Biocontrol introduction
Target pest: Pieris rapae (Lepidoptera: Pieridae), cabbage white butterfly
Agent introduced: Cotesia rubecula (Hymenoptera: Braconidae) = Apanteles rubecula
Imported:
1938-39, 1993
Import source:
1938-39 England,1993 South Australia
Import notes:
Cameron et al. (1989) - five consignments totalling 509 specimens (probably cocoons) were imported (as Apanteles rubecula, Marshall) in 1938-39 from the Imperial Institute of Entomology (now CIBC), England. They were not released as a laboratory colony could not be established.
Cameron et al. (1995) - four shipments totalling 298 C. rubecula were supplied by the University of Adelaide in South Australia. Females from the source culture were mated with field-collected males in Australia to maintain genetic variability. In New Zealand, all importations were reared individually for at least two generations to ensure each shipment contributed parasitoids for release.
Released:
1993
Release details:
Cameron et al. (1989) - the 1938-39 importation was not released.
Cameron et al. (1995) - releases between 22 December 1993 and 10 March 1994: North Island - 156 released in Northland (two sites), 6,253 in Auckland (nine sites), 1,214 in Levin (three sites); South Island - 1,030 in Canterbury (two sites), 903 in Gore (one site).
Cameron & Walker (2002) - in 1994-95, releases were extended to a further 17 sites within the same regions as the 1993-94 releases (Northland, Auckland, Wellington, mid-Canterbury, and Southland) and three more sites in an additional region (Wanganui), with the release of an additional 20,267 parasitoid cocoons. In 1997-99, parasitoids were also released in vegetable Brassica spp. growing regions in Gisborne and Hawke’s Bay on the east coast of the North Island, and south of Auckland in the Waikato region. In total (1993-99) more than 42,000 parasitoid cocoons have been released. Releases of C. rubecula cocoons generally exceeded 2,000 per region, and averaged 842 per release site with a range of 708-2,242.
Wallis et al. (2016) - following a 2010 survey that failed to find C. rubecula in Nelson, cocoons were released at three sites in the Nelson region on 15 April 2013.
Establishment:
Cameron et al. (1995) – recoveries, to May 1994, from the 1993-94 releases were made at 15 of the 17 release sites. Subsequently, overwintering survival was confirmed at four Auckland sites and one Canterbury site. The widespread recoveries and high parasitism rates (up to 97%) show that there are now substantial populations of C. rubecula that are likely to persist in New Zealand.
Cameron & Walker (2002) - by 1995, following the 1993-94 releases, C. rubecula had overwintered at four release sites in the Auckland region, one site in Canterbury. Following the additional releases in the 1994-95 season, C. rubecula also overwintered and established at two sites in each of the Northland, Wanganui, and Wellington regions. Following the 1997-99 releases in Gisborne, Hawke’s Bay and Waikato, overwintering was recorded at one site in the Waikato and recovery of cocoons indicated successful overwintering at one Hawke’s Bay site. Although parasitism was recorded at six sites in Gisborne, parasitoids failed to establish in this region, probably due to a lack of refuge areas that limited the continuity of host insect populations. Surveys have shown the absence of C. rubecula from some sites where it had been recorded previously, indicating that it is patchily distributed and limited in its dispersal capabilities, and may not locate small areas infested by P. rapae. Dispersal from release sites has so far been comparatively slow; records from 1993 to April 2000 indicate an average spread of 2.3 km/yr. Although high levels of hyperparasitism of C. rubecula by Tetrastichus galactopus have been recorded (reaching 60-80% in March and April), this has not prevented the establishment of C. rubecula in most regions.
Wallis et al. (2016) - monitoring in Nelson in the two years (2014-15 and 2015-16) following the releases there recovered C. rubecula from two of the three release sites and another site 9 km away from any release site. This parasitoid is considered to be established in the region.
Impacts on target:
Cameron & Walker (2002) - rates of parasitism by C. rubecula ranged from 48 to 97% and was generally above 70% at experimental sites, but were lower at most commercial sites. At sites with C. rubecula, the density of P. rapae fifth instars reached only 0.25 per plant compared with a minimum of 1.65 per plant at sites without the parasitoid. Consistent differences between the size distribution of P. rapae larvae with and without C. rubecula, together with the high rates of parasitism, indicated that C. rubecula was a major factor in reducing the populations of large, damaging P. rapae larvae. Although C. rubecula reduced parasitism by Cotesia glomerata [introduced as a biocontrol of P. rapae in 1931] in sites where they were both present, total parasitism of P. rapae was increased at these sites. Results indicate that C. rubecula is still expanding its geographic range in New Zealand and, where a suitable succession of Brassica spp. crops is available, it is likely to significantly improve the biological control of P. rapae.
Wallis et al. (2016) - C. rubecula has become an important biological control agent of Pieris rapae in regions where it has established.
Impacts on non-targets:
Cameron et al. (1995) - host range testing of the parasitoiod carried out in Australia prior to its importation supported ecological observations about the specificity of C. rubecula in that country. Anaphaeis java (family Pieridae) occurs in mixed crops where C. rubecula is common in Australia, but has not been known to be parasitised by C. rubecula; wind tunnel experiments confirmed C. rubecula is not attracted to A. java. Similarly, it was not attracted to and would not oviposit in Bassaria itea (yellow admiral) (Nymphalidae), native to both New Zealand and Australia. Confirmatory oviposition tests were carried out in New Zealand by exposing C. rubecula to relatives of P. rapae in the superfamily Papilionoidea - B. itea, Danaus plexippus (monarch butterfly) (Nymphalidae) and Zinina labradus (common blue butterfly) (Lycaenidae) - and to species that might be encountered in vegetable crops - Agrotis ipsilon, Helicoverpa amigera, Thysanoplusia orichalcea, Graphania mutans (all Noctuidae), Uresiphita polygonalis (Pyralidae), Epiphyas postvittana (Tortricidae), Phrissogonus laticostatus and P. xylostella (Geometridae). It was concluded that the Australian source of C. rubecula was specific to the genus Pieris.
Cameron & Walker (2002) - at experimental sites where C. rubecula was absent, maximum rates of parasitism by Cotesia glomerata [introduced as a biocontrol of P. rapae in 1931] exceeded 50%, but was always below 20% when C. rubecula was present. This partial displacement of C. glomerata is consistent with the literature and indicates that C. rubecula is the superior competitor. However, where both parasitoids were present, total parasitism of P. rapae was increased.
References
Cameron PJ, Hill RL, Bain J, Thomas WP (1989). A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1874-1987. Technical Communication No 10. CAB International Institute of Biological Control. DSIR Entomology Division. 424p.
Cameron PJ, Walker GP (2002). Field evaluation of Cotesia rubecula (Hymenoptera: Braconidae), an introduced parasitoid of Pieris rapae (Lepidoptera: Pieridae) in New Zealand. Environmental Entomology 31(2): 367-374 https://academic.oup.com/ee/article/31/2/367/347896
Cameron, PJ, Walker, GP and Keller, MA (1995). Introduction of Cotesia rubecula, a parasitoid of white butterfly. Proc. N.Z. Plant Protection Conf. 48: 345-347 https://nzpps.org/_journal/index.php/pnzppc/article/view/11530/11380
Wallis DR, Shaw PW, Walker GP, and MacDonald FH (2016). Establishment and dispersal of Cotesia rubecula, a larval parasitoid of Pieris rapae, in the Nelson district. New Zealand Plant Protection 69: 319 [Poster abstract]
