Root-feeding Insects Research Articles

A meta-analysis of root herbivore-induced communication cascades affecting above-ground herbivores, parasitoids, and pollinators via host plants

Several research papers over the past three decades have reported the profound influence of root herbivores on above-ground plant-insect interactions. Root-feeding insects significantly alter plant nutrient levels—carbon, nitrogen(N), phosphorus(P), and amino acids(AA)—triggering the production of defensive compounds like terpenoids, phenolics, gossypol, and DIMBOA in shoots. Jasmonate translocation from roots to shoots impairs shoot herbivore performance, while root herbivory suppresses salicylic acid (SA)-mediated defenses, benefiting phloem feeders. Reduced leaf water content and increased abscisic acid (ABA) levels enhance phloem feeder success. Nematode infestations lower AA and N, but increase foliar nicotine, aiding leaf chewers. Mycorrhizal fungi reduce plant N but raise carbon and P, while earthworms increase phytosterols, hindering aphid fecundity. These systemic changes cascade through trophic levels, even affecting hyperparasitoids. This review highlights root herbivory's intricate, cascading effects, reshaping our understanding of plant defense mechanisms and ecological interactions.

When Competitors Join Forces: Consortia of Entomopathogenic Microorganisms Increase Killing Speed and Mortality in Leaf- and Root-Feeding Insect Hosts.

Combining different biocontrol agents (BCA) is an approach to increase efficacy and reliability of biological control. If several BCA are applied together, they have to be compatible and ideally work together. We studied the interaction of a previously selected BCA consortium of entomopathogenic pseudomonads (Pseudomonas chlororaphis), nematodes (Steinernema feltiae associated with Xenorhabdus bovienii), and fungi (Metarhizium brunneum). We monitored the infection course in a leaf- (Pieris brassicae) anda root-feeding (Diabrotica balteata) pest insect after simultaneous application of the three BCA as well as their interactions inside the larvae in a laboratory setting. The triple combination caused the highest mortality and increased killing speed compared to single applications against both pests. Improved efficacy against P. brassicae was mainly caused by the pseudomonad-nematode combination, whereas the nematode-fungus combination accelerated killing of D. balteata. Co-monitoring of the three BCA and the nematode-associated Xenorhabdus symbionts revealed that the four organisms are able to co-infect the same larva. However, with advancing decay of the cadaver there is increasing competition and cadaver colonization is clearly dominated by the pseudomonads, which are known for their high competitivity in the plant rhizosphere. Altogether, the combination of the three BCA increased killing efficacy against a Coleopteran and a Lepidopteran pest which indicates that this consortium could be applied successfully against a variety of insect pests.

Belowground crop responses to root herbivory are associated with the community structure of native arbuscular mycorrhizal fungi

There is growing interest in managing arbuscular mycorrhizal (AM) fungi in agriculture to support plant production. These fungi can support crop growth and nutrient uptake, but also affect plant-herbivore interactions. While our understanding of how AM fungi affect plant responses to herbivory advances, it is less clear how different naturally-occurring (native) fungal communities differentially influence crop responses to root-feeding insects.To explore this, plants (Sorghum bicolor) were grown in a glasshouse experiment without AM fungi (‘no AM fungi’) or with one of three natural soil inocula sourced either from a sclerophyll forest (‘forest inoculum’), a cropped field (‘field inoculum’), or a field in fallow (‘fallow inoculum’), while half the plants were subjected to a root herbivore (Dermolepida albohirtum). We assessed the effects of soil inoculum and root herbivory on root-colonising AM fungal diversity, plant growth, and nutrient content.Root herbivory did not affect AM fungal diversity or composition. Plants grown with the field or fallow inocula were both dominated by the genera Glomus and Claroideoglomus. These plants exhibited reduced biomass in response to inoculation, but were not impacted by root herbivory. In contrast, plants with the forest inoculum had AM fungal communities dominated by Paraglomus and Ambispora. When subjected to root herbivory, the forest inoculated plants and plants without AM fungi exhibited reductions of 44 % and 61 % in root biomass, and reductions of 65 % and 59 % in root phosphorus, respectively.Our study shows inoculation-driven plant responses to root herbivory that were associated with the community structure of their root-colonising AM fungi. Results suggest associations with communities dominated by Claroideoglomus and Glomus may mitigate the impacts of a root-feeding insect. More exploration of how natural assemblages of AM fungi mediate plant-herbivore interactions is needed if we are to effectively manage soil fungi in agriculture.

