J A Harvey

Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, Gelderland, Netherlands

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Publications (54)90.77 Total impact

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    ABSTRACT: Co-evolutionary theory underpins our understanding of interactions in nature involving plant-herbivore and host-parasite interactions. However, many studies that are published in the empirical literature that have explored life history and development strategies between endoparasitoid wasps and their hosts are based on species that have no evolutionary history with one another. Here, we investigated novel associations involving two closely related solitary endoparasitoids that originate from Europe and North America and several of their natural and factitious hosts from both continents. The natural hosts of both species are also closely related, all being members of the same family. We compared development and survival of both parasitoids on the four host species and predicted that parasitoid performance is better on their own natural hosts. In contrast with this expectation, survival, adult size and development time of both parasitoids were similar on all (with one exception) hosts, irrespective as to their geographic origin. Our results show that phylogenetic affinity among the natural and factitious hosts plays an important role in their nutritional suitability for related parasitoids. Evolved traits in parasitoids, such as immune suppression and development, thus enable them to successfully develop in novel host species with which they have no evolutionary history. Our results show that host suitability for specialized organisms like endoparasitoids is closely linked with phylogenetic history and macro-evolution as well as local adaptation and micro-evolution. We argue that the importance of novel interactions and 'ecological fitting' based on phylogeny is a greatly underappreciated concept in many resource-consumer studies.
    Journal of Evolutionary Biology 08/2012; 25(10):2139-48. · 3.48 Impact Factor
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    ABSTRACT: Plants can accumulate and release defensive chemicals by activating various signaling pathways when they are damaged by herbivores or pathogens. The jasmonic acid pathway is activated after damage by chewing herbivores. Here we used jasmonic acid (JA) as an exogenous elicitor to induce feral cabbage plants. In this study, the effects of root JA (RJA) and shoot JA (SJA) induction on the foraging behavior of , a parasitoid of the large cabbage white butterfly , was investigated under semi-field conditions. In all combinations of differently induced plants (RJA, SJA and control plants), the percentages of shoot induced plants that were visited by at least one wasp were significantly higher than those of controls or root induced plants during 3 h of foraging. Consequently, parasitism rates of on shoot-JA induced plants were significantly higher than on plants induced with JA to the roots or control plants in all tests. However, this behavioral preference was not reflected in the allocation of offspring. The clutch sizes of eggs on control, root induced and shoot induced plants were not significantly different from each other in two-choice or three-choice experiments, but did differ with clutch size in the two-choice experiment of uninduced control plants versus SJA. This semi-field study helps to further understand the choice behavior and preferences of parasitoids in natural multitrophic communities in which plants induced with root or shoot herbivores occur together.
    BioControl 01/2012; · 2.22 Impact Factor
  • J. A. Harvey, A. Gumovsky, R. Gols
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    ABSTRACT: Parasitoids have long proven to be model organisms in studying resource-related constraints on immature development. Here we examine the relationship between host cocoon (= pupal) size in the gregarious endoparasitoid wasp, Cotesia glomerata, and development time and adult size in the solitary idiobiont hyperparasitoid, Pteromalus semotus. Little is known about the biology or ecology of this ecto-hyperparasitoid species, although it is one of the major secondary hyperparasitoids of C. glomerata. The size of the adult wasp covaried with the size of the host cocoon at parasitism. Moreover, female wasps were larger than male wasps for a given cocoon size. Adult wasps have remarkably long life-spans, 3 months on average. Longevity did not significantly differ with sex. We also examined how larvae of P. semotus exclude other potential competitors. P. semotus is protandrous, with females taking significantly longer to complete their development than males. In experiments where several eggs of P. semotus were placed on individual pupae of C. glomerata, newly hatched hyperparasitoid larvae moved rapidly over the surface of the host and destroyed the eggs of any conspecifics by biting them before they would initiate feeding on host tissues. Our results are discussed in relation to those with other studies with solitary ichneumonid idiobiont hyperparasitoids of C. glomerata.
