Effect of host plant,prey species and intergenerational changes on the prey preferences of the predatory mirid <Emphasis Type="Italic">Macrolophus caliginosus</Emphasis>

The outdoor establishment of non-native biocontrol agents released for inundative control of glasshouse pests is determined primarily by two factors: ecophysiological compatibility with local climate, particularly winter cold tolerance, and ability to locate and utilise wild prey. Observations on the number and diversity of acceptable wild prey as part of an assessment of establishment potential therefore overlap with more focused studies to determine host range. This study investigated two aspects of the interactions between biocontrol agents and non-target prey that are rarely considered in tests for establishment or host range: the role of different host plant–prey associations in modifying the development and reproduction of biocontrol agents, and the longer term sustainability of such relationships beyond the single generation observed in most laboratory studies. Using the glasshouse whitefly (Trialeurodes vaporariorum) predator Macrolophus caliginosus Wagner (Hemiptera: Miridae) as a case study, the mirid was able to sustain viable populations over three generations on the related cabbage whitefly Aleyrodes proletella (Linnaeus) (Hemiptera: Aleyrodidae) and the aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae), including when these prey were feeding on different host plants (Chinese cabbage, cabbage and Brussels sprout). However, the rate of development, fecundity and mortality of the predator varied between the different prey and host plant combinations, and in all cases differed than when feeding on its glasshouse prey T. vaporariorum reared on tobacco (Nicotiana tabacum). The results are discussed in the light of the current debate on methods for conducting host range testing as part of an environmental risk assessment. Handling Editor: Dirk Babendreier     

Strategies of aphidophagous predators: lessons for modelling insect predator–prey dynamics

Both theoretical and empirical evidence indicate that in systems where insect predators have longer developmental times than their prey the predators have little impact on the abundance of their prey. In assessing the 'effectiveness' of a predator for biological control one should take into account that selection maximizes predator fitness, not its effctiveness as a biocontrol agent. Therefore, predators that have a long developmental time relative to their prey are unlikely to be the best biocontrol agents. If these results can be generalized to other predator–prey systems, then it is clear that an understanding of predator–prey dynamics can only be achieved by studying predators.     

Grape powdery mildew as a food source for generalist predatory mites occurring in vineyards: effects on life-history traits

In several perennial cropping systems, generalist or omnivorous species represent important biocontrol agents. They can persist on plants by feeding on alternative foods when prey is scarce and potentially limit pest outbreaks. Among beneficials characterised by a wide food range, those belonging to the acarine family Phytoseiidae represent important biocontrol agents. Generalist predatory mites can develop and reproduce using various food sources as alternatives to their tetranychid prey. The presence of alternative food sources can also induce switching feeding behaviour of generalist predators from prey to alternative foods. We evaluated in the laboratory the role of the grape powdery mildew (GPM) for the survival, development and reproduction of Amblyseius andersoni and Typhlodromus pyri , two important beneficial phytoseiid mites, in European and North-American vineyards. We also compared life-history parameters obtained when feeding on GPM with those obtained feeding on tetranychids mite prey or cattail pollen. Results indicated that GPM is an adequate food source for generalist mite survival and development. Results suggest that GPM can sustain mite populations in the absence of higher quality food sources. Based on optimal foraging theory, comparison of life-history parameters on GPM and mite prey suggests that the disruption of phytophagous mite control by these predatory mites in the presence of GPM appears unlikely. Implications for biological control in vineyards are discussed.     

Implications of alternative prey on biocontrol of pests by arthropod predators in strawberry

A range of naturally occurring predator species or commercially produced predators can be used in biocontrol strategies for pests. However, multiple potential prey species or other alternative food sources are often present for predatory insects at any one time. The availability of this ‘alternative’ prey may affect specific pest control by predators and thus influence the release rates of predators required for economic pest control. Strawberry aphid (Chaetosiphon fragaefolii), western flower thrips (Frankliniella occidentalis) and European tarnished plant bug (Lygus rugulipennis) are important and damaging pests in strawberry. In this study, laboratory, glasshouse and field experiments were undertaken to assess the effects of the availability of multiple prey species on biocontrol of specific pests. Results indicated that two of the predators tested showed preferences for prey species such that biocontrol of a particular pest was often less effective when a combination of pest species was present than would have been expected from results of experiments with single prey species alone. The experiments indicated that Orius laevigatus preferred C. fragaefolii to F. occidentalis or to L. rugulipennis, and preferred L. rugulipennis to F. occidentalis. Chrysoperla carnea was shown to prefer C. fragaefolii to L. rugulipennis, and C. fragaefolii over F. occidentalis. Therefore, it is important to consider the effects of alternative prey on suppression of pest species when deciding on management strategies and release rates of predators.     

