Effect of plant nitrogen and water status on the foraging behavior and fitness of an omnivorous arthropod

Omnivorous arthropods make dietary choices according to the environment in which they forage, mainly availability/quality of plant and/or prey resources. Such decisions and their subsequent impacts on life‐history traits may be affected by the availability of nutrients and water to plants, that is, through bottom‐up forces. By setting up arenas for feeding behavior observation as well as glasshouse cages for plant preference assessment, we studied effects of the presence of prey (Lepidoptera eggs) and nitrogen/water availability to host tomato plants on the foraging behavior and life‐history traits in the omnivorous predator Macrolophus pygmaeus (Heteroptera: Miridae). In the absence of prey, the predator fed equally on the plants treated with various levels of nitrogen and water. In the presence of prey, however, the feeding rate on plants decreased when the plant received low water input. The feeding rate on prey was positively correlated with feeding rate on plants; that is, prey feeding increased with plant feeding when the plants received high water input. Moreover, plants receiving high water input attracted more M. pygmaeus adults compared with those receiving low water input. For M. pygmaeus fitness, the presence of prey enhanced its fertility and longevity, but the longevity decreased when plants received low compared with high water input. In conclusion, the omnivorous predator may be obliged to feed on plants to obtain water, and plant water status may be a limiting factor for the foraging behavior and fitness of the omnivorous predator.     

Grape downy mildew Plasmopara viticola, an alternative food for generalist predatory mites occurring in vineyards

Generalist phytoseiids are often observed for long periods on plants in the absence of prey, feeding on alternative foods and reaching high population levels. The persistence of generalist predatory mites on plants with a scarcity or absence of prey is a requirement for successful biocontrol strategies of herbivore mites. The importance of pollen as an alternative food for the support of generalist predatory mite populations is widely recognized. However, on grape the presence of pollen is often limited and thus other food sources should contribute towards generalist predatory mite persistence on perennial plants. Previous field observations reported the relationships between the population increases of generalist phytoseiids with late-season spread of grape downy mildew (GDM) Plasmopara viticola. In this study, we test the hypothesis that GDM could be a suitable food source for the predatory mites Amblyseius andersoni and Typhlodromus pyri. In the laboratory we compared the development times, oviposition rates and life-table parameters of predatory mites feeding on pollen or GDM mycelium and spores. Grape downy mildew supported the survival, development and oviposition of T. pyri and A. andersoni. Life-table parameters showed that GDM was a less suitable food source than pollen for both phytoseiid species and that it was more favorable for A. andersoni than for T. pyri. Implications for predator–prey interactions and conservation biological control in vineyards are discussed.     

Stay or move: how Bt‐susceptible Helicoverpa armigera neonates behave on Bt cotton plants

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae occasionally have been reported to survive at management threshold levels in fields of Bollgard II^® cotton, Gossypium hirsutum L. (Malvaceae). The pattern and degree of larval survival is not easily predicted but depends on the ability of first instars to establish on host plants. Experiments were conducted with Bacillus thuringiensis Berliner (Bt)‐susceptible and Bt‐resistant larvae of H. armigera to understand how physiologically Bt‐susceptible H. armigera survive on Bt cotton plants, and examine how their first meal influences survival rates. In assays using cotton plant parts, both strains of larvae displayed similar tendencies to drop‐off specific plant parts of Bt and non‐Bt cotton. However, significantly more Bt‐susceptible larvae dropped off young leaves, mature leaves, and squares of Bt cotton compared to non‐Bt cotton plants. Egg cannibalism significantly improved the survival of Bt‐susceptible H. armigera larvae on Bt cotton plants. Larvae were more likely to eat live aged eggs, than newly laid or dead eggs. Survival significantly improved when larvae cannibalized eggs before feeding on Bt leaves. The behavior of Bt‐susceptible larvae with respect to drop‐off and egg cannibalism may help enhance their survival on Bt cotton plants.     

