Macrolophus caliginosus (Wagner) as an Intraguild Prey for the Zoophytophagous Dicyphus tamaninii Wagner (Heteroptera: Miridae)

The zoophytophagous predator Macrolophus caliginosus (Wagner) (Heteroptera: Miridae) has previously been identified as a potential prey for the intraguild zoophytophagous predator Dicyphus tamaninii Wagner. Its value as an intraguild prey was tested for D. tamaninii nymphal development and adult survival. In the laboratory, plant (red tomato fruit, green tomato fruit, tomato leaf) and animal (aphids, whiteflies, pyralid eggs) resources were compared to frozen nymphs of M. caliginosus as an intraguild resource for D. tamaninii. M. caliginosus nymphs allowed complete and rapid development of D. tamaninii nymphs and generated low mortality of nymphal and adult stages. Performances were higher with the intraguild M. caliginosus resource than with plant resources. Tomato leaves did not allow the complete nymphal development of D. tamaninii. Tomato fruit generated lighter adults and doubled the nymphal developmental time compared with the M. caliginosus resource. In the animal resource group, there were no differences between the M. caliginosus and the other treatments (aphids, whiteflies, pyralid eggs) for nymphal mortality, average number of molts, nymphal developmental time, adult weight, and adult survival. M. caliginosus should be considered a high-quality resource for D. tamaninii.     

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 Starvation on the Searching Path of the Predatory Bug <Emphasis Type="Italic">Deraeocoris Lutescens</Emphasis>

As physiological factors may influence the predatory behavior of insects, this study was designed to evaluate the possible impact that hunger has on the search path of a polyphagous predator: Deraeocoris lutescens Schilling (Heteroptera: Miridae). D. lutescens was fed a diet of Rhopalosiphum padi (Linné) (Homoptera: Aphididae) nymphs and Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs at 21±1 °C and a photoperiod of 16:8 (L:D). After moulting, third and fifth instar nymphs and adults were placed in Petri dishes containing an abundant food source for 24 h. After 24 h, the food was removed and groups were randomly assigned to increasing periods of prey deprivation. Each D. lutescens nymph or adult was placed at the center of an empty arena and its searching path was recorded to calculate different path parameters and to determine the type of movement mode adopted. Results show an effect of starvation on both nymphal and adult D. lutescens searching paths. Satiated third instar nymphs manifested an intensive search path whereas fifth instar nymphs and adults adopted an intermediate one. When starved, the extensive search path appeared early in young nymphs, and later in the last instar nymphs and adults, according to the degree of prey deprivation.     

An immunological approach to quantify consumption of protein-tagged Lygus hesperus by the entire cotton predator assemblage

A new method for post-mortem quantification of predation on prey items marked with protein antigens is described. First, short-term protein marking retention tests were conducted on the targeted prey, immature Lygus hesperus Knight (Heteroptera: Miridae). Chicken IgG, rabbit IgG, or soy milk proteins were readily detectable by a suite of protein specific enzyme-linked immunosorbent assays (ELISA) on the L. hesperus. Then, predator gut content assays were conducted on chewing and piercing–sucking type predators that consumed a 3rd instar L. hesperus marked with rabbit IgG. The rabbit IgG gut content ELISA detected the marked prey in the vast majority of both types of predators for up to 24 h after feeding. Finally, field cage studies were conducted to quantify predation rates of the natural cotton predator assemblage on protein marked L. hesperus nymphs. Each 4th instar L. hesperus marked with rabbit IgG, chicken IgG, and soy milk was released into one of 360 field cages containing a cotton plant and the natural population of predators. After 7 h, each caged plant was pulled from the field, the number of predaceous arthropods in each cage were tallied, and each individual predator was assayed for the presence of marked prey by a suite of protein-specific ELISAs. A procedural error with the soy mark application negated the anti-soy ELISA data, but the anti-rabbit IgG and anti-chicken IgG ELISAs pinpointed exactly which predators preyed on the IgG marked nymphs. The protein-specific gut ELISAs revealed that various members of Araneae, Heteroptera, and Coleoptera were the most common predators of the marked prey items. In all, 74 predation events were recorded in the guts of the 556 predators encountered in the field cages. Of these 26, 23, and 14 marked individuals were eaten by various members of Araneae, Heteroptera, and Coleoptera, respectively. This study verifies that prey immunomarking is a simple, versatile, and effective method for quantifying predation rates on L. hesperus.     