Sub-Lethal Effects of Bifenthrin and Imidacloprid on Megacephala carolina carolina L. (Coleoptera: Carabidae) in Turfgrass.

The tiger beetle, Megacephala carolina carolina L. (Coleoptera: Carabidae), is a common predator in turfgrass and ornamental landscapes in Georgia, USA. Among insecticides used in turfgrass to control foliar and root-feeding insect pests, bifenthrin and imidacloprid are routinely used. It was unclear whether sub-lethal doses of bifenthrin and imidacloprid could cause nontarget effects on larvae and M. carolina carolina adults. Thus, the objective was to determine the sub-lethal effects of bifenthrin and imidacloprid on larvae and M. carolina carolina adults. The results show that M. carolina carolina larvae actively hunt for passing prey by waiting at the hole of the tunnel during the day and nighttime. This larval behavior was affected by sub-lethal doses (up to 25% of full label rate) of bifenthrin but not of imidacloprid. The walking behavior of adult M. carolina carolina was also altered when exposed to sub-lethal doses of bifenthrin as they traveled further distances at greater velocities than the nontreated control. The results imply that turfgrass managers should avoid treating lawns where tiger beetles have actively colonized.

Resporulation of Metarhizium anisopliae granules on soil and mortality of Tenebrio molitor: Implications for wireworm management in sweetpotato

AbstractIn Australia, sweetpotato (Ipomoea batatas L.) is vulnerable to root feeding insect pests such as wireworms (e.g., Agrypnus spp.). The number of registered insecticides to control these insect pests is limited and often pest pressure, for example by wireworms, is severe close to harvest, further limiting what insecticides can be applied. Incorporating biological control agents such as entomopathogenic fungi (e.g., Metarhizium anisopliae) into integrated pest management programmes may be feasible in sweetpotato. M. anisopliae has been shown to be effective in controlling more than 200 insects and it is able to reside and grow in the rhizosphere and rhizoplane, suggesting that M. anisopliae could be a promising candidate against soil insect pests. In the study presented here, M. anisopliae was formulated into calcium alginate granules fortified with nutrients. The resporulation of the fungal granules was tested on four different soil types in the laboratory. The biocontrol efficacy of the resulting fungal growth was also examined using larval mealworms, Tenebrio molitor as a model insect in the laboratory and the glasshouse. Our results indicated that sterilised soil favoured optimal fungal resporulation, although different soil types did not have a significant effect on fungal resporulation. The resulting fungal resporulation and growth on sterilised soil caused high mortality (up to 76%) of larval mealworms in the glasshouse, whereas the fungal granules applied to non‐sterile soil demonstrated poor resporulation that led to low mortality (13%) of larval mealworms. The result of this study indicates that the manipulation of microbial populations in field soil is required to enhance the fungal growth and potential insect control against wireworms in the field.

The impact of whitegrub (Coleoptera: Scarabaeidae) damage on growth of Eucalyptus grandis and Acacia mearnsii plantation trees in South Africa

