Ontogenetic change of prey preference in the generalist predator Zelus renardii and its influence on predator–predator interactions

1. Two field experiments were conducted to test the hypothesis that the intensity of predation by a generalist predator on two species of prey changes with the developmental stage of the predator. The generalist predator studied was Zelus renardii Kolenati (Hemiptera: Reduviidae) and the prey were the lacewing larva, Chrysoperla carnea Stephens, and the cotton aphid, Aphis gossypii Glover.
2. Zelus renardii and lacewings feed on aphids, thereby acting as potential competitors. In addition, Z. renardii feeds on lacewings. Thus, Z. renardii is an intraguild predator of lacewings.
3. Zelus renardii exhibited changes in prey preferences across developmental stages. The older stages of Z. renardii exerted greater mortality on lacewings and fed on larger lacewing larvae than did the younger stages.
4. Lacewings suppressed aphid population growth strongly. In contrast, none of the stages of Z. renardii was an effective control agent of the cotton aphid.
5. The addition of Z. renardii frequently disrupted the effective control of aphids generated by lacewings. In one of the two replicates of the experiment, the disruption increased with the developmental stage of Z. renardii , paralleling the increase in lacewing mortality.
6. Although the developmental stage of Z. renardii can influence the prevalence of intraguild predation and the intensity of the disruption of the aphid biological control, these experiments have demonstrated that even the youngest instars of Z. renardii can cause substantial lacewing mortality and release aphid populations from regulation.     

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.     

The interplay between density- and trait-mediated effects in predator-prey interactions: a case study in aphid wing polymorphism

Natural enemies not only influence prey density but they can also cause the modification of traits in their victims. While such non-lethal effects can be very important for the dynamic and structure of prey populations, little is known about their interaction with the density-mediated effects of natural enemies. We investigated the relationship between predation rate, prey density and trait modification in two aphid-aphid predator interactions. Pea aphids (Acyrthosiphon pisum, Harris) have been shown to produce winged dispersal morphs in response to the presence of ladybirds or parasitoid natural enemies. This trait modification influences the ability of aphids to disperse and to colonise new habitats, and hence has a bearing on the population dynamics of the prey. In two experiments we examined wing induction in pea aphids as a function of the rate of predation when hoverfly larvae (Episyrphus balteatus) and lacewing larvae (Chrysoperla carnea) were allowed to forage in pea aphid colonies. Both hoverfly and lacewing larvae caused a significant increase in the percentage of winged morphs among offspring compared to control treatments, emphasising that wing induction in the presence of natural enemies is a general response in pea aphids. The percentage of winged offspring was, however, dependent on the rate of predation, with a small effect of predation on aphid wing induction at very high and very low predation rates, and a strong response of aphids at medium predation rates. Aphid wing induction was influenced by the interplay between predation rate and the resultant prey density. Our results suggests that density-mediated and trait-mediated effects of natural enemies are closely connected to each other and jointly determine the effect of natural enemies on prey population dynamics.     

Suitability of four different prey species for Dichochrysa tacta (Neuroptera: Chrysopidae)

The prey suitability for generalist insect predators is an important factor in efficient mass rearing. This work constitutes the first biological study of the predatory lacewing Dichochrysa tacta. We tested the effects of four different prey species on the biological parameters of the predatory lacewing D. tacta under laboratory conditions. These prey species consisted of Ephestia kuehniella (Zeller) and the aphids: Aphis fabae, Aphis punicae and Macrosiphum rosae. The results showed that prey species elicited a significant effect on preimaginal development times, survival, adult longevity and fecundity. In contrast, the progeny sex ratio, egg hatch and egg duration were not significantly affected by prey species. Eggs of E. kuehniella were the most suitable prey among those tested, and led to high survival rates, short development times for the preimaginal stages, long adult longevity, high fecundity, highest intrinsic rate of increase (r_m) and highest net reproductive rate (R₀) of D. tacta. Nymphs of both A. punicae and M. rosae were also relatively favourable prey, whereas nymphs of A. fabae were less suitable and resulted in reduced development, survival, adult longevity, fecundity, r_m and R₀. These results could be useful for optimising the mass rearing of D. tacta as an indigenous predator and for understanding its population dynamics in relation to different prey species in the field.     