Egg cannibalism in Ascia monuste in the field; opportunistic, preferential and very frequent

Newly hatched caterpillars of the specialist herbivorous species Ascia monuste (Lepidoptera, Pieridae) feed on egg chorion before ingesting plant material. They also ingest their exoskeletons and perform egg cannibalism in both the field and the laboratory. Females lay eggs on plants which already have conspecifics (eggs and/or caterpillars) leading to the observation of cannibalism in the field. Two favorable conditions are required for such an occurrence: (1) eggs laid close together on the same leaf, and (2) the finding by older caterpillars of eggs on the same plant. Oviposition preference experiments in cages showed that females do not avoid laying on plants with eggs. However, they do avoid laying eggs on plants predated by caterpillars. All instars perform cannibalism in the field and, in addition to this, the ingested eggs are healthy and cannibalism occurs in the presence of abundant food. The ingestion of eggs from their own clutch was more intense when the clutch was large. Contact with eggs is also important for cannibalism. Caterpillars ingested healthy eggs during three successive days. According to the results, it is possible to state that egg cannibalism in A. monuste is opportunistic, preferential and highly frequent and that there is a tolerance to a diet based on animal protein in this species. Since A. monuste obtains nutrients from both animal and vegetable resources, it is probably better to consider it as opportunistic omnivorous.     

Effect of cannibalism on predation,oviposition and longevity of the predacious mite,Agistemus exsertus Gonzalez (Acari: Stigmaeidae)

Cannibalism (intraspecific predation) on conspecific eggs was investigated in the predatory stigmaeid mite, Agistemus exsertus Gonzalez in the absence of eggs of Tetranychus urticae Koch (no-choice tests) and presence of three densities of prey eggs simultaneously (choice tests) in the laboratory. Data show that cannibalism occurs in immatures and adult females of the predator, which successfully developed and reproduced on conspecific eggs as an alternative prey in the absence of prey eggs. In no-choice tests, cannibalism rate on conspecific eggs by A. exsertus stages was significantly lower than the predation rate on T. urticae eggs. The predatory mite exhibited a marked decline in oviposition rate when preyed on conspecific eggs compared with feeding on prey eggs. The developmental duration and longevity of A. exsertus females were significantly longer 1.9 and 1.7 times, respectively, when fed on conspecific eggs than feeding on T. urticae eggs. The propensity of the predator towards cannibalism depends on the prey density, when T. urticae eggs and conspecific eggs are present simultaneously. Provision of increased densities of prey eggs significantly decreased cannibalism and predation by A. exsertus stages, which fed generally less on conspecific eggs than on T. urticae eggs in choice tests. The oviposition rate of the predator increased significantly, as the egg density of the prey increased. The developmental period and longevity of A. exsertus females showed significantly gradual shortness with increasing egg density of the prey.     

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.     

Effect of Diet History on Prey and Pollen Food Choice by Two Lady Beetle Species

Mixed diets of prey and plant-provided foods, such as pollen, have been shown to benefit a wide range of arthropods. However, diet shifting between these two very different food sources remains poorly understood. We hypothesized that previous diet should influence subsequent time allocation between prey and plant food types; to reach a balanced diet, consumers are expected to allocate more time to resources previously lacking in their diet. We tested this hypothesis by observing the foraging choices of larvae of two omnivorous coccinellid species: Coccinella septempunctata L. and Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae), following a diet history of prey, pollen or a mixed diet of both food types. Results showed an asymmetrical tendency of C. septempunctata larvae to complement their previous diet with unfamiliar food: larvae allocated more time to pollen feeding, but not to prey, when each of the foods was previously absent from their diet. Study results have important implications for the use of plant-provided food supplements to enhance biological control by these omnivorous consumers.     

Biological aspects and life table parameters of the predacious mite,Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) consuming food types during immature stages and after adult emergence

