Natural Enemy Guilds Research Articles

Systematic reduction of natural enemies and competition across variable precipitation approximates buffelgrass invasiveness (Cenchrus ciliaris) in its native range.

Invasive grasses cause devastating losses to biodiversity and ecosystem function directly and indirectly by altering ecosystem processes. Escape from natural enemies, plant-plant competition, and variable resource availability provide frameworks for understanding invasion. However, we lack a clear understanding of how natural stressors interact in their native range to regulate invasiveness. In this study, we reduced diverse guilds of natural enemies and plant competitors of the highly invasive buffelgrass across a precipitation gradient throughout major climatic shifts in Laikipia, Kenya. To do this, we used a long-term ungulate exclosure experiment design across a precipitation gradient with nested treatments that (1) reduced plant competition through clipping, (2) reduced insects through systemic insecticide, and (3) reduced fungal associates through fungicide application. Additionally, we measured the interaction of ungulates on two stem-boring insect species feeding on buffelgrass. Finally, we measured a multiyear smut fungus outbreak. Our findings suggest that buffelgrass exhibits invasive qualities when released from a diverse group of natural stressors in its native range. We show natural enemies interact with precipitation to alter buffelgrass productivity patterns. In addition, interspecific plant competition decreased the basal area of buffelgrass, suggesting that biotic resistance mediates buffelgrass dominance in the home range. Surprisingly, systemic insecticides and fungicides did not impact buffelgrass production or reproduction, perhaps because other guilds filled the niche space in these highly diverse systems. For example, in the absence of ungulates, we showed an increase in host-specific stem-galling insects, where these insects compensated for reduced ungulate use. Finally, we documented a smut outbreak in 2020 and 2021, corresponding to highly variable precipitation patterns caused by a shifting Indian Ocean Dipole. In conclusion, we observed how reducing natural enemies and competitors and certain interactions increased properties related to buffelgrass invasiveness.

Impact of Soybean on Natural Enemy Guilds in Intercropping Cotton and Suitability of Trapping Methods for Various Insects

Impact of Soybean on Natural Enemy Guilds in Intercropping Cotton and Suitability of Trapping Methods for Various Insects

A parasitoid regulates 20E synthesis and antibacterial activity of the host for development by inducing host nitric oxide production.

Parasitoids are important components of the natural enemy guild in the biological control of insect pests. They depend on host resources to complete the development of a specific stage or whole life cycle and thus have evolved towards optimal host exploitation strategies. In the present study, we report a specific survival strategy of a fly parasitoid Exorista sorbillans (Diptera: Tachinidae), which is a potential biological control agent for agricultural pests and a pest in sericulture. We found that the expression levels of nitric oxide synthase (NOS) and nitric oxide (NO) production in host Bombyx mori (Lepidoptera: Bombycidae) were increased after E. sorbillans infection. Reducing NOS expression and NO production with an NOS inhibitor (NG-nitro-L-arginine methyl ester hydrochloride) in infected B. mori significantly impeded the growth of E. sorbillans larvae. Moreover, the biosynthesis of 20-hydroxyecdysone (20E) in infected hosts was elevated with increasing NO production, and inhibiting NOS expression lowered 20E biosynthesis. More importantly, induced NO synthesis was required to eliminate intracellular bacterial pathogens that presumably competed for shared host resources. Inhibiting NOS expression down-regulated the transcription of antimicrobial peptide genes and increased the number of bacteria in parasitized hosts. Collectively, this study revealed a new perspective on the role of NO in host-parasitoid interactions and a novel mechanism for parasitoid regulation of host physiology to support its development.