ABSTRACT Eucalyptus grandis and Acacia mearnsii are among the South African forest industry’s most planted commercial species. Whitegrubs are high-status pests affecting plantation forestry; they are root-feeding insects and cause poor seedling growth and elevated mortality. The aim of this study was to elucidate the impact of whitegrub damage on the growth of E. grandis and A. mearnsii trees during the first year of the establishment stage in sites previously planted with A. mearnsii in the KwaZulu-Natal Midlands of South Africa. The hypothesis was that the prophylactic application of insecticides against whitegrubs would increase tree height at six or 12 months after planting. Seven insecticides were assessed in 12 treatments over three trials in Bloemendal, KwaZulu-Natal. Statistical analyses were performed using PRIMER and SAS. Whitegrubs were the predominant mortality factor (17.1%), followed by pathogens (3.3%) and 12 other factors that cumulatively caused the remaining (7.0%) mortality. Pegylis sommeri, Schizonycha affinis and two unknown Maladera species were the most important, typical and prevalent whitegrub species, but their ranking differed between A. mearnsii and E. grandis, suggesting a host preference. The prophylactic application of insecticides against whitegrubs significantly increased tree height for E. grandis. Acacia mearnsii tree height, however, did not consistently show a significant effect with insecticide control, presumably because of additional mortality by pathogens. The crop-rotation scenario may have potentially benefited E. grandis over A. mearnsii and warrants further investigation. Whitegrubs can kill seedlings and reduce tree height when left uncontrolled.

Shoot and root insect herbivory change the plant rhizosphere microbiome and affects cabbage-insect interactions through plant-soil feedback.

Summary Plant–soil feedback (PSF) may influence plant–insect interactions. Although plant defense differs between shoot and root tissues, few studies have examined root‐feeding insect herbivores in a PSF context. We examined here how plant growth and resistance against root‐feeding Delia radicum larvae was influenced by PSF.We conditioned soil with cabbage plants that were infested with herbivores that affect D. radicum through plant‐mediated effects: leaf‐feeding Plutella xylostella caterpillars and Brevicoryne brassicae aphids, root‐feeding D. radicum larvae, and/or added rhizobacterium Pseudomonas simiae WCS417r. We analyzed the rhizosphere microbial community, and in a second set of conspecific plants exposed to conditioned soil, we assessed growth, expression of defense‐related genes, and D. radicum performance.The rhizosphere microbiome differed mainly between shoot and root herbivory treatments. Addition of Pseudomonas simiae did not influence rhizosphere microbiome composition. Plant shoot biomass, gene expression, and plant resistance against D. radicum larvae was affected by PSF in a treatment‐specific manner. Soil conditioning overall reduced plant shoot biomass, Pseudomonas simiae‐amended soil causing the largest growth reduction.In conclusion, shoot and root insect herbivores alter the rhizosphere microbiome differently, with consequences for growth and resistance of plants subsequently exposed to conditioned soil.

Self-Poisoning With Safer Insecticide: A Case Series on Imidacloprid Poisoning.

Imidacloprid (IMI) is a systemic insecticide that belongs to the neonicotinoid group of insecticides. It is highly effective against sucking, boring, and root-feeding insects. Besides, it has a favorable toxicological profile on humans. Currently, IMI is the largest selling insecticide in the world by replacing organophosphates and carbamates. It acts as nicotinic acetylcholine receptor agonist in the central nervous system of insects. To date, there is no specific antidote available for IMI poisoning. Despite a better safety profile on humans, severe toxicity from IMI poisoning is not uncommon. Here, we report a series of 4 cases who were admitted to our tertiary care center with a history of IMI poisoning.

In a belowground multitrophic interaction, Trichoderma harzianum induces maize root herbivore tolerance against Phyllophaga vetula.

Trichoderma spp. are soil fungi that interact with plant roots and associated biota such as other microorganisms and soil fauna. However, information about their interactions with root-feeding insects is limited. Here, interactions between Trichoderma harzianum and the root-feeding insect Phyllophaga vetula, a common insect pest in maize agroecosystems, were examined. Applications of T. harzianum and P. vetula to the root system increased and decreased maize growth, respectively. Induced tolerance against herbivore attack was provided by T. harzianum maintaining a robust and functional root system as evidenced by the increased uptake of Cu, Ca, Mg, Na and K. Herbivore tolerance also coincided with changes in the emission of root volatile terpenes known to induce indirect defense responses and attract natural enemies of the herbivore. More importantly, T. harzianum induced de novo emission of several sesquiterpenes such as β-caryophyllene and δ-cadinene. In addition, single and combined applications of T. harzianum and P. vetula altered the sucrose content of the roots. Finally, T. harzianum produced 6-pentyl-2H-pyran-2-one (6-PP) a volatile compound that may act as an antifeedant-signaling compound mitigating root herbivory by P. vetula. Our results provide novel information about belowground multitrophic plant-microbe-arthropod interactions between T. harzianum and P. vetula in the maize rhizosphere resulting in alterations in maize phenotypic plant responses, inducing root herbivore tolerance.