Notes on paternal care and sibling cannibalism in the giant water bug, Lethocerus deyrolli (Heteroptera: Belostomatidae)

Males of the giant water bug, Lethocerus deyrolli, care for egg masses on vegetation above the water surface. They supply the developing eggs with water and guard them against predators. In the present study, mechanisms by which paternal care is extended were found. Males were found situated just below the water on the natal substrate (usually a stick), and the first instar nymphs were aggregated around the substrate. When disturbed, the males showed aggressive behavior, threatening the intruder with their forelegs. Nymphs up to 12 h old did not attack the offered sibling nymphs or anuran larvae, which are common prey in the field. The 24 h‐old nymphs attacked both prey animals; however, they preferred anuran larvae. Cannibalistic behavior in the nymphs was well developed 72 h after hatching, when the nymphs had already dispersed from the natal substrate. The suppression of sibling cannibalism in younger nymphs would promote the maintenance of tight nymphal aggregations and consequently extend male care in this predatory species.     

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.     

The role of amphibian prey in the diet and growth of giant water bug nymphs in Japanese rice fields

Predatory insects that depend upon particular prey animals are commonly regulated by the prey animal’s abundance. Nymphs of the giant water bug Kirkaldyia (=Lethocerus) deyrolli (Heteroptera: Belostomatidae) are predators regarded as specialists in feeding on tadpoles. We studied the ontogenetic diet shift of aquatic nymphs by quantifying instar abundance and by analyzing captured prey and prey relative abundance during the period of rice irrigation in three localities. We also evaluated the contribution of major prey items (tadpoles, frogs, and Odonata nymphs) on specific growth rates of each nymphal stage in a rearing experiment. First to third-instar nymphs of K. deyrolli fed mainly on tadpoles, regardless of differences in prey availability. Nymphs of subsequent fourth and fifth instar stages shifted from tadpoles to other prey animals within each rice field. A rearing experiment demonstrated that giant water bug nymphs provided with tadpoles had greater specific growth rates at all nymphal stages, except for the final stage, than nymphs fed other prey (frogs and Odonata nymphs). The emergence of young K. deyrolli nymphs seemed to coincide with the period during which tadpoles became abundant in the rice fields. Consumption of tadpoles seems important to allow the nymph to complete its larval development in an unstable temporary habitat. An erratum to this article can be found at     

Plantless rearing of the zoophytophagous bug Nesidiocoris tenuis

Nesidiocoris tenuis Reuter (Heteroptera: Miridae) is widely distributed in the Mediterranean area, where it is used as an augmentative biological control agent of several pests. This zoophytophagous predator maintains a close relationship with its host plants using them not only to feed on, but also as an oviposition substrate. In the present study, a plantless rearing system was developed and developmental and reproductive parameters of bugs that had no access to plant material were compared with their counterparts living on plants. Eggs deposited in an artificial substrate took longer to develop and had lower hatching rates than those laid in tomato leaves. However, the biological parameters of nymphs that had hatched from the artificial substrate did not differ from those of nymphs that had emerged from plants, suggesting that, besides water, no essential nutrients are absorbed from the oviposition substrate during embryogenesis. Our results regarding the role of plant feeding indicate that water acquisition is the critical function of phytophagy in N. tenuis. In addition, supplementary nutrients derived from plants had a positive effect on adult weight and significantly enhanced survival in the absence of prey. Plantless rearing for five generations led to a prolonged preoviposition period and lower egg hatching rates and adult weights, but other developmental and reproductive parameters were not adversely affected. Our experiments suggest that prolonged plantless rearing of N. tenuis is possible provided that the mirid has access to a nutritionally superior food like Ephestia kuehniella eggs.     

