The mymarid egg parasitoid Gonatocerus ashmeadi is a potential candidate for classical biological control of glassy winged sharpshooter (GWSS; Homalodisca vitripennis), should the pest arrive in New Zealand. However, the climate in the parasitoid's native range in the southern USA is considerably warmer than that in New Zealand, which may pose an obstacle to establishment. Although G. ashmeadi is a very effective biocontrol agent in Florida, Hawaii and Western Polynesia, it appears currently to be limited by cooler climate in central and northern California - regions that typically have climates more similar to those in New Zealand. A CLIMEX model was used to predict the survival of G. ashmeadi in New Zealand by comparison with known parameters in the USA and western Pacific Islands. The model indicates that the establishment and distribution of G. ashmeadi is likely to be limited by the climate in New Zealand, although it will probably persist in warmer parts of the North Island. These predictions indicate that biocontrol of GWSS in New Zealand using G. ashmeadi will also require active management through varying regional integrated pest management programmes. Should GWSS arrive in New Zealand, G. ashmeadi should be selected from a population that has adapted to cooler parts of California. However, such a population is not known at present, so preventing GWSS from establishing in New Zealand remains a crucial strategy.