Calcium-alginate beads as a formulation for the application of entomopathogenic nematodes to control rootworms

Entomopathogenic nematodes (EPN) have great potential as biological control agents against root-feeding insects. They have a rapid and long-lasting mode of action, minimal adverse effects on the environment and can be readily mass-produced. However, they have a relatively short shelf-life and are susceptible to desiccation and UV light. These shortcomings may be overcome by encapsulating EPN in Ca2+-alginate hydrogels, which have been shown to provide a humid and UV protective shelter. Yet, current Ca2+-alginate formulations do not keep EPN vigorous and infectious for a prolonged period of time and do not allow for their controlled release upon application. Here, we introduce solid Ca2+-alginate beads which we supplemented with glycerol to better retain the EPN during storage and to ensure a steady release when applied in soil. Glycerol-induced metabolic arrest in EPN (Heterorhabditis bacteriophora) resulting in quiescence and total retainment of EPN when added to beads made with 0.5% sodium alginate and 2% CaCl2·2H2O solutions. More than 4,000 EPN could be embedded in a single 4–5-mm diameter bead, and quiescence could be broken by adding water, after which the EPN readily emerged from the beads. In a field trial, the EPN beads were as effective in reducing root damage by the western corn rootworm (WCR, Diabrotica virgifera virgifera) as EPN that were applied in water. Although further improvements are desirable, we conclude that Ca2+-alginate beads can provide an effective and practical way to apply EPN for the control of WCR larvae.

Molecular Gut-Content Analysis of Adult Ground Beetles (Coleoptera: Carabidae) Provides No Evidence of Predation of Western Corn Rootworm (Coleoptera: Chrysomelidae) in a Nebraska Corn Agroecosystem

Abstract This study was conducted to characterize the ground beetle (Coleoptera: Carabidae) community in Nebraska continuous cornfields and investigate the potential for predation of the western corn rootworm, Diabrotica virgifera virgifera LeConte, a key root-feeding insect pest that is an annual management challenge in this system. Seven collection dates were conducted at five commercial cornfields in west central Nebraska during the growing season of 2014. In each field, carabids were sampled using five 24-h pitfall traps. Carabid specimens were placed in 95% ethanol in the field and stored at –20°C to preserve DNA. After identification to the species level, DNA was extracted and polymerase chain reaction was conducted for gut-content analysis using D. v. virgifera-specific primers. Data from single-plant emergence cages and yellow sticky cards showed high abundance of D. v. virgifera prey in three of the five fields sampled. Sixteen genera and 36 carabid species were found in pitfall traps. Of the total 235 carabid specimens tested in this study, zero tested positive for D. v. virgifera DNA. The lack of positive results for the presence of D. v. virgifera DNA in the gut-contents of carabids, despite abundant pest populations, indicates that, in this system, ground beetles may not be a strong mortality agent of D. v. virgifera. However, results presented here contribute to our knowledge of carabid diversity in agroecosystems and indicate that future D. v. virgifera biological control efforts in this region should focus on other natural enemies and/or other life stages of carabids, such as larvae.