Numerical and Functional Responses of Forest Bats to a Major Insect Pest in Pine Plantations

Global change is expected to modify the frequency and magnitude of defoliating insect outbreaks in forest ecosystems. Bats are increasingly acknowledged as effective biocontrol agents for pest insect populations. However, a better understanding is required of whether and how bat communities contribute to the resilience of forests to man- and climate-driven biotic disturbances. We studied the responses of forest insectivorous bats to a major pine defoliator, the pine processionary moth pityocampa, which is currently expanding its range in response to global warming. We used pheromone traps and ultrasound bat recorders to estimate the abundance and activity of moths and predatory bats along the edge of infested pine stands. We used synthetic pheromone to evaluate the effects of experimentally increased moth availability on bat foraging activity. We also evaluated the top-down regulation of moth population by estimating T. pityocampa larval colonies abundance on the same edges the following winter. We observed a close spatio-temporal matching between emergent moths and foraging bats, with bat activity significantly increasing with moth abundance. The foraging activity of some bat species was significantly higher near pheromone lures, i.e. in areas of expected increased prey availability. Furthermore moth reproductive success significantly decreased with increasing bat activity during the flight period of adult moths. These findings suggest that bats, at least in condition of low prey density, exhibit numerical and functional responses to a specific and abundant prey, which may ultimately result in an effective top-down regulation of the population of the prey. These observations are consistent with bats being useful agents for the biocontrol of insect pest populations in plantation forests.     

Population dynamics of Spalgis epius (Lepidoptera: Lycaenidae), a candidate biocontrol agent of mealybugs and its interaction with mealybug-attendant ants

Spalgis epius is an economically important hemipterophagous butterfly. Detailed information on the population dynamics, natural enemies, and prey range of S. epius and its association with mealybug-attendant ant species is lacking. Three years of field studies conducted at Bangalore University campus, Bengaluru, India on these aspects indicated that the population density of S. epius was greatest from June to December and least from February to May in the low land region. S. epius survived on eight prey species, which were present in different months, of which Phenacoccus indicus was recorded as a prey of S. epius for the first time. Different prey species occurred on 12 species of host plants. The occurrence of S. epius was negatively correlated with temperature and positively correlated with relative humidity and prey populations. Six mealybug-attendant ant species were associated with the larvae of S. epius. The seven general predators of S. epius adults were recorded. Knowledge on the population dynamics and a prey range of S. epius and its interaction with mealybug-attendant ant species could be helpful to using this predator as a major biocontrol agent of various species of mealybugs. This study contributed to our understanding of the population dynamics of a hemipterophagous butterfly.     

Ecology of aphidophagous ladybird Propylea species: A review

Herein, the ecology of genus Propylea, with special reference to its three species — viz. P. dissecta (Mulsant), P. japonica (Thunberg), and P. quatuordecimpunctata Linnaeus is reviewed, with an eye toward its position in natural habitats and amongst other ladybirds and its biocontrol potential. Although Propylea is not as polyphagous as other successful species, it evidences a preference for certain prey, specifically aphids and whiteflies. This genus is a good model for studies of mating, reproduction, sexual selection, etc. Propylea is usually an intraguild prey in the guilds containing ladybirds, such as Harmonia axyridis (Pallas) and Coccinella septempunctata L. It also appears that it retains some intrinsic advantages that aid in the sustenance and survival of the species. Owing to its smaller size and level of victimization in the guild, its biocontrol potential is questionable, but its size disadvantages are counter-balanced by its high intrinsic rate of increase, high predation, reproductive potential, and bioconversion efficiency, as well as the ease with which it can be reared in the laboratory. Further research will be necessary to ascertain clearly the biocontrol potential of Propylea.     

