Effect of Pupal Holding Density on Emergence Rate, Flight Ability, and Yield of Sterile Male Mediterranean Fruit Flies (Diptera: Tephritidae)

The Sterile Insect Technique (SIT) is commonly used to suppress or eradicate infestations of the Mediterranean fruit fly (or medfly) Ceratitis capitata (Wiedemann). Flies are mass-produced, sterilized, and shipped as pupae from the production facility to an eclosion and release facility. Pupae, and then emerging adults, are stored in eclosion towers consisting of 40–60 horizontally stacked, screen-paneled trays. In California, each tray is stocked with 350 ml of pupae, but this amount (the “pupal loading”) varies among medfly SIT programs. Moreover, there exist no published reports regarding the potential impact of pupal loading on the performance of the adult sterile males. The goal of the present study was to compare two parameters—adult emergence and flight ability—across three pupal loadings, i.e., 250, 350, and 450 ml per tray. Two separate experiments were conducted at the eclosion-release facility in Los Alamitos, CA, which receives sterilized pupae from both Guatemala (Gflies) and Hawaii (Hflies). Results from both experiments revealed a negative impact of pupal loading level on flight abil- ity, with a greater decline noted for Gflies than Hflies. Emergence rate was not affected markedly. The number of fliers produced per tower increased with pupal loading level of the constituent trays, but importantly the proportion of pupae that produced flight-capable was significantly lower for the 450 ml pupal loading level than the 250 or 350 ml pupal loading levels. Implications of these results for medfly SIT programs are discussed