Omnivorous Predator Macrolophus Pygmaeus Research Articles

The omnivorous predator Macrolophus pygmaeus induces production of plant volatiles that attract a specialist predator

It has become clear that omnivorous predators can induce plant defences that affect the performance and host plant choice of herbivores. They are also known to induce the production of plant volatiles that can affect the behaviour of herbivores searching for plants. These volatiles may also affect the searching behaviour of other predators, which was investigated here. The predatory mite Phytoseiulus persimilis preferred plants previously exposed to the omnivorous mirid Macrolophus pygmaeus over clean plants. The mites were equally attracted to plants previously exposed to the omnivore and subsequently infested by spider mites (Tetranychus urticae, prey of the predatory mite and the omnivore) and plants infested with spider mites alone. Moreover, the mites were more attracted to plants infested with prey and subsequently exposed to the omnivore than plants infested with prey but not exposed to the omnivore. The predatory mites were also significantly more attracted to plants on which the omnivores were still present. Experience of the predatory mites with volatiles from plants previously exposed to the omnivore and without prey resulted in a loss of the preference for volatiles emitted by plants exposed to the omnivore. Analysis of the volatiles showed that plant exposure to omnivores induced qualitative and quantitative changes in the volatile blend. Together, these results suggest that omnivorous predators induce the production of plant volatiles that can interfere with the searching behaviour of other predators. The consequences of such interference for biological pest control remain to be investigated.

Plant feeding by an omnivorous predator affects plant phenology and omnivore performance

Plant feeding by omnivorous predators can induce plant defences, which decreases the performance of herbivores and influence behaviour of other predators. However, it is not known what are the consequences of this feeding for the plant and how this, in turn, affects the omnivore. We therefore investigated the effects of plant feeding by the omnivorous predator Macrolophus pygmaeus on plant development and reproduction. We also assessed the effects of these plant changes on survival and reproduction of the omnivore. Sweet pepper plants exposed to M. pygmaeus had significantly lower numbers of leaves and open flowers than clean plants, but numbers of fruits were similar. Moreover, the presence of the omnivore significantly shortened the period for flowers to become fruits. The dry weights of leaves plus stems and fruits were similar on clean plants and plants with the omnivore. Significantly higher numbers of seeds were found in fruits from plants with the omnivore than from clean plants. The survival rates of M. pygmaeus females and nymphs increased with numbers of flowers. Our results show that the presence of this omnivorous predator can benefit plants by increasing seed production, but the changes in plant phenology do not seem to benefit the omnivore.

The omnivorous predator Macrolophus pygmaeus, a good candidate for the control of both greenhouse whitefly and poinsettia thrips on gerbera plants.

The poinsettia thrips Echinothrips americanus Morgan is a relatively new pest that has spread rapidly worldwide and causes serious damage in both vegetable and ornamental plants. In this study, we investigated if and how effective this pest can be controlled in gerbera by the omnivorous predator Macrolophus pygmaeus (Rambur). Because herbivores on plants can interact through a shared predator, we also investigated how poinsettia thrips control is affected by the presence of the greenhouse whitefly Trialeurodes vaporariorum (Westwood), a pest that commonly coexists with E. americanus in gerbera. In laboratory studies, we found that the predator M. pygmaeus fed on both pests when offered together. Olfactometer tests showed a clear preference of the predators for plants infested by whiteflies but not by thrips. In a greenhouse experiment, densities of both pests on single gerbera plants were reduced to very low levels by the predator, either with both pests present together or alone. Hence, predator‐mediated effects between whiteflies and thrips played only a minor role. The plant feeding of the shared predator probably reduced the dependence of predator survival and reproduction on the densities of the two pests, thereby weakening potential predator‐mediated effects. Thus, M. pygmaeus is a good candidate for biological control of both pests in gerbera. However, further research is needed to investigate pest control at larger scales, when the pests can occur on different plants.