    Insect Science 01/2012; · 1.79 Impact Factor
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    ABSTRACT: Herbivore-induced plant volatiles (HIPV) provide important information that influences host location behaviour for insect natural enemies, such as parasitoid wasps, that develop in the bodies of herbivorous insects. The dietary breadth of both the parasitoid and its host may affect the extent to which a searching parasitoid relies on HIPV. Specialist species are expected to rely on specific volatile cues to which they respond innately, whereas generalists are expected to show a higher degree of phenotypic plasticity that depends on foraging experience in the parasitoid. We compared the response to HIPV emitted by different plant species damaged by host and nonhost caterpillars for two congeneric parasitoid species, the specialist Diadegma semiclausum and the generalist Diadegma fenestrale, attacking caterpillars of the diamondback moth, Plutella xylostella. For the three tested plant species, Brassica oleracea, a feral Brassica population and Sinapis alba, both parasitoid species preferred volatiles from host-infested plants over those produced by undamaged plants. However, both parasitoid species only distinguished between volatiles induced by host and nonhosts when the caterpillars had been feeding on B. oleracea, the plant on which they had been reared. Chemical analysis of the volatile blends could not explain volatile preferences of the parasitoids. Despite the difference in their dietary breadth, the two parasitoids responded similarly to HIPV and experience treatments. A flexible response to a wide array of volatile blends by parasitoids is probably important in nature, given that different generations of the host and the parasitoid probably develop on different food plants.
    Animal Behaviour 01/2012; 83:1231-1242. · 3.07 Impact Factor
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    ABSTRACT: 1. Intrinsic competition was compared in three species of braconid wasps, the solitary Meteorus pulchricornis Wesmael, and the gregarious Cotesia kariyai (Watanabe) and Cotesia ruficrus Haliday in caterpillars of their common host, the armyworm Mythimna separata Walker. Competition was determined in pair-wise contests consisting of simultaneous and subsequent parasitisms at various time intervals between the first and second attacks (
    Ecological Entomology 01/2012; · 1.95 Impact Factor
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    ABSTRACT: Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.
    Ecology 10/2010; 91(10):3027-36. · 5.18 Impact Factor
  • J A Harvey, E.H. Poelman, R. Gols
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    ABSTRACT: In many parts of the world, the larvae of the cabbage white butterflies, Pieris rapae and P. brassicae, are considered to be major pests in several economically important brassicaceous crops including various cultivars of cabbage and mustard. Thus far, biological control of these pests has focused on parasitoids including species in the genus Cotesia. We examined interactions between the solitary ichneumonid parasitoid, Hyposoter ebeninus, developing in 1st to 3rd (L1–L3) larval instars of both P. rapae and P. brassicae. H. ebeninus is common in central and southern Europe, but has thus far received little attention as a possible biological control agent of cabbage butterflies. Larvae of both pierids continued to grow after they were parasitized, and development was only arrested some 5–7 days later. Caterpillars parasitized in the third instar grew significantly larger than larvae parasitized as L1 or L2. Adult parasitoid body mass was inversely correlated with host instar parasitized, and female wasps were significantly larger than male wasps. Egg-to-adult development time in H. ebeninus did not vary between the two hosts, but the parasitoid exhibited protandry. Parasitoid survival was generally higher in larvae of P. rapae than in larvae of P. brassicae, but varied with instar in the two hosts. Our study shows that H. ebeninus has promise as a biological control agent, particularly against its more suitable host, P. rapae.
    Biological Control 53 (2010) 3. 01/2010;
  • J A Harvey, R. Wagenaar, T.M. Bezemer
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    ABSTRACT: Thus far, few studies have compared life-history traits amongst secondary parasitoids attacking and developing in cocoons of their primary parasitoid hosts. This study examines development and reproduction in Lysibia nana Gravenhorst and Acrolyta nens Hartig (both Hymenoptera: Ichneumonidae), two related and morphologically similar secondary parasitoids that attack pupae of the gregarious endoparasitoid, Cotesia glomerata L. (Hymenoptera: Braconidae). On black mustard, Brassica nigra L. (Brassicaceae) plants in a field plot, adults of L. nana and A. nens frequently emerged from the same cocoon broods of C. glomerata. Based on similarities in their phylogeny and morphology, it was hypothesized that both species would exhibit considerable overlap in other life-history traits. In both L. nana and A. nens, adult wasp size increased with host cocoon mass at parasitism, although L. nana wasps were slightly larger than A. nens wasps, and completed their development earlier. Adult females of both species emerged with no eggs but matured eggs at similar rates over the following days. When provided with 20 host cocoons daily, fecundity in female L. nana was slightly more skewed towards early life than in A. nens, although lifetime fecundity did not differ between the two species. Longevity was significantly reduced in females of both species that were provided with hosts. Both parasitoids were found to exhibit strong similarities in life-history and development traits and in their ecological niche, thereby supporting our general hypothesis. Competition between L. nana and A. nens is presumably diffused because their preferred host (C. glomerata) is relatively abundant in open habitats.
