Context-dependence and the development of push-pull approaches for integrated management of <i>Drosophila suzukii</i>

Sustainable pest control requires a systems approach, based on a thorough ecological understanding of an agro-ecosystem. Such fundamental understanding provides a basis for developing strategies to manipulate the pest's behaviour, distribution, and population dynamics, to be employed for crop protection. This review focuses on the fundamental knowledge required for the development of an effective push-pull approach. Push-pull is a strategy to repel a pest from a crop, while attracting it toward an external location. It often relies on infochemicals (e.g., pheromones or allelochemicals) that are relevant in the ecology of the pest insect and can be exploited as lure or repellent. Importantly, responsiveness of insects to infochemicals is dependent on both the insect's internal physiological state and external environmental conditions. This context-dependency reflects the integration of cues from different sensory modalities, the effect of mating and/or feeding status, as well as diurnal or seasonal rhythms. Furthermore, when the costs of responding to an infochemical outweigh the benefits, resistance can rapidly evolve. Here, we argue that profound knowledge on context-dependence is important for the development and implementation of push-pull approaches. We illustrate this by discussing the relevant fundamental knowledge on the invasive pest species Drosophila suzukii as an example

inducibility, severity and success of egg-killing leaf necrosis depends on plant genotype and egg clustering

Plants employ various defences killing the insect attacker in an early stage. Oviposition by cabbage white butterflies (Pieris spp.) on brassicaceous plants, including Brassica nigra, induces a hypersensitive response (HR) - like leaf necrosis promoting desiccation of eggs. To gain a deeper insight into the arms race between butterflies and plants, we conducted field and greenhouse experiments using different B. nigra genotypes. We investigated variation in HR and consequent survival of P. brassicae egg clusters. Impact of egg density, distribution type and humidity on HR formation and egg survival was tested. HR differed among plant genotypes as well as plant individuals. Egg density per plant did not affect HR formation. Remarkably, egg survival did not depend on the formation of HR, unless butterflies were forced to lay single eggs. Larval hatching success from single eggs was lower on plants expressing HR. This may be due to increased vulnerability of single eggs to low humidity conditions at necrotic leaf sites. We conclude that effectiveness of HR-like necrosis in B. nigra varies with plant genotype, plant individual and the type of egg laying behaviour (singly or clustered). By clustering eggs, cabbage white butterflies can escape the egg-killing, direct plant defence trait

Impacts of farmer field schools in the human, social, natural and financial domain : a qualitative review

The Farmer Field School (FFS) is a widely used method seeking to educate farmers to adapt agricultural decisions to diverse and variable field conditions. Out of 218 screened studies, 65 were selected to review the impact of the FFS. An analytical framework was developed with effects (outputs, outcomes and impacts) arranged according to the human, social, natural and financial domains. Impacts on non-participants of the FFS were addressed as peripheral effects. The FFS demonstrated its potential to enhance human, social, natural and financial capital of rural communities. Human capital was built in the form of critical thinking, innovation, confidence, and quality of life. Effects on social capital included mutual trust, bonding, collective action, networking, and emancipation. Natural capital was enhanced through improvements in field practices, food production, agricultural diversification, and food security. Financial capital was enhanced through increased income and profits, savings and loans schemes, with a potential to reduce poverty. The available body of evidence was unbalanced across the capital domains, providing high coverage of the natural domain but low coverage of the human, social and financial domains. In-depth case studies are needed to elucidate the interactions between livelihood assets, and the influences of the policy, institutional and external environment, in order to adjust FFS interventions aiming to optimize their impacts. Considering the positive effects the FFS can have on rural livelihoods, the FFS has potential to contribute to achieving the Sustainable Development Goals. However, quality assurance of the FFS and a balanced evaluation across the capital domains require attention.</p

Melaza contaminada por insecticidas sistémicos: riesgos para los insectos beneficiosos

El control de plagas en agricultura se basa mayoritariamente en el uso de insecticidas que pueden producir efectos nocivos en insectos beneficiosos. En varios estudios recientes, se ha demostrado que la melaza excretada por los hemípteros que se alimentan de plantas tratadas con insecticidas sistémicos puede contaminarse con dichos insecticidas, y resultar tóxica para los insectos beneficiosos que se alimentan de ella. Esta ruta de exposición ha sido demostrada para tres especies de plantas distintas, cinco insecticidas sistémicos y cuatro especies de hemípteros, por lo que puede ser una ruta de exposición muy común en diferentes agroecosistemas donde el néctar es un recurso escaso y la melaza es la principal fuente de alimentación para los insectos beneficiosos

Genotypic variation in genome-wide transcription profiles induced by insect feeding: Brassica oleracea – Pieris rapae interactions

<p>Abstract</p> <p>Background</p> <p>Transcriptional profiling after herbivore attack reveals, at the molecular level, how plants respond to this type of biotic stress. Comparing herbivore-induced transcriptional responses of plants with different phenotypes provides insight into plant defense mechanisms. Here, we compare the global gene expression patterns induced by <it>Pieris rapae </it>caterpillar attack in two white cabbage (<it>Brassica oleracea </it>var. <it>capitata</it>) cultivars. The two cultivars are shown to differ in their level of direct defense against caterpillar feeding. Because <it>Brassica </it>full genome microarrays are not yet available, 70-mer oligonucleotide microarrays based on the <it>Arabidopsis thaliana </it>genome were used for this non-model plant.</p> <p>Results</p> <p>The transcriptional responses of the two cultivars differed in timing as characterized by changes in their expression pattern after 24, 48 and 72 hours of caterpillar feeding. In addition, they also differed qualitatively. Surprisingly, of all genes induced at any time point, only one third was induced in both cultivars. Analyses of transcriptional responses after jasmonate treatment revealed that the difference in timing did not hold for the response to this phytohormone. Additionally, comparisons between <it>Pieris rapae</it>- and jasmonate-induced transcriptional responses showed that <it>Pieris rapae </it>induced more jasmonate-independent than jasmonate-dependent genes.</p> <p>Conclusion</p> <p>The present study clearly shows that global transcriptional responses in two cultivars of the same plant species in response to insect feeding can differ dramatically. Several of these differences involve genes that are known to have an impact on <it>Pieris rapae </it>performance and probably underlie different mechanisms of direct defense, present in the cultivars.</p

