Do natural enemies really make a difference? Field scale impacts of parasitoid wasps and hoverfly larvae on cereal aphid populations

Naturally occurring predators and parasitoids are known to reduce the abundance of pest invertebrates in arable crops, yet current treatment thresholds do not account for such a contribution to pest management. In the present study, we provide evidence for the presence of natural enemies correlating with a subsequent reduction in pest population growth. The abundance of cereal aphid pests and two key aphidophagous natural enemies, parasitoid wasps (Aphidiinae) and hoverfly larvae (Syrphinae), was assessed at field boundaries and interiors in southeast England. The highest rate of aphid population growth was associated with locations where no natural enemies were found. The presence of either Aphidiinae wasps or predatory Syrphinae larvae was associated with a reduction in the rate of aphid population growth, irrespective of location within the field, and overall aphid population growth was negatively correlated with increasing natural enemy abundance. The results of the present study indicate that natural enemies contribute significantly to pest control, and provide further evidence supporting the use of management strategies for promoting natural enemies in agro-ecosystems. Aphid predators and parasitoids make an important contribution to aphid pest control within cereal fields, and thresholds for insecticide application should account for this to avoid unnecessary treatments

Ants impact the energy reserves of natural enemies through the shared honeydew exploitation

[EN] Ants, as well as many species of parasitoids and predators, rely on sugar-richfoodssuchashoneydewtofulfilltheirenergeticneeds.Thus,antsandnatural enemies may interact through the shared honeydew exploitation. 2.Ant-exclusionexperimentswereperformedinacitrusorchardtotestthehypothesis that ants may impact the energy reserves of predators and parasitoids through the competitionforhoneydew.Throughtheuseofhigh-performanceliquidchromatography (HPLC)thelevelofantactivitywiththeenergyreservesandfeedinghistoryofindividual specimens collected in the field during representative days of spring, summer, and autumn were related. 3. Out of 145 Aphytis chrysomphali Mercet parasitoids captured in the field, 65% were classified as sugar-fed and 24.7% as honeydew-fed. In summer, when ant activity peaked,therewasasignificant negativecorrelationbetweenthelevelofantactivityand the total sugar content and honeydew feeding incidence by A.chrysomphali. Out of 47 individuals of the predator Chrysoperla carnea sensu lato (Stephens), captured in the field, 55.3% were classified as sugar-fed. We found a significant negative effect of the level of ant activity on the sugar-feeding incidence by C.carneain spring. 4.Thepresentstudyprovidesevidencethatantscaninterferewiththeenergyreserves of natural enemies. This interaction may be widespread in various ecosystems with important consequences for the arthropod community composition and with practical implicationsforbiologicalcontrolgiventhatabsenceofsugarfeedingisdetrimentalfor thefitness of many species of predatorsand parasitoidsDr Jerome Casas is greatly acknowledged for valuable comments on earlier versions of the manuscript and Dr Petr Duelli for providing help with the Chrysoperla identifications. We also thank Dr Cristina Navarro Campos and Dr Aleixandre Beltra for their help in the field samplings and for stimulating discussions, Barbara Rodriguez for help in the laboratory analyses and the reviewers for their helpful comments. This work was supported by the project (RTA2010-00012-C02-02) assigned to F. G. M from the Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria (INIA), Spain and the project (BIO2013-48779-C4-1-R) from Spanish Ministry of Science and Innovation and COST action CM1303 on Systems Biocatalysis.Calabuig Gomar, A.; Tena Barreda, A.; Wäkers, FL.; Lucia Fernandez-Arrojo; Plou, FJ.; García Mari, F.; Pekas, A. (2015). Ants impact the energy reserves of natural enemies through the shared honeydew exploitation. Ecological Entomology. 40:687-695. https://doi.org/10.1111/een.12237S68769540Avidov, Z., Balshin, M., & Gerson, U. (1970). Studies onAphytis coheni, a parasite of the California red scale,Aonidiella aurantii in Israel. 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Buffered fitness components: Antagonism between malnutrition and an insecticide in bumble bees.

