To say "too little" or "too few" of something maltro is combined with the preposition
da https://en.wiktionary.org/wiki/da#Esperanto
. For example, "Ni havas maltroda iloj", "We have too few tools".
There exists a difference between "maltro da" and "maltroa", though it is subtle. "Maltro da" expresses a sense of collection, of belonging together somehow; something that is not the case for "maltroa". Consider, for example, the difference between "Maltro da homoj ĝuis la koncerton." (Too few people enjoyed the concert.) and "Maltroaj homoj ĝuis ĉi tiun kompaktdiskon." (Too few people have enjoyed this CD.). The first sentence expresses the notion that the people have listened to the concert together, whereas any such notion is absent from the second sentence.