Yes, you can. One recipe calls for, in each 1/2 teaspoon of rubbing alcohol or vodka, one drop each of Lavender, Cedarwood, Lemongrass and Peppermint.
There are 6 teaspoons in one ounce, so to make 1fl oz of solution, one uses 12 drops of each essential oil. The alcohol can be avoided, and instead this blend can be made by using 1 drop 'tween' for each drop essential oil. Tween keeps the essential oils emulsified in water after shaking well. So this would work out to 12 drops of each of the 4 essential oils listed, plus 48 drops 'tween' (on our 'bottles' page: http://www.anandaapothecary.com/bottles.html#tween
), in about 28ml water (or just know how large your container is; multiply all these numbers by 8 for an 8oz spray bottle, for example).
We've found Catnip to be especially effective for mosquito control, and it was originally discovered tested as a cockroach repellent. If this would also remain true with fleas, we're not sure ~ but cockroach to mosquito is a pretty big leap. If we were to recommend a formula ourselves, it would be 1 drop each: Catnip, Geranium (any type, least expensive is fine), Cedarwood and Peppermint.
These blends can be used as a collar-dip as well as a sponge/spray (remember, not on cats! No EO's for cats! Their liver's don't tolerate them).
It is also recommended to add garlic to the formula. Rather than garlic capsules, though, a crushed clove would be best. You'll have to judge for yourself aroma and efficacy (though we think ANYthing is better than the smell of synthetic, poisonous treatments!)