Legume integration for biological control deserves a firmer scientific base

Diversification measures are widely recognized for their potential to enhance the resilience of agri-food production systems under global change. Nitrogen-fixing legumes commonly feature in diversification schemes, where they exert positive impacts on soil structure, nutrient retention, carbon sequestration or fertilizer reduction. Though legumes are premier tools for conservation agriculture, their impacts on (invertebrate, microbial) biological control are far less clear. As legumes secrete copious amounts of energy-rich (floral, extra-floral) nectar and provide alternative host or prey items for resident natural enemies, their deployment is expected to benefit biological control. Yet, its mechanistic basis is poorly understood and scientific underpinnings weak. In this Perspective piece, we collate data from the published literature and open-access databases on the extent to which different natural enemy guilds interact with 25 legume species that are commonly used as intercrops in the (sub)tropics. Our work unveils how natural enemies regularly forage on legumes, but the portrayal of those interaction linkages –or “biostructure” data- is profoundly incomplete and their ensuing implications for biological control are under-investigated. For instance, merely 4 (out of 167) parasitoids of the globally invasive fall armyworm Spodoptera frugiperda have been recorded in association with legumes. We hope that this Perspective piece will stimulate further thought, drive a new wave of biodiversity x ecosystem function research, and ultimately result in the design and implementation (or preservation) of more resilient, resource-frugal and pest-suppressive farming systems.

FLOWERING PLANTS AND ENTOMOPHAGOUS ARTHROPODS IN THE AGRICULTURAL LANDSCAPE: A PRACTISE-ORIENTED SUMMARY OF A COMPLEX RELATIONSHIP

<List> <ListItem><ItemContent> ● Most entomophagous arthropods consume nectar or pollen as alternative diets. </ItemContent></ListItem> <ListItem><ItemContent> ● The attractive of floral resource with different traits varies in a wide degree. </ItemContent></ListItem> <ListItem><ItemContent> ● Floral resource plays positive effects on not only entomophagous insects but also agricultural biodiversity, multiple ecosystem services and crop production. </ItemContent></ListItem></List> There is a growing demand for high-quality agricultural products and more countries have adopted landscape management by sowing flowering plants in agricultural fields as an important branch of conservation biological control. However, there has been less concern over the interactions and trade-offs between floral plants and entomophagous arthropods. This paper review progress in pollen/nectar feeding habits of entomophagous insects including parasitoids and predators which are important natural enemies of crop pests in agricultural fields. Factors that influence the preference of different guilds of natural enemies are reviewed to guide the selection of flowering plants in conservation biological control practices. Most studies find that floral resources have positive effects on both biological traits of natural enemies and their abundance and diversity, and this is believed to contribute greatly to pest control. Furthermore, the potential impacts of floral resources on crop yields are also discussed with an emphasis on a guild of entomophagous insects that provides both pest control and pollination services.

Beneficial insects are associated with botanically rich margins with trees on small farms

Beneficial insect communities on farms are influenced by site- and landscape-level factors, with pollinator and natural enemy populations often associated with semi-natural habitat remnants. They provide ecosystem services essential for all agroecosystems. For smallholders, natural pest regulation may be the only affordable and available option to manage pests. We evaluated the beneficial insect community on smallholder bean farms (Phaseolus vulgaris L.) and its relationship with the plant communities in field margins, including margin trees that are not associated with forest fragments. Using traps, botanical surveys and transect walks, we analysed the relationship between the floral diversity/composition of naturally regenerating field margins, and the beneficial insect abundance/diversity on smallholder farms, and the relationship with crop yield. More flower visits by potential pollinators and increased natural enemy abundance measures in fields with higher plant, and particularly tree, species richness, and these fields also saw improved crop yields. Many of the flower visitors to beans and potential natural enemy guilds also made use of non-crop plants, including pesticidal and medicinal plant species. Selective encouragement of plants delivering multiple benefits to farms can contribute to an ecological intensification approach. However, caution must be employed, as many plants in these systems are introduced species.

Effects of Prey Distribution and Heterospecific Interactions on the Functional Response of Harmonia axyridis and Aphidius gifuensis to Myzus persicae.

