Search

Plants face many environmental stresses that can impact their survival, development and fitness. Insects are the most diverse, abundant and threatening herbivores in nature. As a consequence, plants produce direct chemical and physical defences to reduce herbivory. They also release volatiles to recruit natural enemies that indirectly protect them from herbivory. The recruitment of parasitic wasps can benefit plant fitness because they ultimately kill their insect hosts.Recently, studies showed that parasitoids can indirectly mediate plant defences by modulating herbivore oral secretions. In addition to the direct benefits of parasitoids in terms of reducing herbivore survival, we tested if the reduction in induced defences by parasitized caterpillars compared to non‐parasitized caterpillars may reduce the costs associated with defence expression.We provide evidence that tomato plants treated with saliva from parasitized caterpillars have significantly higher fitness parameters including increased flower numbers (16.3%) and heavier fruit weight (13.5%), compared to plants treated with saliva from non‐parasitized caterpillars. Since plants were grown without actual herbivores, the higher values for these fitness parameters were due to lower costs of induced defences and not due to reduced herbivory by parasitized caterpillars. Furthermore, the resulting seed germination time was shorter and the germination rate was higher when the maternal plants were previously exposed to parasitized herbivore treatment compared to control (non‐treated) plants.Overall, application of saliva did not result in transgenerational priming of offspring defence responses. However, offspring of parents exposed to caterpillar saliva had lower constitutive levels and higher induced levels of trypsin inhibitor than offspring from unexposed parents.This study shows that the saliva of parasitized caterpillars can modulate plant defences and further demonstrates that the lower induction of plant defences is associated with elevated plant fitness in the absence of herbivore feeding, suggesting that induced plant defences are costly. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Understanding the effects of anthropogenic global warming (AGW) on species interactions is essential for predicting community responses to climate change. However, while effects of AGW on resource–consumer interactions at the first and second trophic level have been well studied, little is known about effects on interactions at higher trophic levels at the terminal end of food chains (e.g. in the third and fourth trophic levels).Here, we examined the effects of temperature variability by simulating heatwaves on functional responses of two species at the fourth trophic level (hyperparasitoids) that parasitize host species at the third trophic level (parasitoid cocoons).We found that host cocoons developed faster under simulated heatwave conditions, decreasing the temporal window of susceptibility of the host cocoons to parasitism by the two hyperparasitoids, and consequently parasitism declined with temperature. However, the effects of a simulated heatwave markedly differed among the two hyperparasitoid species; temperature and host quality had a much stronger effect on early reproduction in the less fecund hyperparasitoid Gelis agilis, than in the more fecund species Acrolyta nens.Our results suggest that exposure to heatwaves, that are expected to increase in frequency, will affect the ability of species at higher trophic levels to exploit transient resources whose suitability is temperature‐dependent. In turn, the observed effects of AGW on the functional responses of the hyperparasitoids may disrupt trophic interactions and have profound impact on population dynamics and ecological processes. A plain language summary is available for this article. Plain Language Summary [ABSTRACT FROM AUTHOR]

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The ability to cope with plant defense chemicals differs between specialist and generalist species. In this study, we examined the effects of the concentration of the two main iridoid glycosides (IGs) in Plantago lanceolata, aucubin and catalpol, on the performance of a specialist and two generalist herbivores and their respective endoparasitoids. Development of the specialist herbivore Melitaea cinxia was unaffected by the total leaf IG concentration in its host plant. By contrast, the generalist herbivores Spodoptera exigua and Chrysodeixis chalcites showed delayed larval and pupal development on plant genotypes with high leaf IG concentrations, respectively. This result is in line with the idea that specialist herbivores are better adapted to allelochemicals in host plants on which they are specialized. Melitaea cinxia experienced less post-diapause larval and pupal mortality on its local Finnish P. lanceolata than on Dutch genotypes. This could not be explained by differences in IG profiles, suggesting that M. cinxia has adapted in response to attributes of its local host plants other than to IG chemistry. Development of the specialist parasitoid Cotesia melitaearum was unaffected by IG variation in the diet of its host M. cinxia, a response that was concordant with that of its host. By contrast, the development time responses of the generalist parasitoids Hyposoter didymator and Cotesia marginiventris differed from those of their generalist hosts, S. exigua and C. chalcites. While their hosts developed slowly on high-IG genotypes, development time of H. didymator was unaffected. Cotesia marginiventris actually developed faster on hosts fed high-IG genotypes, although they then had short adult longevity. The faster development of C. marginiventris on hosts that ate high-IG genotypes is in line with the 'immunocompromized host' hypothesis, emphasizing the potential negative effects of toxic allelochemicals on the host's immune response. [ABSTRACT FROM AUTHOR]

