gorrilla's physiology are very similar to humans, as we all know. they have the same hands with opposable thumbs, and so could operate the complex controls and machinery etc. also, gorrillas are much much more physically stronger than humans, so this would be an advantage over human hosts. and as for the level of intelligence, its not like the yeerks were using human hosts for the humans intelligence and anyway, as the yeerks are way more advanced already. they just need bodies.
so why not just take gorrilla hosts as well, along with taking human hosts? what have they got to lose?
and furthermore, a gorrilla would make much butter hosts then the taxxons and the gedds.
and with numbers problem, they could just implement a breeding program or perhaps cloning or growth acceleration. i'm sure this is not beyond their capabilities. i mean they went to the trouble of trying to infest sharks and horses.