland arthropods with very variable abundances in crops within and between years. Despite their dominance in crops during summer, they overwinter predominantly in perennial non‐crop habitats, and their densities in crops during spring should therefore depend on the amount of favourable overwintering habitat in the surrounding landscape. We tested the effect of landscape composition on sheetweb spider abundance with special attention to the range of their aerial dispersal and weather dependence. Location The study was carried out in 18 non‐overlapping landscape sectors of 3 km radius around the city of Göttingen (Germany), forming a gradient from structurally simple, with up to 85% arable land, to structurally complex, with high percentages of grassland and other non‐crop habitats. Methods Sheetweb spider abundances in winter wheat fields were sampled during May and June 2001–2003 with a distance method. They were related to landscape composition at 11 spatial scales between 95 and 3000 m radius around the study sites. Results In 2001 and 2003, spider abundances were enhanced by high percentages of non‐crop habitats in 1–3 km circumference (e.g. from 18 to 130 m^?2 in late May 2001), and multiplied during consecutive sampling periods (e.g. from on average 36 to 131 m^?2 between mid‐May and late June 2001). Spider abundances were constantly low and unrelated to the landscape context in 2002. In that year, immigration appeared to be inhibited by factors connected to exceptionally high amounts of rain during May. Main conclusions Sheetweb spiders responded to landscape composition up to several kilometres away and the effects varied between years, demonstrating the need to consider large space and time‐scales to understand their population dynamics. Semi‐natural habitats should be preserved to enhance these important natural enemies of crop pests in agricultural landscapes.     

Economic and environmental performance of miscanthus cultivated on marginal land for biogas production

Environmental issues surrounding conventional annual biogas crops have led to growing interest in alternative crops, such as miscanthus. In addition to the better environmental performance, miscanthus can be grown on marginal land where no competition with feed and food crops is anticipated. On marginal land however, biomass yields are significantly lower than on good agricultural land. This raises the question of the economic and environmental sustainability of miscanthus cultivated on marginal land for biogas production. This study assessed the environmental and economic performance of miscanthus cultivated on marginal land for biogas production by conducting a Life‐Cycle Assessment and complementary Life‐Cycle Cost analysis. The functional unit chosen was 1 GJ of electricity (GJ_el.). The substitution of a fossil reference was included using a system expansion approach. Electricity generated by the combustion of miscanthus‐based biogas in a combined heat and power has considerably lower impacts on the environment than the fossil reference in most of the categories assessed. In the impact category “climate change”, the substitution of the marginal German electricity mix leads to a carbon mitigation potential of 256 kg CO₂e/GJ_el.. At 45.12 €/GJ_el., the costs of miscanthus‐based biogas generation and utilization are considerably lower than those of maize (61.30 €/GJ_el.). The results of this study clearly show that it can make economic and environmental sense to cultivate miscanthus on marginal land as a substrate for biogas production. The economic sustainability is however limited by the biomass yield. By contrast, there are no clear thresholds limiting the environmental performance. The decision needs to be made on a case‐by‐case basis depending on site‐specific conditions such as local biodiversity.     

Changes in habitat selection patterns of the gray partridge Perdix perdix in relation to agricultural landscape dynamics over the past two decades

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Spider mite infestations reduce Bacillus thuringiensis toxin concentration in corn leaves and predators avoid spider mites that have fed on Bacillus thuringiensis corn

Perceived benefits of insecticidal transgenic crops include reduced usage of broad‐based insecticides, and therefore lower risk to non‐target organisms. Numerous studies have documented low or no direct toxicity of Bacillus thuringiensis (Bt)‐derived toxins against non‐target organisms, but there has been less research on (a) effects of secondary pest infestations on Bt expressing in crops and (b) behavioural responses by predators feeding on host arthropods from Bt crops – both topics are investigated in this study. We quantified predation by the obligate spider mite predator Phytoseiulus persimilis of carmine spider mites (Tetranychus cinnabarinus), reared on Bt or non‐Bt corn (Zea mays). Both no‐choice and two‐choice studies were conducted. In addition, we quantified toxin levels in corn leaves with/without spider mite infestation. Under no‐choice conditions, P. persimilis consumed non‐Bt spider mites at a faster rate than Bt spider mites. Under two‐choice conditions, P. persimilis spent more time in the vicinity of non‐Bt spider mites than near Bt spider mites. Corn infested with spider mites exhibited lower toxin levels than non‐infested plants. These results suggest potentially complex interactions among non‐target herbivores, their natural enemies and Bt crops.     

