Threat of Infection and Threat-Avoidance Behavior in the Predator <Emphasis Type="Italic">Dicyphus hesperus</Emphasis> Feeding on Whitefly Nymphs Infected with an Entomopathogen

The nature and severity of intraguild interactions between predators and entomopathogens will be determined, in part, by a combination of threat of infection, and avoidance of that threat by the predator. We determined the threat of infection posed by the entomopathogen, Paecilomyces fumosoroseus (as PFR-97™) to the generalist predator, Dicyphus hesperus. We then asked if D. hesperus displays behavioral avoidance of infection while foraging for whitefly nymphs at different stages of infection by the pathogen. When exposed to leaf surfaces treated with the pathogen, 28% of adult female predators died due to infection. Consumption of Ephestia kuehniella eggs by surviving predators over 6 d was significantly reduced, suggesting effects of a sublethal infection. Whitefly nymphs that had been treated with P. fumosoroseus 3 d prior were acceptable as prey to D. hesperus but whitefly nymphs that had been treated with P. fumosoroseus 5 days prior were not. When foraging for whitefly nymphs, adult D. hesperus females rejected infected nymphs 96% of the time, compared to 39% of non-infected nymphs. Paecilomyces fumosoroseus therefore presents a measurable threat to D. hesperus through mortality and reduced prey consumption. Dicyphus hesperus does not avoid initial contact with infected prey but does not feed on such prey. The mechanism underlying these rejections could be due to either avoidance of infection or rejection of prey already consumed by the infectious agent. These results suggest that predation by D. hesperus foraging among infected whitefly nymphs under greenhouse or natural conditions could be reduced through a combination of pathogenicity and reduced efficiency of foraging.     

The effects of mullein plants (Verbascum thapsus) on the population dynamics of Dicyphus hesperus (Heteroptera: Miridae) in tomato greenhouses

The response of Dicyphus hesperus Knight (Heteroptera: Miridae) to whitefly populations in tomato greenhouses was measured in the presence and absence of mullein (Verbascum thapsus L.) as an alternative host plant. The dynamics of the D. hesperus population on tomato (Lycopersicon esculentum Mill.) and on mullein plants were followed through an entire growing season. In houses with mullein plants, more predators occurred on mullein when whitefly density was low on tomato. A mark-release-recapture experiment where rabbit IgG was used as an external marker showed that D. hesperus adults moved from mullein plants to tomato plants. D. hesperus was always more abundant in houses with mullein than in the houses with tomato plants alone. Movements between tomato and mullein plants are discussed as a strategy to optimize predator foraging. The use of mullein as an alternative host plant may contribute to the establishment of D. hesperus and help to preserve the predator population when prey on tomato crops is scarce.     

Patch Retention Time in an Omnivore, Dicyphus hesperus is Dependent on Both Host Plant and Prey Type

We examined patch residence times for an omnivorous predator, Dicyphus hesperus on a variety of plants and prey. Individual D. hesperus were placed in cages containing either mullein, tomato, pepper or chrysanthemum plants, and either no prey, Mediterranean flour moth eggs, greenhouse whitefly pupae or two-spotted spider mite adults. Patch residence times were typically greater than 24 h. The probability of remaining on the patch was greatest on mullein and tomato, followed by chrysanthemum and least on pepper, whereas probability of remaining on the patch was greatest when flour moth eggs were present, and least when no prey were available. Patch residence time in D. hesperus was determined by both the prey, and the species of plant, in an independent fashion. Our results reinforce the notion that for omnivores, the patch itself is as important as the prey that it harbors.     

