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Before the large-scale introduction of chemical insecticides after the Second World War (WW2), birds were considered worldwide as welcome natural allies to control acridids. For their role in acridid control they were worshipped in ancient times and in the first half of the 20th century protected in many countries worldwide. Until WW2, mechanical control e.g. by harvesting grasshoppers with ingenious dozers or digging trenches to interrupt marching hopper bands were chemically supplemented by massive use of arsenicals. The large scale introduction of Dieldrin in locust control around 1955 marked a turning point, as for the first time a persistent chemical became available to treat hopper bands which provided toxic residues killing hoppers emerging afterwards. The high toxicity for man and wildlife and the persistence of Dieldrin lead to a worldwide ban twenty years later, but in locust control it took until 1989 before its use eventually was discontinued. Meanwhile, organophosphorous insecticides had dominated the acridid arena since WW2 with varying contributions of carbamates, pyrethroids and some other chemical families. The interest in birds as natural allies had faded because of a widely held believe that the insecticides did a better job. In addition, the impact on birds of their widespread and large-scale use in Africa had neither been studied, nor assessed for its potential consequences for acridid control.It was against this background that the studies described in this thesis were undertaken to compare the efficacy on acridids and the impact on birds of non-selective chemical and selective biological insecticides, to contribute to efficient locust and grasshopper management with the lowest environmental footprint. Two oganophosphorous insecticides, fenitrothion and chlorpyrifos, both commonly used in acridid control until the present day and the entomopathogenic fungus Metarhizium acridum were studied. Both organophoshates caused direct avian mortality (2

The entomopathogenic fungus Metarhizium acridum in oil-based formulations (Green Muscle® (GM)) is a biopesticide for locust control lacking side-effects on biodiversity, unlike chemical insecticides. Under controlled conditions, GM-treated locusts and grasshoppers attract predators, a complementary advantage in locust control. We assessed avian predation on a population of desert locusts in northern Niger aerially sprayed operationally with GM with 107 g viable conidia ha-1. Populations of adult locusts and birds and vegetation greenness were assessed simultaneously along two transects from 12 days before until 23 days after treatment. Common kestrels Falco tinnunculus and lanners F. biarmicus were the predominant avian predators. Regurgitated pellets and prey remains were collected daily beneath "plucking posts" of kestrels. Locusts started dying five days post-spray and GM had its maximum effect one-two weeks after the spray, with 80% efficacy at day 21. After spraying, bird numbers increased significantly (P<0.05) concurrent with decreasing desert locust densities. Locust numbers decreased significantly (P<0.001) with both time since spraying and decreasing greenness. Before spraying, kestrel food remains under plucking posts accounted for 34.3 ±13.4 prey items day-1, of which 31.0 ±11.9 were adult desert locusts (90.3%), reducing post-spray to 21.1 ±7.3 prey items day-1, of which19.5 ±6.7 were adult desert locusts (92.5%), attributable to decreased use of the plucking-posts by the kestrels rather than an effect of the spray. After spraying, kestrels took significantly (P<0.05) more larger female (75-80%) than smaller male (20-25%) locusts. Avian predation probably enhanced the impact of the GM on the desert locust population, especially by removing large adult females. No direct or indirect adverse side-effects were observed on non-target organisms including locust predators such as ants and birds. These substantial ecological advantages should also be considere