Using a Crop Growth Model to Quantify Regional Biogas Potentials: an Example of the Model Region Biberach (South-West Germany)

Over the last decade, political framework conditions in the energy sector provoked a strong focus on biogas production in Germany. In this context, a sufficient and secure regional biomass supply is needed in order to run biogas plants economically. It is important to estimate which biomass amounts can be produced and are available for bioenergy production in a defined region. The present study focused on a model-based approach quantifying the biomass and, from this, the resulting biogas potential of the model region of Biberach (south-west Germany) using the process-oriented crop growth model DSSAT 4.0. Considering the regional soil and climate conditions of the model region, dry matter yields of maize, triticale, and a crop rotation system (CRS) of maize and triticale including different management systems (change in sowing and harvest date) were simulated. The results indicated an adequate model fit between simulated and measured yields. Dry matter yields of maize (14.7 t ha^?1), triticale (12.7 t ha^?1), and the CRS (18.1–19.2 t ha^?1) differed significantly, indicating that the chosen CRS provided the highest dry matter yields. The biomass potential of all crops was simulated considering different bioenergy scenarios depending on the available agricultural land used for bioenergy. The highest biomass potential was provided by the management system consisting of maize and triticale sown on 1 May and 15 October, respectively. Finally, an additional energy potential of 45,000 kW_el (bioenergy scenario 50/50 % of the agricultural land used for biogas production) and of 5,700 kW_el (bioenergy scenario 25/25 % of the agricultural land used for biogas production) was determined for the county of Biberach by implementing a CRS, which consisted of maize and triticale. It could be concluded that an additional biomass potential for biogas production exists in the county. Suitable areas for the location of biogas plants could be identified based on the available biomass potential.     

Bioenergy production and Skylark (Alauda arvensis) population abundance – a modelling approach for the analysis of land‐use change impacts and conservation options

Bioenergy production is seen as one way of meeting future energy needs. The growing demand for biomass for energy production induces the cultivation of a few fast growing and high‐yielding energy crops on vast areas of arable land. This land‐use change has been found associated with the reduction of habitat suitability for farmland birds and a decline in farmland biodiversity in general. A large number of studies have assessed the ecological effects of energy crop cultivation at the local scale of a single field. This study focuses on regional landscape changes caused by increased energy crop cultivation, which includes reduction of crop‐type richness and spatial concentration of single crop‐types. We present a spatially explicit ecological model to assess the population‐level consequences of these effects on the abundance of the farmland bird species Skylark (Alauda arvensis). We also investigate the impacts of different land‐use scenarios and aim to identify adaptive conservation options. We show that (1) the impacts of increased energy crop cultivation on Skylark population abundance depend strongly on the landscape structure; (2) impacts could be tolerated as long as a certain minimum level of crop‐type heterogeneity is retained at the landscape level and (3) conservation actions are required and effective especially on landscapes where crop‐field size is large.     

The impacts of four potential bioenergy crops on soil carbon dynamics as shown by biomarker analyses and DRIFT spectroscopy