Herbivores avoid host plants previously exposed to their omnivorous predator Macrolophus pygmaeus

Herbivorous arthropods use various cues to choose suitable host plants. We investigated whether three species of herbivores use cues associated with their omnivorous predator Macrolophus pygmaeus to select host plants. Earlier, we found that this omnivore induces plant defences which decreased the performance of two of the herbivores, i.e. the spider mite Tetranychus urticae and the western flower thrips Frankliniella occidentalis, whereas the green peach aphid Myzus persicae was not affected. Hence, the spider mite and thrips were expected to avoid plants that were previously exposed to M. pygmaeus because of their lower quality, and the aphid was not expected to avoid exposed plants because they were of equal quality as unexposed plants. However, the cues left behind by M. pygmaeus may also be indicative of predation risk, in which case all three herbivores were expected to avoid exposed plants. Spider mites and western flower thrips preferred clean plants over plants that had previously been exposed to M. pygmaeus, but no longer harboured this omnivore. Aphids showed no preference, in agreement with their performance, but not in agreement with reducing predation risk. We furthermore showed that the preference of spider mites and thrips for clean plants increased through time. Higher proportions of aphids left plants previously exposed to M. pygmaeus than clean plants through time. Hence, omnivorous predators can decrease herbivore densities on plants not only by killing them but also by indirectly affecting herbivore host plant selection.

Phytophagy of omnivorous predator Macrolophus pygmaeus affects performance of herbivores through induced plant defences

Plants possess various inducible defences that result in synthesis of specialized metabolites in response to herbivory, which can interfere with the performance of herbivores of the same and other species. Much less is known of the effects of plant feeding by omnivores. We found that previous feeding of the omnivorous predator Macrolophus pygmaeus on sweet pepper plants significantly reduced reproduction of the two-spotted spider mite Tetranychus urticae and western flower thrips Frankliniella occidentalis on the same plants, also on leaves that had not been exposed to the omnivore. In contrast, no effect was found on the reproduction of the green peach aphid Myzus persicae. Juvenile survival and developmental time of T. urticae and M. persicae, and larval survival of F. occidentalis were not affected by plant feeding by M. pygmaeus. Larvae of F. occidentalis feeding on leaves previously exposed to M. pygmaeus required longer to develop into adults. Defence-related plant hormones were produced locally and systemically after exposure to M. pygmaeus. The concentrations of 12-oxo-phytodienoic acid and jasmonic acid–isoleucine in the attacked leaves were significantly higher than in the corresponding leaves on the uninfested plants, and jasmonic acid concentrations showed the same trend, suggesting that jasmonic-acid-related defence pathways were activated. In contrast, similar concentrations of salicylic acid were found in the attacked leaves of M. pygmaeus-infested plants and uninfested plants. Our results show that plant feeding by omnivorous predators decreases the performance of herbivores, suggesting that it induces plant defences.

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.

Nitrogen and water limitations in tomato plants trigger negative bottom-up effects on the omnivorous predator Macrolophus pygmaeus

Omnivorous Heteroptera predators play important roles in biological control of a wide range of pest insects. Their predation could be influenced by various biotic or abiotic factors. Here we examined the effects of nitrogen and water inputs to tomato plants (Solanum lycopersicum L.) on the predation strength of the omnivore Macrolophus pygmaeus Wagner (Hemiptera: Miridae) on eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). We tested the hypothesis that a change in plant status, manipulated by sub-optimal nutrients and water inputs, may influence predation on E. kuehniella by the predator M. pygmaeus. Nitrogen and water restrictions depressed the predation of E. kuehniella eggs by M. pygmaeus. Moreover, we observed a 30 % reduction in predator longevity on plants under low water inputs. Therefore, the negative bottom-up effect of nitrogen and water limitations (in tomato plants) toward M. pygmaeus may be detrimental for mirid predator-based IPM programs in tomato crops.

Beyond Predation: The Zoophytophagous Predator Macrolophus pygmaeus Induces Tomato Resistance against Spider Mites.