Effect of plant nutrition on aphid size,prey consumption,and life history characteristics of green lacewing

Plant quality can directly and indirectly affect the third trophic level. The predation by all the instars of green lacewing, Chrysoperla carnea （S.） （Neuroptera： Chrysopidae） on the cereal aphids, Rhopalosiphum padi （L.）, and Sitobion avenae （F.） at varying nitrogen fertilizer levels was calculated under laboratory conditions. Wheat plants were grown on four nitrogen fertilizer levels and aphids were fed on these plants and subsequently offered as food to the C. carnea. Aphid densities of 10, 30, and 90 were offered to first, second, and third instar larvae of green lacewing. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. Aphid consumption by green lacewings was reduced with the increase in nitrogen content in the host plants of aphids. Predation of both aphid species by first, second, and third instars larvae of C. carnea was highest on aphids reared on plants with the lowest rate of fertilization, suggesting a compensatory consumption to overcome reduced biomass （lower aphid size）. Total biomass devoured by C. carnea on all nitrogen fertilizer treatments was not statistically different. Additionally, the heavier host prey influenced by the plant nutrition had an effect on the life history characteristics of green lacewings. The larval duration, pupal weight, pupal duration, fecundity, and male and female longevity were significantly affected by the level of nitrogen fertilization to the aphid＇s host plants, except for pupal duration when fed on S. avenae. This study showed that quantity of prey supplied to the larvae affects the prey consumption and thereafter the life history characteristics of green lacewings.     

Enhancing biological control by an omnivorous lacewing: Floral resources reduce aphid numbers at low aphid densities

The availability of plant resources to omnivorous arthropod predators may have a positive, negative or negligible effect on their population densities and predation rates, depending on the availability of prey. At high prey densities, flowering buckwheat has been shown to negatively impact populations of the brown lacewing, an omnivorous predator, due to the probable increase in parasitism rate of lacewing larvae by their primary parasitoid, Anacharis zealandica. However, little is known about the effect of buckwheat flowers on this insect community at low prey densities. We used field cages to assess the effects of nectar provision by flowering buckwheat on the population dynamics of the pea aphid, the brown lacewing and its parasitoid A. zealandica in an alfalfa field, under low aphid densities in the New Zealand summer. The insects were sampled every 2 weeks with a suction device, then counted and released on each sampling date from 15 January to 15 March 2007. Buckwheat significantly increased lacewing populations and significantly decreased aphid numbers by 70% and 39%, respectively. The buckwheat had its greatest effect at the end of summer (February/March) for both these species. It had no effect on A. zealandica abundance.     

Interaction between plant resistance and predation of Aphis fabae (Homoptera: Aphididae) by Coccinella septempunctata (Coleoptera: Coccinellidae)

We investigated the compatibility of host plant resistance to the black bean aphid in the faba bean crop with the use of the predatory ladybird beetle for biological control under laboratory and greenhouse conditions. Greenhouse experiments indicated that apteriform Aphis fabae reproduced on Vicia faba major (susceptible) and on 79S4 (partially resistant) cultivars at different rates. During the entire experimental period, aphids built up higher populations on V. faba major than on 79S4 cultivar. Aphid numbers on 79S4 were about 37% of those on V. faba major after 14 days. Release of a newly hatched Coccinella septempunctata larva onto each plant significantly reduced aphid density to 32.8% and 57.2% on V. faba major and 79S4 on day 14, respectively. Partial resistance combined with predation was more effective in lessening aphid numbers on faba bean than either the predator or the plant resistance alone. Laboratory tests showed that prey, A.   fabae , raised on susceptible cultivar was more suitable for the predator as food source, enhancing the development rate and fecundity than aphids fed on the partially resistant cultivar. Consumption of aphids reared on susceptible cultivar significantly increased the female fecundity and fertility of C. septempunctata by 37.7% and 33.2%, respectively, more than those fed with aphids from partially resistant cultivar. Pre-oviposition time was shortened by 4.5 days, and oviposition period was extended by 11.4 days. Feeding the predator on aphids from the partially resistant cultivar prolonged the embryonic larval developmental time and the time required from egg laying to adult emergence by 19.8, 10.1 and 32.5 h, respectively. Adult longevity was not influenced by the aphid source. The results are discussed in relation to the compatible utilisation of host plant resistance and biological control in the integrated management of aphids.     

