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Root herbivores pose a major threat to agricultural crops. They are difficult to control and their damage often goes unnoticed until the larvae reach their most devastating late instar stages. Crop diversification can reduce pest pressure, generally without compromising yield. We studied how different diversified cropping systems affected the oviposition and abundance of the specialist cabbage root fly Delia radicum, the most important root herbivore in Brassica crops. The cropping systems included a monoculture, pixel cropping, and four variations of strip cropping with varying intra- and interspecific crop diversity, fertilization and spatial configuration. Furthermore, we assessed whether there was a link between D. radicum and other macroinvertebrates associated with the same plants. Cabbage root fly oviposition was higher in strip cropping designs compared to the monoculture and was highest in the most diversified strip cropping design. Despite the large number of eggs, there were no consistent differences in the number of larvae and pupae between the cropping systems, indicative of high mortality of D. radicum eggs and early instars especially in the strip cropping designs. D. radicum larval and pupal abundance positively correlated with soil-dwelling predators and detritivores and negatively correlated with other belowground herbivores. We found no correlations between the presence of aboveground insect herbivores and the number of D. radicum on the roots. Our findings indicate that root herbivore presence is determined by a complex interplay of many factors, spatial configuration of host plants, and other organisms residing near the roots.

Plant enemies can indirectly affect pollinators by modifying plant traits, but simultaneous tests of herbivore and pathogen effects are lacking, and the role of floral volatiles has seldom been assessed. In this study, we tested for indirect effects of insect herbivores and pathogens on pollinator attraction via altered floral volatile emissions, and its consequences for plant fitness in Brassica rapa. Plants in the field were exposed to either no damage or damage by caterpillars (Mamestra brassicae), aphids (Brevicoryne brassicae), a leaf fungus (Sclerotinia sclerotiorum), or a bacterium (Xanthomonas campestris pv. campestris). We then recorded pollinator visits and measured floral traits (flower number, volatiles) and plant fitness-correlates. We additionally performed a greenhouse experiment with artificial floral emitters to test for effects of target volatiles on pollinator attraction. In the field experiments, relative to controls, plants subjected to herbivory by the aphid B. brassicae (but not those exposed to the other enemies) exhibited a marked reduction in the emission of two volatile organic compounds (nonanal and 2-butyl-1-octanol), experienced lower pollinator visits and produced seeds of lower quality in terms of seed biomass and germination rate, while flower output itself was not affected. Consistently, artificial emitters with reduced amounts of these volatile organic compounds were less attractive to pollinators under greenhouse conditions. Synthesis. These results provide strong evidence for volatile-mediated indirect interactions between plant enemies and pollinators ultimately impacting plant fitness, and further point at enemy and compound specificity in such effects.

Irrigation is considered a form of agricultural intensification and is of significant importance in arid and semi-arid regions, such as those in the Mediterranean basin. This region differs substantially from temperate ones, in terms of climate, land-use policies and types of agricultural systems. Therefore, how biodiversity is affected by agricultural intensification may also differ substantially from countries in north-western Europe. We investigated the effect of irrigation on butterfly diversity and abundance at two different spatial scales in an agricultural region in northern Cyprus, an area representative of typical lowland agricultural practices of the Eastern Mediterranean. We investigated how local field-scale management (irrigated vs rain-fed) and the proportion of irrigated land at a larger scale of 0.25 km2 affected the abundance and diversity of butterflies and herbaceous plant species. Butterflies and herbaceous plants were surveyed in field boundaries adjacent to agricultural fields located in paired plots that had contrasting levels of irrigation. Butterflies in the field boundaries along agricultural fields were strongly positively affected by irrigation in the adjacent fields both in terms of abundance and species diversity, whereas the effect of irrigation at the larger scale of the 0.25-km2 plot was less prominent. Species composition of butterflies and plants did not correlate. However, plant abundance and alpha diversity of the vegetation in the field boundaries correlated with both abundance and alpha diversity of the butterflies when the abundance of plants was relatively low, in particular, when grasses were omitted from the data set. Crop species associated with irrigated fields contributed to the observed patterns. Comparing the results of this study with those reported for temperate regions in northwestern Europe reveals that the effectiveness of management schemes on biodiversity depend on biogeographical region, highlighting the risk o