To investigate the effect of food types on biological aspects and life table parameters of the predacious mite, Neoseiulus californicus (McGregor), immature stages were fed on pollen of maize, Zea mays L. and eggs of Tetranychus urticae Koch, while adult females were offered the same foods and the alternate shift of each food. All individuals of predator females reached adulthood when reared on maize pollen and prey eggs, but their life cycle was significantly longer on pollen than on prey. The shortest preoviposition period of N. californicus occurred after continuous feeding on T. urticae eggs, whereas the longest happened when fed on prey eggs switched to maize pollen. Continuous consuming of maize pollen showed the longest ovipositoin period for the predator, while rearing on maize pollen shifted to prey eggs exhibited the shortest duration. The longest longevity and highest sex ratio of females to total in N. californicus were recorded when continuously utilised pollen, whereas the shortest longevity and lowest sex ratio were noted when continuously consumed prey. On the contrary, the egg production and life table values of the predator were the highest by continuous feeding on prey eggs, while they were the lowest by continuous rearing on maize pollen. Therefore, feeding juveniles on prey eggs and adult females on maize pollen is better for long-term preservation of N. californicus females than continuous feeding on maize pollen due to a shorter developmental duration, a higher egg production and more favourable life table values.     

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.     

Pollen as an alternative food for Harmonia axyridis

The current study examines the potential of the multicoloured Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) to use pollen as a food to sustain development and reproduction in the absence of insect prey. Three populations of H. axyridis were used in this study: a long-term laboratory population (since 1998) and a melanic and non-melanic population originating from field collected individuals in Belgium. The insects were allowed to develop and reproduce on frozen eggs of Ephestia kuehniella Zeller (Lepidoptera: Phycitidae), frozen moist bee pollen or an even mixture of the two. Females of the field population offered the mixed diet initiated oviposition sooner than those fed only E. kuehniella eggs, but other developmental and reproductive traits were similar on these diets. A diet of pollen alone allowed 35–48% of the larvae of the field population of H. axyridis to successfully reach adulthood. However, developmental time for these individuals was prolonged by 31–49% and adult body weight was reduced by 37–68%, compared to individuals offered the diets containing E. kuehniella eggs. When fed exclusively on pollen in their larval and adult life, about 40% of the adult females of either field population were able to produce a small number of viable eggs. The laboratory and field strains differed in their response to diet for a number of developmental and reproductive traits. The exploitation of pollen and other plant foods at times when insect prey is scarce, may offer a further competitive advantage to the non-indigenous coccinellid H. axyridis over native European predatory lady beetles that share the same niche and are less capable of using pollen as an alternative food.     

Effects of single and dual species herbivory on the behavioral responses of three thrips species to cotton seedlings

This study investigated the olfactory responses of 3 thrips species [Frankliniella schultzei Trybom, F. occidentalis Pergrande and Thrips tabaci Lindeman (Thysanoptera: Thripidae)] to cotton seedlings [Gossypium hirsutum L. (Malvales: Malvaceae)] simultaneously damaged by different combinations of herbivores. Cotton seedlings were damaged by foliar feeding Tetranychus urticae Koch (Trombidiforms: Tetranychidae), Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), Aphis gossypii Glover (Hemiptera: Aphididae) or root feeding Tenebrio molitor L. (Coleoptera: Tenebrionidae). Thrips responses to plants simultaneously damaged by 2 species of herbivore were additive and equivalent to the sum of the responses of thrips to plants damaged by single herbivore species feeding alone. For example, F. occidentalis was attracted to T. urticae damaged plants but more attracted to undamaged plants than to plants damaged by H. armigera. Plants simultaneously damaged by low densities of T. urticae and H. armigera repelled F. occidentalis but as T. urticae density increased relative to H. armigera density, F. occidentalis attraction to coinfested plants increased proportionally. Thrips tabaci did not discriminate between undamaged plants and plants damaged by H. armigera but were attracted to plants damaged by T. urticae alone or simultaneously damaged by T. urticae and H. armigera. Olfactometer assays showed that simultaneous feeding by 2 herbivores on a plant can affect predator–prey interactions. Attraction of F. occidentalis to plants damaged by its T. urticae prey was reduced when the plant was simultaneously damaged by H. armigera, T. molitor, or A. gossypii and F. schultzei was more attracted to plants simultaneously damaged by T. urticae and H. armigera than to plants damaged by T. urticae alone. We conclude that plant responses to feeding by 1 species of herbivore are affected by responses to feeding by other herbivores. These plant‐mediated interactions between herbivore complexes affect the behavioral responses of thrips which vary between species and are highly context dependent.     

