Locust epidemic: history repeated?

A major brown locust outbreak is again looming as large numbers of flying swarms, many 5km to 10km long, spread across the Central Karoo. Dr Dick Brown, a noted locust entomologist, ­interprets the signs of what may soon be coming.

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A major brown locust outbreak is again looming as large numbers of flying swarms, many 5km to 10km long, spread across the Central Karoo. Dr Dick Brown, a noted locust entomologist, ­interprets the signs of what may soon be coming.

Motorists travelling from the Northern Cape gasped in awe as clouds of migrating brown locust swarms blazed their way across the N1 highway south of Richmond in the Central Karoo in mid-November.

Just as in the 1930s, when long-suffering SA farmers were recovering from the aftershocks of severe droughts, along came enormous swarms of locusts to deliver another knockout blow to their newly planted crops and add to their woes. The two major farming calamities somehow always went hand in hand.

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Extensive drought-breaking rains fell across the Great and Central Karoo this year, greening the veld and triggering the start of the locust’s life cycle. Widespread and synchronised hatching of brown locust eggs underground occurred in early September, resulting in masses of gregarious rooibaaidjie hopper bands and young flier concentrations developing over vast areas in October. With the locust floodgates open and with millions of these insects coming on the wing and forming fast-flying airborne swarms in November, the control capacity of the embattled agriculture department’s locust control organisation was soon stretched to its limits. Judging by the visual evidence of the picture (below), it seems the locusts won the first round of the fight.

Looking to the future
It is now six to nine years since the last major upsurge of brown locusts in the Karoo died down in 1997, with a final burst of activity again in 2000 in the north Western Cape. Although you would need a crystal ball to accurately predict the course of future locust developments, which are complex and depend heavily on weather-related events – at best notoriously unpredictable – it is nevertheless possible to deduce probable events by analysing historic brown locust outbreak records.

Locust entomologists are of the opinion that the time is now ripe for another major brown lo cust eruption as they are known to take place every decade or so. All will now depend on the amount and distribution of summer rain received in the Karoo in December and January, and the success of the ensuing second locust generation that will likely then emerge.

Very serious brown locust upsurges have in the past been shown to be regularly associated with major rainfall events early in the season – as have now already occurred – with good follow-up summer rains afterwards. The other essential element is that swarms of the first locust generation migrate unchecked over much of the Karoo and seed large areas with egg beds – as they are now doing. Some of the fundamental requirements for a major upsurge are therefore already falling into place. Only time will tell what will happen next, but it would be best for those charged with anti-locust control to be aware of these developments and to be prepared to deal with such an eventuality.

In the late 1990s a critical mass was reached when a brown locust population completed at least three successive generations during one summer when rainfall was sufficient to enable them to breed and spread to all parts of the Karoo.

This being the case, and conditional on swarming going largely uncontrolled, the situation then deteriorates to assume explosive proportions (and from the locust control perspective, is virtually unstoppable) with swarms breaking out of the Karoo and invading adjacent crop farming areas. Losses of grain and pasture may then follow. At this point, migrating swarms may also cross into neighbouring countries, as they last did in the 1985/86 season, resulting in a major locust emergency in Southern Africa.
Call Dr Dick Brown on (012) 460 6490. |fw