Plant enemies can indirectly affect pollinators by modifying plant traits, but simultaneous tests of herbivore and pathogen effects are lacking, and the role of floral volatiles has seldom been assessed. In this study, we tested for indirect effects of insect herbivores and pathogens on pollinator attraction via altered floral volatile emissions, and its consequences for plant fitness in Brassica rapa. Plants in the field were exposed to either no damage or damage by caterpillars (Mamestra brassicae), aphids (Brevicoryne brassicae), a leaf fungus (Sclerotinia sclerotiorum), or a bacterium (Xanthomonas campestris pv. campestris). We then recorded pollinator visits and measured floral traits (flower number, volatiles) and plant fitness-correlates. We additionally performed a greenhouse experiment with artificial floral emitters to test for effects of target volatiles on pollinator attraction. In the field experiments, relative to controls, plants subjected to herbivory by the aphid B. brassicae (but not those exposed to the other enemies) exhibited a marked reduction in the emission of two volatile organic compounds (nonanal and 2-butyl-1-octanol), experienced lower pollinator visits and produced seeds of lower quality in terms of seed biomass and germination rate, while flower output itself was not affected. Consistently, artificial emitters with reduced amounts of these volatile organic compounds were less attractive to pollinators under greenhouse conditions. Synthesis. These results provide strong evidence for volatile-mediated indirect interactions between plant enemies and pollinators ultimately impacting plant fitness, and further point at enemy and compound specificity in such effects.

In many animals, body size is correlated with reproductive success. Selection sometimes generates striking differences in body size between males and females (i.e. sexual size dimorphism, SSD). SSD is common in spiders (Araneae), and is typically explained by selection for larger, more fecund females and rapidly maturing, and consequently smaller, males. Within a species males and females also often vary in body size. In the false widow spider, Steatoda grossa, females are larger than males and males trade body size for rapid development and early maturation. Moreover, males vary considerably in body size, suggesting that under certain conditions there may be advantages to large size. Here, we tested the role of male body size on mating success under noncompetitive and competitive mating conditions (i.e. male–male competition) in S. grossa. We found that body size did not influence mating success or copulation duration under noncompetitive conditions, but that larger males were more successful at obtaining access to females under competitive mating conditions. Additionally, we found that total copulation duration was significantly lower when a rival male was present. Our results show a large male advantage under male–male competition, which we suggest may contribute to the high variation in male body size observed in S. grossa. We further suggest that the reduced copulation duration observed under competitive mating conditions may have potential ramifications for male and female reproductive success and we discuss how patterns of selection acting on male body size might limit the extent of SSD in this species.

In many animals, body size is correlated with reproductive success. Selection sometimes generates striking differences in body size between males and females (i.e. sexual size dimorphism, SSD). SSD is common in spiders (Araneae), and is typically explained by selection for larger, more fecund females and rapidly maturing, and consequently smaller, males. Within a species males and females also often vary in body size. In the false widow spider, Steatoda grossa, females are larger than males and males trade body size for rapid development and early maturation. Moreover, males vary considerably in body size, suggesting that under certain conditions there may be advantages to large size. Here, we tested the role of male body size on mating success under noncompetitive and competitive mating conditions (i.e. male–male competition) in S. grossa. We found that body size did not influence mating success or copulation duration under noncompetitive conditions, but that larger males were more successful at obtaining access to females under competitive mating conditions. Additionally, we found that total copulation duration was significantly lower when a rival male was present. Our results show a large male advantage under male–male competition, which we suggest may contribute to the high variation in male body size observed in S. grossa. We further suggest that the reduced copulation duration observed under competitive mating conditions may have potential ramifications for male and female reproductive success and we discuss how patterns of selection acting on male body size might limit the extent of SSD in this species.

Temperature is a major driver of species interactions as it determines many physiological and behavioural parameters of ectothermic organisms such as insects. Examining the effects of elevated temperature and extreme temperature events within and between different trophic levels is crucial for understanding their broader implications for community and ecosystem level processes. We compared parasitism success of two hymenopteran parasitoid species, Diadegma semiclausum and Cotesia vestalis, under different temperature regimes when foraging intra- and interspecifically. Both parasitoid species can be found in the same habitat and are important biological control agents of the cosmopolitan lepidopteran pest Plutella xylostella, the host species in this study. Because parasitoid density may influence parasitism success through interference competition, we first investigated the effect of parasitoid density (one to four females of the same species) on parasitism success at 22 °C. In all assays, parasitoid females were released in cages with a single plant infested with 30 hosts placed in a greenhouse or climate cabinets set at 22, 27 or 33 °C and removed after 3 h. All cages were returned to 22 °C until pupation of the parasitoids or hosts, which were then counted. When females of the same species foraged together, parasitism success increased with parasitoid density. However, when both species were foraging together, parasitism success of D. semiclausum decreased with increasing temperature at both tested densities, whereas the opposite was found for C. vestalis. Nevertheless, parasitism success of D. semiclausum was always higher than that of C. vestalis, irrespective of parasitoid density or temperature, but competitive superiority of D. semiclausum decreased with increasing temperature. Increases in the magnitude and frequency of extreme temperature events under climate change are likely to have differential effects on species involved in intimate interactions, depen

