well, the "silver dollar" eucalyptus name is applied to both e. cinerea (fairly hardy) and e. polyanthemos (not reliably hardy). BTW, several other potentially hardier eucalyptus species have the rounded leaves including gluacescens, urnigera and perriniana, but NONE of the species listed hardy or otherwise probably are going to really keep mosquitos away---unless you were going to plant a rather large grove with many plants!!! FWIW, the insect repellant chemical citronel is found in the leaves of the very frost tender species e. citriodora (aka corymbia citriodora)---and even then is only really useful in a very concentrated form distilled from the leaves.