First and second instar Mexican fruit fly, Anastrepha ludens (Loew), larvae were more resistant to methyl bromide (MB) than 1, 2, and 3 day old eggs and third instar larvae. Concentrations of 55 and 60 gMB/m3 delivered for 2 h caused 99.9968% mortality of larvae of the Mexican fruit fly and West Indian fruit fly, A. obliqua (Loew), respectively, in mangoes Mangifera indica L. Doses of MB were statistically equal and caused 99.9968% mortality of both larvae and pupae of A. ludens and A. obliqua. At 48 g MB/m3 for 3.3h 99.9968% mortality of Mexican fruit fly larvae was determined. Concentrations of 46 g/m3 were estimated to cause 99.9968% mortality of Mexican fruit fly (based on estimated larvae and larval mortality) in peaches, Prunnis persicae (L.) Batsch, plums, P. salicina Lindl. and nectarines, P. persicae (L.) Batsch nectrina. Temperatures in the climatic chamber at the time of treatment ranged from 13.0°C to 34.6°C and did not reduce efficacy of this fumigant against either fly species.