At first Gustav worked alone, arriving in Brazil where there were many people of German descent ("Deutschbrasilianer") to collect insects for Dresden Zoological Museum.
He visited Germany for the last time in 1900 when he demonstrated 600 Neotropical bird species at a meeting of the Deutsche Ornithologen-Gesellschaft in Leipzig.
In Costa Rica he collected in the areas the railway line in the valley of the Rio Reventazon and on the volcanoes Irazu and Turrialba.
[1] The Garlepp zoological specimens are from Bolivia, Peru Colombia, Panama, Costa Rica Paraguay, Chile and Argentina.
4,000 Garlepp bird skins were purchased by Hans von Berlepsch who had trained Otto and who described the new species.