How predator functional responses and Allee effects in prey affect the paradox of enrichment and population collapses

In Rosenzweig-MacArthur models of predator-prey dynamics, Allee effects in prey usually destabilize interior equilibria and can suppress or enhance limit cycles typical of the paradox of enrichment. We re-evaluate these conclusions through a complete classification of a wide range of Allee effects in prey and predator's functional response shapes. We show that abrupt and deterministic system collapses not preceded by fluctuating predator-prey dynamics occur for sufficiently steep type III functional responses and strong Allee effects (with unstable lower equilibrium in prey dynamics). This phenomenon arises as type III functional responses greatly reduce cyclic dynamics and strong Allee effects promote deterministic collapses. These collapses occur with decreasing predator mortality and/or increasing susceptibility of the prey to fall below the threshold Allee density (e.g. due to increased carrying capacity or the Allee threshold itself). On the other hand, weak Allee effects (without unstable equilibrium in prey dynamics) enlarge the range of carrying capacities for which the cycles occur if predators exhibit decelerating functional responses. We discuss the results in the light of conservation strategies, eradication of alien species, and successful introduction of biocontrol agents.     

Frequency-dependent predation and maintenance of prey polymorphism

In positive frequency-dependent predation, predation risk of an individual prey correlates positively with the frequency of that prey type. In a number of small-scale experiments individual predators have shown frequency-dependent behaviour, often leading to the conclusion that a population of such predators could maintain prey polymorphism. Using simulations, I studied the dynamics of frequency-dependent predation and prey polymorphism. The model suggests that persistence of prey polymorphism decreases with increasing number of predators that show frequency-dependent behaviour, questioning conclusions about polymorphism based on experiments with few predators. In addition, prey population size, prey crypsis, difference in crypsis between prey morphs and the way the behaviour was adjusted affected the persistence of polymorphism. Under some circumstances prey population remained polymorphic for a shorter time under frequency-dependent than under frequency-independent predation. This suggests that although positive frequency-dependent predator behaviour may maintain prey polymorphism, it is not a sufficient condition for persistent prey polymorphism.     

The evolution of plumage polymorphism in birds of prey and owls: the apostatic selection hypothesis revisited

Co-evolution between phenotypic variation and other traits is of paramount importance for our understanding of the origin and maintenance of polymorphism in natural populations. We tested whether the evolution of plumage polymorphism in birds of prey and owls was supported by the apostatic selection hypothesis using ecological and life-history variables in birds of prey and owls and performing both cross taxa and independent contrast analyses. For both bird groups, we did not find any support for the apostatic selection hypothesis being the maintaining factor for the polymorphism: plumage polymorphism was not more common in taxa hunting avian or mammalian prey, nor in migratory species. In contrast, we found that polymorphism was related to variables such as sexual plumage dimorphism, population size and range size, as well as breeding altitude and breeding latitude. These results imply that the most likely evolutionary correlate of polymorphism in both bird groups is population size, different plumage morphs might simply arise in larger populations most likely because of a higher probability of mutations and then be maintained by sexual selection.     

Macro-invertebrate predators of freshwater pulmonate snails in Africa,with particular reference to Appasus grassei (Heteroptera) and Procambarus clarkii (Decapoda)

A range of African and alien macro-invertebrates has been reported preying on freshwater pulmonate snails, including those that serve as intermediate hosts for bloodflukes of the genus Schistosoma. Predation by five molluscivorous taxa is reviewed here: indigenous leeches (Glossiphoniidae), marsh fly larvae (Sciomyzidae), waterbugs (Belostomatidae), crabs (Potamonautidae) and invasive crayfish (Astacidae). Common features are a lack of prey specificity but clear prey-size specificity. Attention is drawn to the ability of invasive snail species (Physidae and Lymnaeidae) to avoid predation by several of these taxa. Evidence suggests that only the alien invasive crayfish Procambarus clarkii has potential as a snail biocontrol agent, but that its use should not be encouraged.     

Larval feeding behaviour of Tetanocera elata (Diptera: Sciomyzidae): potential biocontrol agent of pestiferous slugs

Examining predatory behaviour is useful for determining the potential of novel biocontrol agents. We investigated the predatory behaviour of Tetanocera elata (Fabricius) larvae on the pestiferous slug Deroceras reticulatum (Müller). Results indicate three prey-finding strategies, including the predator reaching its prey without previous contact with it or its mucus trail.     