Many predatory insects that prey on herbivores also feed on the plant, but it is unknown whether plants affect the performance of herbivores by responding to this phytophagy with defence induction. We investigate whether the prior presence of the omnivorous predator Macrolophus pygmaeus (Rambur) on tomato plants affects plant resistance against two different herbivore species. Besides plant-mediated effects of M. pygmaeus on herbivore performance, we examined whether a plant defence trait that is known to be inducible by herbivory, proteinase inhibitors (PI), may also be activated in response to the interactions of this predator with the tomato plant. We show that exposing tomato plants to the omnivorous predator M. pygmaeus reduced performance of a subsequently infesting herbivore, the two-spotted spider mite Tetranychus urticae Koch, but not of the greenhouse whitefly Trialeurodes vaporariorum (Westwood). The spider-mite infested tomato plants experience a lower herbivore load, i.e., number of eggs deposited and individuals present, when previously exposed to the zoophytophagous predator. This effect is not restricted to the exposed leaf and persists on exposed plants for at least two weeks after the removal of the predators. The decreased performance of spider mites as a result of prior exposure of the plant to M. pygmaeus is accompanied by a locally and systemically increased accumulation of transcripts and activity of proteinase inhibitors that are known to be involved in plant defence. Our results demonstrate that zoophytophagous predators can induce plant defence responses and reduce herbivore performance. Hence, the suppression of populations of certain herbivores via consumption may be strengthened by the induction of plant defences by zoophytophagous predators.

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 Myzuspersicae. 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.

Plant food effects on prey consumption by the omnivorous predator Macrolophus pygmaeus

Omnivorous predatory Heteroptera are important biological control agents of pests in several crops. They can feed on plant food resources that may positively affect their biological characteristics. In the current paper, the influence of leaves and flowers on the predation rate of the omnivorous predator Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) was investigated. Its predation rates were recorded on prey offered on (a) a single leaf of tomato, pepper or black nightshade (Solanum nigrum), or (b) a leaf of pepper or S. nigrum plus flowers of pepper or S. nigrum, respectively. In all cases the aphid Myzus persicae (Sulzer) (Homoptera: Aphididae) was used as prey at densities of 4, 8, 12, 16, 20 and 24 nymphs of the second instar. The experiments were conducted in petri dishes at 25 ± 1°C and prey consumption was evaluated after 24 h. The predation rate of M. pygmaeus was significantly higher on leaves of S. nigrum than on those of pepper at the prey density of 20 prey items. Therefore, the hypothesis that increased predation rates should occur on plants of lower suitability for development or reproduction was not supported under our experimental conditions. The flower availability did not alter the prey consumption among the prey densities on S. nigrum. However, the presence of a pepper flower caused a significant decrease in the predation rates on pepper leaves, at prey densities higher than eight prey items. Thus, pepper flowers can provide the predator with nutrient sources that may partially substitute for prey consumption, with practical implications in biological control.

Assessing the suitability of noncultivated plants and associated insect prey as food sources for the omnivorous predator Macrolophus pygmaeus (Hemiptera: Miridae)

The suitability of noncultivated plants Solanum nigrum and Dittrichia viscosa, with or without the nonpest prey Aphis fabae solanella and Capitophorus inulae, respectively, as food sources for the polyphagous predator Macrolophus pygmaeus was investigated. A. f. solanella supported the development and longevity of M. pygmaeus on S. nigrum. However, the fecundity and rate of population increase of the predator fed A. f. solanella were reduced compared with those of other aphid species. M. pygmaeus completed its development feeding solely on S. nigrum and adults survived similarly for a period while feeding on A. f. solanella. The results show that M. pygmaeus can increase in numbers on S. nigrum, suggesting that this plant can support the maintenance of predators in the field. On the other hand, M. pygmaeus performed poorly on D. viscosa. Although it completed its development while feeding on D. viscosa and the aphid C. inulae, females laid only a few eggs; the predator was unable to complete development while feeding on this plant alone. The widespread noncultivated plant S. nigrum may contribute to the conservation of M. pygmaeus in the open field, mostly through supporting its survival and, at a lower rate, its reproduction. The same cannot be said for D. viscosa.