The aggregative numerical response of polyphagous predators to aphids in cereal fields: attraction to what? (original) (raw)
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Relative importance of predators and parasitoids for cereal aphid control
Proceedings of the Royal Society B: Biological Sciences, 2003
Field experiments with manipulations of natural enemies of plant-feeding insects may show how a diverse enemy group ensures an important ecosystem function such as naturally occurring biological pest control. We studied cereal aphid populations in winter wheat under experimentally reduced densities of: (i) ground-dwelling generalist predators (mostly spiders, carabid and staphylinid beetles); (ii) flying predators (coccinellid beetles, syrphid flies, gall midges, etc.) and parasitoids (aphidiid wasps), and a combination of (i) and , compared with open controls. Aphid populations were 18% higher at reduced densities of ground-dwelling predators, 70% higher when flying predators and parasitoids were removed, and 172% higher on the removal of both enemy groups. Parasitoid wasps probably had the strongest effect, as flying predators occurred only in negligible densities. The great importance of parasitism is a new finding for aphid control in cereal fields. In conclusion, a more detailed knowledge of the mechanisms of natural pest control would help to develop environmentally sound crop management with reduced pesticide applications.
Biocontrol, 2004
Generalist predators are potential controlagents of aphids in cereal fields. Becauseaphids are low-quality prey for most generalistpredators, the availability of alternativehigh-quality prey may influence theinteractions between aphids and their predatorsby reducing the predation rate due to loweredpreference for aphids. We analysed this bytesting the ability of six generalist predators(the spiders Erigone atra (Bl.), Clubiona lutescens (Westr.)/reclusaO.P.-C., Pachygnatha degeeri Sundevall,Pardosa prativaga (L.Koch), the carabidbeetle Bembidion lampros (Herbst), andthe harvestman Oligolophus tridens (C.L.Koch)) to suppress Rhopalosiphum padi(Linné) populations in the presence orabsence of alternative prey types (fruit fliesDrosophila melanogaster (Meigen) or thecollembolan Tomocerus bidentatus(Folsom)). Experiments of 10 days duration werecarried out in a microcosm set-up. Withoutalternative prey all predators except B.lampros were able to reduce aphid populationdevelopment significantly relative topredator-free controls. The harvest spider O. tridens was the most efficient predator(<90% reduction). Presence of alternativeprey (fruit flies) had a significant negativeeffect on aphid limitation by P. prativagaand a weak positive effect in B. lampros, but did not influence the ability to reduce aphids in E. atra, Clubiona, P. degeeri and O. tridens. In addition, 24-hours' consumption experiments with adult P. degeeri and subadult C. lutescens/reclusa, using R. padi and D. melanogaster as prey types, showed markedly lower consumption rates of aphid than of fruit fly prey. The microcosm arrangement is a simple way to partly simulate the habitat complexity of an agricultural field under laboratory conditions and proved to be a useful tool for investigating complex predator-prey interactions.
Entomologia Experimentalis et Applicata, 2006
Ecologists may wish to evaluate the potential for predators to suppress prey populations through the costs of induced defensive behaviors as well as through consumption. In this paper, we measure the ratio of non-consumptive, defense-inducing encounters relative to consumptive encounters (henceforth the 'disturbed : consumed ratio') for two species of aphids and propose that these disturbed : consumed ratios can help evaluate the potential for behaviorally mediated prey suppression. For the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), the ratio of induced disturbances to consumption events was high, 30 : 1. For the cotton aphid, Aphis gossypii (Glover) (Homoptera: Aphididae), the ratio of induced disturbances to consumption events was low, approximately 1 : 14.