Aboveground resource allocation in response to root herbivory as affected by the arbuscular mycorrhizal symbiosis

Arbuscular mycorrhizal (AM) fungi associate with the majority of terrestrial plants, influencing their growth, nutrient uptake and defence chemistry. Consequently, AM fungi can significantly impact plant-herbivore interactions, yet surprisingly few studies have investigated how AM fungi affect plant responses to root herbivores. This study aimed to investigate how AM fungi affect plant tolerance mechanisms to belowground herbivory. We examined how AM fungi affect plant (Saccharum spp. hybrid) growth, nutrient dynamics and secondary chemistry (phenolics) in response to attack from a root-feeding insect (Dermolepida albohirtum). Root herbivory reduced root mass by almost 27%. In response, plants augmented investment in aboveground biomass by 25%, as well as increasing carbon concentrations. The AM fungi increased aboveground biomass, phosphorus and carbon. Meanwhile, root herbivory increased foliar phenolics by 31% in mycorrhizal plants, and increased arbuscular colonisation of roots by 75% overall. AM fungi also decreased herbivore performance, potentially via increasing root silicon concentrations. Our results suggest that AM fungi may be able to augment plant tolerance to root herbivory via resource allocation aboveground and, at the same time, enhance plant root resistance by increasing root silicon. The ability of AM fungi to facilitate resource allocation aboveground in this way may be a more widespread strategy for plants to cope with belowground herbivory.

Distinct defense strategies allow different grassland species to cope with root herbivore attack.

Root-feeding insect herbivores are of substantial evolutionary, ecological and economical importance. Plants defend themselves against insect herbivores through a variety of tolerance and resistance strategies. To date, few studies have systematically assessed the prevalence and importance of these strategies for root-herbivore interactions across different plant species. Here, we characterize the defense strategies used by three different grassland species to cope with a generalist root herbivore, the larvae of the European cockchafer Melolontha melolontha. Our results reveal that the different plant species rely on distinct sets of defense strategies. The spotted knapweed (Centaurea stoebe) resists attack by dissuading the larvae through the release of repellent chemicals. White clover (Trifolium repens) does not repel the herbivore, but reduces feeding, most likely through structural defenses and low nutritional quality. Finally, the common dandelion (Taraxacum officinale) allows M. melolontha to feed abundantly but compensates for tissue loss through induced regrowth. Thus, three co-occurring plant species have evolved different solutions to defend themselves against attack by a generalist root herbivore. The different root defense strategies may reflect distinct defense syndromes.

Host preference of sweetpotato weevil, Cylas formicarius elegantulus (Summers): an example of Hopkins’ host-selection principle

Sweetpotato weevil (SPW), Cylas formicarius elegantulus (Summers), is the most damaging root-feeding insect of sweetpotato, Ipomoea batatas (L.) Poir., worldwide. Larval feeding on storage roots reduces yield and induces terpene production, rendering roots inedible. Selection of sweetpotato cultivars with resistance to insect pests has been carried out for over a century but no high yielding, production acceptable varieties are currently available that are resistant to SPW. A cultivar with resistance to SPW oviposition would be a desirable choice for growers since it will reduce the number of larvae and damage level from SPW. Previous studies have compared cultivar effect on the oviposition of SPW but have not considered the effect of previous rearing experience. Hopkins’ host-selection principle (Hopkin’s HSP) states that phytophagous insects have an oviposition preference for the host that they have been reared on. In this study, we tested cultivar effect on oviposition preference of SPW reared on different cultivars for a minimum of two generations. For adults reared on cvs. Beauregard and Evangeline, adult oviposition preference followed their previous living experience. Thus, our results indicate a strong effect of host fidelity, supporting Hopkin’s HSP. Our results also confirm that cv. Murasaki is a resistant cultivar, resulting in reduced oviposition but not oviposition capacity. It is possible that the reduced oviposition is due to the stress-triggered oosorption from the females feeding on cv. Murasaki.