Natural enemy guilds normally forage for prey that is patchily distributed simultaneously. Previous studies have investigated the influence of conspecific interactions and prey distribution on the functional response of natural enemies. However, little is known about how prey distribution and heterospecific interactions between natural enemies could affect their foraging efficiency. We examined the effects of prey distribution (aggregate and uniform) and heterospecific interactions on the functional response of a predator, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) and a parasitoid, Aphidius gifuensis Ashmead (Hymenoptera: Braconidae) to the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). Type II functional responses were observed in all experiments. Functional response curves of single H. axyridis or A. gifuensis were higher in the aggregate treatment than in the uniform treatment when aphid densities were between 40–180 or 70–170, respectively. When comparing between aggregate and uniform treatments with the heterospecific enemy occurrence, no differences were found in the parasitism efficiency of A. gifuensis, while H. axyridis consumed more aphids in the aggregate treatment than in the uniform treatment when aphid densities were between 50–230. The functional response of individual H. axyridis was not affected by A. gifuensis under two aphid distributions. However, the functional response of a single A. gifuensis and the treatment when A. gifuensis concurrently with H. axyridis overlapped in uniform treatment of above approximately 150 aphids. Our results indicate that the predation rate of H. axyridis was affected by aphid distribution, but was not affected by heterospecific interactions. The parasitism rate of A. gifuensis was affected by aphid distribution, and by heterospecific interactions in both the aggregate and uniform treatments. Thus, to optimize the management efficiency of M. persicae, the combined use of H. axyridis and A. gifuensis should be considered when M. persicae is nearly uniformly distributed under relatively high density.

Predator richness predicts pest suppression within organic and conventional summer squash (Cucurbita pepo L. Cucurbitales: Cucurbitaceae)

The biodiversity-ecosystem function (BEF) hypothesis predicts that increased richness within a trophic level supports greater resource capture. However, higher predator richness commonly found within organic compared to conventional agroecosystems does not always result in enhanced pest suppression. The striped cucumber beetle, Acalymma vittatum (Coleoptera: Chrysomelidae), causes damage via direct feeding and pathogen transmission to crops in the family Cucurbitaceae. The aims of this study were to: 1) identify the predators that contribute to A. vittatum suppression using molecular gut content analysis, 2) determine if the richness of predators testing positive for A. vittatum DNA was negatively correlated with prey abundance, and 3) examine how organic versus conventional cucurbit production influenced these relationships. Using a species-specific primer for A. vittatum, we found that a diverse community of predators feed on this pest, including Carabidae, Coccinellidae, Formicidae, Henicopidae, Opiliones, Lycosidae, and Staphylinidae. The richness of predators testing positive for A. vittatum DNA within a cucurbit field was negatively correlated with pest abundance, supporting the BEF hypothesis. We found no effect of farm management on the proportion or richness of predators testing positive for pest DNA, despite a 43.4% greater pitfall trap catch of predatory taxa within organic fields. This illustrates that using traps to measure predator richness and abundance may not accurately predict the strength of biological control service provided by a guild of natural enemies. Application of molecular gut content analysis proves a useful tool in advancing both the theory and practice of conservation biological control.

Field evaluation of Cryptolaemus montrouzieri (Mulsant) (Coleoptera: Coccinellidae) as biological control agent of the mealybug Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae)

Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae) is one of the latest invasive mealybugs in Europe. It causes severe fruit distortion and reduced fruit size leading into important economic losses in citrus. Cryptolaemus montrouzieri (Mulsant) (Coleoptera: Coccinellidae) is probably one of the most-used predators of mealybugs in biological control programs worldwide. However, its impact on D. aberiae is still unknown. Here, we conducted a two-year field study in nine citrus orchards located in eastern Spain in order to describe the population dynamics of D. aberiae and C. montrouzieri and evaluate the effect of the predator on D. aberiae using different approaches. Our results showed that C. montrouzieri and D. aberiae had two main synchronised population peaks per year: early spring and summer. Although D. aberiae and C. montrouzieri seasonal trends were synchronised, C. montrouzieri neither reduced mealybug density within the same year nor prevented fruit damage, which occurs early in the season. Moreover, D. aberiae population growth rates were not correlated with C. montrouzieri density. When two consecutive years were analyzed, the increase of D. aberiae in the second year was negatively correlated with the density of C. montrouzieri in summer of the previous year. Based on our two years of data, C. montrouzieri was not able to regulate D. aberiae on its own or prevent the damages produced by the mealybug but might become a valuable addition to the natural enemy guild when combined with other natural enemies and rational control measures.

