Adult Predators Research Articles

Harmonia axyridis (Coleoptera: Coccinellidae) Exhibits No Preference between Bt and Non-Bt Maize Fed Spodoptera frugiperda (Lepidoptera: Noctuidae)

A recent shift in managing insect resistance to genetically engineered (GE) maize consists of mixing non-GE seed with GE seed known as “refuge in a bag”, which increases the likelihood of predators encountering both prey fed Bt and prey fed non-Bt maize. We therefore conducted laboratory choice-test feeding studies to determine if a predator, Harmonia axyridis, shows any preference between prey fed Bt and non-Bt maize leaves. The prey species was Spodoptera frugiperda, which were fed Bt maize (MON-810), expressing the single Cry1Ab protein, or non-Bt maize. The predators were third instar larvae and female adults of H. axyridis. Individual predators were offered Bt and non-Bt fed prey larvae that had fed for 24, 48 or 72 h. Ten and 15 larvae of each prey type were offered to third instar and adult predators, respectively. Observations of arenas were conducted at 1, 2, 3, 6, 15 and 24 h after the start of the experiment to determine the number and type of prey eaten by each individual predator. Prey larvae that fed on non-Bt leaves were significantly larger than larvae fed Bt leaves. Both predator stages had eaten nearly all the prey by the end of the experiment. However, in all combinations of predator stage and prey age, the number of each prey type consumed did not differ significantly. ELISA measurements confirmed the presence of Cry1Ab in leaf tissue (23–33 µg/g dry weight) and S. frugiperda (2.1–2.2 µg/g), while mean concentrations in H. axyridis were very low (0.01–0.2 µg/g). These results confirm the predatory status of H. axyridis on S. frugiperda and that both H. axyridis adults and larvae show no preference between prey types. The lack of preference between Bt-fed and non-Bt-fed prey should act in favor of insect resistance management strategies using mixtures of GE and non-GE maize seed.

Social familiarity governs prey patch-exploitation, -leaving and inter-patch distribution of the group-living predatory mite Phytoseiulus persimilis.

BackgroundIn group-living animals, social interactions and their effects on other life activities such as foraging are commonly determined by discrimination among group members. Accordingly, many group-living species evolved sophisticated social recognition abilities such as the ability to recognize familiar individuals, i.e. individuals encountered before. Social familiarity may affect within-group interactions and between-group movements. In environments with patchily distributed prey, group-living predators must repeatedly decide whether to stay with the group in a given prey patch or to leave and search for new prey patches and groups.Methodology/Principal FindingsBased on the assumption that in group-living animals social familiarity allows to optimize the performance in other tasks, as for example predicted by limited attention theory, we assessed the influence of social familiarity on prey patch exploitation, patch-leaving, and inter-patch distribution of the group-living, plant-inhabiting predatory mite Phytoseiulus persimilis. P. persimilis is highly specialized on herbivorous spider mite prey such as the two-spotted spider mite Tetranychus urticae, which is patchily distributed on its host plants. We conducted two experiments with (1) groups of juvenile P. persimilis under limited food on interconnected detached leaflets, and (2) groups of adult P. persimilis females under limited food on whole plants. Familiar individuals of both juvenile and adult predator groups were more exploratory and dispersed earlier from a given spider mite patch, occupied more leaves and depleted prey more quickly than individuals of unfamiliar groups. Moreover, familiar juvenile predators had higher survival chances than unfamiliar juveniles.Conclusions/SignificanceWe argue that patch-exploitation and -leaving, and inter-patch dispersion were more favorably coordinated in groups of familiar than unfamiliar predators, alleviating intraspecific competition and improving prey utilization and suppression.