Compatibility of an entomopathogenic fungus with a predator and a parasitoid in the biological control of greenhouse whitefly

An ongoing debate in biological control consists of whether interference between biological agents can disrupt pest control. This study investigated the outcome of interactions between the entomopathogen Beauveria bassiana with the whitefly predator Dicyphus hesperus and the parasitoid Encarsia formosa, as well as their effect on the control of the greenhouse whitefly Trialeurodes vaporariorum on greenhouse tomato crops. Our objective was to determine whether the generalist B. bassiana would disrupt biological control by interfering with D. hesperus or E. formosa. In experimental greenhouses, whitefly, parasitoid and predator populations were established, and over 27 days, tomato plants were sprayed with three applications of the B. bassiana based product BotaniGard® (5.13×10³ conidia/mm²) or water (control). Populations of greenhouse whitefly and biological control organisms were regularly monitored in control and B. bassiana-treated compartments. Overall, 10.6% of all whiteflies in treated compartments were infected, and 0.98% were both infected and parasitized. There were 31.7 and 22.3% fewer immature and adult whiteflies, respectively, on B. bassiana-treated plants relative to controls. Parasitism by E. formosa and predation by D. hesperus occurred at rates of 7.5 and 2.5%, respectively, in B. bassiana-treated compartments, and 5 and 6%, respectively in control compartments. Our study suggests that applications of B. bassiana for short-term biological control of greenhouse whiteflies are compatible with the concurrent use of E. formosa and D. hesperus on greenhouse tomato crops.     

Combined effects of the entomopathogenic fungus, <Emphasis Type="Italic">Paecilomyces fumosoroseus</Emphasis> Apopka-97, and the generalist predator, <Emphasis Type="Italic">Dicyphus hesperus</Emphasis>, on whitefly populations

The effects of intraguild interactions between Dicyphus hesperus Knight (Hemiptera: Miridae) and Paecilomyces fumosoroseus Apopka-97 (PFR-97^TM) (Wize) Brown and Smith (Ascomycota: Hypocreales) on Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) populations were investigated in tomato greenhouse microcosms. Conditions were established in which interference or synergy would most likely occur; namely, a high number of available whiteflies were combined with large numbers of both D. hesperus and PFR-97^TM. We measured live whitefly density in a factorial repeated measures experiment where plants were provided or withheld releases of D. hesperus and/or applications of PFR-97^TM for 6 weeks. Releases of D. hesperus were made at a rate of 10 adults/plant during the first and third week and PFR-97^TM suspensions were applied with a backpack sprayer at a rate of 18 × 10⁷, 1.3 × 10⁷ and 1.2 × 10⁷ viable blastospores/ml during the first, third and fourth week, respectively. Results revealed a non-significant interaction effect between D. hesperus and PFR-97^TM, indicating that their actions were independent. Individual whitefly reductions of 48% and 35% were achieved by PFR-97^TM and D. hesperus, respectively. Collectively, the natural enemies reduced whitefly densities by 62% relative to the controls. The density of D. hesperus adults was unaffected by multiple applications of PFR-97^TM. These results suggest that the combination of generalist entomopathogenic fungi and generalist predators has the potential to cause increased pest mortality despite evidence of minimal interference.     

Colonization of tomato greenhouses by the predatory mirid bugs Macrolophus caliginosus and Dicyphus tamaninii

Colonization of tomato greenhouses by native predatory mirid bugs at the end of the spring cycle is common in the western Mediterranean area when no broad-spectrum insecticides are applied. Due to their polyphagy, these predators interact with pest populations and also with other natural enemies present in the crop. In this work we evaluate the abundance and timing of greenhouse colonization by these predators and their interaction with the greenhouse whitefly Trialeurodes vaporariorum, a key crop pest, and its introduced parasitoid Encarsia formosa. Although quite unpredictable, natural colonization of greenhouses by Macrolophus caliginosus and Dicyphus tamaninii, the two predominant species in our location, usually leads to the establishment of predator populations in the crop that subsequently prey on greenhouse whitefly. No preference for parasitized pupae was observed in greenhouse samples, while laboratory experiments revealed a marked tendency to avoid parasitoid pupae. In our area, IPM programs for greenhouse tomatoes and other vegetables should take advantage of the presence of this predator complex by allowing the immigration and establishment of its populations without disturbing them with highly toxic and non-selective insecticides.     