    Entomologia Experimentalis et Applicata 01/2009; · 1.71 Impact Factor
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    ABSTRACT: In recent years, increasing attention has been paid in exploring the role of direct plant defence, through the production of allelochemicals, on the performance of parasitoid wasps and their hosts. However, few studies have determined if parasitoids can detect differences in plant quality and thus preferentially attack hosts on which their progeny develop most successfully. In this study we examined the development and preference of two endoparasitoids, Diadegmasemiclausum and Cotesia glomerata, developing in larvae of their respective hosts, Plutella xylostella and Pieris brassicae. In turn, these were reared on different wild populations of black mustard Brassica nigra originating in the Netherlands and Sicily (Italy), as well as single cultivated strains of B. nigra and brown mustard, B. juncea. Chemical analyses of foliar glucosinolates and volatile emissions by P. xylostella-damaged plants revealed large differences between B. nigra and B. juncea plants, with smaller differences among the B. nigra populations. The four mustard populations differentially affected development time and body mass of the herbivores and parasitoids. Contrasts among the means revealed significant differences mainly between B. nigra and B. juncea. Both parasitoids, however, preferred to alight on plants in which their progeny developed most successfully. In behavioural bioassays, D. semiclausum did not discriminate among the B. nigra populations and preferred to alight on B. juncea, which was the best plant population for parasitoid development. By contrast, C. glomerata females exhibited the lowest preference for Italian B. nigra populations, on which adult parasitoid size was the smallest. These results reveal that parasitoids can detect even small differences in plant quality presumably through their volatile blends and that plant preference and offspring performance in the two species are 'optimally synchronized'.
    Oikos 01/2009; 118:733-743. · 3.33 Impact Factor
  • R. Soler, T.M. Bezemer, J A Harvey
    Relaciones entre organismos en los sistemas hosepederos-parasitoides simbiontes. 01/2009;
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    ABSTRACT: The oviposition choice of an insect herbivore is based on a complex set of stimuli and responses. In this study, we examined the effect of plant secondary chemistry (the iridoid glycosides aucubin and catalpol) and aspects of size of the plant Plantago lanceolata, on the oviposition behavior of the specialist butterfly Melitaea cinxia. Iridoid glycosides are known to deter feeding or decrease the growth rate of generalist insect herbivores, but can act as oviposition cues and feeding stimulants for specialized herbivores. In a previous observational study of M. cinxia in the field, oviposition was associated with high levels of aucubin. However, this association could have been the cause (butterfly choice) or consequence (plant induction) of oviposition. We conducted a set of dual- and multiple-choice experiments in cages and in the field. In the cages, we found a positive association between the pre-oviposition level of aucubin and the number of ovipositions. The association reflects the butterfly oviposition selection rather than plant induction that follows oviposition. Our results also suggest a threshold concentration below which females do not distinguish between levels of iridoid glycosides. In the field, the size of the plant appeared to be a more important stimulus than iridoid glycoside content, with bigger plants receiving more oviposition than smaller plants, regardless of their secondary chemistry. Our results illustrate that the rank of a cue used for oviposition may be dependent on environmental context.
    Journal of Chemical Ecology 08/2008; 34(9):1202-12. · 2.46 Impact Factor
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    ABSTRACT: Plants attacked by herbivorous insects emit volatile compounds that attract predators or parasitoids of the herbivores. Plant fitness increases when these herbivorous insects are parasitized by solitary parasitoids, but whether gregarious koinobiont parasitoids also confer a benefit to plant fitness has been disputed. We investigated the relationship between parasitoid load of the gregarious Cotesia glomerata (L.) (Hymenoptera: Braconidae), food consumption by larvae of their host Pieris brassicae L. (Lepidoptera: Pieridae), and seed production in a host plant, Brassica nigra L. (Brassicaceae), in a greenhouse experiment. Plants damaged by caterpillars containing single parasitoid broods produced a similar amount of seeds as undamaged control plants and produced significantly more seeds than plants with unparasitized caterpillars feeding on them. Increasing the parasitoid load to levels likely resulting from superparasitization, feeding by parasitized caterpillars was significantly negatively correlated with plant seed production. Higher parasitoid brood sizes were negatively correlated with pupal weight of Cotesia glomerata, revealing scramble competition leading to a fitness trade-off for the parasitoid. Our results suggest that in this tritrophic system plant fitness is higher when the gregarious parasitoid deposits a single brood into its herbivorous host. A prediction following from these results is that plants benefit from recruiting parasitoids when superparasitization is prevented. This is supported by our previous results on down-regulation of synomone production when Brassica oleracea was fed on by parasitized caterpillars of P. brassicae. We conclude that variable parasitoid loads in gregarious koinobiont parasitoids largely explain existing controversies about the putative benefit of recruiting these parasitoids for plant reproduction.
