Biology and host range of Phytomyza vitalbae and its establishment for the biological control of Clematis vitalba in New Zealand

Phytomyza vitalbae Kaltenbach (Diptera: Agromyzidae) creates mines in leaves of Clematis vitalba, a significant environmental weed in New Zealand. Studies in Europe found that most leaves had one mine, but some had many; heavy mining deformed leaves and reduced photosynthetic area.; P. vitalbae was multi-voltine; fecundity averaged 521 eggs per female; and larval parasitism was high. Together, these biological characteristics suggested it had the capacity to produce large populations in the absence of parasitism. P. vitalbae has been recorded on other Clematis species in Europe, and experimental determination of host range confirmed this species was narrowly oligophagous, but posed no significant risk to New Zealand native plants. Results suggested mines might be produced in some exotic Clematis species growing in New Zealand, but only where flies fed on C. vitalba before ovipositing. P. vitalbae was released from quarantine in New Zealand in 1996. It is considered to be established at 20 of the 29 release sites, and populations have grown rapidly at those sites. The fly spread 5 km within 15 months at one site. Three parasitoids have been reared from P. vitalbae mines since its release in New Zealand, but it is uncertain whether parasitism will adversely affect leaf-miner populations.