Perennial bioenergy crops accumulate carbon (C) in soils through minimally disturbing management practices and large root inputs, but the mechanisms of microbial control over C dynamics under bioenergy crops have not been clarified. Root‐derived C inputs affect both soil microbial contribution to and degradation of soil organic matter resulting in differing soil organic carbon (SOC) concentrations, storage, and stabilities under different vegetation regimes. Here, we measured biomarker amino sugars and neutral sugars and used diffuse reflectance mid‐infrared Fourier transform spectroscopy (DRIFTS) to explore microbial C contributions, degradation ability, and SOC stability, respectively, under four potential bioenergy crops, M.×giganteus (Miscanthus × giganteus), switchgrass (Panicum virgatum L.), a mixed prairie, and a maize (Zea mays L.)–maize–soybean (Glycine max(L.) Merr.) (MMS) rotation over six growing seasons. Our results showed that SOC concentration (g/kg) increased by 10.6% in mixed prairie over the duration of this experiment and SOC storage (Mg/ha) increased by 17.0% and 15.6% in switchgrass and mixed prairie, respectively. Conversion of row crops to perennial grasses maintained SOC stability and increased bacterial residue contribution to SOC in M.×giganteus and switchgrass by 20.0% and 15.0%, respectively, after 6 years. Degradation of microbe‐derived labile SOC was increased in M.×giganteus, and degradation of both labile and stable SOC increased in MMS rotation. These results demonstrate that microbial communities under perennial grasses maintained SOC quality, while SOC quantity increased under switchgrass and mixed prairie. Annual MMS rotation displayed decreases in aspects of SOC quality without changes in SOC quantity. These findings have implications for understanding microbial control over soil C quantity and quality under land‐use shift from annual to perennial bioenergy cropping systems.     

Bioenergy crops and farmland biodiversity: benefits and limitations are scale-dependant for a declining mammal,the brown hare

Biomass energy crops are prompting major land-use changes in agricultural and marginal land in an effort to reduce dependency on fossil fuels. Miscanthus × giganteus, a perennial giant grass, is one of the main such crops in Europe but few studies exist of its interaction with farmland wildlife, particularly mammals. Understanding ecological impacts of bioenergy planting schemes is vital for mitigating potential negative effects on already declining farmland biodiversity and for maximising any benefits from these low-management, structurally diverse crops. We assessed in a mixed farming area in the UK the impact of Miscanthus crops on the brown hare (Lepus europaeus), a widespread but declining farmland species of conservation concern. We intensively radio-tracked hares in Miscanthus blocks of contrasting size and analysed hare diet for evidence of the consumption of Miscanthus. Home ranges differed starkly averaging 10.5 versus 49.6 ha in the small and the large Miscanthus blocks, respectively. Despite entirely avoiding the crop as food, hares appeared able to exist and even thrive in areas planted with Miscanthus though their populations may be significantly limited by reduced food availability and increased energy use where dense Miscanthus is planted over a wide area. As a component of a mixed farming landscape, Miscanthus may provide biodiversity benefits by increasing spatial heterogeneity and refuge areas for declining farmland species like brown hares but any effect is likely to be strongly scale-dependant.     

Survival strategies of Dalbulus maidis during maize off‐season in Brazil

Despite the importance of Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) as a vector of maize‐stunting pathogens, it is not understood how this leafhopper survives the maize off‐season in regions where overwintering hosts do not occur. We investigated migration and the use of alternate hosts as possible survival mechanisms for D. maidis during maize off‐season in Brazil. Dalbulus maidis populations were monitored with yellow sticky cards for 16–29 months in Anastácio (Mato Grosso do Sul State), in two farms with perennial pastures (Pasture1 and Pasture2), where maize had not been planted for >5 years, in a subsistence farm >20 km distant, where maize was annually planted (spring) (Maize1), and in Piracicaba (São Paulo State), where maize was grown year round (Maize2). RAPD‐PCR analysis of leafhoppers sampled on maize in two plots (Maize1 and Pasture1) at 15–20 and 110–120 days after germination was performed. Dalbulus maidis was trapped in the maize plots of all areas, but not in weedy or woody vegetation adjacent to the plots. Higher numbers were trapped throughout the year in Piracicaba, where maize was continuously grown under irrigation, and in the subsistence farm of Anastácio, where volunteer maize plants were available for long periods in the maize off‐season. In Anastácio farms, some population peaks were recorded in the absence of maize from midwinter to early spring, especially after soil plowing. RAPD‐PCR analysis showed that D. maidis populations sampled were genetically similar. Our data suggest that D. maidis uses a mixed strategy to survive the over‐season period in Brazil, in which part of the population overwinters locally on volunteer maize plants or nearby irrigated maize crops, whereas the other individuals migrate to colonize new maize crops in distant areas or regions. We hypothesize that immigrant D. maidis uses the contrast between plowed and vegetated soil as a visual cue for locating new maize crops.     

