Arne Janssen

• PhD
• Hon prof at the Federal University of Viçosa and associate prof at University of Amsterdam

Chemical pesticides remain the main agents for control of arthropod crop pests despite increased concern for their side effects. Although chemical pesticide applications generally result in short‐term decreases of pest densities, densities can subsequently resurge to higher levels than before. Thus, pesticide effects on pest densities beyond a sing...

Ecology Letters (2011) 14: 229–236 Phytopathogens and herbivores induce plant defences. Whereas there is evidence that some pathogens suppress these defences by interfering with signalling pathways involved in the defence, such evidence is scarce for herbivores. We found that the invasive spider mite Tetranychus evansi suppresses the induction of t...

Although biologists routinely label animals as predators and prey, the ecological role of individuals is often far from clear. There are many examples of role reversals in predators and prey, where adult prey attack vulnerable young predators. This implies that juvenile prey that escape from predation and become adult can kill juvenile predators. W...

It is well known that young, small predator stages are vulnerable to predation by conspecifics, intra-guild competitors or hyperpredators. It is less known that prey can also kill vulnerable predator stages that present no danger to the prey. Since adult predators are expected to avoid places where their offspring would run a high predation risk, t...

Herbivore densities can be regulated by bottom‐up and top‐down forces such as plant defences and natural enemies, respectively. These forces can interact with each other to increase plant protection against herbivores; however, how much complementarity exists between bottom‐up and top‐down forces still remains to be fully elucidated. Particularly,...

Plant diversity can enhance natural pest control in agriculture by providing resources and conditions that are not regularly available in conventional crops to natural enemies of crop pests. Extrafloral nectar-producing plants, for example, might cause reduction of pest densities on neighboring plants because the nectar can increase the performance...

Recently, we reported brood parasitism in the tiny predatory mite Neoseiulus californicus (Acari: Phytoseiidae); adult females of this species prefer to add their eggs to a cluster of eggs of another predatory mite species, Gynaeseius liturivorus (Acari: Phytoseiidae), which guards its own eggs against egg predators. Here, we investigated the cues...

Several natural enemies are known as predators of the whitefly Bemisia tabaci, which is one of the most invasive pests worldwide and has developed high resistance to pesticides. However, biological control of this pest on tomato is often difficult because the plant’s glandular trichomes release substances that are toxic to arthropods and hinder the...

Tomato plants are attacked by numerous pests and diseases, including the tomato russet mite Aculops lycopersici and powdery mildew, Oidium neolycopersici. Natural enemies of tomato pests are often hindered by the tomato trichomes, while russet mites live under and among these leaf hairs and are therefore protected from these enemies. To find natura...

Group-living animals sometimes cooperatively protect their offspring against predators. This behavior is observed in a wide range of taxa but, to the best of our knowledge, this is the first report of its occurrence in arthropods that are not eusocial. Adult female predatory mites Gynaeseius liturivorus protect their eggs against egg predators, the...

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the major citrus pest worldwide because it can transmit the bacteria associated with citrus greening disease (huanglongbing, HLB). The most common management strategy of this pest is chemical control, but this often results in pest resistance and threatens the sustainabi...

Many animal species protect their eggs against predators, and other species may profit from this by adding their eggs to those of the protecting species. We studied two tiny species of predatory mites that share a food source, are engaged in intraguild predation, and which eggs are attacked by the same egg predator. One of these predatory mites (Ne...

Two mutually unexclusive hypotheses prevail in the theory of nutritional ecology: the balanced diet hypothesis states that consumers feed on different food items because they have complementary nutrient and energy compositions. The toxin-dilution hypothesis poses that consumers feed on different food items to dilute the toxins present in each. Both...

Plant quality for herbivores is usually evaluated with molecular and physiological techniques and with herbivore performance bioassays. These performance assays are usually done either on intact plants or on detached plant parts, such as leaves, leaflets and leaf discs. It is thus far unclear how performance experiments on intact plants and on plan...

