Effects of weed density on the dispersal of Orius majusculus Reuter (Heteroptera Anthocoridae) within maize

Orius majusculus Reuter (Heteroptera: Anthocoridae) is the most common and abundant generalist predator in Spanish maize crops and is sensitive to drastic changes in weed density. We carried out a 2‐year study in the NE Iberian Peninsula to examine the dispersal of O. majusculus in maize plots with moderately high and low weed density. Insects were collected using yellow sticky traps and/or a bug‐vac aspirator. Dispersal was assessed using rubidium as a marker. Dispersal rate of O. majusculus differed between sampling periods, with a maximum between the 16 unfolded leaves (V16) to grain milky (R3) maize growth stages. However, we detected no differences in the distance moved by male and females of O. majusculus from rubidium‐marked areas in plots with moderately high or low weed density suggesting that changes in weed density do not affect the dispersal of O. majusculus within a maize field.     

Change in carbon stable isotope ratios of the predatory bug Orius majusculus after dietary shifts

Orius majusculus Reuter (Hemiptera: Anthocoridae) is an important component of the pest predatory complex in arable crops in Mediterranean areas. It moves between crops searching for prey, and improving knowledge on its dispersal abilities will help to develop conservation biological control strategies. Stable isotope ratios may be used as a tool for tracking insect movements, as the isotopic composition of insect tissues changes to reflect that of their diet when they undergo dietary shifts on moving between isotopically distinct crops. We carried out laboratory diet switch experiments with a stable isotope approach to infer information on dispersal of O. majusculus individuals among C3 and C4 crops to better understand isotopic field data collections. Switching the aphid food source caused a quick change in δ¹³C signatures, regardless of the original and final food source. Changes in the δ¹³C ratio of O. majusculus after diet switching fitted with an exponential model that showed similar turnover rates, and thus half‐lives, between shifting diets up to 20 days. Subsequently, whereas individuals feeding on C4 aphids did not survive, turnover rate decreased in individuals that switched from C4 to C3 aphids. However, δ¹³C traces from the original source remained in the predator until 25 days after switching, and this is enough time to help determine the movement of O. majusculus between crops in the field and to plan the timing of predator sampling and crop practices that may enhance predator ecological services. Orius majusculus that switched to a maize aphid diet showed different turnover rates between sexes, although this did not influence the pattern of switchover.     

Stable isotopes reveal different patterns of inter‐crop dispersal in two ladybeetle species

1. Dispersal plays a key role in structuring the local population densities of many insect species, yet the movement patterns across the landscape of most species are poorly understood. By measuring the stable isotope of carbon (δ¹³C) from multiple tissues, a novel approach applied to field‐collected insects, we were able to infer differences in movement patterns of two species of mobile generalist insect predators. 2. Coccinella septempunctata L (7‐spot ladybeetle) and Harmonia axyridis Pallas (multicoloured Asian ladybeetle) were collected in agricultural habitats in 2003 and 2004, and were assayed for δ¹³C in the elytra (slow turnover) and fat/reproductive tissues (fast turnover). δ¹³C values were used to infer diet use of C3 versus C4 crops. 3. Coccinella septempunctata was relatively more faithful to a particular habitat and tended to stay in alfalfa and soybean (C3‐based photosynthetic crops) over long periods during the summer. This contrasts with H. axyridis which showed isotopic evidence consistent with frequent late‐season movement between C3 and C4 crops such as corn in the landscape. 4. These differing patterns suggest that in the late summer season H. axyridis individuals traverse the environment more extensively and utilise broadly dispersed aphid resources, whereas C. septempunctata adults are more specialised on alfalfa and soybean crops.     