Use of wild and cultivated foods by chimpanzees at Bossou,Republic of Guinea: feeding dynamics in a human‐influenced environment

Increased human population growth and more conversions of natural habitat to agricultural land have resulted in greater proximity between humans and nonhuman primate species. Consequent increases in resource competition including crop‐raiding are a by‐product of both natural resources becoming less available and the nutritional benefits of cultivated foods becoming more known to the nonhuman primates. Chimpanzees at Bossou in the Republic of Guinea, West Africa, consume 17 different types of cultivated foods that are grown extensively throughout their small, fragmented home range. Direct observations of feeding behavior conducted over an 18‐month period revealed that during specific months crops account for up to one quarter of chimpanzee feeding time, with higher overall crop‐raiding levels throughout the periods of wild fruit scarcity. Some cultivated foods, especially sugar fruits, are mostly fallback foods, whereas others, such as rice pith (Oryza sp.) and maize (Zea mays), are consumed according to their availability even when wild foods are abundant. These findings highlight the importance of both crop choice by farmers and a thorough understanding of the ecology of resident primate species when establishing land management techniques for alleviating human–primate conflict. Am. J. Primatol. 71:636–646, 2009. © 2009 Wiley‐Liss, Inc.     

Waste recovered by‐products can increase growth of grass–clover mixtures in low fertility soils and alter botanical and mineral nutrient composition

The effectiveness of four by‐products (biogas digestate, pot ale, rockdust and wood ash) as fertilisers of a perennial ryegrass (Lolium perenne)–red clover (Trifolium pratense) mixture in terms of biomass production, botanical composition and macro‐ and micronutrient concentrations was tested in an outdoor pot trial. This was carried out over two growing seasons using two inherently low‐fertility soils used for forage production. Macro‐ and micronutrients (N, P, K, Ca, Mg, Co, Cu, Mn, Mo and Zn) relevant for crops and livestock were determined in soils and plants. All the by‐products increased overall biomass production and affected nutrient concentrations of the individual plant species to varying degrees. In addition the competitive balance between grass and clover was altered leading to different botanical composition in the different treatments and consequently differences in the nutrient concentrations of the species mixture. Changes were due to the nutrients applied in the by‐products per se and/or to changes in the soil chemistry caused by the by‐products. The results suggest a potential to enhance agricultural productivity through improved production and quality of forage on less fertile land by matching of by‐products and soil properties.     

A comparison of canopy evapotranspiration for maize and two perennial grasses identified as potential bioenergy crops

In the Midwestern US, perennial rhizomatous grasses (PRGs) are considered one of the most promising vegetation types to be used as a cellulosic feedstock for renewable energy production. The potential widespread use of biomass crops for renewable energy production has sparked numerous environmental concerns, including the impacts of land‐use change on the hydrologic cycle. We predicted that total seasonal evapotranspiration (ET) would be higher for PRGs relative to maize resulting from higher leaf area and a prolonged growing season. We further predicted that, compared with maize, higher aboveground biomass associated with PRGs would offset the higher ET and increase water‐use efficiency (WUE) in the context of biomass harvests for liquid biofuel production. To test these predictions, ET was estimated during the 2007 growing season for replicated plots of Miscanthus×giganteus (miscanthus), Panicum virgatum (switchgrass), and Zea mays (maize) using a residual energy balance approach. The combination of a 25% higher mean latent heat flux (λET) and a longer growing season resulted in miscanthus having ca. 55% higher cumulative ET over the growing season compared with maize. Cumulative ET for switchgrass was also higher than maize despite similar seasonal‐mean λET. Based on total harvested aboveground biomass, WUE was ca. 50% higher for maize relative to miscanthus; however, when WUE calculated from only maize grain biomass was compared with WUE calculated from miscanthus harvested aboveground biomass, this difference disappeared. Although WUE between maize and miscanthus differed postsenescence, there were no differences in incremental WUE throughout the growing season. Despite initial predictions, aboveground biomass for switchgrass was less than maize; thus WUE was substantially lower for switchgrass than for either maize scenario. These results indicate that changes in ET due to large‐scale implementation of PRGs in the Midwestern US would likely influence local and regional hydrologic cycles differently than traditional row crops.     