Adult female spiders lay batches of eggs in silken egg sacs, and after hatching, the spiderlings live for transient periods in their mother's web before dispersing. Sibling cannibalism is frequently observed among spiderlings of many species under conditions of food deprivation. Here, we conducted assays in small Petri dishes with different densities of newly hatched (second instar) spiderlings of the false widow spider, Steatoda grossa, using a split-clutch design. Prey (freshly killed fruit flies) availability was manipulated both numerically and temporally. Offspring from 10 different females were separated as siblings into densities of two, four, or eight spiderlings per Petri dish and these were provided with either 0 flies (starvation control), two flies, four flies, or eight flies that were replenished weekly or every 3 weeks. A further control was conducted with solitary spiderlings in Petri dishes deprived of flies. The number of surviving spiderlings per Petri dish was counted every 3 days until only one remained (or until death of the solitary spiderling). Our results show that the rate of cannibalism was lower with increasing spiderling density and when fresh flies were replenished more frequently, whereas the number of flies that were provided did not affect cannibalism. In S. grossa, juvenile cannibalism occurs primarily under conditions of extreme food limitation, although in synanthropic habitats where the spider is abundant, it may be an adaptive strategy owing to the potential scarcity of prey. Under certain conditions, cannibalism in spiderlings is adaptive by eliminating competitors and providing nutrient-rich food.

This data belongs to the paper published in Journal of Pest Science, with the title: Diverse cropping systems lead to higher larval mortality of the cabbage root fly (Delia radicum). See the published paper and the readme files for information on methods, techniques and other relevant information. Abstract: We studied how different diversified cropping systems affected the oviposition and abundance of the specialist cabbage root fly Delia radicum, the most important root herbivore in Brassica crops. The cropping systems included a monoculture, pixel cropping, and four variations of strip cropping with varying intra- and interspecific crop diversity, fertilization and spatial configuration. Furthermore, we assessed whether there was a link between D. radicum and other macroinvertebrates associated with the same plants. Cabbage root fly oviposition was higher in strip cropping designs compared to the monoculture and was highest in the most diversified strip cropping design. Despite the large number of eggs, there were no consistent differences in the number of larvae and pupae between the cropping systems, indicative of high mortality of D. radicum eggs and early instars especially in the strip cropping designs. D. radicum larval and pupal abundance positively correlated with soil-dwelling predators and detritivores and negatively correlated with other belowground herbivores. We found no correlations between the presence of aboveground insect herbivores and the number of D. radicum on the roots. Our findings indicate that root herbivore presence is determined by a complex interplay of many factors, spatial configuration of host plants, and other organisms residing near the roots.

Foraging behaviour of two parasitoid species, Cotesia vestalis and Didegma semiclausum, was studied under conditions of intra- and interspecific competition at three different temperatures, 22, 27 or 33 degrees Celsius. The two species have overlapping host niches but differ in their thermotolerance thresholds. Because the parasitoids were allowed to forage at different densities and density may influence parasitism success through interference competition, we first investigated the effect of parasitoid density on parasitism success. Adult parasitoid females were released in different numbers (1, 2, or 4) and allowed to forage for 3h in a cage with a plant infested with 30 hosts (2nd to 3rd instar Plutella xylostella caterpillars). Diadegma semiclausum was also tested at a density of 8 females. After the 3-h foraging period, the adult parasitoids were removed and the cages with parasitized caterpillars were maintained in a greenhouse at 22 degrees Celsius until parasitoid cocoons were formed. All cocoons, moth pupae and dead caterpillars were counted. Parasitism success was then calculated as the number of cocoons that were formed out of the 30 caterpillars that had initially been placed on the plants. We then continued by comparing parasitism success when both species were foraging together (one or two parasitoids of each species) at 22, 27, 33 degrees Celsius. Parasitoid were only exposed to the higher temperature regimes during foraging (3h). Cages with pararasitized caterpillars were maintained at 22 degrees Celsius until cocoon formation and parasitism success was determined as described for the density treatments. Host density was 30 in all cages and cages were considered the unit of replication., Foraging behaviour of two parasitoid species, Cotesia vestalis and Didegma semiclausum, was studied under conditions of intra- and interspecific competition at three different temperatures, 22, 27 or 33 degrees Celsius. The two species have overlapping host niches but differ in their thermotolerance thresholds. Because the parasitoids were allowed to forage at different densities and density may influence parasitism success through interference competition, we first investigated the effect of parasitoid density on parasitism success. Adult parasitoid females were released in different numbers (1, 2, or 4) and allowed to forage for 3h in a cage with a plant infested with 30 hosts (2nd to 3rd instar Plutella xylostella caterpillars). Diadegma semiclausum was also tested at a density of 8 females. After the 3-h foraging period, the adult parasitoids were removed and the cages with parasitized caterpillars were maintained in a greenhouse at 22 degrees Celsius until parasitoid cocoons were formed. All cocoons, moth pupae and dead caterpillars were counted. Parasitism success was then calculated as the number of cocoons that were formed out of the 30 caterpillars that had initially been placed on the plants. We then continued by comparing parasitism success when both species were foraging together (one or two parasitoids of each species) at 22, 27, 33 degrees Celsius. Parasitoid were only exposed to the higher temperature regimes during foraging (3h). Cages with pararasitized caterpillars were maintained at 22 degrees Celsius until cocoon formation and parasitism success was determined as described for the density treatments. Host density was 30 in all cages and cages were considered the unit of replication.

