Experimental research

New insecticides were developed, and mass-produced (after field trials) for the purpose of locust control.19 The success of these insecticides was limited unless they were dissolved in certain oils to increase their potency for killing locusts. However, the resultant compound was found to be more persistent in the environment—a factor that indicates the disadvantage when applied to vegetation.140 The delays in experimenting with new insecticides and the continued use of harmful ones continued to raise uncertainties. In particular, the application of aerial sprays in remote regions that also served as dispersal areas for migratory birds highlighted the possibility that the insecticides might have undesirable effects on other creatures.141

Between 1952 and 1960, more efficient and safer control methods were developed under coordination of the FAO.142 This included rotary atomizer sprays that were more economical than other methods (such as the baiting method already mentioned, which was labor intensive). The rotary atomizer could spray swarms of locusts while in flight below the plane, thus enabling locust control over large areas within a short period of time.143 However, the application of pesticides over wider areas required the cooperation of local communities.144 The common practice was to send information about the pesticides and spraying campaigns to officials in order to warn local communities.145

Nonetheless, the Desert Locust Control Advisory Committee in East Africa was worried that an essential aspect of research was lacking, since the application of pesticides was based mostly on what was practical. Hence, in 1951 the committee requested the High Commission to approach the Colonial Office for research funds from the Development and the Welfare Grant in order to conduct more focused small-scale trials of the pesticides.

The new experiments were applied over an area of 300-400 acres in Kenya that was densely settled by locust swarms—estimated at 10 to 100 million individuals. After applying 340 gallons of dieldrin, an estimated

100,000 to one million locusts dropped dead within an hour, destroying one swarm. In June 1952 alone, 890 gallons of pesticides were used against four swarms in 21 sorties of aerial dusting. Between 31 December 1952 and 31 January 1953, about 14 swarms, each about 2 km long, were heavily dosed with 3,045 gallons of concentrated pesticides during 93 sorties across Kenya, covering a total of 644 km.146 Any locusts that had escaped from other areas, on entering Kenya were attacked using 45,425 liters of DNC poison in aerial sprays.14' The technique of applying the sprays from above the swarms in flight caused the pesticides to be ‘filtered out by the flying swarms of locusts during spraying’ with insignificant amounts of pesticides reaching the ground.146

Like the desert locust, control of the red locust presented challenges, despite their restricted outbreak areas. The two factors that supported the control of red locusts were their highly fluctuating populations and restricted geography. In 1954, areas in northern Rukwa had become heavily infested by red locust hoppers. Tests had shown that high dosages of gamma BHC powder would destroy the hoppers more economically than other methods. The hoppers were dusted with a 40-ton 6 percent gamma BHC concentration, which destroyed nearly 433 million of them over

28,000 acres.149

In the same area in 1955, Gunn150 used experimental plots of about 20 acres. The use of puffer dusters (by hand, at night) and aerial spraying effectively controlled the adult population. Aerial spraying was most appropriate where many swarms were on the move. In 1955, there were a total of 429 air-to-ground spraying sorties. By the end of 1955, the residual breeding population in Tanganyika was estimated at between 50 and 100 million individuals. However, after the marshes flooded between 1956 and 1957, no more locusts were reported.151

Unfortunately, scientific data on the efficacy of aerial spraying was seriously defective. Although the technique had been carefully developed and field tested in Britain, some adjustments were required in the field for it to be operational in East Africa. It was impossible to extinguish large swarms often covering greater than covering 160 km'. The remnants of targeted swarms spread out and were joined by new swarms, thus posing a continued threat to East Africa.12 Between 1954 and 1955, aerial attacks on individual bands of hoppers were abandoned with the introduction of dieldrin spray lines that were quite effective in killing hoppers.1” It was considered essential to combine control campaigns with careful monitoring, if long-term success was to be achieved in ending locust threats.

 
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