Habitat composition as a determinant of reproductive success of Tengmalm's owls under fluctuating food conditions

The effect of landscape composition on the breeding success of vole-eating Tengmalm's owl ( Aegolius funereus ) was studied in western Finland at five different spatial scales (250–4000 m) around the nests during two consecutive three-year population cycles of voles. Landscape composition had strongest effects on owl breeding in the decrease phase of vole cycles. Significant variation in owl breeding occurred along the productivity gradient from farmland predominated areas to barren hinterland. Owls tended to produce earlier clutches on territories predominated by agricultural areas in increasing vole years. A similar trend was observed in the decreasing phase of the vole cycle; owls breeding on barren hinterland seemed to delay breeding compared to owls breeding near agricultural areas. Surprisingly, nestling survival and fledgling production in the decreasing phase declined steeply with increasing proportion of farmland. Clutch size was not significantly related to landscape composition. The number of fledglings decreased with increases in clear-cut and sapling areas in the decrease phase. During the declining years of vole abundance nestling survival increased from western farmland areas towards the eastern outlying district. These results indicate sudden summer decline of vole populations on farmland predominated habitats. This is probably due to that the number of vole-eating predators, and hence their impact on vole populations is apparently higher in farmland areas than on forested hinterland. This finding gives support for the 'spill-over' hypothesis, which states that predators and their exploitation tends to 'spill over' from luxuriant habitats to the barren habitats.     

The Effects of Landscape Modifications on the Long-Term Persistence of Animal Populations

Background

The effects of landscape modifications on the long-term persistence of wild animal populations is of crucial importance to wildlife managers and conservation biologists, but obtaining experimental evidence using real landscapes is usually impossible. To circumvent this problem we used individual-based models (IBMs) of interacting animals in experimental modifications of a real Danish landscape. The models incorporate as much as possible of the behaviour and ecology of four species with contrasting life-history characteristics: skylark (Alauda arvensis), vole (Microtus agrestis), a ground beetle (Bembidion lampros) and a linyphiid spider (Erigone atra). This allows us to quantify the population implications of experimental modifications of landscape configuration and composition.

Methodology/Principal Findings

Starting with a real agricultural landscape, we progressively reduced landscape complexity by (i) homogenizing habitat patch shapes, (ii) randomizing the locations of the patches, and (iii) randomizing the size of the patches. The first two steps increased landscape fragmentation. We assessed the effects of these manipulations on the long-term persistence of animal populations by measuring equilibrium population sizes and time to recovery after disturbance. Patch rearrangement and the presence of corridors had a large effect on the population dynamics of species whose local success depends on the surrounding terrain. Landscape modifications that reduced population sizes increased recovery times in the short-dispersing species, making small populations vulnerable to increasing disturbance. The species that were most strongly affected by large disturbances fluctuated little in population sizes in years when no perturbations took place.

Significance

Traditional approaches to the management and conservation of populations use either classical methods of population analysis, which fail to adequately account for the spatial configurations of landscapes, or landscape ecology, which accounts for landscape structure but has difficulty predicting the dynamics of populations living in them. Here we show how realistic and replicable individual-based models can bridge the gap between non-spatial population theory and non-dynamic landscape ecology. A major strength of the approach is its ability to identify population vulnerabilities not detected by standard population viability analyses.     

