Desert locust control: The effectiveness of proactive interventions and the goal of outbreak prevention

Authors: Showler, Allan

Submitted to: American Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2018
Publication Date: 9/27/2019
Citation: Showler, A. 2019. Desert locust control: The effectiveness of proactive interventions and the goal of outbreak prevention. American Entomologist. 65(3):180-191. https://doi.org/10.1093/ae/tmz020.
DOI: https://doi.org/10.1093/ae/tmz020

Interpretive Summary: The desert locust occasionally undergoes change as a result of crowding associated with flushes of green vegetation in breeding areas in Sahelian and North Africa, the Arabian Peninsula, and South Asia. Crowding elicits a change from solitary to gregarious forms, producing marching bands of nymphs and flying swarms of adults that can invade neighboring regions, breeding further until sometimes swarms are invading other regions over consecutive years. When use of highly persistent insecticides was discontinued in the 1980s, control has relied on application of insecticides with shorter residual toxicity. There has been confusion in recent years about stages of desert locust population growth, hence, definitions of salient terminology are provided. Similarly, terminology regarding desert locust control strategies is clarified. Proactive control has been conducted with increasing efficacy from the 1990s to the present, dramatically reducing costs and the areas treated with insecticides. Comparisons of the 1986-1989, 1992-1994, 1997-1998, and 2003-2005 desert locust episodes, and the decade 2007-2016, are provided to demonstrate the efficacy of proactive control. Research has made important advances particularly in data collection, integration, and forecasting, and evolving communication methods have permitted the rapid dissemination of such information, enabling desert locust afflicted countries to anticipate and proactively control population increases that involve swarming behavior. While proaction has become increasingly effective during the last 20 years, challenges in some areas include remote and rugged terrain, poor infrastructure, armed conflict, unpreparedness, environmental concerns, politics, dogmas and assumptions, and impediments to research.

Technical Abstract: The desert locust, Schistocerca gregaria (Forskål), occasionally undergoes phase transformation as a result of population increases associated with flushes of green vegetation in often remote breeding areas in Sahelian and North Africa, the Arabian Peninsula, and South Asia. Crowding elicits the transition from the solitary form of the insect to the gregarious form, producing marching bands of nymphs and flying swarms of adults that can invade neighboring regions, breeding further until sometimes swarms are invading many regions across consecutive years. When use of persistent organochlorinated insecticides was discontinued during the 1980s, the main control tactic has been application of insecticides with shorter residual toxicity, forcing control approaches toward targeting nymhal bands and adult swarms instead of spraying longer-lasting barrier strips to kill nymphal bands that enter them. There has been some confusion in recent years about stages of desert locust population growth, hence, definitions of the terms “outbreak”, “upsurge”, “plague status”, “plague”, and “episode” are provided. Similarly, terminology regarding desert locust control strategies has previously been misrepresented and misinterpreted in some of the published literature; therefore, the definitions for “reactive”, “proactive”, “strategic”, and “preventive” strategies are clarified. Reactive control aims at protecting agricultural production against large upsurges and plagues, and it is not aimed at weakening such large episodes by spraying in breeding areas. Strategic control refers to conducting operations in breeding areas during upsurges and plagues, and it can be conducted in combination with reactive control campaigns. Proactive control occurs against outbreaks and upsurges with the aim of suppressing populations to avert population buildups to plague status, and thus represents an early intervention form of strategic control. Preventive control occurs before outbreaks in order to hold desert locust populations in the recession (solitary) phase indefinitely, but this approach has not yet been demonstrated after the persistent insecticides were banned. Proactive control has been conducted with increasing efficacy from the 1990s to the present, dramatically reducing costs and the areas treated with insecticides. Comparisons of the 1986-1989, 1992-1994, 1997-1998, and 2003-2005 desert locust episodes, and the decade 2007-2016, are provided to demonstrate the utility of proactive control. Research has made important advances particularly in data collection, integration, and forecasting, and evolving communication methods have permitted the rapid dissemination of such information, enabling desert locust afflicted countries to anticipate and proactively control population increases that involve gregarization. While proaction has become increasingly effective during the last 20 years, challenges in some areas include remote and rugged terrain, poor infrastructure, insecurity (e.g., armed conflict), unpreparedness, environmental concerns, politics, dogmas and assumptions, and impediments to research.