Monitoring locust swarms

The success of locust control was dependent on the capacity of international organizations to develop effective technologies to make regular surveys in order to monitor fluctuations in locust populations. Regular surveys and careful monitoring of breeding grounds allowed the organizations and researchers to closely observe hopper bands before they reached the gregarious phase and formed massive migratory swarms.154 By focusing on preferred breeding habitats and monitoring rainfall distribution, potential breeding and swarming patterns could be identified. Aerial surveys assisted in spotting early stages of swarm formations, or scattered swarms, and were able to warn ground teams in the countries facing imminent invasion. Aerial surveillance by a single plane could cover 8,000 km2 per day. This allowed surveillance teams to estimate the sizes of swarms and their direction of movement, which were then plotted on maps and grids in order to identify potential target areas.1

Monitoring was also essential in order to support experimental research.16 Experiments were conducted to determine the activities of locusts in relation to changes in humidity, wind speed and upward convectional air currents.15' Different landscapes that the swarms crossed were also examined. In the case of the red locust, the special hydraulic conditions of the flood plain and grasslands of Lake Rukwa in Tanganyika were closely watched.158 Regarding desert locusts, their breeding patterns and synchrony with the onset of the rains were closely monitored.19 In particular, the monitoring unit paid attention to different generations of locusts that had reached high plague densities.160 Ecologists examined changes in the behavior of locusts in relation to changes in population densities, which varied between the solitary phase (during recession) and the swarming phase.161

The monitoring that operated simultaneously with research and control activities had an obvious constraint in terms of the huge budgets required, including the necessity for countries to be members of the DLCOEA. The DLCOEA used aircraft facilities and various stations linked through radio communications to respond to distress information. Using aerial photographic methods to estimate swarm sizes and other variables, fairly reliable information could be relayed in a timely fashion to the ground teams.162 Monitoring continued in order to manage temporary emergencies caused by new outbreaks and avoid diverting attention from producing vital results that would contribute to future planning.165 The reports of 1936 indicate that locust swarms were not being sighted in the northern part of Kenya—a vast arid environment occupied mostly by nomadic communities.164 In 1940, there was a false report that the threats by swarms had ended and that the countries of East Africa were no longer in immediate danger. Even so, the Desert Locust Control survey unit maintained vigilance to be able to act against incipient swarm threats. In 1948 information emerged that swarms had successfully bred in the Aden Protectorate (present-day southern Yemen). By this date, technical advice was being sought from the Anti-Locust Centre in London on appropriate actions to be taken.16’ However, delays in communication enabled the swarms to spread from the breeding grounds and cross into the Horn of Africa.166

The 1940s and 1950s were crisis periods, when series of locust swarms arrived in East Africa one after the other. The 1960s were a major turning point in experimental research, which included regular monitoring and control of the desert and red locusts. While the early 1960s experienced patterns of re-invasion—as had been reported during the previous decades—the late 1960s experienced the lowest infestation rates ever reported. It is difficult to attribute any single factor to the near extermination of the annual swarms in the 1960s167—was it a natural cycle of subsidence in the locust populations, or the cumulative effects of campaigns during earlier decades? In Chapter 10, by way of a synthesis and epilog, we bring the investigations to a close.

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