Perpetual pendulum: Locustana pardalina

By Joh Henschel, Manager, SAEON Arid Lands Node

Tweet

Brown Locust, Locustana pardalina, at the Carnarvon Research Station (Picture: Joh Henschel)

In 1986, the South African government spent R50-million on locust control, which is equivalent to R500-million today. But how much do we really know about locusts ... ?

In 1916, the South African Department of Agriculture reported that "the country is under the great debt of gratitude to the discoveries and elaborations of the methods of destruction now employed and to the wisdom and foresight of the founders of the Central Locust Bureau … In all 28,000 [locust] swarms were destroyed, and some 10,000 gallons of poison and 3,556 spray pumps were issued, and 114 temporary officers employed, the total cost of the campaign amounting to about £10,000 [in current value this would be R20-million]. Although we still have much to learn about the behaviour of locusts in this country ... there is every reason to hope that if the action taken last year is persisted in, the pest may be overcome."

This could have been written today; a century later we still have much to learn about the behaviour of the Brown Locust, whose populations still periodically irrupt despite methods of destruction (aka control) having been employed persistently and developed further “with wisdom and foresight”.

Locust pendulum

Since 1797, agriculturalists have kept records of the oscillations of the Karoo Brown Locust, Locustana pardalina, with the pendulum changing from a solitary morph to gregarious, from few to many, from Karoo to across the southern African subcontinent. Then back again, from many to few, from gregarious to solitary, from subcontinental to Karoo. The locust pendulum perpetually continues despite unrelenting anthropogenic pressure, although this appears to have quickened the pendulum’s rhythm.

SAEON scientists have good reason to be interested - not only are these 200-year-long records a rare long-term dataset, but the Brown Locust is also one of the few surviving Mega-herd phenomena, which periodically reshuffle things across the Karoo.

To top it, scientists have identified a correlation between locust outbreaks and sea surface temperature patterns in this semi hemisphere, though locusts and oceans also show other uncorrelated complexities. These factors are enough to indicate that the locust pendulum warrants observing, but surprisingly, we know rather little about the Brown Locust, besides its natural history.

Swarming locusts (Picture: The Guardian)

Agriculturalists fear the collective consumptive power of billions of locusts, but have never actually quantified the economic effects of all that consumption to justify the costly control measures that have been undertaken, unquestioned.

Conservationists, in the meantime, have been concerned with the impacts of repeated large-scale applications of insecticides on all Karoo biota, while they are amazed by the Brown Locust’s incredible resilience, enduring despite determined efforts for over a century to stop them. Conservationists have not tried to find out the solution for the locust’s tenacity.

Biologists are intrigued by the complexities of different morphs of eggs, hoppers and eggs, alternating in one species. Particularly puzzling are the complexly-coded eggs of the locust’s solitary phase, whose hatching appears to be triggered by very particular combinations, timing, and sequences of seasonal rainfall and temperature, a code that could be the key to the mechanism of population outbreaks. Such complexities may be fascinating, but the mechanisms remain shrouded.

Ecologists laud the locusts’ presumed ecological roles in nutrient recycling, with swarms of locusts briefly feeding here, defecating there, and dying elsewhere, but have not actually investigated this. Furthermore, locusts are thought to lend dynamism to food webs, with numerous predators tracking locust abundance cycles and movements, altogether forming intricate patterns over time and space. Although it is thought that locusts are keystone species, critical for the integrity of Karoo ecology, this remains to be elucidated.

Small swarms of hoppers near Victoria West in the central Karoo (Pictures: Simon Todd)

Most of the research on the Brown Locust mooted at the 1987 Kimberley Locust Conference is still outstanding. By contrast, there is probably no other Karoo species for which so much money has been allocated by government continuously for over a century, not to improve understanding and conservation, but to destroy.

Multi-institutional research and monitoring plan

Alerted to the locusts' potential indicator value for global change and ecological integrity, SAEON is developing a locust research and monitoring plan (Henschel, 2015). This will take into account patterns of rainfall, drought and temperature across the Karoo, the abundance, cover, species composition, nutritional value and regrowth of grass in locust outbreak areas, the densities of locusts of the two morphs, movements of hopper bands, locust swarms, and their predators.

DID YOU KNOW? The locust was probably the first insect ever drawn by humans. This image was copied from a drawing found in a 10,000-year-old bison bone left in a French cave. Source: degreed.com

In collaboration with South African National Parks (SANParks), the Northern Cape Department of Environment and Nature Conservation (DENC) and other organisations managing nature reserves, the plan also entails comparing insecticide-treated areas with untreated areas. Participation by academic institutions is sought to investigate these parameters and test locusts as environmental indicators.

Ultimately SAEON intends to find answers to some of these intriguing questions by monitoring the perpetual locust pendulum.

We gratefully acknowledge extensive assistance and advice provided by Margaret Kieser and Roger Price of the Agricultural Research Council.

Reference

DOI:10.1080/0035919X.2015.1046974