Rubidium marking reveals different patterns of movement in four ground beetle species (Col., Carabidae) between adjacent alfalfa and maize

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Biological control of aphids in the presence of thrips and their enemies

Generalist predators are often used in biological control programs, although they can be detrimental for pest control through interference with other natural enemies. Here, we assess the effects of generalist natural enemies on the control of two major pest species in sweet pepper: the green peach aphid Myzus persicae (Sulzer) and the western flower thrips Frankliniella occidentalis (Pergande). In greenhouses, two commonly used specialist natural enemies of aphids, the parasitoid Aphidius colemani Viereck and the predatory midge Aphidoletes aphidimyza (Rondani), were released together with either Neoseiulus cucumeris Oudemans, a predator of thrips and a hyperpredator of A. aphidimyza, or Orius majusculus (Reuter), a predator of thrips and aphids and intraguild predator of both specialist natural enemies. The combined use of O. majusculus, predatory midges and parasitoids clearly enhanced the suppression of aphids and consequently decreased the number of honeydew-contaminated fruits. Although intraguild predation by O. majusculus on predatory midges and parasitoids will have affected control of aphids negatively, this was apparently offset by the consumption of aphids by O. majusculus. In contrast, the hyperpredator N. cucumeris does not prey upon aphids, but seemed to release aphids from control by consuming eggs of the midge. Both N. cucumeris and O. majusculus did not affect rates of aphid parasitism by A. colemani. Thrips were also controlled effectively by O. majusculus. A laboratory experiment showed that adult predatory bugs feed on thrips as well as aphids and have no clear preference. Thus, the presence of thrips probably promoted the establishment of the predatory bugs and thereby the control of aphids. Our study shows that intraguild predation, which is potentially negative for biological control, may be more than compensated by positive effects of generalist predators, such as the control of multiple pests, and the establishment of natural enemies prior to pest invasions. Future work on biological control should focus on the impact of species interactions in communities of herbivorous arthropods and their enemies.     

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

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

多异瓢虫与七星瓢虫、大草蛉不同虫态间的集团内捕食

多异瓢虫、七星瓢虫和大草蛉是控制蚜虫重要的广谱捕食性天敌昆虫,为明确这些昆虫间的集团内捕食效应与个体发育阶段的关系,观察了多异瓢虫与七星瓢虫、大草蛉各虫态(蛹除外)之间的集团内捕食效应。设置30个虫态(虫龄)组合处理,于温室盆栽棉花(无蚜虫)上接种等量的试虫,观察24 h后的存活数量。结果表明,当参与双方的虫态不同时,晚期虫态的存活数量显著大于早期虫态;当参与双方的幼虫龄期不同时,高龄幼虫的存活数量显著大于低龄幼虫;成虫对卵、1龄和4龄幼虫的捕食程度随虫龄增大而呈抛物线增大,存在显著的二次函数关系。当参与双方的虫态(龄)相同时,多异瓢虫成虫的存活数量显著小于七星瓢虫,但大于大草蛉成虫;多异瓢虫幼虫(1龄和4龄)的存活数量显著小于大草蛉,而与七星瓢虫没有显著差异。研究结果说明,在没有集团外猎物(蚜虫)存在的情况下,多异瓢虫与七星瓢虫、大草蛉之间的集团内捕食效应只在参与者的虫态或虫龄不同时取决于发育阶段,而当参与者虫态或虫龄相同时,还取决于其他因素。     

Alfalfa fields promote high reproductive rate of an invasive predatory lady beetle

Invasive insect species often may attain high fecundity in agricultural habitats, thereby contributing to their establishment in new geographic regions and their displacement of similar native species. Such may be true for predatory lady beetles (Coleoptera: Coccinellidae) that have been introduced to North America in recent decades, raising concerns of adverse impact on native lady beetles. In northern Utah, Coccinella septempunctata L. first appeared in 1991, and is now predominant among lady beetles especially in alfalfa fields. We assessed the suitability of alfalfa fields as breeding habitat for females of C. septempunctata and the native, similarly sized Coccinella transversoguttata richardsoni Brown. The timing and amount of egg production differed significantly between C. septempunctata and C. transversoguttata as populations of aphids increased through spring and early summer. Reproduction by both species conformed to the egg window hypothesis, with populations of the predators producing most eggs before aphid numbers peaked. But consistently among fields and years, females of C. septempunctata produced more eggs, and did so earlier in the spring, than C. transversoguttata females even at low prey density. Furthermore, C. septempunctata females were more successful than females of C. transversoguttata in approaching their maximum body weights and reproductive output as measured in the laboratory under ideal conditions. The strong reproductive success of C. septempunctata may contribute to its displacement of C. transversoguttata in irrigated alfalfa in the generally arid Intermountain West of North America and to its establishment as an abundant species in this region of North America.     