    Entomologia Experimentalis et Applicata 07/2008; 128:172-183. · 1.71 Impact Factor
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    ABSTRACT: In nature, individuals of short-lived plant species (e.g. annuals, biennials) may grow at different times during the growing season. These plants are therefore exposed to different season-related conditions such as light and temperature, which in turn may have consequences for primary and secondary chemistry of the plant. Despite this, many studies examining plant–consumer interactions are performed in single replicates, which may thus ignore temporal variation in the expression of phenotypic plant traits that affect multitrophic interactions. In the present study, we demonstrated that even under strictly controlled conditions in a greenhouse, secondary plant chemistry changes dramatically in plants growing at different times in a single year, i.e. July, August and November. Glucosinolate (GS) contents in herbivore-damaged leaves of two different crucifer species, Brassica oleracea and Sinapis alba were higher in the August and November replicates than in the July replicate and GS concentrations were 10–25 times higher in S. alba than in B. oleracea. The development of a specialist herbivore, Plutella xylostella, also varied significantly over the three replicates. Larvae of P. xylostella that had fed upon either S. alba or B. oleracea, attained the largest biomass and had the fastest development rate in the November replicate. Female P. xylostella moths grew larger on S. alba than on B. oleracea, whereas male biomass was not significantly affected by host-plant species. Plant species, but not season also affected performance of the endoparasitoid, Diadegma semiclausum. Similar to the performance of host females, parasitoid males developed faster and attained the highest biomass when attacking P. xylostella larvae feeding on S. alba. Most importantly, the performance of the herbivore and its parasitoid only appeared to partially conform to levels of GS in damaged leaves, indicating that there is a complex of factors involved in determining the effects of plant quality on higher trophic levels.ZusammenfassungIn der Natur können Individuen von kurzlebigen Pflanzenarten (z.B. Annuelle, Bianuelle) zu verschiedenen Zeiten in der Saison wachsen. Diese Pflanzen sind daher unterschiedlichen jahreszeitlichen Bedingungen wie Licht und Temperatur ausgesetzt, was wiederum Konsequenzen für die primäre und sekundäre Chemie der Pflanze haben kann. Trotzdem sind viele Untersuchungen, welche die Pflanzen-Konsumenten-Interaktionen untersuchen, einfache Ansätze, die so die zeitliche Variation in der Expression von Pflanzenmerkmalen ignorieren, die Einfluss auf multitrophische Interaktionen hat. In der vorliegenden Untersuchung zeigten wir, dass sich selbst unter den strikt kontrollierten Bedingungen im Gewächshaus die sekundäre Pflanzenchemie bei Pflanzen, die zu verschiedenen Zeiten in einem einzigen Jahr, d.h. im Juli, August und November, wuchsen, dramatisch ändert. Die Gehalte an Glukosinolat (GS) in den von Herbivoren beschädigten Blättern von zwei Kreuzblütlerarten, Brassica oleracea und Sinapis alba, waren im August- und November-Ansatz höher als im Juli-Ansatz und die GS-Konzentrationen waren bei S. alba zehn bis zwanzigfach höher als bei B. oleracea. Die Entwicklung des spezialisierten Herbivoren Plutella xylostella, variierte ebenfalls signifikant bei den drei Ansätzen. Die Larven von P. xylostella, die sowohl auf S. alba als auch auf B. oleracea fraßen, erreichten beim November-Ansatz die größte Biomasse und hatten die schnellste Entwicklungsrate. Weibliche P. xylostella Falter wuchsen auf S. alba schneller als auf B. oleracea, während sich die Biomasse der Männchen nicht signifikant zwischen den Wirtsarten unterschied. Die Performanz des Endoparasiten Diadegma semiclausum wurde von der Pflanzenart, nicht aber von der Jahreszeit, beeinflusst. Vergleichbar zur Performanz der Wirtsweibchen entwickelten sich die Parasitoidenmännchen schneller und erreichten die höchste Biomasse, wenn sie P. xylostella Larven befielen, die auf S. alba fraßen. Vor allem aber schien die Performanz des Wirtes und seiner Parasitoiden nur teilweise mit den Gehalten von GS in den beschädigten Blättern übereinzustimmen, was darauf hinweist, dass es einen Komplex von Faktoren gibt, die den Einfluss der Pflanzenqualität auf höhere trophische Ebenen bestimmen.