Parasitoids induce physiological changes in their herbivorous hosts that affect how plants respond to herbivory. The signature of parasitoids on induced plant responses to feeding by parasitized herbivores indirectly impacts insect communities interacting with the plant. The effect may extend to parasitoids and cause indirect interaction between parasitoids that develop inside different herbivore hosts sharing the food plant. However, this type of interactions among parasitoid larvae has received very little attention. In this study, we investigated sequential and simultaneous plant-mediated interactions among two host–parasitoid systems feeding on Brassica oleracea plants: Mamestra brassicae parasitized by Microplitis mediator and Pieris rapae parasitized by Cotesia rubecula. We measured the mortality, development time, and weight of unparasitized herbivores and performance of parasitoids that had developed inside the two herbivore species when sharing the food plant either simultaneously or sequentially. Plant induction by parasitized or unparasitized hosts had no significant effect on the performance of the two herbivore host species. In contrast, the two parasitoid species had asymmetrical indirect plant-mediated effects on each other’s performance. Cotesia rubecula weight was 15% higher on plants induced by M. mediator-parasitized hosts, compared to control plants. In addition, M. mediator development time was reduced by 30% on plants induced by conspecific but not heterospecific parasitoids, compared to plants induced by its unparasitized host. Contrary to sequential feeding, parasitoids had no effect on each other’s performance when feeding simultaneously. These results reveal that indirect plant-mediated interactions among parasitoid larvae could involve any parasitoid species whose hosts share a food plant.

This data set underlies the study that aimed to describe bacterial, fungal and nematode diversity in soil associated with wild cabbage plants (Brassica oleracea) from five different population growing naturally along the Dorset coast in the UK. Samples were taken from bulk soil, rhizosphere soil and the roots of cabbage plants in 2011 and 2012. Nematode composition and abundance was determined in bulk soil, rhizosphere and roots. Presence/absence of fungal and bacterial OTU's was determined only in rhizosphere soil in 2011., This data set underlies the study that aimed to describe bacterial, fungal and nematode diversity in soil associated with wild cabbage plants (Brassica oleracea) from five different population growing naturally along the Dorset coast in the UK. Samples were taken from bulk soil, rhizosphere soil and the roots of cabbage plants in 2011 and 2012. Nematode composition and abundance was determined in bulk soil, rhizosphere and roots. Presence/absence of fungal and bacterial OTU's was determined only in rhizosphere soil in 2011.

Cultivated plants are often much more susceptible to insect herbivores than wild-type plants. In addressing this observation, much attention has focused on a trait-based approach, and especially on how artificial selection via domestication has modified morphological and chemical traits, in particular levels of defensive secondary metabolites. However, larger scale ecological processes, such as the spatial distribution and diversity of species in a plant community, also determine how insects locate and exploit their food plants, and these differ profoundly between natural and agricultural ecosystems. In this paper we discuss these two approaches to better understand differences in levels of insect herbivory between agricultural and natural ecosystems. We argue that studies investigating the effects of secondary metabolites on insect herbivory are compromised by the methodological approach that is often used. Insect feeding assays testing the effect of reduced concentrations of secondary metabolites in domesticated plants rely on testing a limited subset of insect species, usually those that can easily be reared in the laboratory and often are agricultural pest species. The responses of these insects do not reflect the full range of responses of the species present in the plant's natural habitat. This may explain why reduced levels of secondary metabolites in crop plants may only partially explain increased susceptibility to herbivory. Hypotheses explaining larger scale patterns of insect herbivore abundance are often based on studies in agricultural settings. In our opinion, developing broad ecological hypotheses based on studies in agricultural systems do not necessarily apply to natural systems and vice versa. To fully understand how susceptibility or resistance to insect herbivory is affected by plant traits and habitat heterogeneity, these have to be studied together in both natural and agricultural settings.

