The application of a juvenile hormone analogue, methoprene and access to protein in adult diet has been shown to enhance mating success of some tephritid males, supporting their incorporation as a pre-release treatment for males utilized in the sterile insect technique (SIT). The effect of protein-diet (P) (contains hydrolyzed yeast and sugar) and/or treatment with methoprene (M), (in addition to sugar and water) on genetic sexing strain (GSS) of Bactrocera cucurbitae Coquillett (Diptera: Tephritidae) was assessed in the laboratory and in field cages. The males were exposed to either 1) methoprene and protein-diet (M+P+), 2) only protein-diet (M-P+), or 3) only methoprene (M+P-), or 4) only sugar (M-P-). The effect of methoprene and protein-diet on mating behaviour of the four groups of males, on starvation survival and on body protein and lipids was studied. Total body nitrogen (TBN) and total body carbon (TBC) were measured as indicators of body protein and body lipids repectively. The M-P+ males showed increased performance at leks and higher mating success compared to M+P- and M-P- males. Application of methoprene accelerated sexual maturity and enhanced mating competitiveness only in protein-fed males, but not in sugar-fed males. More M+P+ males called and initiated and participated in lek activities than all other types of male, consequently attaining a higher mating success. No adverse effect of methoprene and/ or protein but feeding duration had significant effect on starvation survival. Protein-diet had significantly increased the male body weight, TBN and TBC as compared to only sugar-fed males. Methoprene had no significant effect on males TBN and TBC. The results provide a strong evidence for the benefits of exposing sterile males to methoprene and protein-diet. Treated males achieve higher sexual success, reach sexual maturity several days earlier, and are therefore much closer to sexual maturity when released as part of SIT action programmes after being held in the fly emergence and release facility.