Biological pest control is becoming increasingly important for sustainable agriculture. Although many species of natural enemies are already being used commercially, efficient biological control of various pests is still lacking, and there is a need for more biocontrol agents. In this review, we focus on predatory soil mites, their role as natural...

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 w...

Herbivores select host plants depending on plant quality and the presence of predators and competitors. Competing herbivores change host plant quantity through consumption, but they can also change plant quality through induction of plant defences, and this affects the performance of herbivores that arrive later on the plant. Some herbivores, such...

Damage by herbivores often modifies plant structure and physiology, which may change the behaviour and performance of future herbivores. Here, we studied such interactions among the major coconut pest, the mite Aceria guerreronis (Acari: Eriophyidae), and two minor pests, the mite Steneotarsonemus concavuscutum (Acari: Tarsonemidae) and the moth At...

Diaphorina citri Kuwayama (Hemiptera: Psyllidae) transmits the bacteria associated with Huanglongbing, an incurable and lethal disease affecting citrus productivity and fruit quality worldwide. This vector is prominently phototactic and uses visual cues to find host plants. Yellow sticky traps are used for its monitoring, but their efficiency is li...

Dispersal connects local populations and allows for colonization of new patches, thus contributing to spatial distributions (Clobert et al., 2009). Even Abstract Dispersal is the main determinant of the dynamics and persistence of predator-prey metapopulations. When defining dispersal as a predator exploitation strategy, theory predicts the existen...

The intrinsic rate of natural increase of a population ( r m ) has been in focus as a key parameter in entomology and acarology. It is considered especially important in studies of predators that are potential biological control agents of fast-growing pests such as mites, whiteflies and thrips. Life-table experiments under controlled laboratory con...

One of the ecosystem services of biodiversity is the contribution to pest control through conservation and stimulation of natural enemies. However, whether plant diversity around greenhouses is beneficial or a potential risk is heavily debated. In this review, we argue that most greenhouse pests in temperate climates are of exotic origin and infest...

Plant diversification is a strategy for pest management in agroecosystems. However, a major hurdle in the adoption of this management practice by farmers is related to doubts concerning its effects on crop productivity. Here we assess coffee production and natural control of coffee pests in the presence or absence of leguminous trees bearing extraf...

1. Many animals can actively redress nutrient imbalances in their diet to maximise performance. However, food items are commonly patchily distributed in nature, thus, animals often need to commute between prey patches to mix their diet. 2. We previously found that females of two species of predatory mites showed a higher oviposition rate when feedi...

Major themes in pathogen evolution are emergence, evolution of virulence, host adaptation and the processes that underlie them. RNA viruses are of particular interest due to their rapid evolution. The in vivo molecular evolution of an RNA plant virus was demonstrated here using a necrotic isolate of cowpea mild mottle virus (CPMMV) and a susceptibl...

Ants are one of the most abundant insect groups in citrus orchards. They help in controlling pests, but they can also facilitate the outbreak of other pests, such as those that produce honeydew. Moreover, ants can also affect natural enemies of pests. Here, we review how ants affect pest abundance, considering whether the pest produces honeydew and...

Predators frequently compete with other species for prey but can also interact by preying on each other’s vulnerable stages. Because eggs and juveniles are more vulnerable to this intraguild predation than adults, their survival will depend on maternal strategies to reduce predation risk. Recently, we reported that adult female predatory mites Gyna...

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a vector of the bacteria that cause Huanglongbing, the fatal disease threatening citricul-ture worldwide. One of the most important management methods is the control of D. citri with pesticides, but their intensive use causes development of resistance and pollution. An alternative method is therefo...

Cannibalism is a widespread phenomenon in nature, often occurring when food is scarce, for example among predators that have overexploited a local prey population. Instead of cannibalising, predators can disperse, thereby avoiding being cannibalised or cannibalising related conspecifics, which results in inclusive fitness loss. Theory on prey explo...

Few studies have tested how plant quality and the presence of competitors interact in determining how herbivores choose between different leaves within a plant. We investigated this in two herbivorous spider mites sharing tomato plants: Tetranychus urticae , which generally induces plant defenses, and Tetranychus evansi , which suppresses them, cre...