Prey feeding increases water stress in the omnivorous predator Dicyphus hesperus

The effects of water stress (produced by water deprivation and prey feeding) on plant feeding were investigated in the omnivorous predator Dicyphus hesperus Knight (Hemiptera: Miridae). The objective was to determine if prey feeding aggravated water deficits and thus increased plant feeding. We measured plant feeding in a factorial experiment where female D. hesperus were prepared for experiments by providing or withholding water and/or prey for 24 h. We then evaluated the amount of plant feeding on Nicotiana tabacum seedlings by the direct observation of insects at three different densities of the prey, Ephestia kuehniella eggs. The amount of plant feeding, as measured by frequency of plant feeding bouts and time spent plant feeding during observation, was significantly greater for water‐deprived individuals than for those that had been provided with water. Individuals that had been provided with prey fed on plants at a significantly higher frequency than prey‐deprived individuals at two of the prey densities used in the experiment. These results support the hypothesis that plant feeding in zoophytophagous Hemiptera facilitates prey feeding by providing water that is essential for predation.     

Diel activity pattern and predation rate of the generalist predator Dicyphus hesperus

Abstract This study examined the diel activity pattern and the effect of diel activity pattern on predation rate and prey finding of Dicyphus hesperus Knight (Heteroptera: Miridae). To determine the diel activity pattern of D. hesperus, starved females were placed on tomato leaflets Lycopersicon esculentum Mill. (Solanaceae) under zero, low, or high light intensities at 02:00, 08:00, and 14:00 h, respectively, and the amount of time spent walking or resting during a 30‐min interval was recorded. Predation rates of D. hesperus females on Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) egg patches were determined under either a L16:D8 (long day) or L8:D16 (short day) diel period. Egg patches were removed from D. hesperus females after either 8 or 16 h of dark or 16 or 8 h of light, and the number of eggs consumed was counted. Dicyphus hesperus females spent more time searching for prey at night than during the day. Females ate eggs at a higher rate during the night than during the day. Overall, D. hesperus females had higher predation rates when reared under a long day diel cycle compared with females reared under a short day diel cycle. More females reared at the L16:D8 diel cycle found the egg patch during the night than during the day. There was no difference in egg patch finding between night and day for females reared at L8:D16. Overall, L16:D8 reared females found more egg patches than females reared at L8:D16. Therefore, D. hesperus females are more active and find and consume prey at a higher rate at night than day.     

Density-dependent intraguild predation of an aphid parasitoid

A growing body of research has examined the effect of shared resource density on intraguild predation (IGP) over relatively short time frames. Most of this work has led to the conclusion that when the shared resource density is high, the strength of IGP should be lower, due to prey dilution. However, experiments addressing this topic have been done using micro- or mesocosms that excluded the possibility of intraguild predator aggregation. We examined the effect of shared resource density on IGP of an aphid parasitoid in an open field setting where the effects of prey dilution and predator aggregation could occur simultaneously. We brought potted soybean plants with 2, 20, or 200 soybean aphids (Aphis glycines) and 20 pupae (‘mummies’) of the soybean aphid parasitoid Binodoxys communis into soybean fields in Minnesota, USA. We monitored predator aggregation onto the potted plants, predation of parasitoid mummies, and successful adult emergence of B. communis. We found that predator aggregation was higher at the higher aphid densities on our experimental plants and that this coincided with lower adult emergence of B. communis, indicating that even if a prey dilution effect occurred in our study, it was overcome by short-term predator aggregation. Our results suggest that the effect of shared resource density on IGP may be more nuanced in a field setting than in microcosms due to predator aggregation.     