Parasitoid wasps are important components of insect food chains and have played a central role in biological control programs for over a century. Although the vast majority of parasitoids exploit insect herbivores as hosts, others parasitize predatory insects and arthropods, such as ladybird beetles, hoverflies, lacewings, ground beetles, and spiders, or are hyperparasitoids. Much of the research on the biology and ecology of parasitoids of predators has focused on ladybird beetles, whose parasitoids may interfere with the control of insect pests like aphids by reducing ladybird abundance. Alternatively, parasitoids of the invasive ladybird Harmonia axyridis may reduce its harmful impact on native ladybird populations. Different life stages of predatory insects and spiders are susceptible to parasitism to different degrees. Many parasitoids of predators exhibit intricate physiological interrelationships with their hosts, adaptively manipulating host behavior, biology, and ecology in ways that increase parasitoid survival and fitness.

Climate warming is considered to be among the most serious of anthropogenicstresses to the environment, because it not only has direct effects on biodiver-sity, but it also exacerbates the harmful effects of other human-mediated threats. The associated consequences are potentially severe, particularly interms of threats to species preservation, as well as in the preservation of anarray of ecosystem services provided by biodiversity. Among the most affectedgroups of animals are insects—central components of many ecosystems—forwhich climate change has pervasive effects from individuals to communities.In this contribution to the scientists’warning series, we summarize the effectof the gradual global surface temperature increase on insects, in terms ofphysiology, behavior, phenology, distribution, and species interactions, as wellas the effect of increased frequency and duration of extreme events such as hotand cold spells, fires, droughts, and floods on these parameters. We warn that,if no action is taken to better understand and reduce the action of climatechange on insects, we will drastically reduce our ability to build a sustainablefuture based on healthy, functional ecosystems. We discuss perspectives onrelevant ways to conserve insects in the face of climate change, and we offerseveral key recommendations on management approaches that can beadopted, on policies that should be pursued, and on the involvement of thegeneral public in the protection effort.

Ecosystem engineers are species that manipulate the physical state of ecosystems and thereby affect the behaviour and ecology of other species. Mature larvae of the parsnip webworm, Depressaria radiella Goeze, chew holes in the hollow stems of Heracleum sphondylium L. into which they pupate. The stems are separated into several compartments that are separated by filamentous membranes. Holes excavated by webworm larvae attract several beneficial species of arthropods that use them for shelter in autumn, including the common earwig (Forficula auricularia L.) and the common rough woodlouse (Porcellio scaber Latreille). If artificially made holes mimic the engineering effect of D. radiella, they could be made to attract (local) communities of beneficial arthropods and perhaps facilitate overwintering habitat. We conducted a field experiment to determine whether artificial holes perforated into stem compartments of H. sphondylium mimic the natural situation with D. radiella. At five sites near the city of Leiden, the Netherlands, H. sphondylium plants were exposed to different treatments: a single hole perforated in the first, second or third stem compartment, or in all three compartments. After 3 weeks, arthropod numbers were counted inside and around hogweed stems. The arthropod community in the stems differed from that surrounding the stems; the latter consisted mainly of woodlice and wolf spiders, whereas in the stems, in addition to woodlice, many earwigs were found and no wolf spiders. Both artificial and webworm-excavated holes that were present at one site were used by woodlice and earwigs. The position of the holes along the stem did not affect the number of arthropods found in that segment, although the arthropods exhibited a tendency to move up the stems. The results show that artificial holes mimic webworm-excavated holes in that both attract the same species of beneficial arthropods.

The larvae of insect herbivores feed on plants that may vary nutritionally (qualitatively and/or quantitatively) over the course of insect development. Plant quality may change in response to interactions with the biotic environment that in turn may affect development and biomass of the insects feeding on these plants. However, the larvae of many gregariously feeding herbivores feed on comparatively small plants with limited biomass and may also experience variation in the quantity of plant food available. Pieris brassicae L. (Lepidoptera: Pieridae) is a gregarious butterfly species laying clutches of 10–150 eggs that are often laid on small brassicaceous food plants, including the plant used in this study, Brassica nigra L. (Brassicaceae). A single B. nigra plant provides insufficient resources for the development of an entire brood of P. brassicae. In this study, we investigated the effect of both plant quality and quantity on the performance of P. brassicae when feeding on B. nigra plants. When we compared the effects of changes in plant quality induced by (1) aphid infestation, (2) exposure to pathogenic and non-pathogenic bacteria, and (3) inbreeding depression, which are all biotic stresses known to change plant quality, pupal mass and larval development time of P. brassicae were fairly similar. We then examined the effects of quantitative food constraints during immature development on pupal mass, which correlated strongly with adult size, longevity, and fecundity. Female pupal mass, longevity and fecundity were negatively correlated with the duration of starvation during larval development. No significant effect of male starvation was found on female reproduction and longevity. Thus, P. brassicae larvae were more affected by quantitative than by qualitative constraints in terms of pupal mass, which strongly correlated with female reproduction.