Insect Management for Sweet Corn

Foliar, ear and root feeding insects can routinely cause economic losses to sweet corn if left untreated. The most important pests of sweet corn in Florida are the fall armyworm, corn earworm, lesser cornstalk borer, cutworms, corn silk fly, cucumber beetles, aphids, and wireworms. Less common pests of sweet corn include grasshoppers, corn blotch leafminer, twospotted spider mites, sap beetles, stink bugs, maize weevils and billbugs, white grubs, and white fringed beetles. This document is ENY-472 (which replaces ENY-449), one of a series of the Department of Entomology and Nematology, UF/IFAS Extension. Original publication date November 2001. Revised September 2005. 
 ENY-472/IG158: Insect Management for Sweet Corn (ufl.edu)

Study on host-seeking behavior and chemotaxis of entomopathogenic nematodes using Pluronic F-127 gel.

Pluronic F-127 gel (PF127) has proven to be a powerful medium in which to study host-finding behavior and chemotaxis for plant-parasitic nematodes. Pluronic gel can also be used to study host-habitat seeking behavior of entomopathogenic nematodes (EPN), which are natural enemies of root-feeding insect pests. In this study, PF127 was used to study tritrophic interactions among EPNs, host-habitat roots and insects. We also tested whether EPN aggregated to acetic acid (pH gradient) which mimicked the conditions near the roots. The chive root gnat Bradysia odoriphaga alone significantly attracted more nematodes than chive roots alone or the combination of roots plus insects. The attractiveness of B. odoriphaga differed (3.7-15.4%) among all tested species/strains of EPNs. In addition, we found that Heterorhabditis spp. and Steinernema spp. infective juveniles responded to pH gradients formed by acetic acid in Pluronic gel. The preferred pH ranges for strains of H. bacteriophora and H. megidis were from 4.32-5.04, and from 5.37-6.92 for Steinernema species, indicating that Heterorhabditis spp. prefer low pH conditions than Steinernema species. A narrow pH gradient between 6.84 and 7.05 was detected around chive root tips in which EPN was attracted. These results suggest that Pluronic gel can be broadly used for the study of host or host-habitat seeking behaviors and chemotaxis of nematodes.

Interactions of Root-Feeding Insects with Fungal and Oomycete Plant Pathogens.

Soilborne fungal and oomycete pathogens are the causal agents of several important plant diseases. Infection frequently co-occurs with herbivory by root-feeding insects, facilitating tripartite interactions that modify plant performance and mortality. In an agricultural context, interactions between pathogens, herbivores, and plants can have important consequences for yield protection. However, belowground interactions are inherently difficult to observe and are often overlooked. Here, we review the impact of direct and indirect interactions between root-associated insects, fungi, and oomycetes on the development of plant disease. We explore the relationship between insect feeding injury and pathogen infection, as well as the role of insects as vectors of fungal and oomycete pathogens. Synergistic interactions between insects and phytopathogens may be important in weed suppression, and we highlight several promising candidates for biocontrol. Bridging the gap between entomological and pathological research is a critical step in understanding how interactions between insects and microorganisms modify the community structure of the rhizosphere, and how this impacts plant functioning. Furthermore, the identification of belowground interactions is required to develop effective pest monitoring and management strategies.

Arbuscular mycorrhizal fungi promote silicon accumulation in plant roots, reducing the impacts of root herbivory

Studies have shown that arbuscular mycorrhizal (AM) fungi can reduce the performance of typically detrimental root feeding insects, yet the mechanisms remain unclear. This study aimed to investigate the effects of different sources of AM inocula on plant resistance to a root feeding insect in two different soils with different silicon (Si) concentrations. Sugarcane (Saccharum spp. hybrid) was grown in high or low Si soil; plants were treated with either an inoculum comprising the native AM fungi, a commercial AM fungal inoculum or with no AM fungi. Root herbivore (Dermolepida albohirtum) performance was measured in a feeding assay. In the low Si soil AM fungi increased root Si concentrations and reduced root herbivore performance. Both commercial and native AM treatments increased root Si and also reduced root herbivore growth rates by 107% and 81%, respectively. AM colonisation positively correlated with root Si concentrations. Distinct from this, in the high Si soil AM fungi had no impact on root Si or root herbivore growth. However, root consumption was reduced; a response independent of Si concentrations. Our study suggests AM fungi can enhance Si based plant defences against root herbivores, but also highlights that interactions between AM fungi and root herbivores involves multiple mechanisms requiring further research.