Global insect biodiversity declines due to reduced fitness are linked to interactions between environmental stressors. In social insects, inclusive fitness depends on successful mating of reproductives, i.e. males and queens, and efficient collaborative brood care by workers. Therefore, interactive effects between malnutrition and environmental pollution on sperm and feeding glands (hypopharyngeal glands (HPGs)) would provide mechanisms for population declines, unless buffered against due to their fitness relevance. However, while negative effects for bumble bee colony fitness are known, the effects of malnutrition and insecticide exposure singly and in combination on individuals are poorly understood. Here we show, in a fully-crossed laboratory experiment, that malnutrition and insecticide exposure result in neutral or antagonistic interactions for spermatozoa and HPGs of bumble bees, Bombus terrestris, suggesting strong selection to buffer key colony fitness components. No significant effects were observed for mortality and consumption, but significant negative effects were revealed for spermatozoa traits and HPGs. The combined effects on these parameters were not higher than the individual stressor effects, which indicates an antagonistic interaction between both. Despite the clear potential for additive effects, due to the individual stressors impairing muscle quality and neurological control, simultaneous malnutrition and insecticide exposure surprisingly did not reveal an increased impact compared to individual stressors, probably due to key fitness traits being resilient. Our data support that stressor interactions require empirical tests on a case-by-case basis and need to be regarded in context to understand underlying mechanisms and so adequately mitigate the ongoing decline of the entomofauna

Dietary supplementation with pollen enhances survival and Collembola boosts fitness of a web-building spider

Uncertainties exist about the value of non-prey food for predators that are commonly food-limited, and the dietary conditions where non-prey foods are beneficial for carnivorous species. Prior studies show that large quantities of pollen grains are intercepted in the webs of web-building spiders. We examined the nutritional benefits of pollen as a non-prey food for a common ground-dwelling, sheet web-building spider, Mermessus fradeorum (Berland) (Araneae: Linyphiidae). These predators were provided diets of prey or no prey in the presence and absence of pollen. Treatment effects were quantified by measuring predator body nutrient composition, survival, body size, and offspring production. Per unit dry weight, pollen had less nitrogen and lipids than prey, although relative quantities of these nutrients per meal were not measured. Dietary treatments altered the body tissue composition of the spiders, leading to the highest N content and lipid reserves in spiders provided with Collembola. Supplementing diets with pollen increased both juvenile and adult survival, and the greatest survivorship and offspring production was observed when spiders were provided diets of Collembola supplemented with pollen. Our results show that Collembola are high-quality prey for spiders and pollen has positive effects on nutritional status and survival of a carnivorous species. Foraging on plant material potentially promotes population growth at early and late developmental stages by supplementing diets of poor-quality prey, and preventing starvation when prey are scarce

Shades of yellow: interactive effects of visual and odour cues in a pest beetle

Background: The visual ecology of pest insects is poorly studied compared to the role of odour cues in determining their behaviour. Furthermore, the combined effects of both odour and vision on insect orientation are frequently ignored, but could impact behavioural responses. Methods: A locomotion compensator was used to evaluate use of different visual stimuli by a major coleopteran pest of stored grains (Sitophilus zeamais), with and without the presence of host odours (known to be attractive to this species) in an open-loop setup. Results: Some visual stimuli – in particular, one shade of yellow, solid black and high contrast black-against-white stimuli – elicited positive orientation behaviour from the beetles in the absence of odour stimuli. When host odours were also present, at 90° to the source of the visual stimulus, the beetles presented with yellow and vertical black-against-white grating patterns changed their walking course and typically adopted a path intermediate between the two stimuli. The beetles presented with a solid black-on-white target continued to orient more strongly towards the visual than the odour stimulus. Discussion: Visual stimuli can strongly influence orientation behaviour, even in species where use of visual cues is sometimes assumed to be unimportant, while the outcomes from exposure to multimodal stimuli are unpredictable and need to be determined under differing conditions. The importance of the two modalities of stimulus (visual and olfactory) in food location is likely to depend upon relative stimulus intensity and motivational state of the insect

Microorganisms from aphid honeydew attract and enhance the efficacy of natural enemies

Aphids are one of the most serious pests of crops worldwide, causing major yield and economic losses. To control aphids, natural enemies could be an option but their efficacy is sometimes limited by their dispersal in natural environment. Here we report the first isolation of a bacterium from the pea aphid Acyrthosiphon pisum honeydew, Staphylococcus sciuri, which acts as a kairomone enhancing the efficiency of aphid natural enemies. Our findings represent the first case of a host-associated bacterium driving prey location and ovipositional preference for the natural enemy. We show that this bacterium has a key role in tritrophic interactions because it is the direct source of volatiles used to locate prey. Some specific semiochemicals produced by S. sciuri were also identified as significant attractants and ovipositional stimulants. The use of this host-associated bacterium could certainly provide a novel approach to control aphids in field and greenhouse systems