Continuous Traveling Waves for Prey-Taxis

Spatially moving predators are often considered for biological control of invasive species. The question arises as to whether introduced predators are able to stop an advancing pest or foreign population. In recent studies of reaction–diffusion models, it has been shown that the prey invasion can only be stopped if the prey dynamics observes an Allee effect. In this paper, we include prey-taxis into the model. Prey-taxis describe the active movement of predators to regions of high prey density. This effect leads to the observation that predators are drawn away from the leading edge of a prey invasion where its density is low. This leads to counterintuitive result that prey-taxis can actually reduce the likelihood of effective biocontrol.     

Differential foraging success across a light level spectrum explains the maintenance and spatial structure of colour morphs in a polymorphic bird

Detectability of different colour morphs under varying light conditions has been proposed as an important driver in the maintenance of colour polymorphism via disruptive selection. To date, no studies have tested whether different morphs have selective advantages under differing light conditions. We tested this hypothesis in the black sparrowhawk, a polymorphic raptor exhibiting a discrete white and dark morph, and found that prey provisioning rates differ between the morphs depending on light condition. Dark morphs delivered more prey in lower light conditions, while white morphs provided more prey in brighter conditions. We found support for the role of breeding season light level in explaining the clinal pattern of variation in morph ratio across the species range throughout South Africa. Our results provide the first empirical evidence supporting the hypothesis that polymorphism in a species, and the spatial structuring of morphs across its distribution, may be driven by differential selective advantage via improved crypsis, under varying light conditions.     

Interaction between life stages in a phytoseiid predator: western flower thrips prey killed by adults as food for protonymphs of Amblyseius cucumeris

Alternative feeding strategies are important in determining the lifestyle of polyphagous spider mite prodators, and could play a key role in their use for biocontrol of prey such as thrips. The small size of Amblyseius cucumeris relative to western flower thrips, Frankliniella occidentalis, limits its survival and development when this prey is the only food available. We show that when A. cucumeris nymphs were reared either alone or with a gravid female on live larvae of F. occidentalis as the only source of food, survival was increased and development was accelerated by the presence of the adult. Similar performance by predator nymphs reared alone on freshly killed thrips larvae indicated that those nymphs reared on live prey with an adult were benefiting from feeding on prey killed by the adult. Variation of the period when an adult female was present with the nymph showed that food provided as a result of the adult's preying activities was beneficial until approximately one third through nymphal development, after which protonymphs became independent predators, with good survival and rapid development when provided only with live F. occidentalis larvae. The results are discussed in relation to adult dispersal in specialist as opposed to generalist phytoseiids, and its potential manipulation in using A. cucumeris for thrips biocontrol.     

More intraguild prey than pest species in arachnid diets may compromise biological control in apple orchards

Understanding the full diet of natural enemies is necessary for evaluating their role as biocontrol agents, because many enemy species do not only feed on pests but also on other natural enemies. Such intraguild predation can compromise pest control if the consumed enemies are actually better for pest control than their predators. In this study, we used gut metabarcoding to quantify diets of all common arachnid species in Swedish and Spanish apple orchards. For this purpose, we designed new primers that reduce amplification of arachnid predators while retaining high amplification of all prey groups. Results suggest that most arachnids consume a large range of putative pest species on apple but also a high proportion of other natural enemies, where the latter constitute almost a third of all prey sequences. Intraguild predation also varied between regions, with a larger content of heteropteran bugs in arachnid guts from Spanish orchards, but not between orchard types. There was also a tendency for cursorial spiders to have more intraguild prey in the gut than web spiders. Two groups that may be overlooked as important biocontrol agents in apple orchards seem to be theridiid web spiders and opilionids, where the latter had several small-bodied pest species in the gut. These results thus provide important guidance for what arachnid groups should be targets of management actions, even though additional information is needed to quantify all direct and indirect interactions occurring in the complex arthropod food webs in fruit orchards.     