Assessing Performance and Competition Among ThreeLaricobius(Coleoptera: Derodontidae) Species, Predators of Hemlock Woolly Adelgid,Adelges tsugae(Hemiptera: Adelgidae)

Predation, egg production, and survivorship of Laricobius nigrinus Fender, L. rubidus LeConte, and L. osakensis Montgomery and Shiyaki, predators of hemlock woolly adelgid, Adelges tsugae Annand, were investigated in the laboratory and in the field. In individual assays in the laboratory, L. rubidus oviposited fewer eggs than either L. nigrinus or L. osakensis. In assays containing congeneric or conspecific groups of adult Laricobius, L. osakensis preyed upon the greatest number of ovisacs. The number of ovisacs preyed upon was not different between treatments with all three species and those with only L. osakensis or L. nigrinus. Adult predators fed on few predator eggs and when they did no species preference was observed. The numbers of A. tsugae ovisacs fed upon did not differ significantly by groups of congeneric or conspecific Laricobius larvae. Laricobius adults and larvae had high survival rates throughout all experiments. In the field, L. nigrinus and L. rubidus were enclosed in sleeve cages with both high (>120 ovisacs) and low (<90 ovisacs) A. tsugae densities for 1 wk. All branches with caged beetles had significantly greater numbers of ovisacs preyed upon than branches caged without beetles. No differences in predation or egg production were found among the conspecific and congeneric groupings. Predation was uniformly greater on high prey-density branches than on low prey-density branches. Survivorship among predators did not differ significantly at either prey density. Results from both laboratory and field experiments suggest that these species are able to coexist and can be released in the same location for biological control of A. tsugae.

Indirect interactions in seagrasses: fish herbivores increase predation risk to sea urchins by modifying plant traits

Summary The dominant paradigm of top‐down control of ecological communities through direct consumption pathways is giving way to a more nuanced understanding of trophic interactions with the recognition that subtler indirect effects can often play an important role in structuring communities. Direct and indirect trophic and non‐trophic processes could well be acting simultaneously within the same food web, and their overall effects may even interact with each other. We studied indirect interactions in a relatively simple trophic system comprising a single producer, two herbivores and a guild of predators. In particular, we assessed whether (i) the principal herbivore fish, Sarpa salpa, is capable of modifying a seagrass trait, canopy height, by grazing and (ii) whether grazing‐induced habitat alteration can trigger an environment‐mediated modification of the interaction between herbivorous sea urchins Paracentrotus lividus and their predators. We tested these hypotheses with field experiments including fish herbivore‐exclusion experiments (to examine the ability of S. salpa to modify seagrass habitats) and predation experiments using tethered sea urchins in a meadow with varying canopy heights (to test whether habitat modification can mediate urchin predation risk). The effect of S. salpa herbivory was highly significant. Canopy height in herbivore‐excluded plots was more than 3·5 times higher than in uncaged control plots. In addition, adult sea urchin predation risk in the most highly grazed plots was 4–5 times higher than plots with higher canopy heights. In contrast, predation risk on juvenile urchins was not influenced by canopy height. Our results show that predation pressure on a key herbivore can be modified both by the environmental context within which it finds itself and by the actions of another herbivore that modifies the plant traits that create this environmental context. These act as two discrete pathways that interact in potentially nonlinear ways, mediating top‐down control in these ecosystems. Herbivores, particularly when acting as ecosystem engineers, may have the potential to mediate and increase predation risk, as they substantially modify habitat structure, with consequences for refuge availability, among others. Assessing these indirect interactions is not just important to understand the functioning of the system itself but may have important management and conservation consequences.

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.

Philopatric predisposition to predation-induced ecological traps: habitat-dependent mortality of breeding eiders

