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To promote circularity in agriculture, the residual –streams from the production of insects as feed and food, such as insect exuviae (moulted skins), can be a sustainable novel organic soil amendment for crop production. Organic soil amendments can influence soil composition by providing nutrients and stimulating the growth of beneficial microorganisms. Soil composition significantly impacts plant growth and resistance against herbivores. However, little is known about the effect of soil composition on flower visitors and seed production. Here, black soldier fly (BSF; Hermetia illucens) exuviae was added to soil to investigate the effects on plant growth, plant resistance against two insect herbivores, and the consequences for attraction of pollinators and seed yield. Brassica nigra seeds were sown in field soil or in field soil mixed with powdered BSF exuviae. Three-week-old plants and the soil of each pot were planted in a common garden. The effects on vegetative and flower traits, interactions with flower visitors and seed yield were quantified. In addition, the performance of the leaf-chewing larvae of Pieris brassicae and the piercing-sucking aphid Brevicoryne brassicae were assessed. Brassica nigra plants grown on soil amended with BSF exuviae showed increased growth, had more flowers and flower visitors, and higher seed production. Herbivory neither affected number of flowers nor seed production, suggesting tolerance and compensatory growth responses to herbivory compared to plants growing in soil without the addition of BSF exuviae. After five weeks fewer aphids were found on plants growing in amended soil. Our findings show that BSF exuviae added to soil can positively affect tolerance to herbivory and seed production of B. nigra, an insect-pollinated plant species. Moreover, adding insect exuviae as soil amendment in the field benefits plant-pollinator mutualism and seed yield even during herbivore attack in the field. Use of by-products from insect production as soil amendment can contribute to sustainable agricultural practices along with the conservation of ecosystem services.

Soil composition and herbivory are two environmental factors that can affect plant traits including flower traits, thus potentially affecting plant–pollinator interactions. Importantly, soil composition and herbivory may interact in these effects, with consequences for plant fitness. We assessed the main effects of aboveground insect herbivory and soil amendment with exuviae of three different insect species on visual and olfactory traits of Brassica nigra plants, including interactive effects. We combined various methodological approaches including gas chromatography/mass spectrometry, spectroscopy and machine learning to evaluate changes in flower morphology, colour and the emission of volatile organic compounds (VOCs). Soil amended with insect exuviae increased the total number of flowers per plant and VOC emission, whereas herbivory reduced petal area and VOC emission. Soil amendment and herbivory interacted in their effect on the floral reflectance spectrum of the base part of petals and the emission of 10 VOCs. These findings demonstrate the effects of insect exuviae as soil amendment on plant traits involved in reproduction, with a potential for enhanced reproductive success by increasing the strength of signals attracting pollinators and by mitigating the negative effects of herbivory.

Insects such as the black soldier fly (BSF) are a nutritious feed component for livestock with high protein levels. BSF can be reared on a wide range of organic residual streams. This allows for local production within a circular agriculture, decoupling livestock production from import of expensive feed components, such as fishmeal or soymeal. Rearing of BSF can be done by smallholder farmers, thus contributing to their livelihood, economic sustainability and social status. Smallholder farmers contribute importantly to food security, which is a prerequisite for a stable society. In armed conflicts, smallholder farmers are usually the first to suffer. In countries recovering from conflict, agricultural development should focus on restoring food production by smallholder farmers, improving their socio-economic position, thereby contributing to sustainable development goals 2 (zero hunger) and 16 (peace and justice). Here, we focus on these SDGs with an example of reintegration of ex-combatants as smallholder insect producers in post-conflict Colombia.

Beneficial soil microorganisms can contribute to biocontrol of plant pests and diseases, induce systemic resistance (ISR) against attackers, and enhance crop yield. Using organic soil amendments has been suggested to stimulate the abundance and/or activity of beneficial indigenous microbes in the soil. Residual streams from insect farming (frass and exuviae) contain chitin and other compounds that may stimulate beneficial soil microbes that have ISR and biocontrol activity. Additionally, changes in plant phenotype that are induced by beneficial microorganisms may directly influence plant–pollinator interactions, thus affecting plant reproduction. We explore the potential of insect residual streams derived from the production of insects as food and feed to promote plant growth and health, as well as their potential benefits for sustainable agriculture.

1. Pollinating insects exploit visual and olfactory cues associated with flower traits indicative of flower location and reward quality. Pollination can induce changes in these flower-associated cues, thereby influencing the behaviour of flower visitors. 2. This study investigated the main cues exploited by the syrphid fly Episyrphus balteatus and the butterfly Pieris brassicae when visiting flowers of Brassica nigra and Raphanus sativus plants. Whether pollen is used as a cue and whether pollination-induced changes affect flower volatile emission and the behavioural responses of the two pollinator species were also studied. 3. Pollinator preference was investigated by offering visual and olfactory cues individually as well as simultaneously in two-choice bioassays. Plant treatments included emasculation, hand-pollination and untreated control plants. The composition of flower volatiles from pollinated and unpollinated control plants was analysed by gas chromatography-mass spectrometry. 4. Both pollinators exhibited a strong bias for visual cues over olfactory cues. Neither pollinator used pollen as a cue. However, E. balteatus discriminated between newly opened and long-open flowers at short distance only when pollen was available. Flower visits by pollinators were influenced by pollination-induced changes in B. nigra but not R. sativus flowers. Pieris brassicae only responded to pollination-induced changes when visual and olfactory cues were offered simultaneously. The blend of volatiles emitted by B. nigra, but not R. sativus inflorescences was affected by pollination. 5. Collectively, the findings of this study show that different pollinators exploit different visual and olfactory traits when searching for flowers of two brassicaceous plant species.