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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.

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.

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.