Black Soldier Fly Larvae Adapt to Different Food Substrates through Morphological and Functional Responses of the Midgut.

Marco Bonelli,Ling Tian,Matteo Brilli,Daniele Bruno,Gianluca Tettamanti,Silvia Caccia,Novella Gianfranceschi,Morena Casartelli

doi:10.3390/ijms21144955

Abstract

Modulation of nutrient digestion and absorption is one of the post-ingestion mechanisms that guarantees the best exploitation of food resources, even when they are nutritionally poor or unbalanced, and plays a pivotal role in generalist feeders, which experience an extreme variability in diet composition. Among insects, the larvae of black soldier fly (BSF), Hermetia illucens, can grow on a wide range of feeding substrates with different nutrient content, suggesting that they can set in motion post-ingestion processes to match their nutritional requirements. In the present study we address this issue by investigating how the BSF larval midgut adapts to diets with different nutrient content. Two rearing substrates were compared: a nutritionally balanced diet for dipteran larvae and a nutritionally poor diet that mimics fruit and vegetable waste. Our data show that larval growth performance is only moderately affected by the nutritionally poor diet, while differences in the activity of digestive enzymes, midgut cell morphology, and accumulation of long-term storage molecules can be observed, indicating that diet-dependent adaptation processes in the midgut ensure the exploitation of poor substrates. Midgut transcriptome analysis of larvae reared on the two substrates showed that genes with important functions in digestion and absorption are differentially expressed, confirming the adaptability of this organ.

Highlights

In animals, the regulation of food intake and post-ingestion mechanisms are two important and strategic aspects to ensure optimal performance and healthy conditions [1]
Since this study aims to analyze the response of the black soldier fly (BSF) larval midgut to different nutrient availability, we preliminarily determined the nutrient composition of the two diets used to rear the larvae
The former refers to the diet as fed to the larvae, the latter is computed on a moisture-free basis

Summary

Introduction

The regulation of food intake and post-ingestion mechanisms are two important and strategic aspects to ensure optimal performance and healthy conditions [1]. The presence and robustness of these mechanisms is of particular relevance in generalist feeders Their responses, which include the modulation of nutrient digestion and absorption, the redirection of metabolism, and regulation of excretory system activity, have evolved to maximize food exploitation in order to meet nutritional requirements in the case of poor (i.e., with diluted or extremely diluted nutrients) or unbalanced diets, and to compensate for the extreme variability of intake composition [1,7]. In this scenario, the gut plays a key homeostatic role, which strongly impacts on overall animal performance and fitness [1]

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