Target pest: Plutella xylostella (Lepidoptera: Yponomeutidae), diamondback moth
Agent introduced: Diadegma fenestrale (Hymenoptera: Ichneumonidae) = Diadegma fenestralis, Angitia fenestralis
Cameron et al. (1989) - from early-August 1936 until mid-January 1937, 14 consignments of D. fenestrale [as D. fenestralis] were imported, totalling 14,518 parasitoid cocoons (some reared from the 25,410 host pupae sent containing either D. semiclausum or D. fenestrale), from which at least 4,561 adult D. fenestrale emerged. Six subsequent importations between mid-January and late-February 1937 contained a mixture of D. semiclausum and D. fenestrale, from which at least 4,894 adults (both species combined) emerged. All importations were from England. Laboratory rearing started at Palmerston North as soon as the first shipment (August 1936) arrived, while mass-rearing outdoors started in September 1936. From October 1936 until early-1937 imported consignments of both D. fenestrale and D. semiclausum were immediately sent from Palmerston North to Hawkeâ€™s Bay for mass-rearing in field cages. Each species was kept separate until early January 1937, when the colonies were combined [Cameron et al. (1989) expressed doubt that these are distinct species, but see the taxonomic note in â€˜General commentsâ€™ section]. The Palmerston North colony was transferred to Nelson in August 1937.
Cameron et al. (1989) - releases of unstated numbers of D. fenestrale were made at Palmerston North, North Island in 1936-37, and from a shipment which arrived in September 1936, 3,000 adults (including an unknown number of D. semiclausum) were released in Hawkeâ€™s Bay, North Island. Combined releases of D. fenestrale and D. semiclausum were made in 1937 in Hawkeâ€™s Bay (more than 6,600) and in 1937-38 at Nelson, Waimea West and Blenheim in the South Island (31,229). However, in a 1940 publication, Given was of the opinion that D. fenestrale had probably died out of the mixed colonies and that this parasitoid was therefore never released in the South Island.
Cameron et al. (1989) - no recovery of D. fenestrale has been made in New Zealand.
Taxonomic note (29 January 2023) - Cameron et al. (1989), referencing a 1938 publication, noted there was doubt that D. semiclausum and D. fenestrale were distinct species because, while the diagnostic differences were clear, under certain conditions the two species could interbreed, with the morphological characters used varying widely and a range of intermediate forms found in the laboratory and field. Based on this information, Wagener et al. (2006) recognised that additional studies were needed to confirm the existence of separate species; their molecular study showed both species clearly separated on distinct clades in the phylogenetic trees. Juric et al. (2017) concluded that since the two species are morphologically very similar it is conceivable that D. fenestrale has inadvertently been introduced to some countries together with, or even instead of, D. semiclausum. The New Zealand specimen (from Pukekohe, Auckland) used by Wagener et al. (2006) as part of their study was identified as D. semiclausum.
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.
Juric I, Salzburger W, Balmer O (2017). Spread and global population structure of the diamondback moth Plutella xylostella (Lepidoptera: Plutellidae) and its larval parasitoids Diadegma semiclausum and Diadegma fenestrale (Hymenoptera: Ichneumonidae) based on mtDNA. Bulletin of Entomological Research 107(2): 155-164
Wagener B, Reineke A, LÃ¶hr B, Zebitz CPW (2006). Phylogenetic study of Diadegma species (Hymenoptera: Ichneumonidae) inferred from analysis of mitochondrial and nuclear DNA sequences. Biological Control 37(2): 131-140 https://doi.org/10.1016/j.biocontrol.2006.01.004