Egg cannibalism in Helicoverpa armigera on sorghum and pigeonpea

Egg cannibalism by Helicoverpa armigeraHübner (Lepidoptera: Noctuidae) larvae was studied in the laboratory and in the field. In laboratory experiments, first instars were exposed to increasing densities of H. armigera eggs on sorghum, Sorghum bicolor (L.) Moench, and pigeonpea, Cajanus cajan (L.) Millsp. The number of eggs eaten per larva increasedsignificantly as egg availability increased on both sorghum and pigeonpea. In small cages 21–37% of eggs were eaten on sorghum, 4–12%on pigeonpea. Plant feeding declinedsignificantly on both sorghum and pigeonpea asegg density increased. Cannibalism was greateron sorghum than on pigeonpea while plantfeeding was greater on pigeonpea than onsorghum. Only around 8% of eggs were eaten inlarger cages with sorghum. The response toincreasing egg availability in all experimentswas linear. Immunoassay with an anti-vitellinmonoclonal antibody showed that egg cannibalismoccurs on pigeonpea under field conditions.Seven percent of all larvae had egg protein intheir gut. Cannibalism may make a significantcontribution to H. armigera populationsuppression.     

Polyphagy and primary host plants: oviposition preference versus larval performance in the lepidopteran pest Helicoverpa armigera

Oviposition preference and several measures of offspring performance of Helicoverpa armigera (Hübner) were investigated on a subset of its host plants that were selected for their reputed importance in the field in Australia. They included cotton, pigeon pea, sweet corn, mungbean, bean and common sowthistle. Plants were at their flowering stage when presented to gravid female moths. Flowering pigeon pea evoked far more oviposition than did the other plant species and was the most preferred plant for neonate larval feeding. It also supported development of the most robust larvae and pupae, and these produced the most fecund moths. Common sowthistle and cotton were equally suitable to pigeon pea for larval development, but these two species received far fewer H. armigera eggs than did pigeon pea. Mungbean also received relatively few eggs, but it did support intermediate measures of larval growth and survival. Fewest eggs were laid on bean and it was also the least beneficial in terms of larval growth. Among the host plant species tested, only flowering pigeon pea supported a good relationship between oviposition preference of H. armigera and its subsequent offspring performance. Australian H. armigera moths are thus consistent with Indian H. armigera moths in their ovipositional behaviour and larval performance relative to pigeon pea. The results suggest that the host recognition and acceptance behaviour of this species is fixed across its geographical distribution and they support the theory that pigeon pea might be one of the primary host plants of this insect. These insights, together with published results on the sensory responses of the females to volatiles derived from the different host plant species tested here, help to explain why some plant species are primary targets for the ovipositing moths whereas others are only secondary targets of this polyphagous pest, which has a notoriously broad host range. Handling Editor: Joseph Dickens     

Interference and competitive behaviour of the aphid predators,Chrysoperla carnea andCoccinella septempunctata in the laboratory

Interference and competition betweenChrysoperla carnea (Stephens) andCoccinella septempunctata L. was investigated in the absence and presence of aphid prey. When larvae of similar vigour encountered each other,C. carnea larvae were superior toC. septempunctata. Otherwise the larger of 2 individuals always killed the smaller. In the absence of preyC. carnea adults were attacked by their own 2nd and 3rd instar larvae as well as by 3rd instar larvae ofC. septempunctata. In all encounters the adults ofC. septempunctata were superior. Since the eggs ofC. carnea are protected to some extent by being on egg stalks, they were less susceptible to cannibalism and predation thanC. septempunctata eggs which are deposited in batches directly on plant leaves. In the presence of prey cannibalism and predation were reduced, especially between larvae. Only eggs and 1st instar larvae were endangered. In the present experimentsC. carnea showed a slight superiority overc. septempunctata. Paper presented at the 17th International Congress of Entomology held in August 20–26 1984 in Hamburg, F.R. Germany.     