Predatory mites of the Phytoseiidae family are important biological control agents. Many species of this family are omnivores, i.e., besides on prey, they can feed on plant resources such as nectar and pollen. It has been shown that the addition of alternative food for predators to a crop enhances biological control. However, factors such as food a...

• Several animal species are known to distinguish between their own eggs and eggs of unrelated conspecifics. However, the cues involved in this discrimination are often unknown. These cues were studied using the predatory mite Gynaeseius liturivorus Ehara. • Adult females of these predatory mites oviposit in clusters and avoid oviposition close to...

Because plant phenotypes can change in response to attacks by herbivores in highly variable ways, the distribution of herbivores depends on the occurrence of other herbivore species on the same plant. We carried out a field study to evaluate the co-occurrence of three coconut pests, the mites Aceria guerreronis (Acari: Eriophyidae), Steneotarsonemu...

Because predators may interfere with each other, an important step towards the implementation of successful release of multiple predators in biocontrol programs requires resolving how predators respond to the presence of heterospecific competitors. Several species of predatory mites are important biocontrol agents and the species Phytoseiulus macro...

It is known that many social insects and arthropod predators and parasitoids can learn the association between a resource and volatile cues. Although there are various studies on the effect of experience in immature arthropods on behavior later in adult life, not much is known about the effects of such experiences on immature behavior. This was inv...

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 omnivor...

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 spid...

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...

The size or stage of interacting individuals is known to affect the outcome of ecological interactions and can have important consequences for population dynamics. This is also true for intraguild predation (the killing and eating of potential competitors), where the size or ontogenetic stage of an individual determines whether it is the intraguild...

When predators commonly overexploit local prey populations, dispersal drives the dynamics in local patches, which together form a metapopulation. Two extremes in a continuum of dispersal strategies are distinguished: the “Killer” strategy, where predators only start dispersing when all prey are eliminated, and the “Milker” strategy, in which predat...

Intraguild predation is a mix of competition and predation and occurs when one species feeds on another species that uses similar resources. Theory predicts that intraguild predation hampers coexistence of species involved, but it is common in nature. It has been suggested that increasing habitat complexity and the presence of alternative food may...

Many phytoseiid species, including Phytoseiulus persimilis, are known to engage in cannibalism when food is scarce and when there is no possibility to disperse. In nature adult females of P. persimilis are known to disperse when prey is locally depleted. Males, in contrast, are expected to stay and wait for potential mates to mature. During this ph...

Together with farmers, we evaluated nutrient availability from vermicomposted gneiss powder, assessed its influence on growth promotion, nutrition and heavy metal accumulation in maize plants and the effect on soil chemical properties in the field. Three soil treatments were applied: fertilization with vermicompost with gneiss powder, fertilization...

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...

Unfortunately, the citation of one of the papers was published erroneously in the original version and corrected here by this Erratum. The original article was corrected.

Pest control is an important ecosystem service that can be enhanced by increasing plant diversity. One of the simplest forms of plant diversification is making use of the occurring weeds that may benefit natural enemies of crop pests. We investigated the interaction between tomato plants, beggar-ticks (Bidens pilosa, Asteraceae), a common weed in B...

It is well known that herbivore-induced plant defence alter host plant quality and can affect the behavior and performance of later arriving herbivores. Effects of sequential attacks by herbivores that either suppress or induce plant defenses are less well studied. We sequentially infested leaves of tomato plants with a strain of the phytophagous s...

Intraguild predation is the combination of exploitative competition and predation among potential competitors that use similar resources. It has the potential to shape population dynamics and community structure. Although there is much empirical evidence for the occurrence of intraguild predation in natural ecosystems, the study of its effects is m...

The broad mite is a key pest of various crops worldwide, including chili pepper (Capsicum frutescens), where it is controlled with chemical pesticides. Two phytoseiid predators (Amblyseius herbicolus and Neoseiulus barkeri) and a blattisociid mite species (Lasioseius floridensis) occur in association with the broad mite in Brazil. Predation of broa...