Microcosm studies on intraguild predation between female erigonid spiders and lacewing larvae and influence of single versus multiple predators on cereal aphids

Abstract: Intraguild predation between female erigonid spiders [Erigone atra (Blackwall) and Oedothorax apicatus (Blackwall), Araneae, Erigonidae] and lacewing larvae (second instar larvae of Chrysoperla carnea (Stephens), Neuropt., Chrysopidae) and interaction effects of predator combinations on cereal aphids were investigated in a microcosm system under laboratory conditions. The microcosm experiments were run for 7 days and consisted of 15wheat seedlings, 15 Sitobion avenae (F) (Hom., Aphididae) as start population, plus a female spider or a lacewing larva or a combination of a spider plus a lacewing larva. The mortality rate of lacewing larvae was significantly increased by 44 and 31% due to intraguild predation by female spiders of E. atra and O. apicatus in comparison with lacewing larvae that were kept alone. The final aphid numbers in the microcosms were significantly reduced by all single predator treatments (spiders, lacewing larvae) and the predator combinations in comparison with controls without predators. The predation effect on aphid populations due to both spider species was similar and not statistically different. An additive effect of the predator combinations ‘spider plus surviving lacewing larva’ was found for both spider species resulting in reduced aphid numbers compared with the single predator treatments. When the lacewing larva was killed by an E. atra female the effects on aphids were non‐additive, but aphid numbers were not statistically increased compared with the lacewing larva treatment. When the lacewing larva was killed by an O. apicatus female, the effects of spider and C. carnea larva were additive on aphid numbers. In the presence of additional prey (fruit flies and Collembola) intraguild predation was not found and E. atra females had no significant effect on the survival of lacewing larvae. In addition, E. atra females had no significant effect on aphid numbers in the presence of fruit flies and Collembola, but in combination with a lacewing larva that survived, a significantly greater reduction of the aphid population was observed compared with the lacewing larva treatment. The body mass of lacewing larvae at the end of the experiment was not statistically influenced by the presence or absence of an E. atra female.     

Predation of cotton bollworm by green lacewings in the presence of cotton aphid as alternative prey on transgenic Bt and conventional cotton

Experiments were conducted in small arenas and on whole plants to explore the effect of cotton aphids, Aphis gossypii Glover (Hemiptera: Aphididae), as alternative prey on the predation of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) larvae by green lacewing larvae, Mallada signatus Schneider (Neuroptera: Chrysopidae). Transgenic Bt (Bollgard II^®) and conventional cotton plants were included to explore potential differences in the predator's performance on these cotton types. In small arenas, the presence of 20 aphids reduced predation on H. armigera larvae by 22% (from 5.5 to 3.3 of 10) by a single lacewing larva over a 24‐h period. The presence of H. armigera reduced predation on aphids by ca. 29% (from 16.8 to 11.0 of 20) over 24 h. On whole plants, the presence of alternative prey had no effect on the number of H. armigera larvae or aphids remaining after 3 days. The presence of H. armigera larvae alone, without the predator, caused a 24% reduction in the numbers of aphids on conventional, but not on Bt cotton plants. The combination of Bt cotton and lacewing larvae caused a 96.6% removal of early‐stage H. armigera larvae, a statistically significant increase over the addition of the proportions (91.6%) removed by each factor measured separately, providing evidence of synergism. These studies suggest that the presence of aphids as alternative prey would not necessarily disrupt the predation by green lacewing on larvae of H. armigera, especially on Bt cotton.     

Functional response of Euseius concordis to densities of different developmental stages of the cassava green mite

Both prey density and developmental stage of pests and natural enemies are known to influence the effectiveness of biological control. However, little is known about the interaction between prey density and population structure on predation and fecundity of generalist predatory mites. Here, we evaluated the functional response (number of prey eaten by predator in relation to prey density) of adult females and nymphs of the generalist predatory mite Euseius concordis to densities of different developmental stages of the cassava green mite Mononychellus tanajoa, as well as the fecundity of adult females of the predator. We further assessed the instantaneous rate of increase, based on fecundity and mortality, of E. concordis fed on eggs, immatures and adults of M. tanajoa. Overall, nymphs and adults of E. concordis feeding on eggs, immatures and females of M. tanajoa had a type III functional response curve suggesting that the predator increased prey consumption rate as prey density increased. Both nymphs and adult females of the predator consumed more eggs than immatures of M. tanajoa from the density of 20 items per leaf disc onwards, revealing an interaction between prey density and developmental stage in the predatory activity of E. concordis. In addition, population growth rate was higher when the predator fed on eggs and immatures in comparison with females. Altogether our results suggest that E. concordis may be a good candidate for the biological control of M. tanajoa populations. However, the efficiency of E. concordis as a biological control agent of M. tanajoa is contingent on prey density and population structure.     