Performance of Orius insidiosus on alternative foods

Orius insidiosus is economically important for biological control of pests of vegetable and ornamental crops. To improve pest control with this predator, its densities in the crops can be enhanced by the provision of alternative foods, especially when prey are scarce. We therefore compared the performance of O. insidiosus on three alternative foods (Ricinus sp. pollen, bee pollen and the mixed stages of the astigmatid prey Tyrophagus putrescentiae) that are cheaper than frozen eggs of Ephestia kuehniella. Juvenile development was significantly shorter on E. kuehniella and T. putrescentiae than on Ricinus sp. pollen and on bee pollen and lowest without food. Female bugs had a higher oviposition rate when fed either E. kuehniella or T. putrescentiae, but produced fewer eggs when feeding on bee pollen and Ricinus sp. pollen. This shows that T. putrescentiae can possibly be used as cheap alternative food to boost predator populations in periods of low prey densities.     

Pollen increases fitness and abundance of Orius insidiosus Say (Heteroptera: Anthocoridae) on banker plants

Banker plants are intended to enhance biological control by sustaining populations of natural enemies. Banker plants do this by providing alternative sources of food for natural enemies, such as pollen for omnivorous predators, thus decreasing the likelihood of their starvation and emigration from a cropping system when pest populations are low or absent. A banker plant system consisting of the Black Pearl pepper, Capsicum annuum ‘Black Pearl’, and the omnivorous minute pirate bug, Orius insidiosus Say (Hemiptera: Anthocoridae) has recently been proposed to improve biological control of thrips. Therefore, we studied how pollen from the Black Pearl pepper plant affects O. insidiosus fitness and abundance through a series of laboratory and greenhouse experiments. We found that a mixed diet of pollen and thrips increased O. insidiosus female longevity, decreased nymphal development time, and yielded larger females compared to a diet of thrips alone. Furthermore, O. insidiosus abundance was greater on flowering pepper plants than non-flowering pepper plants. From these results, we suggest that pollen from Black Pearl pepper banker plants could increase adult O. insidiosus abundance for the purpose of biological control in two ways: (1) reduce starvation and increase longevity of O. insidiosus when prey is absent; (2) enhance O. insidiosus fitness and fecundity when prey is present by mixing plant and prey diets. These results encourage future studies with the Black Pearl pepper as a banker plant for improving biological control of thrips in commercial greenhouses.     

Does feeding behavior of a zoophytophagous mirid differ between host plant and insect prey items?

Many mirid bugs are omnivores, and several species are key pests of agricultural crops. While mirid feeding behavior on plant hosts is relatively well studied, little attention has been paid to foraging, acceptance, and consumption of insect prey items. In this study, we investigated the feeding behavior and stylet penetration of the green mirid bug Apolygus lucorum on insect prey (Helicoverpa armigera eggs), plant hosts (green bean Phaseolus vulgaris pod), and combined plant + prey diets. Direct observation and electrical penetration graph (EPG) assays were used to assess feeding on either food item. Overall feeding time was highest on combined diets (48.18 ± 4.92 % of total time) and plant foods (42.23 ± 3.36 %), compared with only 28.95 ± 2.27 % feeding time on H. armigera eggs. When exposed to combined diets, A. lucorum spent 3.8 times longer feeding on green bean pod than on H. armigera eggs. The overall duration of stylet penetration was 5866.27 ± 800.39 s on green bean pod versus 3644.81 ± 715.19 s on H. armigera eggs, representing a 37.87 % reduction in duration. Similarly, the duration of a single probing event was significantly higher on green bean pod (355.76 ± 50.13 s) versus H. armigera eggs (236.20 ± 25.17 s), with a 33.61 % reduction. This first work in which omnivory is studied by combined use of observational studies and EPG assays (1) provides further insights into A. lucorum omnivory, (2) further elucidates its trophic position in agroecosystems, and (3) guides the development of artificial diets for this pest species.     

