The role of phytophagy by predators in shaping plant interactions with their pests

Begomovirus Transmission to Tomato Plants Is Not Hampered by Plant Defenses Induced by Dicyphus hesperus Knight

Plants can respond to insect infestation and virus infection by inducing plant defenses, generally mediated by phytohormones. Moreover, plant defenses alter host quality for insect vectors with consequences for the spread of viruses. In agricultural settings, other organisms commonly interact with plants, thereby inducing plant defenses that could affect plant-virus-vector interactions. For example, plant defenses induced by omnivorous insects can modulate insect behavior. This study focused on tomato yellow leaf curl virus (TYLCV), a plant virus of the family Geminiviridae and genus Begomovirus. It is transmitted in a persistent circulative manner by the whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), posing a global threat to tomato production. Mirids (Hemiptera: Miridae) are effective biological control agents of B. tabaci, but there is a possibility that their omnivorous nature could also interfere with the process of virus transmission. To test this hypothesis, this study first addressed to what extent the mirid bug Dicyphus hesperus Knight induces plant defenses in tomato. Subsequently, the impact of this plant-omnivore interaction on the transmission of TYLCV was evaluated. Controlled cage experiments were performed in a greenhouse setting to evaluate the impact of mirids on virus transmission and vector acquisition by B. tabaci. While we observed a reduced number of whiteflies settling on plants exposed to D. hesperus, the plant defenses induced by the mirid bug did not affect TYLCV transmission and accumulation. Additionally, whiteflies were able to acquire comparable amounts of TYLCV on mirid-exposed plants and control plants. Overall, the induction of plant defenses by D. hesperus did not influence TYLCV transmission by whiteflies on tomato.

Two in one: the neotropical mirid predator Macrolophus basicornis increases pest control by feeding on plants

BACKGROUND

Plant defenses activated by European zoophytophagous predators trigger behavioral responses in arthropods, benefiting pest management. However, repellence or attraction of pests and beneficial insects seems to be species-specific. In the neotropical region, the mirid predator Macrolophus basicornis has proved to be a promising biological control agent of important tomato pests; nevertheless, the benefits of its phytophagous behavior have never been explored. Therefore, we investigated if M. basicornis phytophagy activates tomato plant defenses and the consequences for herbivores and natural enemies.

RESULTS

Regardless of the induction period of M. basicornis on tomato plants, Tuta absoluta females showed no preference for the odors emitted by induced or control plants. However, Tuta absoluta oviposited less on plants induced by M. basicornis for 72 h than on control plants. In contrast, induced plants repelled Bemisia tabaci females, and the number of eggs laid was reduced. Although females of Trichogramma pretiosum showed no preference between mirid-induced or control plants, we observed high attraction of the parasitoid Encarsia inaron and conspecifics to plants induced by M. basicornis. While the mirid-induced plants down-regulated the expression of genes involving the salicylic acid (SA) pathway over time, the genes related to the jasmonic acid (JA) pathway were up-regulated, increasing emissions of fatty-acid derivatives and terpenes, which might have influenced the arthropods' host/prey choices.

CONCLUSION

Based on both the molecular and behavioral findings, our results indicated that in addition to predation, M. basicornis benefits tomato plant resistance indirectly through its phytophagy. This study is a starting point to pave the way for a novel and sustainable pest-management strategy in the neotropical region. © 2022 Society of Chemical Industry.

Evaluation of Natural and Factitious Food Sources for Pronematus ubiquitus on Tomato Plants

Simple Summary

Biocontrol practitioners have increasingly released generalist predators to control a variety of greenhouse pests. In this study, the effects of alternative food sources on the oviposition rate and the population dynamics of the mite Pronematus ubiquitus were assessed. The alternative food sources were selected among those the mite may encounter or be applied to the tomato crop.

Abstract

Pronematus ubiquitus (McGregor) is a small iolinid mite that is capable of establishing on tomato plants. Once established, this mite has been shown to control both tomato russet mite, Aculops lycopersici (Tryon) (Acari: Eriophyidae), and tomato powdery mildew (Oidium neolycopersici L. Kiss). In the present study, we explored the effects of a number of alternative food sources on the oviposition rate in the laboratory. First, we assessed the reproduction on food sources that P. ubiquitus can encounter on a tomato crop: tomato pollen and powdery mildew, along with tomato leaf and Typha angustifolia L. In a second laboratory experiment, we evaluated the oviposition rate on two prey mites: the astigmatid Carpoglyphus lactis L. (Acari: Carpoglyphidae) and the tarsonemid Tarsonemus fusarii Cooreman (Acari: Tarsonemidae). Powdery mildew and C. lactis did not support reproduction, whereas tomato pollen and T. fusarii did promote egg laying. However, T. angustifolia pollen resulted in a higher oviposition in both experiments. In a greenhouse trial on individual caged tomato plants, we evaluated the impact of pollen supplementation frequency on the establishment of P. ubiquitus. Here, a pollen addition frequency of every other week was required to allow populations of P. ubiquitus to establish.