Coleomegilla maculata (Coleoptera: Coccinellidae) predation on pea aphids promoted by proximity to dandelions

The impact of a predator on its prey may depend on the presence of other species in the community. In particular, if predators are attracted to areas containing one prey species, another prey species may suffer greater predation if it occurs in the same areas. If the predator is omnivorous, this may occur even if one prey species is an animal and the other is a plant. We investigated the role of local dandelion densities on the impact of the predator Coleomegilla maculata on pea aphids in alfalfa fields. At small spatial scales, increased dandelion densities were associated with high C. maculata densities, presumably because these omnivorous ladybird beetles aggregated to pollen resources. In turn, the high C. maculata densities were associated with low aphid densities, presumably because of increased predation. We used laboratory cages to simulate C. maculata foraging in two adjacent patches of alfalfa, one with dandelions and one without. As in the field, the laboratory experiment showed that C. maculata aggregated to alfalfa interspersed with dandelions, which resulted in increased predation on aphids on alfalfa. This study demonstrates that a pollen-producing plant can indirectly decrease nearby herbivore densities by attracting an omnivorous predator.     

The negative effects of pathogen‐infected prey on predators: a meta‐analysis

Intra‐guild predation (IGP) – where a top predator (IG_Pred) consumes both a basal resource and a competitor for that resource (IG_Prey) – has become a fundamental part of understanding species interactions and community dynamics. IGP communities composed of intraguild predators and prey have been well studied; however, we know less about IGP communities composed of predators, pathogens, and resources. Resource quality plays an important role in community dynamics and may influence IGP dynamics as well. We conducted a meta‐analysis on predator–pathogen–resource communities to determine whether resource quality mediated by the pathogen affected predator life‐history traits and if these effects met the theoretical constraints of IGP communities. To do this, we summarized results from studies that investigated the use of predators and pathogens to control insect pests. In these systems, the predators are the IG_Pred and pathogens are the IG_Prey. We found that consumer longevity, fecundity, and survival decreased by 26%, 31% and 13% respectively, when predators consumed pathogen‐infected prey, making the infected prey a low quality resource. Predators also significantly preferred healthy prey over infected prey. When we divided consumers by enemy type, strict predators (e.g. wolf spiders) had no preference while parasitoids preferred healthy prey. Our results suggest that communities containing parasitoids and pathogens may rarely exhibit intraguild predation; whereas, communities composed of strict predators and pathogens are more likely dominated by IGP dynamics. In these latter communities, the consumption of low and high quality resources suggests that IGP communities composed of strict predators, pathogens and prey should naturally persist, supporting IGP theory. Synthesis We investigated how consuming pathogen‐infected prey influence important life‐history parameters of insect predators. Pathogens are used in a variety of biocontrol programs, especially to control crop pests. We found that true predators (i.e. wolf spiders) have no preference for healthy or infected prey and have reduced fecundity, survival and longevity consuming infected prey. However, parasitoids avoided infected prey when possible. In biocontrol programs with multiple control agents, parasitoids and pathogens would do a better job controlling pests as predators would reduce the amount of pathogen available and have reduced fitness from consuming infected prey. However, theory suggests that true predators, prey and pathogens may coexist long term.     

