Quantity does play some role in successful extraction; mosquitoes are much smaller than butterflies. (I do not know whether there is enough DNA to directly measure in our successful extractions; the lab tests by doing a trial PCR reaction.) We at Leptree have successfully sequenced nuclear genes from partial abdomens or whole legs of several dry museum specimens (recently collected) and also have sent some dry leg specimens to the DNA Barcoding center in Guelph, Canada. The Barcoding center has been quite successful with whole legs of small butterflies and moths and parts of very large ones from museum collections. However, they sequence COI from mitochondrial DNA, which has many times more copies per cell than nuclear DNA. Even then, their success with sequencing does decrease with age of the specimen, that is, years since collection, with specimens older than 15 years having a low probability of success. Anything collected within about 2 years will almost surely work; up to 10-15 years will probably work for COI (probably not for nuclear genes), but some specimens at 10 years of age will not work. The barcoding center has the fall-back option (for older specimens) of alternate primers that give shorter PCR products.