Plant and supplementary food sources effect the development of <Emphasis Type="Italic">Dicyphus errans</Emphasis> (Hemiptera: Miridae)

Dicyphus errans (Wolff) (Hemiptera: Miridae) is an omnivorous predator of several pests attacking tomato and other vegetable crops. The nymphal development of D. errans was studied in the presence of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs with or without a water source and in the presence of a leaf of cucumber, eggplant or tomato supplemented with variable food types (E. kuehniella eggs, Artemia sp. cysts, pollen or milk powder) or without the provision of any food. Water provision was found to be essential for the completion of nymphal development even when animal food was offered to predators. When nymphs foraged on leaves in the absence of any food type, development was significantly more favoured on eggplant and cucumber than on tomato. E. kuehniella eggs and Artemia sp. cysts enhanced development of D. errans in comparison to milk powder and pollen. Development and female weight were improved when the food types were offered to the nymphs on a plant leaf than when were provided together with only water. This study contributes to understanding the importance of water vs. plant feeding for the development of D. errans and reveals implications for its mass rearing and application in biological control.     

The effects of mullein plants (Verbascum thapsus) on the population dynamics of Dicyphus hesperus (Heteroptera: Miridae) in tomato greenhouses

The response of Dicyphus hesperus Knight (Heteroptera: Miridae) to whitefly populations in tomato greenhouses was measured in the presence and absence of mullein (Verbascum thapsus L.) as an alternative host plant. The dynamics of the D. hesperus population on tomato (Lycopersicon esculentum Mill.) and on mullein plants were followed through an entire growing season. In houses with mullein plants, more predators occurred on mullein when whitefly density was low on tomato. A mark-release-recapture experiment where rabbit IgG was used as an external marker showed that D. hesperus adults moved from mullein plants to tomato plants. D. hesperus was always more abundant in houses with mullein than in the houses with tomato plants alone. Movements between tomato and mullein plants are discussed as a strategy to optimize predator foraging. The use of mullein as an alternative host plant may contribute to the establishment of D. hesperus and help to preserve the predator population when prey on tomato crops is scarce.     

Effects of prey availability, facultative plant feeding, and plant defenses on a generalist insect predator

This study examined the effects of feeding interval, access to host plants (thus, a source of sap), and plant defenses on the predatory insect, Podisus maculiventris Say (Hemiptera: Pentatomidae). The experiment consisted of a 2 × 2 design with two feeding intervals (1 day or 5 days) and predators living on either tomato plants or plastic plants. Females fed every day had greater body weights and egg hatch rates than females fed every five days. Females on tomato plants lived longer than females on plastic plants. However, access to plants did not alleviate the effects of low prey level on predator weight or reproductive output. In a second experiment, third instar nymphs were placed on either tomato plants or plastic plants for four days to examine the effects of tomato trichome defenses on these predators. Nymphs on tomato plants experienced 50% mortality compared to 15% mortality for nymphs on plastic plants. Some nymphs living on tomato plants were trapped by the hairy trichomes of the plant; others had gummed up legs from the exudates of the plants’ glandular trichomes, which inhibited their movement and ability to feed on prey. Although predators appeared to benefit from feeding on tomato plants, their ability to live on the plants was negatively affected by the defensive features of the plants. The potential effects of trichome defenses on predator survival and population dynamics must be considered when evaluating the benefits of plants on insect predator life histories and efficacy as biological control agents.     

Plant preference in relation to life history traits in the zoophytophagous predator Dicyphus hesperus