With climate change, the occurrence of extreme weather events such as heatwaves is expected to increase. Extreme temperature events are short periods of high temperature (i.e., >95th percentile of temperature distribution), and their occurrences are difficult to predict. These extreme temperature events pose great challenges to living organisms, especially ectotherms such as insects whose body temperature is greatly influenced by environmental temperature. Temperature is known to play an essential role in driving insect performance as well as inducing behavioral changes. Exposure to extreme temperatures causes physiological damage leading to potential long-lasting effects on insect performance. We aimed at assessing the impact of direct (i.e., current) and indirect (previously experienced) exposure to extreme temperature on the oviposition success of Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae). Diadegma semiclausum is a larval endoparasitoid of Plutella xylostella L. (Lepidoptera: Plutellidae), a worldwide pest of brassicaceous crops. Oviposition success, measured as the percentage of parasitized P. xylostella, was significantly lower at 33 °C than at 25 °C. However, previous exposure to 33 °C did not significantly impact the egg-laying performance of D. semiclausum, indicating that, after a heatwave, the egg-laying performance can recover. Neither the direct nor indirect exposure to extreme temperature altered D. semiclausum host-instar preference. These results indicate that temperature directly impacts D. semiclausum parasitism performance, although more detailed research is needed to disentangle direct physiological mechanisms from behavioral responses. Overall, these study results confirm others, suggesting that control of P. xylostella by D. semiclausum is likely to be impaired by more frequent heatwaves predicted under climate change scenarios.

We conducted a field experiment to determine if artificial holes perforated into stem compartments of Heracleum sphondylium mimic the natural situation with Depressaria radiella. At five locations near the city of Leiden, the Netherlands, H. sphondylium plants were exposed to different treatments: a single hole perforated in the first, second or third stem compartment, or in all three compartments. After three weeks, arthropod numbers were counted inside and around hogweed stems., We conducted a field experiment to determine if artificial holes perforated into stem compartments of Heracleum sphondylium mimic the natural situation with Depressaria radiella. At five locations near the city of Leiden, the Netherlands, H. sphondylium plants were exposed to different treatments: a single hole perforated in the first, second or third stem compartment, or in all three compartments. After three weeks, arthropod numbers were counted inside and around hogweed stems.

The larvae of insect herbivores feed on plants that may vary qualitatively and/or quantitatively during their immature development. In this study we investigated the effects of both quantitative and qualitative differences on insect performance in an insect herbivore (gregarious Pieris brassicae caterpillars) that can be confronted with both variation in plant nutrition and plant availability during immature development. In the first experiment we compared larval performance until pupation of caterpillar on plants that differed in their nutritional quality. Plants (Brassica nigra) had been exposed to aphid infestation, pathogen infection or were in or outbred, factors that have previously been shown to affect nutritional quality of plants including B. nigra. These three factors had no or only marginal effects on pupal mass and development time until pupation. We continued by examining the effects of quantitative food constraints during immature development on pupal mass, which correlated strongly with adult size. Female pupal mass and fecundity were negatively correlated with the duration of starvation during larval development. Starvation of the male mating partner had no significant effect on female reproduction. The results showed that caterpillars of P. brassicae were more affected by quantitative than by qualitative constraints in terms of pupal mass, which strongly correlated with female reproduction., The larvae of insect herbivores feed on plants that may vary qualitatively and/or quantitatively during their immature development. In this study we investigated the effects of both quantitative and qualitative differences on insect performance in an insect herbivore (gregarious Pieris brassicae caterpillars) that can be confronted with both variation in plant nutrition and plant availability during immature development. In the first experiment we compared larval performance until pupation of caterpillar on plants that differed in their nutritional quality. Plants (Brassica nigra) had been exposed to aphid infestation, pathogen infection or were in or outbred, factors that have previously been shown to affect nutritional quality of plants including B. nigra. These three factors had no or only marginal effects on pupal mass and development time until pupation. We continued by examining the effects of quantitative food constraints during immature development on pupal mass, which correlated strongly with adult size. Female pupal mass and fecundity were negatively correlated with the duration of starvation during larval development. Starvation of the male mating partner had no significant effect on female reproduction. The results showed that caterpillars of P. brassicae were more affected by quantitative than by qualitative constraints in terms of pupal mass, which strongly correlated with female reproduction.