Essential versus alternative foods of insect predators: benefits of a mixed diet

Although many predatory insects appear to be opportunistic generalists in their selection of prey, only a subset of prey species may in fact serve as “essential foods” capable of supporting immature growth and adult reproduction. It has been suggested that other, “alternative foods” serve only to maintain the predator when essential foods are not available, but little research has evaluated the significance of a mixed diet of essential and alternative foods for predator growth or reproduction. Here we test the general hypothesis that although alternative prey may be inadequate to support reproduction when consumed alone by adult predators, consumption of such prey may enhance the predator's reproductive output when the predator also has access to essential prey. We compared egg production by two aphidophagous lady beetles, Coccinella septempunctata and C. transversoguttata, provided with diets of aphids (essential prey) and weevils (alternative prey). As predicted, female predators produced greater numbers of eggs when a diet of pea aphids in limited number was supplemented by alfalfa weevil larvae. The predators laid no eggs when provided only with weevils or only with sugar. But once aphids were added to the diet, females of C. transversoguttata (but not C. septempunctata) laid eggs in greater numbers when they had fed previously on weevils than on sugar. Females of both species also produced eggs in modest numbers when provided with both weevils in excess and sugar, but this diet supported a lower rate of egg production than did a diet of weevils in excess plus a limited number of aphids. Although C. septempunctata has a longer history of association with the alfalfa weevil than does C. transversoguttata, the former species was not more effective in exploiting this alternative prey in support of reproduction. The tendency of generalist predators such as adult lady beetles to consume alternative as well as essential prey probably enhances considerably their ability to capitalize on short-lived and scattered opportunities as they seek out suitable sites in which to reproduce. Received: 11 May 1998 / Accepted: 1 May 1999     

On the biology of anthocorid bugs (Heteroptera,Anthocoridae), predators of grass aphids in the forest-steppe zone of West Siberia

Four species of the heteropteran family Anthocoridae, Orius niger Wolff., O. majusculus Reut., O. minutus L., and Anthocoris confusus Reut., feeding on grass aphids on grains and bird cherry occur in the foreststeppe zone of Western Siberia. Orius niger and O. majusculus possess the greatest population numbers, with 98% of all the bugs collected in 1987 and 1988 belonging to these species. In 1998–2000, O. niger was predominant (97–100%). Data on the bionomics, seasonal abundance, feeding intensity, and role of anthocorids in the control of aphids are reported. Density of Orius bugs on wheat has been shown to be independent of the preceding culture. Permanent wheat is a preferable habitat of the predatory anthocorids. Mass reproduction of Orius bugs on pea-oat and alfalfa has been recorded.     

Trophic regulation of postdiapause ovariole maturation inCoccinella septempunctata [Col.: Coccinellidae]

In 1977 the vernal maturation ofCoccinella septempunctata L. females was investigated in relation to the variation in aphid population density on alfalfa and cereals in central Bohemia. The ovarioles do not ripen unless the aphid population density reaches a certain threshold. This leads to considerable variability in the time of vernal reproductive activity (up to 1.5 months in the same geographic locality) among subpopulations living on crops with different aphid densities. This mechanism enables the reproduction of the aphidophagous insect to synchronize with the population development of the aphid.     

Impact of arbuscular mycorrhizal fungi (AMF) and atmospheric CO2 concentration on the biomass production and partitioning in the forage legume alfalfa

