Biocontrol introduction
Target pest: Pieris rapae (Lepidoptera: Pieridae), cabbage white butterfly
Agent introduced: Pteromalus puparum (Hymenoptera: Pteromalidae)
Imported:
1933
Import source:
England
Import notes:
Cameron et al. (1989) - Pteromalus puparum inside host pupae were obtained from the Imperial Institute of Entomology (now CIBC), England. Adults emerging in New Zealand from imported host pupae were either directly released or used to start a laboratory colony.
Released:
1933
Release details:
Cameron et al. (1989) - 10,812 adults, originally from England, were released in Hawke's Bay in 1933 with more in 1934. In the 1934-35 season liberations were made into other North Island regions, notably Wellington and Manawatu. Further releases from 1935-36 to 1937-38 were as follows: North Island - Auckland/Bay of Plenty (39,305), Poverty Bay (1,200), Taranaki-Manawatu (14,935), Hawke's Bay/Waiarapa (2,450) and Wellington (1,340); South Island - Nelson-Marlborough (18,265), Canterbury (120,550), Otago (27,343) and Southland-Westland (4,160). Plans were made to release another 100,000 adults in 1938-39 but it is unclear if this eventuated.
Establishment:
Cameron et al. (1989) - initial releases were in Hawke’s Bay in 1933; by autumn of that year 58% of P. rapae pupae were parasitised. While further releases were undertaken in Hawke’s Bay the next season, these were apparently unnecessary as the initial release had established and offspring survived to spread at least 110 km from the initial release site. By autumn 1934, 89% of host pupae were parasitised at Hawke's Bay release sites. By 1938, P. puparum had been recovered from, and established in, all regions of New Zealand.
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. Pteromalus puparum is more efficient during the latter part of the season and therefore probably does not markedly reduce host population levels until subsequent generations.
Cameron et al. (1993) - Pteromalus puparum, in conjunction with Cotesia glomerata [see the C. glomerata introduction entry], is categorised as exerting “substantial” control (defined as “other control measures are only occasionally required”) over P. rapae.
Impacts on non-targets:
Cameron et al. (1993) - in the 1930s, P. puparum was imported on the correct assumption that literature records of its wide host range greatly overestimated its field host range. At that time, its predicted ability to attack the native species Bassaris gonerilla [red admiral butterfly] was not noted as a disadvantage. No other non-target hosts have been recorded in New Zealand since the release of P. puparum.
Barron et al. (2003) - Pteromalus puparum has been recorded parasitising up to 14% of pupae of the endemic red admiral butterfly (Bassaris gonerilla (F.)) and probably has permanently enhanced mortality in B. gonerilla populations but the level of this is likely to be low.
References
Barron, M.C., Barlow, N.D. and Wratten, S.D. (2003). Non-target parasitism of the endemic New Zealand red admiral butterfly (Basaris gonerilla) by the introduced biological control agent Pteromalus puparum Biological Control 27. 329-335
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