Effects of shrub crop interplanting on apple pest ecology in a temperate agroforestry system

Pest control by wild arthropods is an important ecosystem service in fruit crops, especially due to markets that value minimal pesticide use. Techniques to augment on-farm habitat for wild arthropods have focused on flowering ground cover planted within orchards and hedgerows on field borders. However, natural enemies found in groundcover often do not favor tree canopy habitat. Conversely, while hedgerows can effectively provide natural enemies that prefer woody microhabitats, their impact diminishes away from field edges. Shrub crops interplanted within orchards could resolve both problems, providing woody habitat for natural enemies directly adjacent to target crop trees. In a multi-layer agroforestry system in Illinois, we vacuum sampled arthropod communities across layers and recorded vegetation characteristics and pest damage on apples. Using generalized linear models, information theoretic model selection, and non-metric multidimensional scaling, we evaluated the effects of three shrub treatments (raspberries, hazelnuts, and both species) on pest and natural enemy guilds in apple trees and shrubs, and on the frequency of pest damage on apples. Shrub composition was an important predictor of arthropod communities on shrubs. However, shrub treatment had only minor impacts on arthropods in apple canopies, indicating the habitats are less similar than anticipated. While two arthropod guilds in apple canopies were linked to pest damage frequency, neither was sensitive to changes in the shrub layer. Results suggest that shrub crop interplanting does not inherently resolve the ecological complexities that impede existing approaches in conservation biological control.

Complementarity among natural enemies enhances pest suppression

Natural enemies have been shown to be effective agents for controlling insect pests in crops. However, it remains unclear how different natural enemy guilds contribute to the regulation of pests and how this might be modulated by landscape context. In a field exclusion experiment in oilseed rape (OSR), we found that parasitoids and ground-dwelling predators acted in a complementary way to suppress pollen beetles, suggesting that pest control by multiple enemies attacking a pest during different periods of its occurrence in the field improves biological control efficacy. The density of pollen beetle significantly decreased with an increased proportion of non-crop habitats in the landscape. Parasitism had a strong effect on pollen beetle numbers in landscapes with a low or intermediate proportion of non-crop habitats, but not in complex landscapes. Our results underline the importance of different natural enemy guilds to pest regulation in crops, and demonstrate how biological control can be strengthened by complementarity among natural enemies. The optimization of natural pest control by adoption of specific management practices at local and landscape scales, such as establishing non-crop areas, low-impact tillage, and temporal crop rotation, could significantly reduce dependence on pesticides and foster yield stability through ecological intensification in agriculture.

The effect of landscape context on the biological control of Sitobion avenae: temporal partitioning response of natural enemy guilds

Landscape contexts with high complexity may promote diversity of natural enemies, although the effect on biocontrol remains under discussion. Although biocontrol of Sitobion avenae is a well-studied system, little is known about the temporal effect of landscape context on the natural enemy assemblages. In a previous study, we showed a positive effect of predators in the decline of aphids; however, this effect had a temporal pattern responding to different landscape contexts. We study here two contrasting agricultural contexts, high landscape complexity with low intensification and low complexity with high intensification. Abundance and diversity of parasitoids was examined via a molecular approach, using a combination of diagnostic multiplex and singleplex PCR assays to test field-collected samples of S. avenae with genus- and species-specific parasitoid primer pairs. Temporal population dynamics were analyzed and differences related to these two contexts were observed. Parasitism rates were greater in the mid-sampling dates in high intensification simple landscapes, which were not observed for the low intensification complex landscapes. According to our results, we suggest that the greater landscape complexity in combination with a low agricultural intensification increase negative interactions for parasitoid population built-up; however, early predation by coccinellids was able to control the aphid populations. In contrast, under a simple landscape context with a high agricultural intensification, our results suggest an important role of parasitism with a complementary effect of late predation. We highlight the importance of different natural enemy guilds and their temporal dynamics under contrasting agricultural settings to further understand the relationship between functional diversity and biological control.