Dicyphus hesperus Knight (Heteroptera: Miridae) is an omnivorous predator used to control pests of greenhouse vegetables. Plant preferences and life history traits were studied using nine plant species: Lycopersicon esculentum Mill. (Solanaceae), Capsicum annuum L. (Solanaceae), Verbascum thapsus L. (Scrophulariaceae), Nepeta cataria L. (Lamiaceae), Stachys albotomentosa (Lamiaceae), Nicotiana tabacum L. (Solanaceae), Vicia sativa L. (Fabaceae), Zea mays L. (Gramineae), and Chrysanthemum coronarium L. (Asteraceae). Plants were selected from among potential target crops, natural hosts, plants used for mass rearing, and plants on which D. hesperus has not been reported. Plant preference was measured by multi‐choice host plant selection and oviposition assays. Development and reproduction were measured on each of the plant species on both a plant diet alone and on a plant diet supplemented with Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs. Dicyphus hesperus females and nymphs expressed a preference for some plants over others. Plant preference ranged from low preference plants, such as Z. mays, V. sativa, C. coronarium, and C. annuum, to high preference plants such as V. thapsus, N. tabacum, and S. albotomentosa. When E. kuehniella eggs were supplied, there were few differences in the development time and fecundity of D. hesperus among plants, with the exception of corn and broad bean, where fecundity was lower. On a plant diet alone, nymphs were able to complete their development on V. thapsus, C. annuum, and N. cataria. However, mortality and development time were much lower on V. thapsus than on C. annuum and N. cataria. On most of the plant species D. hesperus did not lay any eggs when fed on a plant diet alone. On V. thapsus, females laid a few eggs and lived longer than when fed on prey. Dicyphus hesperus females tended to prefer host plants on which nymph survival without prey was greatest.     

Plant and Prey Consumption Cause a Similar Reductions in Cannibalism by an Omnivorous Bug

Cannibalism is usually more intense when other food sources are scarce, be it prey or plant-based foods. We hypothesized that feeding on plants would reduce cannibalism to a lesser extent than feeding on prey, because plants are considered nutritionally inferior compared to prey. We used the omnivorous bug Orius laevigatus Say (Heteroptera: Anthocoridae) to test this prediction. Starved female bugs were individually held with five second-instar conspecific nymphs and offered (i) Helicoverpa armigera eggs (prey); (ii) pollen (plant); (iii) H. armigera eggs and pollen (prey+plant); or (iv) no eggs or pollen. Fewer cannibalistic events and shorter feedings on conspecifics were recorded in the presence of pollen, prey or both than in their absence. Data therefore do not support our hypothesis that cannibalism is differentially affected by foods of different nutritional values. It seems that omnivorous feeding habits enable predators to sustain themselves on plant sources in the absence of prey, without the need to resort to cannibalism.     

The brine shrimp Artemia sp. as alternative prey for rearing the predatory bug Macrolophus caliginosus

The predatory bug Macrolophus caliginosus, which is widely used in greenhouse crops, is limited in its application by its high price. An important factor in the cost is the high price of Ephestia kuehniella eggs, the prey used in their mass rearing. In order to reduce their price, alternatives to moth eggs are currently being investigated. The brine shrimp Artemia sp. is produced in large quantities in saline lakes and is fed as live food source to the larvae of a variety of marine and freshwater organisms. In this study, we tested Artemia sp. as prey for rearing M. caliginosus from two strains. We evaluated developmental and reproduction parameters of the predator when fed nauplii, enriched nauplii with a fatty acid, dry cysts and hydrated cysts, and were compared with those obtained when the predator was fed with E. kuehniella eggs. Nauplii had a significant reduction in survivorship, a delay in development of nymphs and a low reproduction of adults. Nauplii enriched with docosahexaenoic acid (DHA, 22:6n − 3), a common practice for larviculture of some marine fish species, resulted toxic to M. caliginosus nymphs and survival was quite low. On the contrary, either dry or hydrated cysts from the two strains tested of the brine shrimp produced the same nymphal survivorship, nymphal development time and weight and fecundity of adults as those obtained with E. kuehniella eggs. Demographic parameters of the eighth generation of the predator reared with cysts of the two strains, either dry or hydrated, were as good as those of moth eggs. We concluded that Artemia sp. cysts were a good substitution prey for the mass rearing of M. caliginosus.     

Patch Retention Time in an Omnivore, Dicyphus hesperus is Dependent on Both Host Plant and Prey Type

We examined patch residence times for an omnivorous predator, Dicyphus hesperus on a variety of plants and prey. Individual D. hesperus were placed in cages containing either mullein, tomato, pepper or chrysanthemum plants, and either no prey, Mediterranean flour moth eggs, greenhouse whitefly pupae or two-spotted spider mite adults. Patch residence times were typically greater than 24 h. The probability of remaining on the patch was greatest on mullein and tomato, followed by chrysanthemum and least on pepper, whereas probability of remaining on the patch was greatest when flour moth eggs were present, and least when no prey were available. Patch residence time in D. hesperus was determined by both the prey, and the species of plant, in an independent fashion. Our results reinforce the notion that for omnivores, the patch itself is as important as the prey that it harbors.     