    Basic and Applied Ecology 07/2008; 8(5):421-433. · 2.70 Impact Factor
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    ABSTRACT: Black mustard, Brassica nigra (L.) Koch, is a wild annual species found throughout Europe and fed on by larvae of the large cabbage-white butterfly, Pieris brassicae L. We examined the impact of herbivory from P. brassicae, a gregarious herbivore, on B. nigra grown from wild seed collected locally. In greenhouse studies, the response of B. nigra to four herbivore densities in two developmental stages of the plant was quantified by measuring leaf damage, plant height, days to flowering, silique number, and seed production. Pieris brassicae readily attacked B. nigra leaves, although the timing of the attack did not affect seed production; attacked plants produced as many seeds as as nonattacked plants. Plant height was affected when plants were attacked early, but not later, in development, suggesting a connection between their belowground zone of influence and ability to regain biomass. These results demonstrate that at the herbivore densities and timing of damage studied, B. nigra tolerates folivory from Pieris brassicae through compensation.
    Botany 05/2008; 86:641-648. · 1.23 Impact Factor
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    ABSTRACT: Black mustard, Brassica nigra (L.) Koch, is a wild annual species found throughout Europe and fed on by larvae of the large cabbage-white butterfly, Pieris brassicae L. We examined the impact of herbivory from P. brassicae, a gregarious herbivore, on B. nigra grown from wild seed collected locally. In greenhouse studies, the response of B. nigra to four herbivore densities in two developmental stages of the plant was quantified by measuring leaf damage, plant height, days to flowering, silique number, and seed production. Pieris brassicae readily attacked B. nigra leaves, although the timing of the attack did not affect seed production; attacked plants produced as many seeds as as nonattacked plants. Plant height was affected when plants were attacked early, but not later, in development, suggesting a connection between their belowground zone of influence and ability to regain biomass. These results demonstrate that at the herbivore densities and timing of damage studied, B. nigra tolerates folivory from Pieris brassicae through compensation.
    Botany-botanique - BOTANY. 01/2008; 86(6):641-648.
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    ABSTRACT: Most studies on plant defenses against insect herbivores investigate direct and indirect plant defenses independently. However, these defenses are not necessarily mutually exclusive. Plant metabolites can be transmitted through the food chain and can also affect the herbivore's natural enemies. A conflict may arise when a natural enemy is attracted to a plant that is suboptimal in terms of its own fitness. In addition, plant defenses are often studied in cultivated plant species in which artificial selection may have resulted in reduced resistance against insect herbivores. In this study, we investigated both direct and indirect plant defenses in two closely related wild brassicaceous plant species, Brassica nigra L. and Sinapis arvensis L. The herbivore Pieris brassicae L. (Lepidoptera: Pieridae), which is specialized on brassicaceous plant species, developed faster and attained higher pupal mass when reared on B. nigra than on S. arvensis. In contrast, Cotesia glomerata L. (Hymenoptera: Braconidae), which is a gregarious endoparasitoid of P. brassicae caterpillars, developed equally well on P. brassicae irrespective of the food plant on which its host had been reared. The feeding strategy of the parasitoid larvae, that is, selectively feeding on hemolymph and fat body, is likely to allow for a much wider host-size range without affecting the size or development time of the emerging parasitoids. In flight chamber experiments, C. glomerata, which had an oviposition experience in a host that fed on Brussels sprout, exhibited significant preference for host-damaged B. nigra over host-damaged S. arvensis plants. Headspace analysis revealed quantitative and qualitative differences in volatile emissions between the two plant species. This parasitoid species may use a range of cues associated with the host and the host's food plant in order to recognize the different plant species on which the host can feed. These results show that there is no conflict between direct and indirect plant defenses for this plant¿host¿parasitoid complex.
