Biocontrol introduction
Target pest: Pieris rapae (Lepidoptera: Pieridae), cabbage white butterfly
Agent introduced: Cotesia glomerata (Hymenoptera: Braconidae) = Apanteles glomeratus
Imported:
1931-34, 1938-39
Import source:
1931-34 England, 1938-39 USA.
Import notes:
Cameron et al. (1989) - 1931-34 importations of C. glomerata (as Apanteles glomeratus (L.)) from the Imperial Institute of Entomology (now CIBC), England totalled over 500,000 cocoons in three shipments. During the 1938-39 season 6,000 cocoons of American C. glomerata (as A. glomeratus) were imported from the Bureau of Entomology, Washington, USA. The English material was secured from Pieris brassicae hosts, while the American material was obtained from P. rapae hosts.
Released:
1931
Release details:
Cameron et al. (1989) - in 1931-34, over 250,000 adults were liberated throughout the North Island. In 1938-39, 2,317 adults were released near Nelson in the South Island. Following establishment in Nelson, a single release was undertaken outside that district [presumably in a neighbouring district] during the 1943-44 season, followed by other releases from 1944 until 1947, including a release in Hawkes Bay, North Island, in 1944-45 [numbers not recorded]. In 1960, 700 adults were released at Palmerston North, Manawatu, North Island, and possibly there were other releases, based on areas of subsequent recoveries (see 'Establishment' section). The American C. glomerata was released in 1954-55 on Chatham Island.
Establishment:
Cameron et al. (1989) - the European strain appeared not to establish. Following the 1931-34 releases, small numbers of C. glomerata were recovered in Hawke's Bay during the season they were released there and the following season, but no recoveries were recorded in subsequent years. A three-year survey in the southern North Island, 1955-58, failed to locate C. glomerata, although some were found in this region in 1959 and its presence confirmed here in 1960-61; it was suggested the parasitoid had spread naturally from Nelson in the South Island to Wellington in the North Island and become established in the southern North Island sometime prior to 1959. It was postulated that a likely factor in the apparent failure of the European strain was the origin of the parasitoid from the host P. brassicae and its failure to adapt to P. rapae in New Zealand. Following the American importation releases, C. glomerata was recovered from Nelson in 1938-39 and well established there by 1943-44. It was recorded in Canterbury in 1946-47 and it then became widely established throughout the South Island. It was noted in the south Auckland area in 1973 and must have spread, or been released, there prior to that date. There are no reports of establishment on Chatham Island.
Impacts on target:
Cameron et al. (1989) - of the biocontrol agents of P. rapae known to occur in New Zealand, the parasitoids Cotesia glomeratus and Pteromalus puparum, a granulosis virus and predation appear to have the main impact. While these factors have reduced the serious, and probably constant, P. rapae threat to the point where damage varies with seasons and districts, no single agent can consistently be rated as the most important. The dominant mortality factor(s) can change between generations, over a number of seasons and in response to population density and weather conditions. The granulosis virus (which can attack both P. rapae and its parasitoids) has been shown to have a deleterious effect on C. glomerata. It is possible the presence of disease, the high level of pupal parasitism by Pteromalus puparum and its interaction with C. glomerata, and severe hyperparasitism by Eupteromalus sp. have acted to delay the establishment and lessen the impact of C. glomerata.
Cameron et al. (1993) - Cotesia glomerata, in conjunction with Pteromalus puparum [see the P. puparum introduction entry], is categorised as exerting “substantial” control (defined as “other control measures are only occasionally required”) over P. rapae.
Cameron & Walker (2002) - Cotesia glomerata is not well synchronized with P. rapae and often provides insufficient control in the summer season. Surveys to evaluate the dispersal and impact of Cotesia rubecula [introduced as a biocontrol of P. rapae in 1993] found that at experimental sites where C. rubecula was absent, maximum rates of parasitism by Cotesia glomerata 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.
Impacts on non-targets:
Cameron et al. (1993) - in the 1930s, C. glomerata was imported on the correct assumption that literature records of its wide host range greatly overestimated its field host range. No non-target hosts have been recorded in New Zealand since its release.
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, Hill RL, Bain J, Thomas WP (1993). Analysis of importations for biological control of insect pests and weeds in New Zealand. Biocontrol Science and Technology 3(4): 387-404
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