Parasitic wasps avoid ant-protected hemipteran hosts via the detection of ant cuticular hydrocarbons

This research was partially funded by Instituto Nacional de Investigaciones Agrarias Project RTA2017-00095 and the Conselleria d'Agricultura, Pesca i Alimentacio de la Generalitat Valenciana. A.M. was a recipient of a MSc scholarship from Bodossaki Foundation (Greece).Mouratidis, A.; Vacas, S.; Herrero, J.; Navarro-Llopis, V.; Dicke, M.; Tena Barreda, A. (2021). Parasitic wasps avoid ant-protected hemipteran hosts via the detection of ant cuticular hydrocarbons. Proceedings of The Royal Society B Biological Sciences. 288(1942):1-10. https://doi.org/10.1098/rspb.2020.1684S110288194

Order of herbivore arrival on wild cabbage populations influences subsequent arthropod community development

In plant-arthropod associations, the first herbivores to colonise a plant may directly or indirectly affect community assembly on that particular plant. Whether the order of arrival of different arthropod species further modulates community assembly and affects plant fitness remains unclear. Using wild Brassica oleracea plants in the field, we manipulated the order of arrival of early-season herbivores that belong to different feeding guilds, namely the aphid Brevicoryne brassicae and caterpillars of Plutella xylostella. We investigated the effect of herbivore identity and order of arrival on community assembly on two B. oleracea plant populations during two growth seasons. For this perennial plant, we evaluated whether foliar herbivory also affected herbivore communities on the flowers and if these interactions affected plant seed production. Aphid infestation caused an increase in parasitoid abundance, but caterpillars modulated these effects, depending on the order of herbivore infestation and plant population. In the second growth season, when plants flowered, the order of infestation of leaves with aphids and caterpillars more strongly affected abundance of herbivores feeding on the flowers than those feeding on leaves. Infestation with caterpillars followed by aphids caused an increase in flower-feeding herbivores compared to the reversed order of infestation in one plant population, whereas the opposite effects were observed for the other plant population. The impact on plant seed set in the first reproductive year was limited. Our work shows that the identity and arrival order of early season herbivores may have long-term consequences for community composition on individual plants and that these patterns may vary among plant populations. We discuss how these community processes may affect plant fitness and speculate on the implications for evolution of plant defences

The Herbivore-Induced Plant Volatile Methyl Salicylate Negatively Affects Attraction of the Parasitoid Diadegma semiclausum

The indirect defense mechanisms of plants comprise the production of herbivore-induced plant volatiles that can attract natural enemies of plant attackers. One of the often emitted compounds after herbivory is methyl salicylate (MeSA). Here, we studied the importance of this caterpillar-induced compound in the attraction of the parasitoid wasp Diadegma semiclausum by using a mutant Arabidopsis line. Pieris rapae infested AtBSMT1-KO mutant Arabidopsis plants, compromised in the biosynthesis of MeSA, were more attractive to parasitoids than infested wild-type plants. This suggests that the presence of MeSA has negative effects on parasitoid host-finding behavior when exposed to wild-type production of herbivore-induced Arabidopsis volatiles. Furthermore, in line with this, we recorded a positive correlation between MeSA dose and repellence of D. semiclausum when supplementing the headspace of caterpillar-infested AtBSMT1-KO plants with synthetic MeSA

Plant responses to butterfly oviposition partly explain preference–performance relationships on different brassicaceous species

The preference–performance hypothesis (PPH) states that herbivorous female insects prefer to oviposit on those host plants that are best for their offspring. Yet, past attempts to show the adaptiveness of host selection decisions by herbivores often failed. Here, we tested the PPH by including often neglected oviposition-induced plant responses, and how they may affect both egg survival and larval weight. We used seven Brassicaceae species of which most are common hosts of two cabbage white butterfly species, the solitary Pieris rapae and gregarious P. brassicae. Brassicaceous species can respond to Pieris eggs with leaf necrosis, which can lower egg survival. Moreover, plant-mediated responses to eggs can affect larval performance. We show a positive correlation between P. brassicae preference and performance only when including the egg phase: 7-day-old caterpillars gained higher weight on those plant species which had received most eggs. Pieris eggs frequently induced necrosis in the tested plant species. Survival of clustered P. brassicae eggs was unaffected by the necrosis in most tested species and no relationship between P. brassicae egg survival and oviposition preference was found. Pieris rapae preferred to oviposit on plant species most frequently expressing necrosis although egg survival was lower on those plants. In contrast to the lower egg survival on plants expressing necrosis, larval biomass on these plants was higher than on plants without a necrosis. We conclude that egg survival is not a crucial factor for oviposition choices but rather egg-mediated responses affecting larval performance explained the preference–performance relationship of the two butterfly species.</p