Manipulating field margins to increase predation intensity in fields of winter wheat (Triticum aestivum)

AbstractThe effectiveness of natural enemies to control pests can be enhanced through habitat manipulation. However, due to the differences in their ecology, generalist and specialist species may respond differently to the same manipulation. Moreover, interactions among natural enemies (i.e. cannibalism, intraguild predation, hyperparasitism) may complicate the assumption that a higher density of natural enemies would increase the level of biological control. We investigated the natural enemy guild composition and the predation rate along flower vs. grass margins at the edge of winter wheat (Triticum aestivum) fields in Denmark. Natural enemies were sampled by pitfall trapping and by suction sampling; predation intensity was measured using two different sentinel prey methods: artificial caterpillars made of plasticine, and sentinel aphid colonies. Specialist and generalist species responded differently to the two margin types: specialists (mostly parasitic wasps) were attracted by the flower margins, while generalists (ground beetles, rove beetles and spiders) were more active in grass margins. The number of artificial caterpillars attacked was significantly greater in grass margins (mean = 48.9%, SD = 24.3) than in flower margins (mean = 30.7%, SD = 17.4). We found a significant positive relationship between the number of artificial caterpillars attacked by chewing insects, and activity density for large (≥15 mm) ground beetles. Predation of sentinel aphids in wheat fields did not vary significantly in relation to margin type. Our results suggest that flowering margins may be beneficial for canopy‐active specialist natural enemies, but grassy margins are more useful for ground‐active generalist predators.

Direct and indirect effects of the spatial context on the natural biocontrol of an invasive crop pest

Natural biocontrol of pests can be influenced by both direct effects (spatial context, natural enemies) and indirect effects (spatial effects on natural enemies). The objectives of this study were to: 1) Evaluate the relative influence of natural enemies and spatial context on the natural biocontrol of the soybean aphid (direct effects), and 2) Determine the effect of the spatial context on the guild of natural enemies best associated with the natural biocontrol (indirect effects). Regarding the first objective, our results showed that, in 2011 (high infestation), the soybean aphid natural biocontrol was mainly explained by a shared effect of natural enemies (entomopathogenic fungi, predators, functional diversity) and spatial context (presence of buckthorn, proportion of soybean, crop richness), accounting for 50% of the variation. The functional diversity was the only natural enemy variable positively associated with the natural biocontrol (negative effect on the cumulative aphid-days). In 2012, (moderate infestation), the natural biocontrol was mainly explained by the natural enemies (species richness, 23.5% of variation) followed by a shared effect of natural enemies and landscape context (15.5%). Regarding the second objective, we found the natural enemies positively influenced by the proportion of woodlands, and negatively influenced by the proportion of soybean in the landscape. Our results suggest that the integrated pest management of the soybean aphid should include management of habitats that conserve the natural enemies, especially those promoting functional diversity. For instance, a better natural biocontrol could be achieved by reducing the proportion of soybean, increasing crop richness and conserving woodlands.

Conservation tillage mitigates the negative effect of landscape simplification on biological control

Summary Biological pest control is a key ecosystem service, and it depends on multiple factors acting from the local to the landscape scale. However, the effects of soil management on biological control and its potential interaction with landscape are still poorly understood. In a field exclusion experiment, we explored the relative effect of tillage system (conservation vs. conventional tillage) on aphid biological control in 15 pairs of winter cereal fields (barley and wheat) selected along a gradient of landscape complexity. We sampled the abundance of the main natural enemy guilds, and we evaluated their relative contribution to aphid predation and parasitism. Conservation tillage was found to support more abundant predator communities and higher aphid predation (16% higher than in the fields managed under conventional tillage). In particular, both the abundance and the aphid predation of vegetation‐ and ground‐dwelling arthropods were increased under conservation tillage conditions. Conservation tillage also increased the parasitism rate of aphids. A high proportion of semi‐natural habitats in the landscape enhanced both aphid parasitism and predation by vegetation‐dwelling organisms but only in the fields managed under conventional tillage. The better local habitat quality provided by conservation tillage may compensate for a low‐quality landscape. Synthesis and applications. Our study stresses the importance of considering both soil management and landscape composition when planning strategies to maximize biological control services in agro‐ecosystems, highlighting the role played by conservation tillage in supporting natural enemy communities. In simple landscapes, the adoption of conservation tillage will locally improve biological control provided by both predators and parasitoids mitigating the negative effects of landscape simplification. Moreover, considering the small scale at which both predation and parasitism responded to landscape composition, a successful strategy to improve biological control would be to establish a fine mosaic of crop and non‐crop areas such as hedgerows, tree lines and small semi‐natural habitat patches.

