agronomy Review Ecological and Human Diet Value of Locusts in a Changing World Gabriella J. Kietzka 1, * , Michel Lecoq 2 and Michael J. Samways 1   Citation: Kietzka, G.J.; Lecoq, M.; Samways, M.J. Ecological and Human Diet Value of Locusts in a Changing World. Agronomy 2021, 11, 1856. https://doi.org/10.3390/ agronomy11091856 Academic Editor: Andrea Sciarretta Received: 16 August 2021 Accepted: 9 September 2021 Published: 16 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch 7600, South Africa; samways@sun.ac.za 2 CIRAD, UMR CBGP, F-34398 Montpellier, France; mlecoq34@gmail.com * Correspondence: gabikietzka@gmail.com; Tel.: +27-81-030-4491 Abstract: Since ancient times, locusts have been serious pests wreaking havoc on settled agriculture throughout much of the world. Numerous locust practices have been developed to control infesta- tions. This has led to most commentaries portraying locust infestations only in a negative light while focusing on finding best management practices for suppressing locust populations and lessening crop damage caused by swarms. Yet, locusts are also of great ecological significance in being not only an extraordinary natural phenomenon but also major components of ecosystem nutrient cycling, arising long before settled agriculture. Furthermore, for humans, locusts are a nutritious food source, historically and currently being consumed directly. Locust control today should more regularly include their harvesting. This is now more feasible, as environmentally friendly biopesticides can be used to replace harmful organic pesticides. We focus here on the ecological significance of locusts by using calculations based on a 1 km 2 area of swarming and breeding Desert locusts, Schistocerca gregaria, and show that the huge biomass of locust individuals contributes greatly to ecosystem processes while also having great potential use in human nutrition, especially where there is an urgent need for improved dietary intake and nutrition. Keywords: Schistocerca gregaria; Desert locust; ecosystem processes; nutrient cycling; nutritional value 1. Introduction “Their (locusts) disappearance ... would not interfere with any other food chain, be- cause locusts are not the basic food of any other bird or beast. So, if we could invoke mystic powers and say, ‘All locusts, be gone’, I don’t think this would make very much difference to world ecology” [1]. This statement by Haskell (1971), during his John Curtis ‘Woodstock’ Lecture on International Locust Research and Control, whether spoken out of bravado or ignorance, disregards the ecological significance of everything in nature, even locusts. In the ancient Egyptian texts of the New Kingdom (1070–1550 BCE), locusts are positively referred to as the might of the Egyptian army while negatively as the defeated enemy armies, with ‘locusts’ being a metaphor for ‘multitude’ [2]. This double perspective has a biological equivalent: locusts as an extraordinary and ecologically important natural phenomenon yet also a harbinger of human hardship through resource loss and pestilence. A locust outbreak in the northwestern provinces, including Egypt, in the early fourth century is even thought to have led to an outbreak of rats (and their associated fleas) through an abundance of food provided by locust cadavers, which would have caused a devastating plague among the local human population [3]. A locust is a grasshopper (Orthoptera: Acrididae), normally solitarious but period- ically displaying a massive increase in abundance, largely in response to changed and favorable weather conditions [4]. The great population increase is often associated with changes in its biochemistry, physiology, morphology, and behavior, known as density- dependent phase polyphenism [5]. The changed form often becomes nomadic, causing Agronomy 2021, 11, 1856. https://doi.org/10.3390/agronomy11091856 https://www.mdpi.com/journal/agronomy