Use of plant resources by an omnivorous predator and the consequences for effective predation

Plant-provided food may enhance survival and establishment of omnivorous predators on target crops but on the other hand they may adversely affect predation rates and thus their potential for biological control of target pests. However, it is not known how predation is affected by plant food quality and prey density. The omnivorous predator Macrolophus pygmaeus is commonly used in augmentative releases in greenhouse crops. Experiments have shown its ability to utilize plant resources; eggplant and pepper plant leaves are the most and least suitable, respectively. In this study we searched the effects of floral resources (pollen or flower) of eggplant or pepper plant on the predation rate of M. pygmaeus. We used experiments in dishes (leaves) and cages (plants) under a range of densities of its prey, the aphid Myzus persicae. We did not find evidence that the consumption rates and the type of the functional responses of M. pygmaeus were affected by the plant leaf (eggplant vs pepper plant) or the increase in the spatial scale (leaf vs plant). However, the presence of pollen or a flower of eggplant and to a lesser extent of pepper plant reduced the plateau of the functional response to aphid density and increased the handling time per prey. The extent of prey feeding replacement by flower resources was dependent on the interaction between plant species and prey density. It seems that there is a constant rate of prey consumption replacement at intermediate and high prey densities on eggplant but only at intermediate prey densities on pepper plant. These results indicate the interactions between plant and prey resources in diets of omnivores and may be useful for its efficacy in pest control on eggplant and pepper plant.     

Local and distant prey-related cues influence when an acarine predator leaves a prey patch

Over relatively long distances, the predatory mite Phytoseiulus persimilis is able to detect volatiles produced by bean plants that are infested by its prey, Tetranychus urticae, the twospotted spider mite. Our investigation examined the separate and combined effects of prey, their products, and prey-induced plant volatiles on when P. persimilis left a potential prey host plant. In wind tunnels, we assessed the relative importance of and interaction among local and distant prey-related cues. The examination of local cues included: (1) all local cues (prey eggs, webbing, and prey-induced plant volatiles), (2) food (prey eggs) and webbing only, (3) plant volatiles only, and (4) no prey-related cues. The examination of distant cues involved the presence or absence of prey-induced plant volatiles from upwind plants. External volatile cues, produced by placing prey-infested plants upwind in the wind tunnel, resulted in more predators leaving downwind plants, and leaving sooner, than when clean plants were upwind, regardless of the availability of prey or prey-related cues on the local plant. However, local cues, especially the presence of food/webbing, had a greater effect than distant cues on timing of predator leaving. Predators remained in larger numbers and for longer times on prey-infested plants. However, the presence of either locally-produced plant volatiles or food/webbing alone still reduced the number of predators leaving a plant in the first hour compared to clean plants. After the first hour, the number of predators leaving was primarily driven by the presence of food/webbing. When no food/webbing was available, predators left plants rapidly; if food/webbing was available, some predatory mites remained on plants at least 24 hours. Even if no food/webbing was available, predators presented with local volatiles remained on plants for several hours longer than on clean plants without local volatiles. These small changes in leaving rates may lead to differences in local population dynamics, and possibly regional persistence, of the predator-prey interaction in patchy environments.     

Effect of pollen supplement on intraguild predatory interactions between two omnivores: The importance of spatial dynamics

Arthropods often engage in complex trophic interactions such as intraguild predation (IGP), true omnivory (i.e., feeding on plants and prey), and apparent competition. Theoretical treatments of the effects of such interactions on herbivore populations have been concerned almost entirely with equilibrium conditions. Yet these interactions are common in non-equilibrium settings such as agroecosystems, where they are likely to have a strong influence on pest populations. We therefore tested short-term effects of IGP and food supplementation on interactions between two predators (the phytoseiid mite Neoseiulus cucumeris and the anthocorid bug Orius laevigatus) and their shared prey, Frankliniella occidentalis, on strawberry plants. All three consumers feed on strawberry pollen, both mites and bugs prey on thrips, and the bug also feeds on the mites (IGP). Strong IGP on mites (IG prey) by the bugs (IG predator) was recorded in structurally-simple arenas. In a more complex setting (whole-plants), however, the intensity of IGP differed among plant structures. Likewise, pollen supplementation reduced both IGP and predation on thrips in a structurally simple setting. In the whole-plant experiment, IGP was more intense on pollen-bearing than pollen-free flowers. The study illustrated how spatial dynamics, generated when consumers track food sources differently in the habitat and possibly when herbivorous and IG prey alter their distribution to escape predation, led to site-specific configuration of interacting populations. The intensity of resulting trophic interactions was weakened by food supplementation and by increased complexity of the habitat.