Intraguild predation by the generalist predator Orius majusculus on the parasitoid Encarsia formosa

Intraguild predation of Orius majusculus (Reuter) (Heteroptera: Anthocoridae) on Encarsia formosa (Gahan) (Hymenoptera: Aphelinidae), both natural enemies of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was studied under laboratory conditions. The experiments quantified prey consumption by 5th instar nymphs and adults of O. majusculus offered unparasitised 3rd, early 4th or 4th instar B. tabaci nymphs or parasitised nymphs containing 2nd or 3rd larval instar or pupal parasitoids. In addition, prey preference of the two stages of O. majusculus for parasitised or unparasitised whitefly nymphs was studied using nine different prey combinations. Both predator stages readily preyed upon on both unparasitised and parasitised B. tabaci. In no-choice experiments, predation on 3rd instar E. formosa by adult predators was the highest, while predator nymphs preyed most on unparasitised 3rd instar B. tabaci and 2nd instar parasitoids. Predation of predator stages was lowest on 4th instar B. tabaci and E. formosa pupae. In all prey combinations, both stages of O. majusculus showed a significant preference for parasitised over unparasitised whitefly nymphs except for the combination of 5th instars of O. majusculus with early 4th instar whiteflies and E. formosa pupae. The results indicate that intraguild interactions between O. majusculus and E. formosa may have negative effects on biological control of B. tabaci.     

The Mirid Bug Dicyphus tamaninii as a Greenhouse Whitefly and Western Flower Thrips Predator on Cucumber

Dicyphus tamaninii Wagner is a polyphagous predator that also feeds on plants. Its effectiveness against several pests has been tested and good results have been obtained on tomato, but not on cucumber. This paper reports the results of three exclusion cage experiments. The first was carried out to evaluate the effectiveness of D. tamaninii for reducing greenhouse whitefly and western flower thrips populations on cucumber. The second experiment examined the safety of the mirid bug in terms of the potential for damaging cucumber fruits even at very low prey densities. Two predator (3 and 18 insects/plant) and variable prey release rates were used. The predator was able to reduce whitefly populations greatly, even at high initial pest infestation levels, especially at the higher release rate. Western flower thrips populations were maintained at very low densities a few weeks after the predator had been introduced into cages at the two release rates tested. The mirid bug was barely able to reproduce on cucumber in the absence of prey. Mirid feeding punctures on cucumber fruit or yield decrease due to the action of mirids were not observed. The potential of this mirid bug for inoculative and conservation biological control is discussed.     

A growth/mortality trade-off in larval salamanders and the coexistence of intraguild predators and prey

Behavioral and morphological traits often influence a key trade-off between resource acquisition and vulnerability to predation, and understanding trait differences between species can provide critical insight into their interactions with other species and their distributions. Such an approach should enhance our understanding of the criteria for coexistence between species that can interact through both competition and predation (i.e. intraguild predators and prey). I conducted a common garden experiment that revealed strong differences between three guild members (larval salamanders Ambystoma laterale, A. maculatum, and A. tigrinum) in behavior, morphology, and growth in the presence and absence of a shared top predator (the larval dragonfly Anax longipes). All three species also reduced their activity and modified their tail fin depth, tail muscle length, and body length in response to non-lethal Anax. Species that act as intraguild predators were more active and could grow faster than their intraguild prey species, but they also suffered higher mortality in laboratory predation trials with Anax. I also used survey data from natural communities to compare the distribution of Ambystoma species between ponds differing in abiotic characteristics and predatory invertebrate assemblages. An intraguild prey species (A. maculatum) was found more reliably, occurred at higher densities, and was more likely to persist late into the larval period in ponds with more diverse invertebrate predator assemblages. Taken together, these results indicate that top predators such as Anax may play an important role in influencing intraguild interactions among Ambystoma and ultimately their local distribution patterns.     