Bacterial phytopathogen infection disrupts belowground plant indirect defense mediated by tritrophic cascade.

Plants can defend themselves against herbivores through activation of defensive pathways and attraction of third‐trophic‐level predators and parasites. Trophic cascades that mediate interactions in the phytobiome are part of a larger dynamic including the pathogens of the plant itself, which are known to greatly influence plant defenses. As such, we investigated the impact of a phloem‐limited bacterial pathogen, Candidatus Liberibacter asiaticus (CLas), in cultivated citrus rootstock on a well‐studied belowground tritrophic interaction involving the attraction of an entomopathogenic nematode (EPN), Steinernema diaprepesi, to their root‐feeding insect hosts, Diaprepes abbreviatus larvae. Using belowground olfactometers, we show how CLas infection interferes with this belowground interaction by similarly inducing the release of a C12 terpene, pregeijerene, and disconnecting the association of the terpene with insect presence. D. abbreviatus larvae that were not feeding but in the presence of a CLas‐infected plant were more likely to be infected by EPN than those near uninfected plants. Furthermore, nonfeeding larvae associated with CLas‐infected plants were just as likely to be infected by EPN as those near noninfected plants with D. abbreviatus larval damage. Larvae of two weevil species, D. abbreviatus and Pachnaeus litus, were also more attracted to plants with infection than to uninfected plants. D. abbreviatus larvae were most active when exposed to pregeijerene at a concentration of 0.1 μg/μl. We attribute this attraction to CLas‐infected plants to the same signal previously thought to be a herbivore‐induced plant volatile specifically induced by root‐feeding insects, pregeijerene, by assessing volatiles collected from the roots of infected plants and uninfected plants with and without feeding D. abbreviatus. Synthesis. Phytopathogens can influence the structuring of soil communities extending to the third trophic level. Field populations of EPN may be less effective at host‐finding using pregeijerene as a cue in citrus grove agroecosystems with high presence of CLas infection.

Impacts of root herbivory on seedlings of three species of boreal forest trees

Current meta-analysis has identified the shortage of information on responses of woody plants to root damage as the most critical gap in studies of belowground insect herbivory. We explored the impacts of natural and simulated root herbivory on seedlings of three boreal forest-forming trees, Pinus sylvestris, Picea abies and Betula pendula. We compared the effects of natural herbivory and mechanical damage by placing one larva of the common cockchafer, Melolontha melolontha, of different instars (to manipulate root loss) into a pot with a one-year-old seedling or we excised a portion of the roots by inserting a 13-mm diameter cork borer into the soil. During the experiment, which lasted from 2 to 8 weeks, the larvae consumed 53–73% of root biomass, whereas the mechanical damage treatment removed 30–40% of roots. Seedling mortality was low (5%) across all treatments, but the aboveground biomass decreased by 3–43% due to natural herbivory and by 6–30% due to mechanical damage. The M. melolontha larvae consumed a larger amount of roots from B. pendula than from either P. sylvestris or P. abies, but the larvae showed similar relative growth rates and mass gains, indicating a different efficiency of conversion of ingested food (ECI). The values of ECI calculated for larvae of M. melolontha (2.3–3.5%) appeared much lower than the 17% reported earlier for larvae of foliage-feeding beetles, presumably due to the high energetic cost of locomotion in the soil. Consequently, root-feeding insects consume much more plant biomass than leaf-feeding insects do to gain similar body mass, and therefore they inflict relatively more damage to plants per unit of mass gained. Based on the biomass of insect herbivores in European forests, we estimate that they consume 0.5% of the available fine root biomass. The effects of low levels of root damage on growth and reproduction of woody plants remain virtually unknown, emphasising the need for studies of plant- and ecosystem-level effects of minor but chronic root herbivory.