Because population size is sensitive to changes in adult survival, adult survival may be buffered against environmental variability. Philopatry may be adaptive in changing environments, but it could also constrain breeding habitat selection under changing conditions such as shifting predation regimes. Habitat preference and quality could become decoupled in long-lived philopatric species that evolved in stable environments when suddenly faced by increased adult predation risk, as dispersal may be triggered by past reproductive failure. We evaluated whether the Baltic eider (Somateria m. mollissima) population may currently face a predation-induced ecological trap. Eiders are philopatric and nest on open and forested islands. We hypothesized that open-nesting females would be disproportionately affected by increased predation. We compared female annual survival in these two habitats in 1996-2010. We also tested for effects of time trends, winter severity (NAO), female body condition, and habitat-specific predation pressure on survival. Our results revealed the lowest survival recorded for this species (Φ=0.720), and survival on open islands was significantly lower (Φ=0.679) than on forested islands (Φ=0.761). Nonetheless, only 0.7% of females changed breeding habitat type despite ample availability of alternative islands, and breeding phenology in both habitats was similar. Female survival increased with body condition, while it was unrelated to winter climate and stable over time. Open islands had a higher predation pressure on incubating females. Breeding philopatry results in a predator-mediated ecological trap for open-nesting eiders. Our results contribute to explaining the drastic decline of the Baltic eider population.

Missing Pieces, Repetitive Practices

The sexual abuse and exploitation of children is a serious problem. Adult sexual predators often use strategies known as grooming to entice their victims. These include targeting particularly vulnerable youth, gift giving, and systematically engaging in desensitizing sexual behaviors. Less commonly discussed is the notion of institutional grooming, the practice of strategically placing themselves in positions of public trust where they have access to children yet appear beyond reproach. Once situated, they can abuse children for decades without deterrence in spite of the fact that individuals around them may be aware–or partially aware–of their behavior. This article examines three cases, one involving a priest, another a football coach, and the third a pediatrician and considers the institutional practices and cultures that permit (or potentially permit) abuse and exploitation to flourish. Among other things it finds: confidentiality mandates and other codes of silence and secrecy impede information sharing; departmental or programmatic silos exist each with their own independent and competing agendas; confused reporting lines within the institution often end in the hands of powerful individuals who have an interest in non-disclosure; barriers exist to investing within the institution and reporting outside the institution often including mistrust and disempowerment of law enforcement and child protective services; extreme power differences exist between and among victims, predators, reporters, and other institutional players; and finally, intense loyalties personal, professional, and institutional are present. These factors produce institutional cultures that protect pedophiles and conspire against their vulnerable, individual, child victims.

Long-term effects of forest management on territory occupancy and breeding success of an open-nesting boreal bird species, the Siberian jay

In large parts of the world forests are intensively managed, affecting stand structure and biodiversity. Since re-growth of trees can be slow and management cycles can span over 100years, long-term longitudinal data are needed to assess the effects of forestry on organisms living in these habitats. Here, we draw upon 50years of population data of an open-nesting, sedentary bird species, typically of boreal forests, the Siberian jay (Perisoreus infaustus). Forests at the study site were managed by clear-cutting and re-plantation, and a management cycle spanning over 120years. We tracked changes in forest structure in the nest vicinity and the whole territory with the help of aerial images, and linked them to territory occupancy and offspring production in 13 territories. While territories were occupied in 77.2% of all instances, reproduction was only successful in 19.6% of all instances. Both parameters were positively influenced by a large proportion of unthinned forests older than 50years, which provide visual protection from nest and adult predators. Thus, it is crucial to assess both territory occupancy and reproductive output to understand the effects of forestry on bird populations. Moreover, our results suggest that in forests with slow turnover cycles, management which avoids thinning (such as green tree retention forestry) can promote population persistence of open-nesting bird species.

A test of the coupling of predator defense morphology and behavior variation in two threespine stickleback populations