Macrolophus caliginosus (Wagner) as an Intraguild Prey for the Zoophytophagous Dicyphus tamaninii Wagner (Heteroptera: Miridae)

The zoophytophagous predator Macrolophus caliginosus (Wagner) (Heteroptera: Miridae) has previously been identified as a potential prey for the intraguild zoophytophagous predator Dicyphus tamaninii Wagner. Its value as an intraguild prey was tested for D. tamaninii nymphal development and adult survival. In the laboratory, plant (red tomato fruit, green tomato fruit, tomato leaf) and animal (aphids, whiteflies, pyralid eggs) resources were compared to frozen nymphs of M. caliginosus as an intraguild resource for D. tamaninii. M. caliginosus nymphs allowed complete and rapid development of D. tamaninii nymphs and generated low mortality of nymphal and adult stages. Performances were higher with the intraguild M. caliginosus resource than with plant resources. Tomato leaves did not allow the complete nymphal development of D. tamaninii. Tomato fruit generated lighter adults and doubled the nymphal developmental time compared with the M. caliginosus resource. In the animal resource group, there were no differences between the M. caliginosus and the other treatments (aphids, whiteflies, pyralid eggs) for nymphal mortality, average number of molts, nymphal developmental time, adult weight, and adult survival. M. caliginosus should be considered a high-quality resource for D. tamaninii.     

Intraguild Interactions Between the Predatory Mites Neoseiulus californicus and Phytoseiulus persimilis

Species at the same trophic level may interact through competition for food, but can also interact through intraguild predation. Intraguild predation is widespread at the second and third trophic level and the effects may cascade down to the plant level. The effects of intraguild predation can be modified by antipredator behaviour in the intraguild prey. We studied intraguild predation and antipredator behaviour in two species of predatory mite, Neoseiulus californicus and Phytoseiulus persimilis, which are both used for control of the two-spotted spider mite in greenhouse and outdoor crops. Using a Y-tube olfactometer, we assessed in particular whether each of the two predators avoids odours emanating from prey patches occupied by the heterospecific predator. Furthermore, we measured the occurrence and rate of intraguild predation of different developmental stages of P. persimilis and N. californicus on bean leaves in absence or in presence of the shared prey. Neither of the two predator species avoided prey patches with the heterospecific competitor, both when inexperienced with the other predator and when experienced with prey patches occupied by the heterospecific predator. Intraguild experiments showed that N. californicus is a potential intraguild predator of P. persimilis. However, P. persimilis did not suffer much from intraguild predation as long as the shared prey was present. This is probably because N. californicus prefers to feed on two-spotted spider mites rather than on its intraguild prey.     

Supplemental releases of specialist parasitic wasps improve whitefly and psyllid control by <Emphasis Type="Italic">Dicyphus hesperus</Emphasis> in tomato

Dicyphus hesperus Knight (Heteroptera: Miridae) can contribute to the suppression of populations of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) and Bactericera cockerelli Sulcer (Hemiptera: Psyllidae) in tomato. Nevertheless, the remaining levels of these pests could still be too high for the crop to tolerate. We thus tested here whether the combination of D. hesperus with the specialist parasitoids Eretmocerus eremicus Rose & Zolnerowich (Hymenoptera: Aphelinidae) (whitefly) and Tamarixia triozae (psyllid) can result in better pest control compared with methods based exclusively on single-species releases in tomato. We conducted two simultaneous experiments in tomato (‘Whitefly’ and ‘Psyllid’ Experiment), where we compared the effectiveness against B. tabaci and B. cockerelli in cages receiving releases of the predator or the specialist parasitoid alone, or in combination. Although all natural enemies reduced pest levels when released separately, the combination of D. hesperus with E. eremicus and D. hesperus with T. triozae resulted in better whitefly and psyllid control, respectively, compared with the separate releases.     