Potential cotton aphid,Aphis gossypii,population suppression by arthropod predators in upland cotton

The cotton aphid, Aphis gossypii Glover, predation rate of convergent lady beetle, Hippodamia convergens Guerin‐Meneville, was determined by assigning a single predator randomly to each of four prey density treatments in the laboratory. Prey densities included 25, 50, 100, and 200 aphids per Petri dish arena. Predation response was recorded at 1, 4, 8, 16, 24, and 48 h after assigning predators to their prey treatments. Rate of consumption increased through time, with all 25 aphids consumed during the first 4 h of the experiment. At the highest density, adult lady beetle consumed on average 49, 99, 131, 163, 183, and 200 aphids within 1, 4, 8, 16, 24 and 48 h, respectively. Predators showed a curvilinear feeding response in relation to total available time, indicating that convergent lady beetles have the potential to suppress larger populations of aphids through continuous feeding by regulating their predation efficiency during feeding. The analysis of age‐specific mortality in absence of prey revealed that lady beetles could survive for an extended period of time (more than 2 weeks) without prey. The ability of a predator to survive without prey delays or prevents the rebound of pest populations that is a significant factor in natural biological control. A two‐year field sampling of 10 cotton arthropod predator species showed that spiders (27%) were the most dominant foliage dwelling predators in the Texas High Plains cotton followed by convergent lady beetles (23.5%), hooded beetles (13.5%), minute pirate bugs (11%), green lacewings (9.5%), bigeyed bugs (7.5%), scymnus beetles (3%), soft‐winged flower beetles (2%), damsel bugs (1.5%), and assassin bugs (1.5%). A field cage study showed that one H. convergens adult per plant released at prey density of one aphid per leaf kept the aphid population below economic threshold for the entire growing season.     

Effects of prey density and spatial distribution on prey consumption of the adult predatory ladybird beetle

The effects of prey density and spatial distribution on prey consumption of the adult predatory ladybird, Harmonia axyridis , were investigated by using a 2 × 2 factorial design in large scale cages. Prey density influenced prey consumption of the ladybirds, and the frequency with which predation occurred was quite different between the prey distributions. The ladybirds consumed a relatively constant and small number of aphids when the prey were uniformly distributed, whereas the number of prey consumed per day when predation occurred was large and much more variable when the prey were contagiously distributed. At high prey density, the number of prey consumed was highest during the first day of the experiment; thereafter, only 10–20 aphids were consumed during the following 3 days. However, these patterns of prey consumption were not observed at low prey density. The percentage of aphids that remained on the host plants when the experiments were terminated was higher at low prey density than at high prey density, suggesting that predator foraging efficiency at low prey density was lower than at high prey density. Ladybirds foraging for high prey density were more frequently observed on the plants with aphids than ladybirds foraging for low prey density. Prey distribution also influenced the frequency of residence of ladybirds on the plants. The different predation patterns observed in the two spatial distributions, in which prey consumption was much more variable for the contagious distribution, might be explained by the difference in prey encounter rate of the predator between the distributions. This study indicated that the ladybirds had limited ability to search out prey over large spatial scales.     

Foraging Behavior of Lacewing Larvae (Neuroptera: Chrysopidae) on Plants with Divergent Architectures

We investigated the effects of plant architecture on predator–prey interactions by quantifying the behavior of green lacewing larvae on perennial grasses with divergent leaf architectures. Crested wheatgrass produces flat, broad leaves similar to those of wheat, whereas Indian ricegrass bears linear leaves that are tightly rolled inward. In the absence of prey, lacewing time budgets and residence times were similar on the two grasses, although predators tended to search longer on crested wheatgrass. On plants infested with the Russian wheat aphid, lacewing larvae dislodged, contacted, and captured significantly more aphids on Indian ricegrass than on crested wheatgrass. Comparisons between aphid-free and aphid-infested plants suggest that differences in plant architecture modified prey accessibility rather than predator movement. Aphids on seedlings and mature plants of crested wheatgrass frequently occurred in concealed locations, such as in the rolls of immature leaves or in the blade–sheath junctions of mature leaves; aphids on Indian ricegrass were more likely to feed in exposed locations. Our focal-animal observations were consistent with results from population-level experiments and suggest that short-term, behavioral studies may help predict the effectiveness of predators at larger spatial and temporal scales.     

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.     