When predators can use several prey species as food sources, they are known to select prey according to foraging efficiency and food quality. However, interactions between the prey species may also affect prey choice, and this has received limited attention. The effect of one such interaction, intraguild predation between prey, on patch selection b...

The ‘enemy-free space’ hypothesis predicts that herbivorous insects can escape their natural enemies by switching to a novel host plant, with consequences for the evolution of host plant specialisation. However, if natural enemies follow herbivores to their novel host plants, enemy-free space may only be temporary. We tested this by studying the co...

Orius insidiosus is economically important for biological control of pests of vegetable and ornamental crops. To improve pest control with this predator, its densities in the crops can be enhanced by the provision of alternative foods, especially when prey are scarce. We therefore compared the performance of O. insidiosus on three alternative foods...

The simultaneous infestation of a plant by several species of herbivores may affect the attractiveness of plants to the natural enemies of one of the herbivores. We studied the effect of coconut fruits infested by the pests Aceria guerreronis and Steneotarsonemus concavuscutum , which are generally found together under the coconut perianth. The pre...

Supplying predators with alternative food can have short-term positive effects on prey densities through predator satiation (functional response) and long-term negative effects through increases of predator populations (numerical response). In biological control, alternative food sources for predators are normally supplied on the crop plants; using...

Herbivorous spider mites occurring on tomato plants (Solanum lycopersicum L.) cope with plant defences in various manners: the invasive Tetranychus evansi reduces defences below constitutive levels, whereas several strains of T. urticae induce such defences and others suppress them. In the Mediterranean region, these two species co-occur on tomato...

Predators face the challenge of accessing prey that live in sheltered habitats. The coconut mite Aceriaguerreronis Keifer (Acari: Eriophyidae) lives hidden beneath the perianth, which is appressed to the coconut fruit surface, where they feed on the meristematic tissue. Its natural enemy, the predatory mite Neoseiuluspaspalivorus De Leon (Acari: Ph...

Prey are known to invest in costly antipredator behaviour when perceiving cues of dangerous, but not of relatively harmless predators. Whereas most studies investigate one type of antipredator behaviour, we studied several types (changes in oviposition, in escape and avoidance behaviour) in the spider mite Tetranychus evansi in response to cues fro...

The diversity of prey and food sources in crops has a major effect on biological pest control by generalist predators. In this study, we tested if and how supplemental prey or food affects the control of the citrus mealybug Planococcus citri (Risso) by larvae of the green lacewing Chrysoperla lucasina (Lacroix). The larvae of this predator are the...

When intraguild prey and intraguild predators feed and reproduce in the same habitat and relatively immobile juveniles are the vulnerable stage, predation risk depends on oviposition site selection by the adult females. We studied how the availability of oviposition sites affected the distribution of two predatory mite species, Neoseiulus cucumeris...

Most herbivorous arthropods are host specialists and the question is which mechanisms drive the evolution of such specialization. The theory of antagonistic pleiotropy suggests that there is a trade-off between adaptation of herbivores to a novel host and their native host. The mutation accumulation hypothesis proposes that herbivores on a novel ho...

Many omnivorous arthropods are important natural enemies because they can feed on plantprovided pollen and several prey species, and thus persist in crops even in the absence of the target pest. Hence, populations of these predators can be established in a crop by providing alternative food, thus increasing biological control. We investigated how a...

Many herbivorous arthropods construct shelters on their host plant that offer protection against natural enemies. This has resulted in selection on natural enemies to enter these shelters, where they can feed on prey that are inaccessible for competing predators and parasitoids. The spider mite Tetranychus evansi produces a shelter consisting of a...

Plants respond to attacks by herbivores with various defences, which are mounted through the activation of different biochemical pathways that are known to interact. Thus, the attack of a plant by one herbivore species may result in changes in the performances of other species on the same plant. It has been suggested that species with comparable fe...

Plants are hotbeds for parasites such as arthropod herbivores, which acquire nutrients and energy from their hosts in order to grow and reproduce. Hence plants are selected to evolve resistance, which in turn selects for herbivores that can cope with this resistance. To preserve their fitness when attacked by herbivores, plants can employ complex s...