Aphid parasitoid generalism: development, assessment, and implications for biocontrol

Host specialization in aphid parasitoids is important both from a theoretical and an applied point of view. It arises from various ecological mechanisms involving their interactions with aphids, host plants, and endosymbiotic bacteria, as well as with potential competitors and enemies. From an applied point of view, host specialization in aphid parasitoids has a great importance as it determines the biological control they provide through their capacity to switch between different hosts, to persist in the agrosystem in the absence of the pest, and to regulate pest outbreaks in a rapidly changing system. It also conditions the risk of undesirable effects on non-target species in the case of introduction or augmentation of populations of parasitoids. Biocontrol literature that looks at the benefits of generalist and specialists natural enemies is mainly focused on differences between different guilds of natural enemies and does not consider the differences in host specialization within a single guild. This review synthesizes the mechanisms related to host-use by aphid parasitoids, focusing on the differences between generalist and specialist species. Second, this work describes the difficulty to determine the host range of generalist parasitoid species. Our review points out some observational artifacts, as is the existence of cryptic species or spatiotemporal variability in host acceptance, which may lead to misinterpretations about host specialization and result in pest management failures. Regarding biological control services, moderately generalized species that could use various host species to sustain their populations may ensure the long-term control, whereas specialist species would provide higher parasitism rates. At the community level, the co-occurrence of specialist and generalist parasitoids may maximize biological control services both in terms of efficiency and in terms of stability in space and time.

Pest control of aphids depends on landscape complexity and natural enemy interactions.

Aphids are a major concern in agricultural crops worldwide, and control by natural enemies is an essential component of the ecological intensification of agriculture. Although the complexity of agricultural landscapes is known to influence natural enemies of pests, few studies have measured the degree of pest control by different enemy guilds across gradients in landscape complexity. Here, we use multiple natural-enemy exclosures replicated in 18 fields across a gradient in landscape complexity to investigate (1) the strength of natural pest control across landscapes, measured as the difference between pest pressure in the presence and in the absence of natural enemies; (2) the differential contributions of natural enemy guilds to pest control, and the nature of their interactions across landscapes. We show that natural pest control of aphids increased up to six-fold from simple to complex landscapes. In the absence of pest control, aphid population growth was higher in complex than simple landscapes, but was reduced by natural enemies to similar growth rates across all landscapes. The effects of enemy guilds were landscape-dependent. Particularly in complex landscapes, total pest control was supplied by the combined contribution of flying insects and ground-dwellers. Birds had little overall impact on aphid control. Despite evidence for intraguild predation of flying insects by ground-dwellers and birds, the overall effect of enemy guilds on aphid control was complementary. Understanding pest control services at large spatial scales is critical to increase the success of ecological intensification schemes. Our results suggest that, where aphids are the main pest of concern, interactions between natural enemies are largely complementary and lead to a strongly positive effect of landscape complexity on pest control. Increasing the availability of seminatural habitats in agricultural landscapes may thus benefit not only natural enemies, but also the effectiveness of aphid natural pest control.