International Journal of Zoological Investigations, 2021
The present study sheds light on the consumptive effects (CEs) and the non-consumptive effects (NCEs) of a generalist, Oxyopes javanus Thorell, and a specialist arthropod predator, Coccinella transversalis Fabricius, on an aphid, Aphis gossypii Glover, a pest of an extrafloral nectar-bearing, Clerodendrum infortunatum L. plant. Our results revealed that the percentage of aphids consumed (i.e. CE) by the two species of arthropod predators was significantly higher in the absence of the two species of plant-visiting ants, Camponotus compressus (Fabricius) and Crematogaster subnuda Mayr, than in the presence of either of the two ant species. Further, the ladybird beetle, Coccinella transversalis consumed a significantly higher percentage of aphids in the presence of the ant Crematogaster subnuda than in the presence of Camponotus compressus, indicating the differential effects of the two ant species on the CEs of the aphidophagous ladybird beetle. The NCEs of the predators on the aphids was insignificantly higher in the absence of both of the ant species. The inclusion of ants along with the two species of arthropod predators in the experimental arena significantly reduced the anti-predatory escape response exhibited by the aphids. This suggests that the facultative ant-aphid mutualistic association influences the CEs as well as the NCEs of the arboreal predators on the aphid pests. These results have significant implications in the use of arthropod predators as biocontrol agents in the management of honeydew producing hemipteran pests, under field conditions.
Bulletin of Entomological Research, 2004
The distribution of aphid predators within arable fields has been previously examined using pitfall traps. With this technique predominantly larger invertebrate species are captured, especially Carabidae, but the technique provides no estimate of density unless mark–recapture is used. However, many other numerically important aphid predators occur in arable fields and relatively little is known about their distribution patterns nor whether they exhibit a density dependent response to patches of cereal aphids. Identification of the most effective predators can allow management practices to be developed accordingly. In this study, the distribution of cereal aphids and their predators was examined by suction sampling within a field of winter wheat in Devon, UK, along with visual estimates of weed patchiness. Sampling was conducted on four occasions in 1999 across a grid of 128 sample locations. The distribution of 11 predatory taxa from the Carabidae, Staphylinidae and Linyphiidae was examined. Additionally, the total number of aphid predators and a predation index were used in these analyses. Carabid adults and larvae, along with staphylinid larvae showed the strongest aggregation into patches and the most temporal stability in their distribution. Other taxa had more ephemeral distributions as did the cereal aphids. The distribution of carabid larvae was disassociated from the distribution of cereal aphids for the first two sampling occasions indicating biocontrol was occurring. Other predatory groups showed both association and disassociation. Carabid larvae, Bathyphantesand total numbers of Linyphiidae showed a strong correlation with weed cover for two of the sample dates. Cereal aphids were disassociated from weed cover on three sampling occasions.
The value of three cereal aphid species as food for a generalist predator
Physiological Entomology, 2008
The value of the cereal aphid species Metopolophium dirhodum (Wlk.), Sitobion avenae (F.) and Rhopalosiphum padi (L.) as prey for the linyphiid spider Erigone atra (Bl.) was assessed. Fecundity of females was determined for spiders fed on eight experimental diets: three single-species aphid diets, a mixed diet of all three aphid species, three mixed diets with each aphid species in combination with fruit¯ies Drosophila melanogaster (Meig.), and pure D. melanogaster as a high quality comparison diet. The development and survival of ®rst-instar juveniles fed on three diets of single aphid species, and on a diet of Collembola were compared with those subjected to starvation. Prey value for adult females was assessed by egg production, hatching success and offspring size.
