Insect exuviae as soil amendment affect flower reflectance and increase flower production and plant volatile emission

Abstract

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.

Soil amendment with insect frass and exuviae affects rhizosphere bacterial community, shoot growth and carbon/nitrogen ratio of a brassicaceous plant

“…Although amendment with house cricket exuviae clearly outperformed the synthetic fertiliser, amendment with black soldier fly frass resulted in a less strong increase in plant biomass. Insect frass and exuviae are rich in plant nutrients (Nurfikari 2022;Beesigamukama et al 2022) and insect frass can improve the growth of leafy vegetables and barley (Poveda et al 2019;Houben et al 2020;Izza Bukari et al 2021;Butnan et al 2022), while soil amendment with black soldier fly exuviae increased shoot growth and flower production of Brassica nigra (Barragán-Fonseca et al 2022b. Furthermore, soil amendment with chitin, a major component of exuviae, can stimulate the growth of lettuce and rockcress among other plant species (Debode et al 2016;Winkler et al 2017;Li et al 2022).…”

Agricultural soil legacy influences multitrophic interactions between crops, their pathogens and pollinators

“…Moreover, we have a poor understanding of how the outcomes of plantantagonist-pollinator interactions depend on broader ecological contexts, such as soil environment. While poor soil conditions could amplify the negative effects of antagonists on floral traits, high quality soil could buffer or even reverse these negative effects through overcompensation in the form of increased flower production or pollinator attraction [13][14][15]. Therefore, the costs and benefits of different agricultural soil management practices may depend on how these practices affect plant biotic interactions.…”