Distribution and Incorporation of Orally Ingested Cyromazine into House Fly Eggs

In addition to milk and sugar solution provided ad libitum a 839 ppm [14C]cyromazine was fed to female house flies at the rate of 1 MU l/day for up to 4 days. The radioactivity excreted ranged from 85 to 90% of the total ingested after 1 or 4 days, respectively. The radioactivity retained in the body was distributed in hemolymph (0.9%), ovary including eggs (1%), and carcass (0.7%). When the female flies were allowed to deposit eggs, 0.6% of the radioactivity was found in the eggs deposited in the first gonotrophic cycle, which consequently reduced the radioactivity present in the ovary. These results clearly demonstrate that cyromazine ingested by female flies is incorporated into eggs and inhibits larval development in the F1 generation. To study the mechanism of cyromazine incorporation into eggs, vitellogenin was separated from the hemolymph on native-PAGE and incubated with [14C]cyromazine. A Sephadex G-25 gel filtration of the incubation mixture resolved two radioactive peaks. A major peak was associated with the protein fraction and a minor one corresponded to the free cyromazine fraction. It is likely that cyromazine in the female hemolymph was bound to vitellogenin and incorporated into eggs.