The influence of mycorrhizal symbiosis, atmospheric CO₂ concentration and the interaction between both factors on biomass production and partitioning were assessed in nodulated alfalfa (Medicago sativa L.) associated or not with arbuscular mycorrhizal fungi (AMF) and grown in greenhouse at either ambient (392 μmol?mol^?1) or elevated (700 μmol?mol^?1) CO₂ air concentrations. Measurements were performed at three stages of the vegetative period of plants. Shoot and root biomass achieved by plants at the end of their vegetative period were highly correlated to the photosynthetic rates reached at earlier stages, and there was a significant relationship between CO₂ exchange rates and total nodule biomass per plant. In non-mycorrhizal alfalfa, the production of leaves, stems and nodules biomass significantly increased when plants had been exposed to elevated CO₂ concentration in the atmosphere for 4 weeks. Regardless CO₂ concentration at which alfalfa were cultivated, mycorrhizal symbiosis improved photosynthetic rates and growth of alfalfa at early stages of the vegetative period and then photosynthesis decreased, which suggests that AMF shortened the vegetative period of the host plants. At final stages of the vegetative period, AMF enhanced both area and biomass of leaves as well as the leaves to stems ratio when alfalfa plants were cultivated at ambient CO₂. The interaction of AMF with elevated CO₂ improved root biomass and slightly increased the leaves to stems ratio at the end of the vegetative growth. Therefore, AMF may favor both the forage quality of alfalfa when grown at ambient CO₂ and its perennity for next cutting regrowth cycle when grown under elevated CO₂. Nevertheless, this hypothesis needs to be checked under natural conditions in field.     

Predator-induced morphological shift in the pea aphid

Aphids exhibit a polymorphism whereby individual aphids are either winged or unwinged. The winged dispersal morph is mainly responsible for the colonization of new plants and, in many species, is produced in response to adverse environmental conditions. Aphids are attacked by a wide range of specialized predators and predation has been shown to strongly influence the growth and persistence of aphid colonies. In two experiments, we reared two clones of pea aphid (Acyrthosiphon pisum) in the presence and absence of predatory ladybirds (Coccinella septempunctata or Adalia bipunctata). In both experiments, the presence of a predator enhanced the proportion of winged morphs among the offspring produced by the aphids. The aphid clones differed in their reaction to the presence of a ladybird, suggesting the presence of genetic variation for this trait. A treatment that simulated disturbance caused by predators did not enhance winged offspring production. The experiments indicate that aphids respond to the presence of a predator by producing the dispersal morph which can escape by flight to colonize other plants. In contrast to previous examples of predator-induced defence this shift in prey morphology does not lead to better protection against predator attack, but enables aphids to leave plants when mortality risks are high.     

Water Transfer in an Alfalfa/Maize Association : Survival of Maize during Drought

We investigated the possibility of interspecific water transfer in an alfalfa (Medicago sativa L.) and maize (Zea mays L.) association. An alfalfa plant was grown through two vertically stacked plastic tubes. A 5 centimeter air gap between tubes was bridged by alfalfa roots. Five-week old maize plants with roots confined to the top tube were not watered, while associated alfalfa roots had free access to water in the bottom tube (the −/+ treatment). Additional treatments included: top and bottom tubes watered (+/+), top and bottom tubes droughted (−/−), and top tube droughted after removal of alfalfa root bridges and routine removal of alfalfa tillers (−^*). Predawn leaf water potential of maize in the −/+ treatment fell to −1.5 megapascals 13 days after the start of drought; thereafter, predawn and midday potentials were maintained near −1.9 megapascals. Leaf water potentials of maize in the −/− and −^* treatments declined steadily; all plants in these treatments were completely desiccated before day 50. High levels of tritium activity were detected in water extracted from both alfalfa and maize leaves after ³H₂O was injected into the bottom −/+ tube at day 70 or later. Maize in the −/+ treatment was able to survive an otherwise lethal period of drought by utilizing water lost by alfalfa roots.     

Acceptability of Drosophila suzukii as prey for common predators occurring in cherries and berries