Poinsettia (Euphorbia pulcherrima Willd Ex Koltz) Cultivar-Mediated Differences in Performance of Five Natural Enemies of Bemisia argentifolii Bellows and Perring, n. sp. (Homoptera: Aleyrodidae)

Laboratory evaluations of five natural enemies of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, n. sp., were conducted to determine their potential as biological control agents in greenhouse poinsettia ranges. Adult longevity, prey consumption or host feeding and parasitism rates, and parasitoid emergence were measured for one predator, Delphastus pusillus LeConte, and four parasitoids, Encarsia formosa Gahan, Encarsia luteola Howard, Encarsia pergandiella Howard, and Encarsia transvena (Timberlake), as possible indicators of efficacy. Characterization of each parameter was performed on two poinsettia cultivars: the first, ′Annette Hegg Brilliant Diamond,′ has trichome densities on the leaf undersurfaces approximately 15% less than the trichome densities on the leaf undersurfaces of the second cultivar, ′Lilo.′ Adult longevity varied significantly between natural enemies (ranging from an average high of 85.2 days for female D. pusillus feeding on B. argentifolii nymphs to an average low of 2.8 days for the Canada colony of E. formosa), but not between cultivar. Prey consumption and oviposition by D. pusillus varied between prey type (nymphs consumed > eggs consumed) and poinsettia cultivar (′Annette Hegg Brilliant Diamond′ > ′Lilo′). Host feeding, parasitism and total number of B. argentifolii nymphs killed varied significantly among Encarsia spp., but no single wasp performed better than the rest across all three parameters. Host feeding, parasitism, and total number of nymphs killed were greater on ′Annette Hegg Brilliant Diamond′ than on ′Lilo′ and this difference was consistent among the four parasitoid species. Among parasitoid species differences in percentage emergence were consistent between the two poinsettia cultivars with emergence from parasitized nymphs on ′Lilo′ being greater than emergence on ′Annette Hegg Brilliant Diamond.′ Results from these evaluations suggest that the probability of achieving successful augmentative biological central will be greater on poinsettia cultivars with fewer trichomes. In addition, achieving biological control is likely to be difficult with releases of E. transvena, but a greater chance for success may be possible through releases of D. pusillus when whitefly densities are high or through releases of E. formosa (Beltsville colony) or mated E. pergandiella independent of whitefly densities.     

Invasion success in communities with reciprocal intraguild predation depends on the stage structure of the resident population

The probability of individuals being targeted as prey often decreases as they grow in size. Such size‐dependent predation risk is very common in systems with intraguild predation (IGP), i.e. when predatory species interact through predation and competition. Theory on IGP predicts that community composition depends on productivity. When recently testing this prediction using a terrestrial experimental system consisting of two phytoseiid mite species, Iphiseius degenerans as the IG‐predator and Neoseiulus cucumeris as the IG‐prey, and pollen (Typha latifolia) as the shared resource, we could not find the predicted community shift. Instead, we observed that IG‐prey excluded IG‐predators when the initial IG‐prey/IG‐predator ratio was high, whereas the opposite held when the initial ratio was low, which is also not predicted by theory. We therefore hypothesized that the existence of vulnerable and invulnerable stages in the two populations could be an important driver of the community composition. To test this, we first demonstrate that IG‐prey adults indeed attacked IG‐predator juveniles in the presence of the shared resource. Second, we show that the invasion capacity of IG‐predators at high productivity levels indeed depended on the structure of resident IG‐prey populations. Third, we further confirmed our hypothesis by mimicking successive invasion events of IG‐predators into an established population of IG‐prey at high productivity levels, which consistently failed. Our results show that the interplay between stage structure of populations and reciprocal intraguild predation is decisive at determining the species composition of communities with intraguild predation.     

Resource quality,resource availability,and intraguild predation among omnivorous mirids