Predators and Parasitoids-in-First: From Inundative Releases to Preventative Biological Control in Greenhouse Crops

Repeated mass introductions of natural enemies have been widely used as a biological control strategy in greenhouse systems when the resident population of natural enemies is insufficient to suppress the pests. As an alternative strategy, supporting the establishment and population development of beneficials can be more effective and economical. The preventative establishment of predators and parasitoids, before the arrival of pests, has become a key element to the success of biological control programs. This “Predators and parasitoids-in-first” strategy is used both in Inoculative Biological Control (IBC), and in Conservation Biological Control (CBC). Here, we provide an overview of tools used to boost resident populations of biocontrol agents.

Induced eggplant resistance against Trialeurodes vaporariorum triggered by jasmonic acid, abscisic acid, and Nesidiocoris tenuis feeding

Greenhouse whitefly, Trialeurodes vaporariorum Westwood, is one of the major insect pests of agricultural crops such as eggplant. Due to various difficulties associated with synthetic pesticides, more environmentally friendly alternative methods are greatly appreciated for controlling pests. In the present study, the induction of resistance was investigated in eggplant using root and foliar application of jasmonic acid, abscisic acid, as well as Nesidiocoris tenuis (Reuter) either individually or in combination against T. vaporariorum. The experiments were carried out under laboratory conditions inside a growth chamber, which was set at 27 ± 2°C, 50 ± 5% relative humidity with a 16 h day length. Our results showed an increase in plant resistance due to the higher immature mortality rates, longer immature periods, lower longevity of adults, and fecundity. In free-choice situation, oviposition on root jasmonic acid (RJA) + N. tenuis and root abscisic acid (RABA) + N. tenuis was similar, but numbers of eggs deposited on these plants were lower than other treatments and control plants. The plant enzyme activity and phenolic content were significantly greater in RJA + N. tenuis and RABA + N. tenuis, intermediate in individual treatments, and the lowest in control plants. Correspondingly, T. vaporariorum longevity, number of eggs produced per female, oviposition preference, all were lowest when the insects fed on these treatments. These findings suggest that the induction of resistance in eggplants with the physiological changes in the host plant leads to a reduction in whitefly damage.

Zoophytophagous predator-induced defences restrict accumulation of the tomato spotted wilt virus

BACKGROUND

The use of zoophytophagous predators in protected crops has been widely adopted to manage pests in southern Europe. We hypothesized that plant defence responses would be induced by zoophytophagous predators and this induction could affect plant virus occurrence; the phytophagy of these predators induces plant defences similarly to that of viral infection. Therefore, we evaluated whether or not mirid predator-activated plant defences limited the accumulation of Tomato Spotted Wilt Virus (TSWV) in mechanically infected sweet pepper.

RESULTS

Our results revealed TSWV accumulation in mirid-punctured plants to be significantly lower than in intact plants. This is most likely associated with the upregulation of the jasmonate acid pathway triggered by mirid phytophagy.

CONCLUSION

Activation of induced defences by mirid predators has been demonstrated for the first time to limit the accumulation of TSWV in sweet pepper. This novel approach can offer new control strategies for the management of plant diseases. © 2019 Society of Chemical Industry.

Life Table Parameters of the Zoophytophagous Predator Brontocoris tabidus (Heteroptera: Pentatomidae) on Introduced and Native Plants

Brontocoris tabidus Signoret (Heteroptera: Pentatomidae) is a zoophytophagous predator of lepidopteran defoliators of eucalyptus in Brazil. This predator complements its diet with plants, which is fundamental for its population maintenance. The objective was to evaluate the B. tabidus development, reproduction, and life table parameters in the field on Eucalyptus cloeziana F. Muell. (T1), Psidium guajava Linn (Myrtales: Myrtaceae) (T2), or without plants (T3). The parameters estimated were: net reproductive rate (Ro); generation duration (DG); time for the population to double in size (TD); intrinsic population growth rate (rm), survival rate (lX), specific fertility (mx), life expectancy (ex), and mortality risk (qx). Ro, DG, TD, and rm were higher in the T1 and T2 than in T3. Plant presence favored the lx, mx, and qx. Ex values were 36.1 and 56.9 in the T3 and T1, respectively. The B. tabidus fertility, longevity, and life table parameters improvement on E. cloeziana and P. guajava plants are due to the water and nutrients obtained from them. B. tabidus can be reared with Tenebrio molitor Linnaeus (Coleoptara: Tenebrionidae) pupae on E. cloeziana or P. guajava plants in the field.

Zoophytophagous mirids provide pest control by inducing direct defences, antixenosis and attraction to parasitoids in sweet pepper plants

BACKGROUND

In addition to their services as predators, mirid predators are able to induce plant defences by phytophagy. However, whether this induction occurs in sweet pepper and whether it could be an additional benefit to their role as a biological control agent in this crop remain unknown. Here, these questions were investigated in two model insects, the mirids Nesidiocoris tenuis and Macrolophus pygmaeus.