Testing the optimal defence hypothesis for two indirect defences: extrafloral nectar and volatile organic compounds

Many plants respond to herbivory with an increased production of extrafloral nectar (EFN) and/or volatile organic compounds (VOCs) to attract predatory arthropods as an indirect defensive strategy. In this study, we tested whether these two indirect defences fit the optimal defence hypothesis (ODH), which predicts the within-plant allocation of anti-herbivore defences according to trade-offs between growth and defence. Using jasmonic acid-induced plants of Phaseolus lunatus and Ricinus communis, we tested whether the within-plant distribution pattern of these two indirect defences reflects the fitness value of the respective plant parts. Furthermore, we quantified photosynthetic rates and followed the within-plant transport of assimilates with 13C labelling experiments. EFN secretion and VOC emission were highest in younger leaves. Moreover, the photosynthetic rate increased with leaf age, and pulse-labelling experiments suggested transport of carbon to younger leaves. Our results demonstrate that the ODH can explain the within-plant allocation pattern of both indirect defences studied

Effects of Volatiles from Maruca vitrata Larvae and Caterpillar-Infested Flowers of Their Host Plant Vigna unguiculata on the Foraging Behavior of the Parasitoid Apanteles taragamae

The parasitoid wasp Apanteles taragamae is a promising candidate for the biological control of the legume pod borer Maruca vitrata, which recently has been introduced into Benin. The effects of volatiles from cowpea and peabush flowers and Maruca vitrata larvae on host selection behavior of the parasitoid Apanteles taragamae were investigated under laboratory conditions by using a Y-tube olfactometer. Naïve and oviposition-experienced female wasps were given a choice between several odor sources that included (1) uninfested, (2) Maruca vitrata-infested, and (3) mechanically damaged cowpea flowers, as well as (4) stem portions of peabush plants carrying leaves and flowers, (5) healthy M. vitrata larvae, and moribund (6), and live (7) virus-infected M. vitrata larvae. Responses of naïve and oviposition-experienced female wasps did not differ for any of the odor source combinations. Wasps were significantly attracted to floral volatiles produced by cowpea flowers that had been infested with M. vitrata larvae and from which the larvae had been removed. Apanteles taragamae females also were attracted to Maruca vitrata-infested flowers after removal of both the larvae and their feces. Female wasps discriminated between volatiles from previously infested flowers and mechanically damaged flowers. Uninfested cowpea flowers attracted only oviposition-experienced wasps that had received a rewarding experience (i.e. the parasitization of two M. vitrata larvae feeding on cowpea flowers) before the olfactometer test. Wasps also were attracted to uninfested leaves and flowers of peabush. Moreover, they were also attracted to healthy and live virus-infected M. vitrata larvae, but not when the latter were moribund. Our data show that, similarly to what has been extensively been reported for foliar volatiles, flowers of plants also emit parasitoid-attracting volatiles in response to being infested with an herbivore

Conditioning Individual Mosquitoes to an Odor: Sex, Source, and Time

Olfactory conditioning of mosquitoes may have important implications for vector-pathogen-host dynamics. If mosquitoes learn about specific host attributes associated with pathogen infection, it may help to explain the heterogeneity of biting and disease patterns observed in the field. Sugar-feeding is a requirement for survival in both male and female mosquitoes. It provides a starting point for learning research in mosquitoes that avoids the confounding factors associated with the observer being a potential blood-host and has the capability to address certain areas of close-range mosquito learning behavior that have not previously been described. This study was designed to investigate the ability of the southern house mosquito, Culex quinquefasciatus Say to associate odor with a sugar-meal with emphasis on important experimental considerations of mosquito age (1.2 d old and 3–5 d old), sex (male and female), source (laboratory and wild), and the time between conditioning and testing (<5 min, 1 hr, 2.5 hr, 5 hr, 10 hr, and 24 hr). Mosquitoes were individually conditioned to an odor across these different experimental conditions. Details of the conditioning protocol are presented as well as the use of binary logistic regression to analyze the complex dataset generated from this experimental design. The results suggest that each of the experimental factors may be important in different ways. Both the source of the mosquitoes and sex of the mosquitoes had significant effects on conditioned responses. The largest effect on conditioning was observed in the lack of positive response following conditioning for females aged 3–5 d derived from a long established colony. Overall, this study provides a method for conditioning experiments involving individual mosquitoes at close range and provides for future discussion of the relevance and broader questions that can be asked of olfactory conditioning in mosquitoes