The invasive cherry vinegar fly, Drosophila suzukii, has been identified in Europe as a destructive fruit pest since its arrival in 2008. In the present laboratory study, three predatory insects (Orius majusculus, Chrysoperla carnea, and Forficula auricularia) naturally occurring on fruit crops in Europe were investigated for their ability to attack and feed on D. suzukii within and outside fruits. The predators were provided with various D. suzukii life stages (eggs, larvae, pupae or adults) exposed or within infested cherries. The anthocorid bug O. majusculus fed on eggs and larvae, but was not able to attack pupae. Larvae of the lacewing C. carnea preyed upon D. suzukii eggs, larvae and pupae and also captured adult flies. The European earwig F. auricularia was the most voracious predator of these three tested species. Although the earwigs were not able to catch adult flies, they readily preyed upon every other developmental stage. Adult O. majusculus or third instar larvae of C. carnea significantly reduced the offspring of D. suzukii from infested cherries, when these contained the egg stage of the pest. None of the predators were able to attack early larval stages inside the cherries. But pupae that protruded from the fruit epicarp or that had pupated outside the fruit were accessible to lacewing larvae and earwigs and significantly reduced by them. Orius bugs, lacewing larvae and earwigs were able, under laboratory conditions, to capture and prey upon various life stages of the invasive pest, if not completely concealed inside the fruit. Our findings suggest that these generalist predators may have some control capacity on infested fruit in cultivated fruit crops and also in non‐crop habitats.     

Changes in the dynamics of functional groups in communities of dung beetles in Atlantic forest fragments adjacent to transgenic maize crops

We investigated the composition and structure of dung beetle communities (Coleoptera, Scarabaeidae, Scarabaeinae) inhabiting areas of forest fragments next to either conventional or Bt-transgenic maize crops. The purpose of the study was to examine possible impacts of transgenic plants on non-target organisms associated with mammals through their food chain. In February 2011, we collected a total of 1502 beetles belonging to 33 species in Campos Novos, Santa Catarina state (SC), Brazil. Beetles were captured using 200 pitfall traps distributed among 20 forest fragments, 10 fragments in each site type (adjacent to conventional vs. Bt crops). In the fragments adjacent to conventional maize, 805 dung beetles from 27 species were collected. In the fragments adjacent to Bt-transgenic maize, 697 dung beetles from 27 species were caught. Dung beetle community composition was affected by fragment size and environmental complexity, and by distance between fragments. However, it did not explain the differences related to the two crop types, i.e., the functional group of dwellers was significantly over-represented in the fragments surrounded by transgenic maize. Hence, the dweller species Eurysternus francinae and Eurysternus parallelus were more frequent and abundant in fragments located near the transgenic maize, while the tunneler species Onthophagus tristis, Uroxys terminalis, Ontherus sulcator and the roller species Canthon lividus seminitens were more frequent and abundant in fragments surrounded by conventional maize. This observed impact of transgenic crops on functional group dynamics within dung beetle communities could potentially lead to impaired capacity for feces removal, seed dispersal, edaphic aeration, and incorporation of organic matter in the soil in these areas, as such ecosystem services are not performed by the dominant functional group (i.e., dwellers).     

Does nitrogen limitation promote intraguild predation in an aphidophagous ladybird?

Reciprocal intraguild predation occurs between the two aphidophagous ladybird beetles Coccinella septempunctata L. and Harmonia axyridis Pallas (Coleoptera: Coccinellidae). However, its direction is asymmetrical; H. axyridis generally acts as an intraguild predator, and C. septempunctata as an intraguild prey. According to Denno and Fagan's prediction that nitrogen shortages in predators may promote intraguild predation, it was hypothesized that growth of intraguild predator H. axyridis is more limited by nitrogen than that of intraguild prey C. septempunctata, and that H. axyridis growth is enhanced by feeding on C. septempunctata compared to feeding on aphids. To determine nitrogen‐limited growth in H. axyridis, the following two predictions were examined. First, it was predicted that the nitrogen content of H. axyridis would be higher than that of C. septempunctata when both feed on aphids. However, nitrogen content did not differ between the two ladybirds. Second, it was predicted that nitrogen‐use efficiency of H. axyridis would be lower than that of C. septempunctata. However, there was no significant difference between species. These results did not support the hypothesis that growth of H. axyridis is more limited by nitrogen than that of C. septempunctata. In addition, the present study showed that dry mass and nitrogen growth of H. axyridis were not enhanced, but rather decreased, by eating high‐nitrogen C. septempunctata, compared to eating low‐nitrogen aphids. Overall, the present study did not support the hypothesis that nitrogen shortages in predators may promote intraguild predation.     