Efficacy of multiple biocontrol agents against the sweet potato whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on tomato

Abstract: Biological control provides an environmentally harmonious and potentially stable management tactic to combat noxious pests such as Bemisia tabaci, notorious for its resistance to synthetic pesticides. Bioassays conducted under control chamber conditions integrating applications of the parasitoid Encarsia formosa, reared for 20 years on Trialeurodes vaporariorum, and the fungus Verticillium lecanii on the third‐fourth instar nymphs of B. tabaci on tomato, showed a comparable effect between the parasitoid‐fungus combined treatment and the fungus treatment alone (70.7% vs. 70.4%). Analysis of our results indicates antagonism between the two biocontrol agents related to the parasitoids’ ability to discriminate between infected and healthy B. tabaci nymphs. The parasitoid treatment alone produced 36.3% mortality, with no mortality in the distilled water controls. The behavioural performance of the parasitoid could have either genetic or environmental causes. Bioassays studying the feeding habit of the imported mirid predator Macrolophus caliginosus (adults) and the indigenous mirid Camptotylus reuteri (nymphs and adults) on eggs, or early second instar nymphs of B. tabaci, and choice preference tests indicated a significant difference in feeding between M. caliginosus and C. reuteri. There was no significant difference in percentage feeding of M. caliginosus on eggs (2.2%) or second instar nymphs (8.0%). There was a significant difference in feeding of M. caliginosus adults (18.6%) when offered eggs and second instars in the same arena compared with eggs or second instars offered separately. These results could be attributed to the biological behaviour of the predator having a type III functional response. Studies with the local C. reuteri species showed no significant difference in adult and nymphal consumption on second instars of B. tabaci compared with nymphs on eggs. However, C. reuteri adults fed less on eggs compared with nymphs. This local predatory species appears to be more efficient than M. caliginosus in feeding on particular stages of B. tabaci without depending on prey density. This is further supported by the low consumption of both adults and nymphs in the choice test (4% and 2.3%, respectively) compared with M. caliginosus adults (18.6%).     

Intraguild interactions between the predator Macrolophus pygmaeus and the parasitoid Eretmocerus mundus,natural enemies of Bemisia tabaci

The native parasitoid Eretmocerus mundus Mercet and the predator Macrolophus pygmaeus Rambur are widely used to control Bemisia tabaci (Gennadius) in Mediterranean tomato greenhouses. An optimal biological control strategy for B. tabaci should take into account intraguild interactions between these natural enemies. In this study, predator's prey preferences and prey consumption were studied when offered different parasitoid and whitefly stages. The effect of the host plant on the adults of both natural enemies was also examined. M. pygmaeus preferred to consume B. tabaci over E. mundus when immature stages and adults of B. tabaci and E. mundus were offered. They consumed a larger amount of healthy B. tabaci nymphs and adults than of parasitised nymphs or E. mundus adults. The predator M. pygmaeus interfered with the reproduction of E. mundus females on cotton but not on tomato. However, B. tabaci nymphal mortality on tomato associated with parasitoid host feeding was also lower when the adult parasitoids coexisted with the predators. The joint release of M. pygmaeus and E. mundus adults did not increase the control of the whitefly B. tabaci.     