Intraguild predation (IGP) among predatory species can influence many plant-arthropod associations. However, the relevance of IGP is poorly understood for truly omnivorous species such as those that can complete development on both animal and plant diets. Here we test the hypothesis that IGP among two omnivorous mirids is more common when extraguild food is either absent or not suitable. Laboratory experiments were performed in experimental cages in order to determine the effect of intraguild prey densities and diet availability on direction and intensity of IGP between Dicyphus tamaninii and Macrolophus caliginosus (Heteroptera: Miridae). Intraguild predation was symmetrical between the two mirid species in the absence of alternative food. Increasing densities of intraguild prey enhanced drastically the incidence of IGP. Intraguild predation was reduced when mirids were in the presence of green or red tomato fruits, but the presence of any other extraguild resources had no impact on IGP level. However, when given before the experiments, all resources with the exception of tomato leaves significantly reduced IGP. A second experiment was performed on live plants to compare the results of the previous trials with that obtained in a more natural setting. No IGP was observed when both mirid species were present on a plant. However, development of the intraguild prey (the more vulnerable stage) was hindered by the presence of the intraguild predator. The potential of such results is discussed from community ecology and biological control perspective.     

Intraguild Predation among the Hoverfly Episyrphus balteatus de Geer (Diptera: Syrphidae) and Other Aphidophagous Predators

Aphidophagous predators compete for the same prey species. During their foraging activity they frequently encounter heterospecific aphid predators. These situations can lead to intraguild predation and may disrupt biological control efforts against aphids where more than one predator species is present. We investigated the behavior of larvae of the hoverfly Episyrphus balteatus de Geer and its interaction with three other aphid predators: the ladybird Coccinella septempunctata L., the lacewing Chrysoperla carnea Stephens, and the gall midge Aphidoletes aphidimyza (Rondani). Interspecific interactions between predators were examined in arenas of different sizes and in the presence of extraguild prey. The outcome of interactions between E. balteatus larvae and the other predators depended predominantly on the relative body size of the competitors. Relatively large individuals acted as intraguild predators, while relatively smaller individuals became intraguild prey. Eggs and first- as well as second-instar larvae of E. balteatus were highly susceptible to predation by all other predators, whereas pupae of E. balteatus were preyed upon only by the larvae of C. carnea. Interactions between A. aphidimyza and E. balteatus were asymmetric and always favored the latter. Eggs and first- as well as second-instar larvae of E. balteatus sustained intraguild predation irrespective of the size of the arena or the presence of extraguild prey. However, the frequency of predation on third-instar larvae of E. balteatus was significantly reduced. This study indicated that the same species can be both intraguild predator and intraguild prey. It is suggested that combinations of predators must be carefully chosen for success in biological control of aphids.     

Density-dependent prey behaviours and mutable predator foraging modes induce Allee effects and over-prediction of prey mortality rates

1. Predator–prey models are often used to represent consumptive interactions between species but, typically, are derived using simple experimental systems with little plasticity in prey or predator behaviours. However, many prey and predators exhibit a broad suite of behaviours. Here, we experimentally tested the effect of density-dependent prey and predator behaviours on per capita relative mortality rates using Florida bass (Micropterus floridanus) consuming juvenile Bluegill (Lepomis macrochirus).
2. Experimental ponds were stocked with a factorial design of low, medium, and high prey and predator densities. Prey mortality, prey–predator behaviours, and predator stomach contents were recorded over or after 7 days. We assumed the mortality dynamics followed foraging arena theory. This pathologically flexible predator–prey model separates prey into invulnerable and vulnerable pools where predators can consume prey in the latter. As this approach can represent classic Lotka–Volterra and ratio-dependent dynamics, we fit a foraging arena predator–prey model to the number of surviving prey.
3. We found that prey exhibited density-dependent prey behaviours, hiding at low densities, shoaling at medium densities, and using a provided refuge at high densities. Predators exhibited ratio-dependent behaviours, using an ambush foraging mode when one predator was present, hiding in the shadows at low prey–high predator densities, and shoaling at medium and high prey–high predator densities. The foraging arena model predicted the mortality rates well until the high prey–high predator treatment where group vigilance prey behaviours occurred and predators probably interfered with one another resulting in the model predicting higher mortality than observed.
4. This is concerning given the ubiquity of predator–prey models in ecology and natural resource management. Furthermore, as Allee effects engender instability in population regulation, it could lead to inaccurate predictions of conservation status, population rebuilding or harvest rates.