The brown locust refocussed- Knowns, unknowns and the relevance of Locustana pardalina (Walker) to Karoo ecosystems and rangeland management

Populations of brown locusts Locustana pardalina (Walk.) (Orthoptera, Acididae, Oedipodinae) alternate between resident solitaria grasshoppers in the Karoo via a transiens phase to nomadic gregaria locusts that periodically swarm across and beyond the Karoo. Concerns about crop damage led to this species being declared a pest in 1911 to be controlled with insecticides. Despite over 225 years of records of brown locust outbreak events and a considerable body of research during the early to mid-20th century, research impetus waned while outbreak events, as well as efforts at, and financial and ecological costs of chemical control, have steadily escalated. This review highlights particularly insightful field observations made by scientists between the 1920s and 1960s, which have yet to be followed up with further research. We revivify knowledge of brown locust solitaria ecology, including their diet, mainly consisting of the short grass, Enneapogon desvauxii, the cumulative build-up of egg banks with quiescent embryos, and how five to seven successive generations build up densities until crowding of nymphs brings about incipient outbreaks of gregaria locusts, which can aggregate into large swarms that depart to remote locations. Surprisingly, no quantitative records exist of the potential negative impacts at large scales of brown locusts on rangeland grazing or crop yields, nor have their potentially important roles for Karoo ecosystem functioning been well-documented. Although the quality of rangeland management affects the dynamics of outbreak centres, this recognition has not been followed up with experiments and detailed observations to make definite recommendations on farming practices. We suggest several avenues of research that build on the existing knowledge with modern techniques and fill the most important knowledge gaps to improve managing brown locust populations sustainably.

Automated summary

Populations of brown locusts in the Karoo alternate between resident solitaria grasshoppers and nomadic gregaria locusts. Despite decades of research, there is still a lack of follow-up studies on insightful field observations made in the early to mid-20th century. The potential negative impacts and important roles of brown locusts on rangeland and crop yields have not been well-documented.