Biological control of Orobanche spp. with Phytomyza orobanchia, a review

This review summarises the available information on the biocontrol agent Phytomyza orobanchia Kalt. (Diptera, Agromyzidae). It gives an overview of a rare example of weed biocontrol using insects in an inundative approach. A high diversity of phytophagous insects has been collected on parasitic weeds of the genus Orobanche (Orobanchaceae). For biological control of Orobanche spp., only insects like P. orobanchia whose host range is restricted to Orobanche spp. are of interest. Of the 140 Orobanche spp. described in total, P. orobanchia is reported from 21 species. The larvae of P. orobanchia mine in Orobanche shoots and capsules. As a consequence, a natural reduction of Orobanche seed production by 30 to almost 80% has been reported from different countries. The efficacy of P. orobanchia under natural conditions is limited by low temperatures, cultural practices and natural enemies. To strengthen the natural population and its impact, inundative releases of P. orobanchia adults at the beginning of Orobanche emergence have to be undertaken. Different methods for the application of P. orobanchia in biocontrol of Orobanche spp. have been developed in the former Soviet Union. Releases of 500 to 1000 adults/ha resulted in a reduction of up to 96% of the Orobanche seed production. However, due to the 10 to 15 year longevity of Orobanche seeds, further infestations will occur in the following cropping seasons. Consequently, releases of P. orobanchia have to be repeated continuously over several years to reduce the infestation to a tolerable level.