Mixing of prey that differ in nutrient content or toxic compounds (dietary mixing) may allow synovigenic predatory arthropods to balance their diet or dilute toxins of different prey items to maximize performance: dietary mixing may therefore explain the prevalence of polyphagy in this functional group. Several predatory arthropods can redress nutr...

1. To reduce the risk of being eaten by predators, prey alter their morphology or behaviour. This response can be tuned to the current danger if chemical or other cues associated with predators inform the prey about the risks involved. 2. It is well known that various prey species discriminate between chemical cues from predators that fed on consp...

Predators are usually larger than their prey, but because size changes during ontogeny, predator and prey roles may be reversed. Hence, an individual may be prey when juvenile, but as an adult, it may counterattack the juveniles of its childhood enemy. Earlier, we showed that juvenile predatory mites, Iphiseius degenerans, recognize adults of anoth...

Many animals use volatile chemicals to detect and locate their food, but they frequently have to cope with a large variation in volatile blends associated with food. It has often been suggested that they do this by learning the association between odors and the presence of food. Indeed, associative learning was demonstrated for a range of animals u...

Plant diversity may increase natural enemy populations because some plants can provide alternative food to natural enemies. Extrafloral nectar is such an alternative food and plants producing extrafloral nectar are known to suffer less from herbivory. Little is known about the effect of plants with extrafloral nectaries on herbivory of neighbouring...

Generalist predators have the potential advantage to control more than one pest and to be more persistent than specialist predators because they can survive on different foods. Moreover, their population growth rate may be elevated when offered a mixture of prey species. We studied a generalist predatory mite Balaustium sp. that shows promise for b...

Leaves of plants of several families possess small cavities or tufts of hair where leaf veins bifurcate. These so-called acarodomatia are usually inhabited by predatory and fungivorous mites, which utilize domatia as shelter against adverse conditions or against other predators and cannibals. Plants may benefit from the presence of the mites throug...

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 flowe...

There is increasing evidence that the structure and functioning of ecological communities and ecosystems are strongly influenced by flexible traits of individuals within species. A deep understanding of how trait flexibility alters direct and indirect species interactions is crucial for addressing key issues in basic and applied ecology. This book...

1. Indirect interactions between populations of different prey species mediated by a shared predator population are known to affect prey dynamics. 2. Depending on the temporal and spatial scale, these indirect interactions may result in positive (apparent mutualism), neutral or negative effects (apparent competition) of the prey on each other's den...

Plants infected with pathogens often attract the pathogens' vectors, but it is not clear if this is advantageous to the vectors. We therefore quantified the direct and indirect (through the host plant) effects of a pathogen on its vector. A positive direct effect of the plant-pathogenic Tomato spotted wilt virus on its thrips vector (Frankliniella...

Whereas prey are known to avoid habitats with their predators, it is less well established whether they are triggered to emigrate to new habitats when exposed to predators in their current habitat. We studied plant-to-plant dispersal of adult whiteflies in response to the presence of predatory mites on the plant on which the whiteflies were release...

It is generally assumed that the choice of oviposition sites in arthropods is affected by the presence of food for the offspring on the one hand and by predation risk on the other hand. But where should females oviposit when the food itself poses a predation risk for their offspring? Here, we address this question by studying the oviposition behavi...

Omnivores obtain resources from more than one trophic level, and choose their food based on quantity and quality of these resources. For example, omnivores may switch to feeding on plants when prey are scarce. Larvae of the western flower thrips Frankiniella occidentalis Pergande (Thysanoptera: Thripidae) are an example of omnivores that become pre...

Biologische bestrijding van plagen in kassen was lange tijd voornamelijk gericht op specialistische natuurlijke vijanden die sterk zijn aangepast aan hun prooi. Gerben Messelink onderzocht de rol van generalistische predatoren bij de bestrijding van meerdere plagen in de teelt van vruchtgroenten in kassen. Uit zijn resultaten blijkt dat spintmijten...