    Entomologia Experimentalis et Applicata 01/2008; 128:99-108. · 1.71 Impact Factor
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    ABSTRACT: Plants can act as vertical communication channels or `green phones¿ linking soil-dwelling insects and insects in the aboveground ecosystem. When root-feeding insects attack a plant, the direct defense system of the shoot is activated, leading to an accumulation of phytotoxins in the leaves. The protection of the plant shoot elicited by root damage can impair the survival, growth and development of aboveground insect herbivores, thereby creating plant-based functional links between soil-dwelling insects and insects that develop in the aboveground ecosystem. The interactions between spatially separated insects below- and aboveground are not restricted to root and foliar plant-feeding insects, but can be extended to higher trophic levels such as insect parasitoids. Here we discuss some implications of plants acting as communication channels or `green phones¿ between root and foliar-feeding insects and their parasitoids, focusing on recent findings that plants attacked by root-feeding insects are significantly less attractive for the parasitoids of foliar-feeding insects
    Plant Signaling & Behavior 3 (2008) 8. 01/2008;
  • Plant signaling & behavior 01/2008;
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    ABSTRACT: Interactions between butterflies and caterpillars in the genus Pieris and plants in the family Brassicaceae are among the best explored in the field of insect-plant biology. However, we report here for the first time that Pieris brassicae, commonly assumed to be a typical folivore, actually prefers to feed on flowers of three Brassica nigra genotypes rather than on their leaves. First- and second-instar caterpillars were observed to feed primarily on leaves, whereas late second and early third instars migrated via the small leaves of the flower branches to the flower buds and flowers. Once flower feeding began, no further leaf feeding was observed. We investigated growth rates of caterpillars having access exclusively to either leaves of flowering plants or flowers. In addition, we analyzed glucosinolate concentrations in leaves and flowers. Late-second- and early-third-instar P. brassicae caterpillars moved upward into the inflorescences of B. nigra and fed on buds and flowers until the end of the final (fifth) instar, after which they entered into the wandering stage, leaving the plant in search of a pupation site. Flower feeding sustained a significantly higher growth rate than leaf feeding. Flowers contained levels of glucosinolates up to five times higher than those of leaves. Five glucosinolates were identified: the aliphatic sinigrin, the aromatic phenylethylglucosinolate, and three indole glucosinolates: glucobrassicin, 4-methoxyglucobrassicin, and 4-hydroxyglucobrassicin. Tissue type and genotype were the most important factors affecting levels of identified glucosinolates. Sinigrin was by far the most abundant compound in all three genotypes. Sinigrin, 4-hydroxyglucobrassicin, and phenylethylglucosinolate were present at significantly higher levels in flowers than in leaves. In response to caterpillar feeding, sinigrin levels in both leaves and flowers were significantly higher than in undamaged plants, whereas 4-hydroxyglucobrassicin leaf levels were lower. Our results show that feeding on flower tissues, containing higher concentrations of glucosinolates, provides P. brassicae with a nutritional benefit in terms of higher growth rate. This preference appears to be in contrast to published negative effects of volatile glucosinolate breakdown products on the closely related Pieris rapae.
    Journal of Chemical Ecology 11/2007; 33(10):1831-44. · 2.46 Impact Factor
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    ABSTRACT: Host size is considered a reliable indicator of host quality and an important determinant of parasitoid fitness. Koinobiont parasitoids attack hosts that continue feeding and growing during parasitism. In contrast with hemolymph-feeding koinobionts, tissue-feeding koinobionts face not only a minimum host size for successful development but also a maximum host size, because consumption of the entire host is often necessary for successful egression. Here we study interactions between a generalist tissue-feeding larval endoparasitoid, Hyposoter didymator Thunberg (Hymenoptera: Ichneumonidae) and two of its natural hosts, Spodoptera exigua Hübner and Chrysodeixis chalcites Esper (Lepidoptera: Noctuidae). Larvae of C. chalcites are up to three times larger than corresponding instars of S. exigua and also attain much higher terminal masses before pupation. We hypothesized that the range of host instars suitable for successful parasitism by H. didymator would be much more restricted in the large host C. chalcites than in the smaller S. exigua. To test this hypothesis, we monitored development of H. didymator in all instars of both host species and measured survival, larval development time, and adult body mass of the parasitioid. In contrast with our predictions, C. chalcites was qualitatively superior to S. exigua in terms of the survival of parasitized hosts, the proportion of parasitoids able to complete development, and adult parasitoid size. However, in both hosts, the proportion of mature parasitoid larvae that successfully developed into adults was low at the largest host sizes. Our results suggest that qualitative, as well as quantitative, factors are important in the success of tissue-feeding parasitoids.
    Environmental Entomology 11/2007; 36(5):1048-53. · 1.31 Impact Factor