Aggregation of polyphagous predators in response to multiple prey: ladybirds (Coleoptera: Coccinellidae) foraging in alfalfa

The spatial distribution of polyphagous predators may often reflect the integration of aggregative responses to local densities of multiple species of prey, and as such may have consequences for the indirect linkages among the prey sharing these predators. In a factorial field experiment in which we manipulated local prey densities within a field of alfalfa in Utah (USA), we tested whether aphidophagous ladybirds would aggregate not only in response to their primary aphid prey, but also in response to an abundant alternative prey, the alfalfa weevil (Hypera postica [Gyllenhal]). Native North American ladybirds (primarily Hippodamia convergens Guerin and H. quinquesignata quinquesignata [Kirby]) responded only to spatial variation in aphid density. In contrast, the introduced ladybird, Coccinella septempunctata L., aggregated also at local concentrations of the weevil late in the experiment when weevil density was high and aphid density was relatively low throughout all experimental plots. The results support the hypothesis that C. septempunctata is more responsive than are native ladybirds to the availability of alternative prey in alfalfa, which may account in part for the displacement of native ladybirds from alfalfa by the introduced species as aphid numbers have declined. The differing responses of the native and introduced ladybirds to spatial patterns of the alternative prey underscore the importance of extending the study of predator aggregation to understand better how polyphagous predators distribute themselves in response to spatial patterns of multiple species of potential prey.     

Mast-seeding in the cycad genus Encephalartos: a test of the predator satiation hypothesis

Mast-seeding behaviour was monitored in 18 populations of eight species of the African cycad genus Encephalartos between 1988 and 1991. The coefficient of variation (V) in annual cone production for each population ranged between 88 and 200, indicating large fluctuations in reproductive effort between years. Data were collected to determine whether mast-seeding reduced levels of predispersal seed predation by satiating seed predators in mast years and whether it resulted in a reproductive advantage over plants which reproduced more frequently. Masting intensity was greatest in those populations in which individual plants suffered the highest levels of predispersal seed predation in years when only a few plants produced seeds. The principal seed predators were two congeneric weevil species, Antliarhinus zamiae and A. signatus, which develop exclusively on cycad seeds. The lowest intensity of mast-seeding was recorded for cycad populations with low levels of seed predation and in which A. zamiae and A. signatus occurred only in low numbers or were entirely absent. Larger seed crops appeared to result in lower levels of seed predation by A. zamiae and A. signatus in four populations of E. altensteinii, and differences in seed crop size accounted for 48–66% of variation in levels of seed predation in populations of five cycad species. In one population of E. altensteinii, lower levels of seed predation in plants reproducing periodically resulted in a reproductive advantage over plants reproducing more frequently. These results are consistent with the predator satiation hypothesis. However, in most cycad populations, numbers of seed predators did not appear to decrease significantly after a period of 2–8 years between reproductive episodes and, in two of three populations examined, periodic reproduction did not increase the number of seeds surviving to dispersal over a 4-year period. These results are interpreted to mean that periodic reproduction has not evolved in response to selection imposed by seed predators, but that selection may favour those plants which experience lower levels of seed predation by coning in synchrony with the majority of plants in the population.     

Food quality of Ephestia eggs,the aphid Rhopalosiphum padi and mixed diet for Orius majusculus

We studied the food quality of the aphid Rhopalosiphum padi to the pirate bug Orius majusculus using Ephestia eggs as high-quality comparison prey. Several performance parameters were tested on individuals that had been reared and maintained on each of the two single-prey diets or on a mixed diet. All fitness parameters were lower in individuals fed aphids only, indicating poor food quality of this prey. Compared with the pure Ephestia egg diet, the mixed diet enhanced teneral mass, while adult survival and female starvation tolerance were negatively affected and all other traits were unaffected. Body protein proportions were constant across diets, whereas lipid proportion was low in the aphid treatment. Preference for aphids was lower following a monotypic aphid diet than when reared on Ephestia eggs or a mixed diet. The results confirm that R. padi is low-quality food for O. majusculus as it is for other generalist predators, even though O. majusculus may contribute significantly to population suppression of the aphid.