Biocontrol introduction
Target pest: Plutella xylostella (Lepidoptera: Yponomeutidae), diamondback moth
Agent introduced: Diadromus collaris (Hymenoptera: Ichneumonidae) = Thyraeella collaris
Imported:
1937-39
Import source:
Netherlands via England
Import notes:
Cameron et al. (1989) - Diadromus collaris was imported from colonies in England which originated from parasitoid collections in the Netherlands. Eight shipments, totalling 11,404 parasitoid cocoons (in host pupae) arrived between late-October 1937 and mid-May 1938, followed by a single importation of 200 cocoons in 1938-39. Although only 140 individuals (61 males, 79 females) emerged from the 1937-38 importations, and none from the 1938-39 importation, field-cage rearing at Nelson was successful with a rapid increase in numbers from September to December 1938. Large numbers of parasitised pupae were sent to Hawke’s Bay in January 1939 where mass field-cage rearing as again successful. Rearing at Hawke’s Bay ceased about 1941 and colonies were maintained at Nelson until at least 1942-43.
Released:
1938
Release details:
Cameron et al. (1989) - 240 adults were released in November 1938 in the Nelson area of the South Island. In autumn 1939, 10,000 were released at Nelson, and in the North Island, 18,000 at Hawke’s Bay and 8,000 at Palmerston North. Another 2,000 were released at Palmerston North in early-1940. Between November 1940 and March 1941, 9,400 were released in Auckland and 4,100 around Levin in the North Island, and 2,400 at Ashburton and 650 in Alexandra in the South Island. Releases in 1941-42 were intended for central and northern North Island regions and southwards from mid-Canterbury in the South Island; it is unclear if these eventuated.
Establishment:
Cameron et al. (1989) - limited numbers of D. collaris were recovered in Palmerston North (48 adults), Nelson (17) and Hawke’s Bay (217) following the early-1939 releases. In 1939-40 the parasitoid was found to be well established in these regions, where it has spread at least 105 km southwards in Hawke’s Bay and from Nelson to Marlborough (10 adults found). It was recovered from Lincoln, Canterbury in the 1940-41 season and by 1943-44 was well established throughout the country.
Impacts on target:
Cameron et al. (1989) - in conjunction with the introduced biocontrol agent Diadegma semiclausum and the naturally occurring fungus Zoophthora radicans, D. collaris has provided a high level of control of the diamondback moth complex (impact on the two most common Plutella spp. is unknown as studies have not distinguished P. xylostella from P. antiphona) in North Island cruciferous fodder crops. However, insecticide applications are still sometimes necessary on these crops in the South Island, and are essential on brassicas grown for human consumption.
Cameron et al. (1993) - Diadromus collaris, in conjunction with Diadegma semiclausum [see the D. semiclausum introduction entry], is categorised as exerting “substantial” control (defined as “other control measures are only occasionally required”) over P. xylostella.
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