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Larvae of the moth, Hadena bicruris, constitute the most important predispersal seed predator on Silene latifolia (Caryophyllaceae). Parasitoids attacking the larvae of this specialist noctuid can potentially decrease the amount of damage to the plant. This paper describes and quantifies the parasitoid complex associated with H. bicruris in the Netherlands, and documents life history characters of its species. Forty-four percent of larval H. bicruris were parasitized by at least 13 species of parasitoids. The most prevalent of these were the braconids Microplitis tristis (22.9%) and Bracon variator (4.9%) and the ichneumonids Eurylabus tristis (11.7%) and Ophion pteridis (3.4%). Other species occurring sporadically were: the ichneumonids Scambus brevicornis, S. buolianae, Erigorgus cerinops, and Hyposoter sp.; the tachinids Phryxe vulgaris, P. nemea, Blondelia nigripes and Siphona geniculata; and a Mermithidae sp. The ichneumonid hyperparasitoid Mesochorus lanceolatus was found occasionally in larvae of M. tristis. The hyperparasitoid ichneumonids Gelis agilis, G. hortensis and the chalcids Baryscapus endemus, Pteromalus chrysos and P. vibulenus were found in cocoons of both M. tristis and B. variator. The primary parasitoids M. tristis, E. tristis, and to a lesser extent, O. pteridis, are believed to be specialized on Hadena. The effect of the parasitoids on herbivory by their host is probably small because the most common parasitoid species are koinobionts that attack large, late instar hosts. Only B. variator and Scambus spp., which are ectoparasitoids, arrest host development immediately upon parasitism, but like the other parasitoids they kill mainly large L4 or L5 hosts. The gregarious M. tristis and B. variator produce clutches with a female-biased sex ratio, in contrast to the solitary E. tristis where the sex ratio approaches equality. The ectoparasitoid B. variator produces mostly single-sex clutches, probably avoiding deleterious effects of inbreeding. The clutch size distributions suggest that large clutches of M. tristis and B. variator are probably caused by multiple parasitisms. [ABSTRACT FROM AUTHOR]

1. The Lack clutch size theory predicts how many eggs a female should lay to maximise her fitness gain per clutch. However, for parasitoids that lay multiple clutches it can overestimate optimal clutch size because it does not take into account the future reproductive success of the parasitoid.2. From egg-limitation and time-limitation models, it is theoretically expected that (i) clutch size decreases with age if host encounter rate is constant, and (ii) clutch size should increase with host deprivation and hence with age in host-deprived individuals.3. Clutch sizes produced by ageing females of the koinobiont gregarious parasitoidMicroplitis tristisNees (Hymenoptera: Braconidae) that were provided daily with hosts, and of females ageing with different periods of host deprivation were measured.4. Contrary to expectations, during the first 2 weeks, clutch size did not change with the age of the female parasitoid, neither with nor without increasing host-deprivation time.5. After the age of 2 weeks, clutch size decreased for parasitoids that parasitised hosts daily. The decrease was accompanied by a strong decrease in available eggs. However, a similar decrease occurred in host-deprived parasitoids that did not experience egg depletion, suggesting that egg limitation was not the only factor causing the decrease in clutch size.6. For koinobiont parasitoids likeM. trististhat have low natural host encounter rates and short oviposition times, the costs of reproduction due to egg limitation, time limitation, or other factors are relatively small, if the natural lifespan is relatively short.7. Koinobiont parasitoid species that in natural situations experience little variation in host density and host quality might not have strongly evolved the ability to adjust clutch size. [ABSTRACT FROM AUTHOR]

Abstract Gregarious koinobiont parasitoids attacking a range of host sizes have evolved several mechanisms to adapt to variable host resources, including the regulation of host growth, flexibility in larval development rate, and adjustment of clutch size. We investigated whether the first two mechanisms are involved in responses of the specialist gregarious parasitoid Microplitis tristis Nees (Hymenoptera: Braconidae) to differences in the larval weight and parasitoid load of its host Hadena bicruris Hufn. (Lepidoptera: Noctuidae). In addition, we examined the effects of parasitism on food consumption by the host. Parasitoids were offered caterpillars of different weight from all five instars, and parasitoid fitness correlates, including survival, development time, and cocoon weight, were recorded. Furthermore, several host growth parameters and food consumption of parasitized and unparasitized hosts were measured. Our results show that M. tristis responds to different host weights by regulating host growth and by adjusting larval development rate. In hosts with small weights, development time was increased, but the increase was insufficient to prevent a reduction in cocoon weight, and as a result parasitoids experienced a lower chance of successful eclosion. Cocoon weight was negatively affected by parasitoid load, even though host growth was positively affected by parasitoid load, especially in hosts with small weights. Later instars were more optimal for growth and development of M. tristis than early instars, which might reflect an adaptation to the life-history of the host, whose early instars are usually concealed and inaccessible for parasitism on its food plant, Silene latifolia Krause (Caryophyllaceae). Parasitism by M. tristis greatly reduced total host food consumption for all instar stages. Whether plants can benefit directly from the attraction of gregarious koinobiont parasitoids of their herbivores is a subject of current debate. Our results... [ABSTRACT FROM AUTHOR]