December 2010. A scale infestation on mango from Ethopia.
A member said that is was difficult to see enough detail to be certain, but the infestation looks like Aulacaspis tubercularis or something similar. It sounds as if this may be a new introduction to Ethiopia? However, for authoritative identification the adult females need to be studied in microscope slide mounts. For more information, see: http://nlbif.eti.uva.nl/bis/diaspididae.php?selected=beschrijving&menuentry=soorten&id=95
A search of Google Images for Aulacaspis tubercularis brings up lots of photos, but probably only the top 2 rows plus the distribution map in the 3rd row are definitely A. tubercularis ??? below that level, some photos are accurate and some are incorrect.
Using chemicals is hazardous and expensive, and often causes other pest problems to develop because their natural enemies are killed by the pesticide. In the long term, it would be more cost effective to get the insect identified authoritatively and look at importing a suitably screened biological control agent (a hymenopteran endoparasitoid would be best), to suppress the populations permanently.