Abstract Among-population differences in morphology and behaviors such as boldness have been shown to co-vary with ecological conditions, including predation regime. However, between- and within-population covariation of predator defense morphology with variation in behaviors relevant to ecology and evolution (boldness, exploration, activity, sociability and aggressiveness, often defined as personality traits when they are consistent across time and contexts) have never been quantified together in a single study in juvenile fish from populations found in contrasting environments. We measured predator defense morphology differences between adults from two freshwater populations of threespine sticklebacks with different ecological conditions. We then quantified five behaviors in juveniles from both populations raised in a common environment. Wild-caught adults showed significant differences in predator defense morphology. One population had significantly lower lateral plate number, shorter dorsal spine, pelvic spine and pelvic girdle. Furthermore, 61% of individuals from that population showed an absence of pelvic spine and girdle. At the population level, we found that differences in defense morphology in adults between the two lakes were coupled with differences in behaviors in juveniles raised in a common environment. Levels of activity, aggressiveness and boldness were higher in juveniles from the population lacking predator defense structures. At the individual level, anti-predator morphology of adult females could not predict their offspring’s behavior, but juvenile coloration predicted individual boldness in a population-specific manner. Our results suggest that ecological conditions, as reflected in adult predator defense morphology, also affect juvenile behavior in threespine sticklebacks, resulting in trait co-specialization, and that there is a genetic or epigenetic component to these behavioral differences.

Unexpected lack of influence of tree rows on the dynamics of wheat aphids and their natural enemies in a temperate agroforestry system

Trees at low density and cereals may be combined in silvoarable agroforestry systems: tree rows and their companion vegetation introduce an heterogeneity in the cropped field that may modify the dynamics of insects crop pests and their predators. This hypothesis was tested in tree-wheat systems by monitoring aphids and their predators for two years in southern France, in two fields in 2006 and one in 2007. Tree row vegetation diversity was either suppressed by weeding or stimulated by seeding flowering species that could attract adult predators of aphids. The dynamics of aphids and predators were recorded by tiller sampling and yellow trap monitoring. Between 3500 and 5000 aphids were collected from each studied field. Surprisingly, no differences could be evidenced on the dynamics of both aphids and their predators between agroforestry and monocropping plots, nor between weeded and flowered plots. The heterogeneity induced by the tree row in the cropped field was probably not strong enough to alter the populations dynamics. A high landscape diversity in the area due to nearby forest patches and fallows may have blurred the impact of the tree lines. Different results may be expected in areas with lower biodiversity like cereal monocropping zones.

Changes in muscle composition during the development of diving ability in the Australian fur seal

During development the Australian fur seal transitions from a terrestrial, maternally dependent pup to an adult marine predator. Adult seals have adaptations that allow them to voluntarily dive at depth for long periods, including increased bradycardic control, increased myoglobin levels and haematocrit. To establish whether the profile of skeletal muscle also changes in line with the development of diving ability, biopsy samples were collected from the trapezius muscle of pups, juveniles and adults. The proportions of different fibre types and their oxidative capacity were determined. Only oxidative fibre types (Type I and IIa) were identified, with a significant change in proportions from pup to adult. There was no change in oxidative capacity of Type I and IIa fibres between pups and juveniles but there was a two-fold increase between juveniles and adults. Myoglobin expression increased between pups and juveniles, suggesting improved oxygen delivery, but with no increase in oxidative capacity, oxygen utilisation within the muscle may still be limited. Adult muscle had the highest oxidative capacity, suggesting that fibres are able to effectively utilise available oxygen during prolonged dives. Elevated levels of total creatine in the muscles of juveniles may act as an energy buffer when fibres are transitioning from a fast to slow fibre type.

Coexistence of Predator and Prey in Intraguild Predation Systems with Ontogenetic Niche Shifts

In basic intraguild predation (IGP) systems, predators and prey also compete for a shared resource. Theory predicts that persistence of these systems is possible when intraguild prey is superior in competition and productivity is not too high. IGP often results from ontogenetic niche shifts, in which the diet of intraguild predators changes as a result of growth in body size (life-history omnivory). As a juvenile, a life-history omnivore competes with the species that becomes its prey later in life. Competition can hence limit growth of young predators, while adult predators can suppress consumers and therewith neutralize negative effects of competition. We formulate and analyze a stage-structured model that captures both basic IGP and life-history omnivory. The model predicts increasing coexistence of predators and consumers when resource use of stage-structured predators becomes more stage specific. This coexistence depends on adult predators requiring consumer biomass for reproduction and is less likely when consumers outcompete juvenile predators, in contrast to basic IGP. Therefore, coexistence occurs when predation structures the community and competition is negligible. Consequently, equilibrium patterns over productivity resemble those of three-species food chains. Life-history omnivory thus provides a mechanism that allows intraguild predators and prey to coexist over a wide range of resource productivity.