Visual and olfactory location of biotopes, prey patches, and individual prey by the ladybeetleChilocorus nigritus

Foraging behaviour of the predatorChilocorus nigritus (Fabricius) (Coleoptera: Coccinellidae) at the three spatial levels of biotope, prey patch and individual prey, was studied in the laboratory, and related to behaviour in the field. Vertically oriented parallel lines were more attractive than the same shapes in a horizontal position. A simulated horizon with a tree line was preferred to a simulated flat horizon. They were attracted to a tree image for the first 2 h of exposure, but were less attracted after longer exposure, possibly due to habituation. Leaf shape was recognised, and simple ovate leaves were preferred to compound bipinnate leaves and to squares. These responses were associated with biotope selection for feeding and aggregation at aestivation sites. The location of prey patches by adults involved prey odour but the location of such sites by larvae did not. Adults detected individual prey visually and olfactorily over short distances but physical contact with prey was required for detection by larvae. Location of individual prey and prey patches by adults and larvae was facilitated by alternation between intensive and extensive search. The differences in the ability of larvae and adults to locate prey, stem from the adults being the active locators of biotope and patch, whereas the comparatively immobile larvae depend on their parents’ ability for long-range location of prey. Two hypotheses concerning coccinellid foraging behaviour are proposed. Firstly, the duration of response to a visual cue is related to the distance over which such a cue may be perceived. It follows that habituation to closer range cues occurs more rapidly than to longer range cues. Secondly, visual cues used by adults at the different spatial levels of prey location, and the location of mates and aggregation sites, have the same or similar shape. These results also provide guidelines for orchard management to maximise the biocontrol value of this species.     

The biocontrol potential of Philodromus (Araneae,Philodromidae) spiders for the suppression of pome fruit orchard pests

A number of different generalist (polyphagous) predators occur in agroecosystems. Yet their biocontrol potential has been little investigated in detail. Philodromus species (Philodromidae) belong to the dominant spider species occurring in commercial orchards. We studied in detail the trophic functional traits of Philodromus albidus, Philodromus aureolus, and Philodromus cespitum (Philodromidae) by means of (1) the analysis of natural prey; and (2) experiments on acceptance of a variety of prey taxa. We found that the three philodromids are euryphagous. We classified prey species into three categories according to their function in the orchard: beneficial species, indifferent species, and pests. Philodromid spiders captured mostly other spiders in the field because spiders were most available. As concerns pests, the philodromids preyed mostly on Brachycera and Sternorrhyncha. They selected Acari and Brachycera. Indifferent species, such as Collembola and Nematocera, were also highly selected. In the laboratory, philodromids accepted mostly pests, such as lepidopterans, brachycerans, and aphids, while other spiders were accepted the least. The three philodromids have differentiated trophic niches with respect to prey size not only in the adult stage but throughout their ontogenetic development: P. albidus utilized smaller prey than the other two species. We conclude that the philodromids have a potential as biocontrol agents because they prey mostly on pests but their predation pressure is reduced due to higher selectivity for the indifferent fauna.     

Ecology and Biocontrol Potential of a Scale-Predator, Chilocorus nigritus

Chilocorus nigritus (Fabricius) is a common predator of scale insects, especially Diaspididae. It is an effective colonist, native to India and may easily establish in pest prevalent regions. Several attempts have been made in the recent past to exploit it for the biocontrol of diaspids infesting sugarcane, citrus and other horticultural crops. The scattered information on its global distribution, foraging, prey range and predation habits, growth and development, reproduction, mass rearing and releases is reviewed. The interpretation of the empirical data has been made and inferences drawn, wherever needed. There is an asymmetry in the literature available, since much emphasis has been given to sampling, mass rearing and field releases of the predator, whereas its ecological and reproductive aspects are poorly dealt with. There are a number of gaps in the information, such as, influences of its age, reproductive, adaptive and survival strategies, its role in the guild and artificial diets which require further investigation.     

Combined effect of an antifeedant α-amylase inhibitor and a predator Cheyletus malaccensis in controlling the stored-product mite Acarus siro

Abstract.  Acarus siro is the most abundant and frequent mite to infest stored-food products, causing allergies and transmitting mycotoxin producing fungi. The predatory mite Cheyletus malaccensis is a candidate species in the biocontrol programme for this pest. In vitro , the α-amylase inhibitor acarbose is effective against the α-amylase of A. siro but not against that of C. malaccensis . In vivo , the impact of acarbose on a population of A. siro is investigated along with the interaction with the predator. Various densities of adult parthenogenetic females of C. malaccensis are reared on A. siro feeding on either a control diet or a diet containing different acarbose concentrations. The combined action of both factors significantly improved the final biocontrol efficiency with C. malaccensis , compensating for the lower energetic content of the prey on acarbose by increasing the number of prey caught. Acarbose had no negative effects on the longevity and the length of oviposition period of C. malaccensis but partially reduced its fecundity. The results are discussed in the context of the integrated control of stored-product mite pests.