Establishment and dispersal of Cotesia rubecula a larval parasitoid of Pieris rapae in the Nelson district

Cotesia rubecula is a solitary larval parasitoid of Pieris rapae the small white butterfly (SWB) and has become an important biological control agent in regions where it has established since its release into New Zealand in 1993 It was first released in the Nelson region at three sites on 15 April 2013 after a survey in 2010 failed to find the parasitoid The cocoons of C rubecula for this release came from collections of SWB larvae at a trial site at Pukekohe and from unsprayed forage brassica plants growing near Burnham midCanterbury Monitoring of C rubecula and the established parasitoid C glomerata took place over two seasons 201415 and 201516 with all stages of SWB larvae collected at five properties across the Nelson region from Richmond to Motueka C rubecula were recovered from two of the original release sites for the next two years and appeared to spread to another site 9 km away from any release site This parasitoid is considered to be established in the region and should disperse naturally to become an important biological control agent of SWB in most habitats

Natural dispersal of Cotesia rubecula the recently introduced larval parasitoid of Pieris rapae through the South Island

The natural dispersal of Cotesia rubecula the important larval parasitoid of Pieris rapae (small white butterfly) was assessed through the South Island over 2 years as part of an SFF project to improve management of foliage pests on forage vegetable and seed brassicas grown in the South Island This parasitoid has dispersed naturally from its initial release sites at Lincoln and Christchurch as far south as Dunedin airport as far north as north Cheviot and inland to Methven and Hanmer Springs However it has failed to establish in Southland and is not present in central Otago or Nelson/Marlborough Seasonal surveys indicate that this parasitoid is well synchronised with its host sometimes parasitising complete cohorts in a cropping area There is also strong evidence that C rubecula is displacing the earlier introduced and much less effective larval parasitoid Cotesia glomerata The hyperparasitoid Baryscapus galactopus is also affecting the new primary parasitoid A new SFF project is supporting the introduction of C rubecula into the Nelson/Marlborough region where its future interaction with C glomerata and possibly its other host Pieris brassicae (great white butterfly) a new incursion into New Zealand will be an interesting study