Additive effects of predator diversity on pest control caused by few interactions among predator species

1. Studies of the impact of predator diversity on biological pest control have shown idiosyncratic results. This is often assumed to be as a result of differences among systems in the importance of predator–predator interactions such as facilitation and intraguild predation. The frequency of such interactions may be altered by prey availability and structural complexity. A direct assessment of interactions among predators is needed for a better understanding of the mechanisms affecting prey abundance by complex predator communities. 2. In a field cage experiment, the effect of increased predator diversity (single species vs. three‐species assemblage) and the presence of weeds (providing structural complexity) on the biological control of cereal aphids were tested and the mechanisms involved were investigated using molecular gut content analysis. 3. The impact of the three‐predator species assemblages of aphid populations was found to be similar to those of the single‐predator species treatments, and the presence or absence of weeds did not alter the patterns observed. This suggests that both predator facilitation and intraguild predation were absent or weak in this system, or that these interactions had counteracting effects on prey suppression. Molecular gut content analysis of predators provided little evidence for the latter hypothesis: predator facilitation was not detected and intraguild predation occurred at a low frequency. 4. The present study suggests additive effects of predators and, therefore, that predator diversity per se neither strengthens nor weakens the biological control of aphids in this system.     

Prey: predator ratio dependence in the functional response of a freshwater amphipod

1. First known for their shredding activity, freshwater amphipods also behave as active predators with consequences for prey population regulation and amphipod coexistence in the context of biological invasions. 2. A way to quantify predation is to determine the average consumption rate per predator, also known as its functional response (FR). 3. Although amphipods are gregarious and can display social interactions that can alter per capita consumption rates, previous studies using the FR approach to investigate amphipod predation ignored such potential mutual interference because they did not consider variations in predator density. 4. We investigated the FR of Echinogammarus berilloni feeding on dipteran larvae with joint variations in prey and predator densities. This bivariate experimental design allowed us to estimate interference and to compare the fits of the three main classes of theoretical FR models, in which the predation rate is a function of prey density alone (prey‐dependent models), of both prey and predator densities (predator‐dependent models) or of the prey‐to‐predator ratio (ratio‐dependent models). 5. The Arditi–Ginzburg ratio‐dependent FR model provided the best representation of the FR of E. berilloni, whose predation rate showed a decelerating rise to a horizontal asymptote as prey abundance increased. 6. Ratio dependence means that mutual interference between amphipods leads to prey sharing. Mutual interference is likely to vary between amphipod species, depending on their level of aggressiveness.     

Two common invertebrate predators show varying predation responses to different types of sentinel prey

Sentinel prey (an artificially manipulated patch of prey) are widely used to assess the level of predation provided by natural enemies in agricultural systems. Whilst a number of different methodologies are currently in use, little is known about how arthropod predators respond to artificially manipulated sentinel prey in comparison with predation on free‐living prey populations. We assessed how attack rates on immobilized (aphids stuck to cards) and artificial (plasticine lepidopteran larvae mimics) sentinel prey differed to predation on free‐moving live prey (aphids). Predation was assessed in response to density of the common invertebrate predators, a foliar‐active ladybird Harmonia axyridis (Coleoptera: Coccinellidae), and a ground‐active beetle Pterostichus madidus (Coleoptera: Carabidae). Significant increases in attack rates were found for the immobilized and artificial prey between the low and high predator density treatments. However, an increased predator density did not significantly reduce numbers of free‐living live aphids included in the mesocosms in addition to the alternate prey. We also found no signs of predation on the artificial prey by the predator H. axyridis. These findings suggest that if our assessment of predation had been based solely on the foliar artificial prey, then no increase in predation would have been found in response to increased predator density. Our results demonstrate that predators differentially respond to sentinel prey items which could affect the level of predation recorded where target pest species are not being used.     

Effect of floral and extrafloral resources on predation of Aphis spiraecola by Harmonia axyridis on Apple

Flowering companion plants and plants producing extrafloral nectar are being proposed to enhance biological control in apple (Malus domestica Borkh.) orchards. This experiment evaluated the impact of floral and extrafloral resources on predation of spirea aphid (Aphis spiraecola Patch) on apple by adult Harmonia axyridis (Pallas) under greenhouse conditions. Predation of spirea aphids was not affected by the presence of flowering buckwheat (Fagopyrum esculentum) as compared with either buckwheat with flowers removed or an uninfested apple shoot. However, there was a significant reduction in predation of spirea aphids on an apple shoot in the presence of a peach shoot with extrafloral nectar glands compared with either a peach shoot of the same cultivar without nectar glands or an uninfested apple shoot. These findings demonstrate that alternative food resources potentially could interfere with rates of biological control and, therefore, need to be carefully evaluated before incorporating in an orchard design. More studies are needed to adequately gauge the net effects of adding floral or extrafloral resources in orchards for conservation biological control.