Trait‐mediated diversification in nematode predator–prey systems

Nematodes are presumably the most numerous Metazoans in terrestrial habitats. They are represented at all trophic levels and are known to respond to nutrient limitation, prey availability, and microbial resources. Predatory nematodes reside at the highest trophic level, and as such their feeding habits could have a major impact on soil food web functioning. Here, we investigate the effects of gender and developmental stage on the nematode body sizes in coarse and loamy soils. Besides Neodiplogasteridae, our predators are much larger than other soil-dwelling nematodes from their early developmental stage onwards. From juvenile to adult, the predatory Aporcelaimellus (Kruskal–Wallis P < 0.001), Dorylaimoides, and Tripyla (both P < 0.01) show great length increases during their developmental growth, in contrast to their possible prey (almost all P < 0.001). Less than 4% of the prey exceeds the length of the predatory adults, but more than 30% of the prey exceeds the length of the predatory juveniles. Potential body size ratios and some physical problems experienced by small fluid feeders attacking large prey are discussed in an attempt to summarize different prey-searching mechanisms and aggregative predatory responses in the soil system.

Simple Life-History Omnivory: Responses to Enrichment and Harvesting in Systems with Intraguild Predation

This article analyzes the nature of top-down and bottom-up effects and alternative states in systems characterized by life-history omnivory. The analysis is based on a three-species food web with intraguild predation (IGP). The top predator population has juvenile and adult stages, which consume the basal resource and the intermediate prey, respectively; the prey consumes only the resource. The per capita reproduction of the adult predators depends on their consumption rate of prey, while the maturation rate of the juvenile predators depends on their resource consumption rate. Enriching the resource can increase or decrease the abundances of one or both of the two consumer species; an increased density is more likely in the intermediate species than in the systems where IGP is not based on stage differences. Alternative states that have or lack the predator occur frequently, particularly when the prey population is capable of reducing the resource to very low densities. These results differ from those of several other recent models of life-history omnivory. They suggest that life-history omnivory may be one of the primary reasons why exploited populations undergo sudden collapses and why collapsed populations fail to recover in spite of large reductions in the exploitation rate.

Intraguild predation of Serangium parcesetosum (Coleoptera: Coccinellidae), on whitefly Bemisia tabaci (Homoptera: Aleyrodidae) parasitized by Eretmocerus mundus (Hymenoptera: Aphelinidae)

We studied intraguild predation of Serangium parcesetosum on Eretmocerus mundus, both natural enemies of Bemisia tabaci, on eggplant under laboratory conditions. Fourth instar and adult predators attacked parasitized and unparasitized hosts equally if immature parasitoids were larvae, but avoided predating on parasitized hosts containing pupae.

Optimal control of effort of a stage structured prey–predator fishery model with harvesting

This paper describes a prey–predator fishery model with stage structure for prey. The adult prey and predator populations are harvested in the proposed system. The dynamic behavior of the model system is discussed. It is observed that singularity induced bifurcation phenomenon is appeared when variation of the economic interest of harvesting is taken into account. We have incorporated state feedback controller to stabilize the model system in the case of positive economic interest. Fishing effort used to harvest the adult prey and predator populations is used as a control to develop a dynamic framework to investigate the optimal utilization of the resource, sustainability properties of the stock and the resource rent earned from the resource. Pontryagin’s maximum principle is used to characterize the optimal control. The optimal system is derived and then solved numerically using an iterative method with Runge–Kutta fourth-order scheme. Simulation results show that the optimal control scheme can achieve sustainable ecosystem.