Threat of Infection and Threat-Avoidance Behavior in the Predator <Emphasis Type="Italic">Dicyphus hesperus</Emphasis> Feeding on Whitefly Nymphs Infected with an Entomopathogen

The nature and severity of intraguild interactions between predators and entomopathogens will be determined, in part, by a combination of threat of infection, and avoidance of that threat by the predator. We determined the threat of infection posed by the entomopathogen, Paecilomyces fumosoroseus (as PFR-97™) to the generalist predator, Dicyphus hesperus. We then asked if D. hesperus displays behavioral avoidance of infection while foraging for whitefly nymphs at different stages of infection by the pathogen. When exposed to leaf surfaces treated with the pathogen, 28% of adult female predators died due to infection. Consumption of Ephestia kuehniella eggs by surviving predators over 6 d was significantly reduced, suggesting effects of a sublethal infection. Whitefly nymphs that had been treated with P. fumosoroseus 3 d prior were acceptable as prey to D. hesperus but whitefly nymphs that had been treated with P. fumosoroseus 5 days prior were not. When foraging for whitefly nymphs, adult D. hesperus females rejected infected nymphs 96% of the time, compared to 39% of non-infected nymphs. Paecilomyces fumosoroseus therefore presents a measurable threat to D. hesperus through mortality and reduced prey consumption. Dicyphus hesperus does not avoid initial contact with infected prey but does not feed on such prey. The mechanism underlying these rejections could be due to either avoidance of infection or rejection of prey already consumed by the infectious agent. These results suggest that predation by D. hesperus foraging among infected whitefly nymphs under greenhouse or natural conditions could be reduced through a combination of pathogenicity and reduced efficiency of foraging.     

Prey‐mediated changes in the selectivity of the predator Macrolophus pygmaeus (Heteroptera: Miridae)

When foraging in communities with mixed prey, generalist predators may be confronted with prey species that differ in quality, size and mobility and interact with one another. To examine prey selection, predation by Macrolophus pygmaeus (Heteroptera: Miridae) was recorded by providing a diet of either one or two prey species of Myzus persicae (third‐instar nymphs), Aphis gossypii (fourth‐instar nymphs), Trialeurodes vaporariorum (third‐instar nymphs) and Ephestia kuehniella (eggs). In the experiments, prey mobility, prey quality and prey biomass were considered. The biomass consumed by the predator was dependent on the combination of prey species and the quantity of biomass offered. In choice experiments with diets mixed of two prey species at equal densities, the predation to A. gossypii was significantly reduced in the presence of E. kuehniella but the rate of consumption of M. persicae, T. vaporariorum and E.kuehniella was not significantly affected by the coexistence of any other species in the mixed prey diet. When equal amounts of biomass from two prey species were provided in combination, the total consumed biomass was significantly reduced in the mixed prey diets composed of E. kuehniella eggs and aphid nymphs. Thus, under the mixed‐prey situation, prey selection by predators may be affected by interactions among prey species differing in traits such as quality, mobility and size.     

Cardenolide‐defended milkweed bugs do not evoke learning in Nephila senegalensis spiders

Antipredator defense of herbivorous insects often relies on the potential toxicity of defensive chemicals sequestered from their host plants. The colorful Lygaeinae (Heteroptera: Lygaeidae) store a concentrated mixture of toxic cardenolides (cardiac glycosides) in specialized storage compartments of the bugs' integument, from which they are released upon attack. Larvae and adults of the large milkweed bug Oncopeltus fasciatus (Heteroptera: Lygaeinae) are specialized to feed on cardenolide‐containing milkweeds in the plant genus Asclepias and display a conspicuous red and black colorations. To investigate whether O. fasciatus gained improved protection by feeding on a toxic host plant (Asclepias syriaca), compared to a nontoxic alternative (sunflower seeds), we fed nymphs and adults of O. fasciatus to the golden orb‐weaver Nephila senegalensis. While visually oriented vertebrates, such as avian predators, have been intensively investigated for their reaction to defensive compounds and aposematic coloration, less attention has been paid to invertebrate predators. Their different perceptual abilities can provide important opportunities for testing hypotheses on warning coloration and chemical defenses. The predation trials showed that the bugs fed on Asclepias were significantly less likely to be killed than the bugs reared on a cardenolide‐free diet. This suggests that sequestered cardenolides in O. fasciatus nymphs and adults represent a significant fitness advantage on an individual level against this invertebrate predator. Yet, when testing for avoidance learning in the spiders, negative experience did not change the way how similar prey was attacked at the next encounter. In this case, visual or chemical aposematism thus does not seem to matter for predator learning.