Plants face attackers aboveground and belowground. Insect root herbivores can lead to severe crop losses, yet the underlying transcriptomic responses have rarely been studied. We studied the dynamics of the transcriptomic response of Brussels sprouts (Brassica oleracea var. gemmifera) primary roots to feeding damage by cabbage root fly larvae (Delia radicum), alone or in combination with aboveground herbivory by cabbage aphids (Brevicoryne brassicae) or diamondback moth caterpillars (Plutella xylostella). This was supplemented with analyses of phytohormones and the main classes of secondary metabolites; aromatic, indole and aliphatic glucosinolates. Root herbivory leads to major transcriptomic rearrangement that is modulated by aboveground feeding caterpillars, but not aphids, through priming soon after root feeding starts. The root herbivore downregulates aliphatic glucosinolates. Knocking out aliphatic glucosinolate biosynthesis with CRISPR-Cas9 results in enhanced performance of the specialist root herbivore, indicating that the herbivore downregulates an effective defence. This study advances our understanding of how plants cope with root herbivory and highlights several novel aspects of insect–plant interactions for future research. Further, our findings may help breeders develop a sustainable solution to a devastating root pest.

Aphids are serious pests of many crops in agroecosystems and their biological control is focused on enhancing the performance of specialized natural enemies of aphids such as parasitoid wasps and predators like ladybirds. However, ladybirds are often attacked by their own parasitoids in the fourth trophic level that can negatively affect ladybird performance and, hence, their effectiveness as control agents. The biology and ecology of these parasitoids has been less well explored. This study compared various life-history traits in two closely related parasitoids of the seven-spot ladybird, Coccinella septempunctata (Coleoptera: Coccinellidae): Oomyzus scaposus and O. spiraculus (Hymenoptera: Eulophidae), which naturally co-occur in eastern China and are facultatively gregarious koinobiont larval-pupal endoparasitoids of ladybird beetles. They can oviposit and develop in all four larval instars of their hosts but kill and emerge from the pupae. Both parasitoids did not have a clear oviposition preference for any host instar, but oviposition duration tended to increase in first to third instar hosts. Moreover, oviposition time was significantly longer for O. spiraculus than for O. scaposus. Adult eclosion from parasitized hosts (ranging between 35 and 45%) and sex ratios (85–90% female) were similar in both species and did not differ among host instars. Brood sizes were similar in both species but tended to increase in first to third instar hosts. Egg-to-adult development time was shorter and the eclosing adults of O. scaposus were heavier than those of O. spiraculus. In both species, development time decreased with host instar at parasitism, but instar-specific effects on biomass differed between the two species: heavier O. scaposus adults developed from second and third instar hosts, whereas biomass of for O. spiraculus tended to decrease with instar at parasitism. In both species, females were significantly larger than males. Our results show that expression of

In three Dutch populations of the native small hogweed (Heracleum sphondylium), and one of the invasive giant hogweed (H. mantegazzianum), interactions between a specialist herbivore, the parsnip webworm (Depressaria radiella), and its associated parasitoids were compared during a single growing season. We found plant population and/or host plant species-related differences in the abundance of moth pupae, the specialist polyembryonic endoparasitoid, Copidosoma sosares, the specialist pupal parasitoid, Barichneumon heracliana, and a potential hyperparasitoid of C. sosares, Tyndaricus scaurus. Adult D. radiella body mass was similar across the three small hogweed populations, but moths and their pupal parasitoid B. heracliana were smaller when developing on giant than on small hogweeds where the two plants grew in the same locality (Heteren). Mixed-sex and all-male broods of C. sosares were generally bigger than all-female broods. Furthermore, adult female C. sosares were larger than males and adult female mass differed among the three small hogweed populations. The frequency of pupal parasitism and hyperparasitism also varied in the different H. sphondylium populations. These results show that short-term (intra-seasonal) effects of plant population on multitrophic insects are variable among different species in a tightly linked food chain., In three Dutch populations of the native small hogweed (Heracleum sphondylium), and one of the invasive giant hogweed (H. mantegazzianum), interactions between a specialist herbivore, the parsnip webworm (Depressaria radiella), and its associated parasitoids were compared during a single growing season. We found plant population and/or host plant species-related differences in the abundance of moth pupae, the specialist polyembryonic endoparasitoid, Copidosoma sosares, the specialist pupal parasitoid, Barichneumon heracliana, and a potential hyperparasitoid of C. sosares, Tyndaricus scaurus. Adult D. radiella body mass was similar across the three small hogweed populations, but moths and their pupal parasitoid B. heracliana were smaller when developing on giant than on small hogweeds where the two plants grew in the same locality (Heteren). Mixed-sex and all-male broods of C. sosares were generally bigger than all-female broods. Furthermore, adult female C. sosares were larger than males and adult female mass differed among the three small hogweed populations. The frequency of pupal parasitism and hyperparasitism also varied in the different H. sphondylium populations. These results show that short-term (intra-seasonal) effects of plant population on multitrophic insects are variable among different species in a tightly linked food chain.