Recruitment of aphidophagous arthropods to sorghum plants infested with Melanaphis sacchari and Schizaphis graminum (Hemiptera: Aphididae)

A significant question in biological control is the extent to which indigenous natural enemies might be pre-adapted to exploit invasive species that constitute novel prey. We observed the recruitment of natural enemies to aphid microcosms – pots containing four sorghum plants infested with either Melanaphis sacchari (Zehntner), a newly invasive aphid, or Schizaphis graminum (Rondani), an established pest. The first cohort was monitored in open habitat along a tree line near riparian parkland and urban plantings, and the second, within a sorghum monoculture. Both aphid species were eliminated by natural enemies within 13days in the first cohort, but in the second, M. sacchari reached higher numbers than S. graminum and survived a week longer. Biological control was successful in both cases; neither aphid produced a generation of alates, nor did plants sustain significant damage. Syrphid larvae, primarily Allograpta obliqua (Say), caused most aphid mortality in the first cohort, whereas adult Coccinellidae, primarily Hippodamia convergens Guerin-Meneville, caused most mortality in the second. Eggs and larvae of Chrysoperla carnea Stephens were present in both cohorts, but appeared to suffer more intraguild predation in the first. Flower flies and velvet mites were present only in the first cohort, and flower bugs, only in the second. Aphelinus sp. successfully parasitized both aphids, but Lysiphlebus testaceipes Cresson did not develop in M. sacchari due to their infection with the secondary endosymbiont Hamiltonella defensa (confirmed by DNA analysis). Thus, sorghum infested with M. sacchari attracted the same guild of natural enemies as S. graminum and had similar biological control outcomes. The findings suggest that the capacity of indigenous aphidophagous guilds to respond to, and ultimately control, invasive aphid species may be underestimated.

Intra‐ and interspecific interactions between Nephus includens and Cryptolaemus montrouzieri

AbstractThe introduced coccinellid Cryptolaemus montrouzieri is extensively used by biological control practitioners against mealybugs. Potential risks on native guilds of natural enemies have recently been recognized, as C. montrouzieri has managed to establish in many of the regions, it has been released. We investigated in the laboratory the direct trophic interactions between Cryptolaemus montrouzieri and Nephus includens, a predatory coccinellid native to the Mediterranean region. For both adult coccinellid species, predation rates on conspecific or heterospecific juvenile stages, with different amounts of shared prey, were recorded after 24 h. Both predators consumed eggs and larvae, but only C. montrouzieri preyed upon pupae. In general, cannibalism decreased with shared prey abundance, regardless of species. A high level of asymmetry was found on intraguild predation, in favour of C. montrouzieri. The probability of displacement threat of N. includens by C. montrouzieri in nature, in addition to possible effects of the studied trophic interactions on the outcome of biological control, is discussed.

Identification of top-down forces regulating cotton aphid population growth in transgenic Bt cotton in central China.

The cotton aphid Aphis gossypii Glover is the main aphid pest in cotton fields in the Yangtze River Valley Cotton-planting Zone (YRZ) in central China. Various natural enemies may attack the cotton aphid in Bt cotton fields but no studies have identified potential specific top-down forces that could help manage this pest in the YRZ in China. In order to identify possibilities for managing the cotton aphid, we monitored cotton aphid population dynamics and identified the effect of natural enemies on cotton aphid population growth using various exclusion cages in transgenic Cry1Ac (Bt)+CpTI (Cowpea trypsin inhibitor) cotton field in 2011. The aphid population growth in the open field (control) was significantly lower than those protected or restricted from exposure to natural enemies in the various exclusion cage types tested. The ladybird predator Propylaea japonica Thunberg represented 65% of Coccinellidae predators, and other predators consisted mainly of syrphids (2.1%) and spiders (1.5%). The aphid parasitoids Aphidiines represented 76.7% of the total count of the natural enemy guild (mainly Lysiphlebia japonica Ashmead and Binodoxys indicus Subba Rao & Sharma). Our results showed that P. japonica can effectively delay the establishment and subsequent population growth of aphids during the cotton growing season. Aphidiines could also reduce aphid density although their impact may be shadowed by the presence of coccinellids in the open field (likely both owing to resource competition and intraguild predation). The implications of these results are discussed in a framework of the compatibility of transgenic crops and top-down forces exerted by natural enemy guild.