The Child as Pornographer

Law enforcement can no longer feasibly contain child pornography within its former borders, since the Internet and digital technology have made images simple to produce in private and even simpler to distribute globally in an instant with little concern for national borders, local laws, or the rights of the performers. Ironically, the largest producers of child pornography in the world may now be the children themselves, who are circulating digital images of one another, sometimes casually, sometimes for pay, that are legally actionable. Justin Berry, the subject of an ethically controversial New York Times exposé of child pornography and prostitution online, created his own porn site with his teenaged self as the main attraction. Once he was caught, however, he was able to enact a gothic and improbable melodrama of innocence seduced and betrayed by adult sexual predators online. The digital “child who knows” has generated a paradox of “erotic innocence” emblematic of the Internet itself as the blameless conduit for the mass obscenity of its users.

Leaf domatia reduce intraguild predation among predatory mites

1. Although theory suggests that intraguild predation destabilises food webs and may result in exclusion of species, empirical observations of food webs reveal that it is a common interaction. It has been proposed that habitat structure reduces the interaction strength of intraguild predation, thus facilitating the coexistence of species. 2. This was tested using acarodomatia, tiny structures on plant leaves, and predatory mites, which usually reside in these domatia. Sweet pepper plants (Capsicum annuum L.) were used, which possess domatia consisting of tufts of hair, and coffee plants (Coffea arabica L.) with pit-shaped domatia. 3. On sweet pepper, the predatory mites Neoseiulus cucumeris Oudemans and Iphiseius degenerans Berl. feed on each other's juveniles. Larvae of each of the species were therefore used as intraguild prey with adult females of the other species as intraguild predators. On coffee, a similar set-up was used, with larvae and adult females of Amblyseius herbicolus Chant and Iphiseiodes zuluagai Denmark & Muma as intraguild prey and intraguild predators, respectively. 4. Domatia on detached, isolated sweet pepper and coffee leaves were either closed with glue or left open, after which larvae and adult predators were released. As a control, larvae were released on leaves with open or closed domatia without an adult predator. 5. Survival of larvae was high in the absence of the adult (intraguild) predator. In the presence of the intraguild predator, survival was significantly higher on leaves with open domatia than on leaves with closed domatia. 6. This shows that even such tiny structures as plant domatia may significantly affect the interaction strength of intraguild predation.

Dial behavioral responses of Metamysidopsis elongata atlantica (Crustacea, Mysida) to gradients of salinity and temperature

Metamysidopsis atlantica elongata (Bascescu, 1968) is a common mysid in the surf zone of sandy beaches from the state of Rio Grande do Sul, Brazil, where it is frequently recorded forming dense aggregations. Trough laboratory trials, behavioral responses to salinity (10, 20, 25, 28, 30, 40 e 45), temperature (10, 15, 20, 30±1ºC) and light (yes/no) were tested using adult males, adult females and juveniles. Although there was no response to temperature, the species showed clear response to salinity and light. In the presence of light, organisms remained in the bottom of the aquaria, but moved to surface when bottom salinities were increased. In the absence of light, adults moved to the surface. However, juveniles moved down to or remained on the bottom, maybe as a response to avoid adult predation.

Optimal control of harvest and bifurcation of a prey–predator model with stage structure

This paper describes a prey–predator model with stage structure for prey. The adult prey and predator populations are harvested in the proposed system. The dynamic behavior of the model system is discussed. It is observed that singularity induced bifurcation phenomenon is appeared when variation of the economic interest of harvesting is taken into account. State feedback controller is incorporated to stabilize the model system in case of positive economic interest. Harvesting of prey and predator population are used as controls to develop a dynamic framework to investigate the optimal utilization of the resource, sustainability properties of the stock and the resource rent earned from the resource. The Pontryagin’s maximum principle is used to characterize the optimal controls. The optimality system is derived and then solved numerically using an iterative method with Runge–Kutta fourth order scheme. Simulation results show that the optimal control scheme can achieve sustainable ecosystem.