Locust times – monitoring populations and outbreak controls in relation to Karoo natural capital

Abstract

Three decades ago a locust conference in Kimberley deliberated on the Brown Locust Locustana pardalina (Walker), its biology, feeding ecology, population dynamics, outbreak extent and frequency, swarm movements and artificial control of outbreaks. The current paper evaluates recommendations made at this conference. In contrast to the high levels of effort and funding allocated for over a century to the control of locust swarms by means of insecticides, relatively little has been spent on research of the Brown Locust, not even to verify and characterise the actual problem. Methods of locust control have improved and environmental impacts of current applications are somewhat reduced. A critical, comprehensive cost-benefit analysis, necessary to evaluate whether costly control measures and continuous interventions are warranted, has still not been conducted. Many other knowledge gaps remain, such as the ecological significance of locusts as one of the remaining swarming phenomena of the Karoo. Swarms of locusts feed here, defecate there, and die elsewhere, while numerous predators track locust abundance cycles and movements, altogether forming intricate patterns over time and space of dynamic food webs and nutrient recycling across the Karoo and beyond. Past records of Brown Locust population irruptions and crashes in the Karoo extend over 200 years. Suggestions are made on how long-term monitoring could be continued and broadened to encompass knowledge gaps. Brown Locusts are potentially useful indicators of ecosystem integrity and climate change, a potential that should be tested.

Keywords:

• population irruption
• plague
• insecticide application
• keystone species

ACKNOWLEDGEMENTS

I thank Louis Scott for prompting me to examine long-term data in the Karoo; this paper is in honour of his lifetime work. I am grateful to Roger Price and Margaret Kieser for sharing information and impressions concerning locusts. Helga van der Merwe, Marco Pauw and three referees provided helpful comments on earlier versions of this manuscript.