The quality of aphids as food for generalist predators: implications for natural control of aphids
European Journal of Entomology, 2005
The paper reviews existing data on the food quality of cereal aphids for generalist predators. Data are presented for spiders, harvestmen, carabid and staphylinid beetles, cockroaches, ants and one species of bird. All results agree that cereal aphids are low-quality food compared to alternative prey types (in most studies fruit flies). This is associated both with a low consumption capacity for aphids and a low utilization efficiency of the aphid food. A pure aphid diet allows full juvenile development in only a few species. Aphids as part of mixed diets can have negative, neutral or positive effects, which depends on the quality of the remaining diet. The low consumption capacity for aphids is due to the development of a specific feeding aversion. Genetic variation in the ability to tolerate aphids has been documented, indicating that predators may be able to adapt to a higher proportion of aphids in the diet in areas where outbreaks are frequent. A consequence of these findings is that predator populations rely on alternative prey (e.g. Collembola and Diptera) for maintenance and reproduction, and are probably unable to benefit nutritionally from an aphid outbreak. The low food quality of aphids to generalist predators explains why generalist and specialist predators have widely different roles in aphid biocontrol, but does not rule out that under some conditions the generalists may be able to inhibit aphid population growth sufficiently to prevent an outbreak, as field experiments have indicated. Simulation modelling shows that a low consumption capacity for aphids has little influence on the ability to prevent aphid population increase at low aphid immigration rates, but a great influence at high aphid immigration rates. Modelling also indicates that there may be an optimal availability of high-quality alternative prey that maximizes the impact of generalist predators on aphid population growth.
BioControl, 2009
Spiders are common generalist predators in agroecosystems and have been suggested to lower herbivore abundance in crops. It is not clear, however, if spiders can effectively suppress pest populations, and if so, by what mechanisms. In a microcosm experiment, we examined the consumption of the bird cherry-oat aphid, Rhopalosiphum padi L. (Homoptera: Aphididae), a pest species in wheat fields, by three spider species that differ in their hunting methods. We then tested the effect of additional prey type on the ability of erigonid spiders to reduce aphids. In a 48-h experiment Mermessus denticulatus (Banks) (Araneae: Linyphiidae; Erigoninae) consumed more aphids than did Enoplognatha gemina Bosmans and Van Keer (Araneae: Theridiidae) and Bathyphantes cf. extricatus (OÁP.-Cambridge) (Araneae: Linyphiidae; Linyphiinae). This difference may be due to the ability of erigonids to forage actively on the vegetation in addition to using their webs to catch prey. In a 7-week experiment, we provided springtails (Collembola) in high and low densities as additional prey to mated erigonids, prior to aphid introduction. Spiders in the low-density springtail treatment built more webs on the vegetation, and caused a 50% reduction in aphid populations. There were significantly fewer aphids in the low-density springtail treatment, but not in the high-density treatment, in comparison to the control (high-density springtails without spiders). The results suggest that additional prey density affects predatory interactions between M. denticulatus and R. padi and that erigonids, which occur in high densities in wheat fields in the Negev desert, may be involved in aphid suppression in these agroecosystems.
Searching behavior of an aphid parasitoid and its hyperparasitoid with and without floral nectar
Biological Control, 2011
While enhancing the searching ability of a natural enemy can give a major improvement in host population suppression, it is important to demonstrate selectivity in favor of the third trophic level when changes, such as added floral resources, are made to agro-ecosystems to enhance biological control efficacy. To explore this question, a pea-aphid endoparasitoid, Aphidius ervi, and its hyperparasitoid, Dendrocerus aphidum, were used to test the effects of prior feeding with buckwheat nectar on searching behavior of both the parasitoid and hyperparasitoid. Digital video was used to record behavior and data were scored and analyzed using Observer Video-Pro software. A. ervi females in nectar treatments spent a higher proportion of their time actively searching than those with access to water only. Fed parasitoids antennated, stung and groomed significantly more than unfed female parasitoids, and spent almost twice as much time attacking and carried out nearly twice as many attacks as unfed parasitoids. D. aphidum spent the greatest proportion of time attacking potential hosts in both 'fed' and 'unfed' treatments. However, although fed females spent a significantly longer time antennating, there was no significant difference in walking or grooming between treatments. Unfed female hyperparasitoids spent significantly more time stationary than fed females. The results demonstrate that the searching efficiency of both third and fourth trophic level parasitoids is enhanced by access to floral nectar. Nectar provision can therefore potentially have positive or negative effects on biological control, depending on the relative proportion of each species.