RESULTS

Plant feeding behaviour was observed in both N. tenuis and M. pygmaeus on sweet pepper and occupied 33% and 14% of total time spent on the plant, respectively. The punctures caused by mirid plant feeding induced the release of a blend of volatile organic compounds (VOCs) which repelled the herbivore pests Frankliniella occidentalis and Bemisia tabaci and attracted the whitefly parasitoid Encarsia formosa. The repellent effect on B. tabaci was observed for at least 7 days after initial exposure of the plant to N. tenuis, and attraction of E. formosa remained functional for 14 days.

CONCLUSION

Plant defences induced by the feeding of mirid predators, their subsequent effects on the behaviour of both pests and natural enemies, and the persistence of these observed effects open the door to new control strategies in the sweet pepper crop. Further application of this research is discussed, such as the vaccination of plants by zoophytophagous mirids in the nursery before transplantation. © 2017 Society of Chemical Industry.

Induced Tomato Plant Resistance Against Tetranychus urticae Triggered by the Phytophagy of Nesidiocoris tenuis

The zoophytophagous predator Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is capable of inducing plant defenses in tomato due to its phytophagous behavior. These induced defenses, which include the release of herbivore-induced plant volatiles (HIPVs), have been proven to affect the oviposition behavior and reduce the subsequent performance of some tomato pests. However, the effect of induction of plant defenses by N. tenuis on the preference, development, and reproduction of the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) remains unknown. In this research, T. urticae did not show preference for the odor source emitted by intact tomato plants when compared with N. tenuis-punctured plants and jasmonic acid (JA) deficient mutant tomato plants. Furthermore, the number of eggs laid by T. urticae on intact tomato plants or on N. tenuis-punctured plants was similar. However, in a greenhouse experiment conducted to evaluate whether the defense induction mediated by N. tenuis had an effect on T. urticae the infestation of T. urticae was significantly reduced by 35% on those plants previously activated by N. tenuis when compared to the control. The expression of a JA-responsive gene that was upregulated and the transcription of the plant protein inhibitor II was higher on activated plants relative to the control. These results can serve as a basis for the development of new management strategies for T. urticae based on plant defense mechanisms induced from the phytophagous behavior of N. tenuis.

A Conceptual Framework for Integrated Pest Management

The concept of integrated pest management (IPM) has been accepted and incorporated in public policies and regulations in the European Union and elsewhere, but a holistic science of IPM has not yet been developed. Hence, current IPM programs may often be considerably less efficient than the sum of separately applied individual crop protection actions. Thus, there is a clear need to formulate general principles for synergistically combining traditional and novel IPM actions to improve efforts to optimize plant protection solutions. This paper addresses this need by presenting a conceptual framework for a modern science of IPM. The framework may assist attempts to realize the full potential of IPM and reduce risks of deficiencies in the implementation of new policies and regulations.

Induced plant defences in biological control of arthropod pests: a double-edged sword

Biological control is an important ecosystem service delivered by natural enemies. Together with breeding for plant defence, it constitutes one of the most promising alternatives to pesticides for controlling herbivores in sustainable crop production. Especially induced plant defences may be promising targets in plant breeding for resistance against arthropod pests. Because they are activated upon herbivore damage, costs are only incurred when defence is needed. Moreover, they can be more specific than constitutive defences. Nevertheless, inducible defence traits that are harming plant pest organisms may interfere with biological control agents, such as predators and parasitoids. Despite the vast fundamental knowledge on plant defence mechanisms and their effects on natural enemies, our understanding of the feasibility of combining biological control with induced plant defence in practice is relatively poor. In this review, we focus on arthropod pest control and present the most important features of biological control with natural enemies and of induced plant defence. Furthermore, we show potential synergies and conflicts among them and, finally, identify gaps and list opportunities for their combined use in crop protection. We suggest that breeders should focus on inducible resistance traits that are compatible with the natural enemies of arthropod pests, specifically traits that help communities of natural enemies to build up. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Stage-Related Defense Response Induction in Tomato Plants by Nesidiocoris tenuis

The beneficial effects of direct predation by zoophytophagous biological control agents (BCAs), such as the mirid bug Nesidiocoris tenuis, are well-known. However, the benefits of zoophytophagous BCAs’ relation with host plants, via induction of plant defensive responses, have not been investigated until recently. To date, only the females of certain zoophytophagous BCAs have been demonstrated to induce defensive plant responses in tomato plants. The aim of this work was to determine whether nymphs, adult females, and adult males of N. tenuis are able to induce defense responses in tomato plants. Compared to undamaged tomato plants (i.e., not exposed to the mirid), plants on which young or mature nymphs, or adult males or females of N. tenuis fed and developed were less attractive to the whitefly Bemisia tabaci, but were more attractive to the parasitoid Encarsia formosa. Female-exposed plants were more repellent to B. tabaci and more attractive to E. formosa than were male-exposed plants. When comparing young- and mature-nymph-exposed plants, the same level of repellence was obtained for B. tabaci, but mature-nymph-exposed plants were more attractive to E. formosa. The repellent effect is attributed to the signaling pathway of abscisic acid, which is upregulated in N. tenuis-exposed plants, whereas the parasitoid attraction was attributed to the activation of the jasmonic acid signaling pathway. Our results demonstrate that all motile stages of N. tenuis can trigger defensive responses in tomato plants, although these responses may be slightly different depending on the stage considered.