Fecundity and oviposition in laboratory colonies of the screwworm fly (Diptera: Calliphoridae).

The screwworm fly is mass-produced using an artificial larval diet and an artificial oviposition substrate. On the artificial diet, mean fecundity was 185 eggs per female, whereas host-reared flies averaged 280 eggs per female. Host-reared flies were generally larger (head capsule width [HCW] > 3.6 mm) than laboratory-reared flies (HCW < 3.6 mm). Larger flies are generally more fecund, and size is related to larval nutrition. Only 75-89% of females reared on artificial diet and maintained at 30 degrees C were gravid at 6 d of age compared with 100% of host-reared females tested at 5-6 d. When gravid females were offered artificial substrate for oviposition, approximately 28% failed to oviposit and another 11% laid only partial clutches. Among all females tested for oviposition, 25% of the total egg production was withheld. Fecundity influenced oviposition, because the more mature eggs a female had, the more likely she was to oviposit. Supplementing the adult diet of honey and water with raw meat increased fecundity by 14% under normal laboratory conditions, but by as much as 350% in flies in which larval feeding was curtailed by removal of the larvae from the media 1 d before the normal completion of development. Many females became gravid in 4-5 d at 30 degrees C versus 8-9 d at 22 degrees C. But fecundity and oviposition rate were more variable (less synchronous) in colonies maintained at the higher temperature. This suggests that there may be greater selection for laboratory adaptation at the higher maintenance temperatures.