Evolutionary arms-races between plants and insect herbivores have long been proposed to generate key innovations such as plant toxins and detoxification mechanisms that can drive diversification of the interacting species. A novel front-line of plant defence is the killing of herbivorous insect eggs. We test whether an egg-killing plant trait has an evolutionary basis in such a plant–insect arms-race. Within the crucifer family (Brassicaceae), some species express a hypersensitive response (HR)-like necrosis underneath butterfly eggs (Pieridae) that leads to eggs desiccating or falling off the plant. We studied the phylogenetic distribution of this trait, its egg-killing effect on and elicitation by butterflies, by screening 31 Brassicales species, and nine Pieridae species. We show a clade-specific induction of strong, egg-killing HR-like necrosis mainly in species of the Brassiceae tribe including Brassica crops and close relatives. The necrosis is strongly elicited by pierid butterflies that are specialists of crucifers. Furthermore, HR-like necrosis is linked to PR1 defence gene expression, accumulation of reactive oxygen species and cell death, eventually leading to egg-killing. Our findings suggest that the plants’ egg-killing trait is a new front on the evolutionary arms-race between Brassicaceae and pierid butterflies beyond the well-studied plant toxins that have evolved against their caterpillars.

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Plant chemical defences impact not only herbivores, but also organisms in higher trophic levels that prey on or parasitize herbivores. While herbivorous insects can often detoxify plant chemicals ingested from suitable host plants, how such detoxification affects endoparasitoids that use these herbivores as hosts is largely unknown. Here, we used transformed plants to experimentally manipulate the major detoxification reaction used by Plutella xylostella (diamondback moth) to deactivate the glucosinolate defences of its Brassicaceae host plants. We then assessed the developmental, metabolic, immune, and reproductive consequences of this genetic manipulation on the herbivore as well as its hymenopteran endoparasitoid Diadegma semiclausum. Inhibition of P. xylostella glucosinolate metabolism by plant-mediated RNA interference increased the accumulation of the principal glucosinolate activation products, the toxic isothiocyanates, in the herbivore, with negative effects on its growth. Although the endoparasitoid manipulated the excretion of toxins by its insect host to its own advantage, the inhibition of herbivore glucosinolate detoxification slowed endoparasitoid development, impaired its reproduction, and suppressed the expression of genes of a parasitoid-symbiotic polydnavirus that aids parasitism. Therefore, the detoxification of plant glucosinolates by an herbivore lowers its toxicity as a host and benefits the parasitoid D. semiclausum at multiple levels.

In three Dutch populations of the native small hogweed (Heracleum sphondylium L. [Apiales: Apiaceae]), and one of the invasive giant hogweed (H. mantegazzianum Sommeier \amp; Levier [Apiales: Apiaceae]), interactions between a specialist herbivore, the parsnip webworm (Depressaria radiella), and its associated parasitoids were compared during a single growing season. We found host plant species-related differences in the abundance of moth pupae, the specialist polyembryonic endoparasitoid, Copidosoma sosares, the specialist pupal parasitoid, Barichneumon heracliana, and a potential hyperparasitoid of C. sosares, Tyndaricus scaurus Walker (Hymenoptera: Encyrtidae). Adult D. radiella body mass was similar across the three small hogweed populations, but moths and their pupal parasitoid B. heracliana were smaller when developing on giant than on small hogweeds where the two plants grew in the same locality (Heteren). Mixed-sex and all-male broods of C. sosares were generally bigger than all-female broods. Furthermore, adult female C. sosares were larger than males and adult female mass differed among the three small hogweed populations. The frequency of pupal parasitism and hyperparasitism also varied in the different H. sphondylium populations. These results show that short-term (intra-seasonal) effects of plant population on multitrophic insects are variable among different species in a tightly linked food chain.