Bt maize pollen exposure and impact on the garden spider, Araneus diadematus

Concerns have been raised that Bt maize pollen may have adverse effects on non‐target organisms; consequently, there is a general call for Bt maize risk assessment evaluating lethal and sublethal side effects. Spiders play an important economic and ecological role as pest predators in various crops, including maize. Web‐building spiders, especially, may be exposed to the Cry1Ab toxin of Bt maize by the ingestion of pollen via ‘recycling’ of pollen‐dusted webs and intentional pollen feeding. In this study, the potential Bt maize pollen exposure of orb‐web spiders was quantified in maize fields and adjacent field margins, and laboratory experiments were conducted to evaluate the possible effects of Bt maize pollen consumption on juvenile garden spiders, Araneus diadematus (Clerck) (Araneae: Araneidae). In maize fields and neighbouring field margins, web‐building spiders were exposed to high amounts of Bt maize pollen. However, a laboratory bioassay showed no effects of Bt maize pollen on weight increase, survival, moult frequency, reaction time, and various web variables of A. diadematus. A pyrethroid insecticide (Baythroid) application affected weight increase, survival, and reaction time of spiders negatively. In conclusion, the insecticide tested showed adverse effects on the garden spider, whereas the consumption of Bt maize pollen did not. This study is the first one on Bt maize effects on orb‐web spiders, and additional research is recommended in order to account for further spider species, relative fitness parameters, prey‐mediated effects, and possible long‐term chronic consequences of Bt exposure.     

Population‐specific effect of Wolbachia on the cost of fungal infection in spider mites

Many studies have revealed the ability of the endosymbiotic bacterium Wolbachia to protect its arthropod hosts against diverse pathogens. However, as Wolbachia may also increase the susceptibility of its host to infection, predicting the outcome of a particular Wolbachia‐host–pathogen interaction remains elusive. Yet, understanding such interactions and their eco‐evolutionary consequences is crucial for disease and pest control strategies. Moreover, how natural Wolbachia infections affect artificially introduced pathogens for biocontrol has never been studied. Tetranychus urticae spider mites are herbivorous crop pests, causing severe damage on numerous economically important crops. Due to the rapid evolution of pesticide resistance, biological control strategies using entomopathogenic fungi are being developed. However, although spider mites are infected with various Wolbachia strains worldwide, whether this endosymbiont protects them from fungi is as yet unknown. Here, we compared the survival of two populations, treated with antibiotics or naturally harboring different Wolbachia strains, after exposure to the fungal biocontrol agents Metarhizium brunneum and Beauveria bassiana. To control for potential effects of the bacterial community of spider mites, we also compared the susceptibility of two populations naturally uninfected by Wolbachia, treated with antibiotics or not. In one population, Wolbachia‐infected mites had a better survival than uninfected ones in absence of fungi but not in their presence, whereas in the other population Wolbachia increased the mortality induced by B. bassiana. In one naturally Wolbachia‐uninfected population, the antibiotic treatment increased the susceptibility of spider mites to M. brunneum, but it had no effect in the other treatments. These results suggest that natural Wolbachia infections may not hamper and may even improve the success of biological control using entomopathogenic fungi. However, they also draw caution on the generalization of such effects, given the complexity of within‐host–pathogens interaction and the potential eco‐evolutionary consequences of the use of biocontrol agents for Wolbachia‐host associations.     

Tracing dietary origins of aphids and the predatory beetle Propylea japonica in agricultural systems using stable isotope analyses

Tracing dietary origins of the predatory beetle Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) aids understanding their roles in the food web and provides information to develop strategies for effective conservation in agroecosystems comprised of wheat [Triticum aestivum L. (Poaceae)], cotton [Hirsutum spp. (Malvaceae)], and maize [Zea mays L. (Poaceae)]. Intrinsic markers of carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) in P. japonica need to be developed to ascertain the source(s) of diet. Experiments were carried out to examine the changes of δ¹³C and δ¹⁵N among the three crops, pests (wheat, cotton, and maize aphids; all Hemiptera: Aphididae), and P. japonica fed on aphids of each of the three crops. Results indicated that δ¹³C values in P. japonica fed on wheat, cotton, and maize aphids were ?27.2 to ?26.5‰, ?24.2 to ?23.9‰, and ?11.0 to ?10.7‰, respectively, whereas their δ¹⁵N values were 1.1 to 2.9‰, 6.0 to 7.4‰, and ?0.6 to 0.1‰, respectively. δ¹³C and δ¹⁵N plots clearly identify the three crops, the dietary origins of the aphids, and the host origins of the aphid prey consumed by the ladybird beetles, as each pathway displays a non‐overlapping pattern. Based on the values of δ¹³C and δ¹⁵N of the three food webs, dietary origins can be traced in the predatory beetle P. japonica derived from wheat, cotton, and maize crops.