Biocontrol introduction
Target pest: Sirex noctilio (Hymenoptera: Siricidae), sirex wood wasp
Agent introduced: Ibalia leucospoides leucospoides (Hymenoptera: Ibaliidae)
Imported:
1931, 1950, 1951
Import source:
Wales and England (1931), England (1950, 1951)
Import notes:
Cameron et al. (1989) - during 1931, 382 I. l. leucospoides larvae collected in Wales and the south of England were sent to New Zealand. Only 21 survived the journey; one (a male) was reared to adult. Between October and December 1950, 19 male and 18 female adult I. l. leucospoides were received from England. Oviposition occurred into S. noctilio embryos and newly-hatched larvae in insectaries and the first New Zealand generation of I. l. leucospoides emerged in early-1952. Also received alive in 1950 were 117 I. l. leucospoides larvae and 104 siricid (host) larvae thought to be parasitised, but rearing was not successful. From August to October 1951, 70 male and 95 female adult I. l. leucospoides were imported from England. Oviposition occurred and progeny emerged January-March 1953. Twenty larvae were received in November 1951 from which four males were reared. Insectary rearing for releases continued until 1959.
Released:
1954
Release details:
Cameron et al. (1989) - releases up until 1959 were made from laboratory colonies; subsequent liberations were redistributions from established field populations. Releases were made in Whakarewarewa (Bay of Plenty, North Island) and Eyrewell (North Canterbury, South Island) forests in 1954 and thereafter in forests and plantations throughout the country annually until 1963, and then in the years 1965, 1966, 1968 and 1976-78. Generally, not fewer than 30 females were released at any one time. In addition, logs containing I. l. leucospoides were placed in seven forests in the Southland, Central Otago and Dunedin areas of the South Island in 1963-65.
Establishment:
Cameron et al. (1989) - became readily established, even where very small numbers were released, and spread rapidly. The first field recovery of I. l. leucospoides was from Rotoehu (Bay of Plenty) in 1957, two years after release. By 1987 it had been recorded from 97 forests and plantations and is certainly present throughout the country wherever S. noctilio occurs.
Impacts on target:
Cameron et al. (1989) - the presence of successfully introduced parasitoids [including I. l. leucospoides], together with the accidentally introduced nematode Deladenus siricidicola [subsequently reclassified as Beddingia siricidicola] and good forest management has been effective in keeping losses caused by S. noctilio at a low level. Parasitism by I. l. leucospoides is usually 25-35%, but can be as high as 55%, and the combined effect of this and the other introduced parasitoids may kill over 70% of S. noctilio larvae in a particular forest area.
Cameron et al. (1993) - Ibalia leucospoides leucospoides, in conjunction with Rhyssa persuasoria persuasoria, Ibalia leucospoides ensiger and Megarhyssa nortoni nortoni [see the R. p. persuasoria, I. l. ensiger and M. n. nortoni introduction entries], is categorised as exerting “partial” control (defined as “additional control remains commonly necessary but…pest outbreaks occur less frequently”) over Sirex noctilio. [Though note that while one table in this publication indicates these four agents in combination exert "partial" control, another table categorises I. l. leucospoides as exerting "substantial" control (defined as “other control measures are only occasionally required”).]
Hurley et al. (2020) - Ibalia leucospoides leucospoides is considered one of the most successful parasitic wasps introduced into the southern hemisphere for the control of S. noctilio.
General comments:
Cameron et al. (1989) - the well established I. l. leucospoides is known to interbreed with I. l. ensiger [also introduced against S. noctilio] and separate populations in New Zealand cannot be recognised. [But see the Hurley et al. (2020) entry below.]
Hurley et al. (2020) - two sub-species of the parasitoid I. leucospoides (I. l. leucospoides and I. l. ensiger) have been introduced to the southern hemisphere as a biological control agent for Sirex noctilio and are reported to have hybridised. However, an investigation of the genetic variation of I. leucospoides in its native and introduced ranges using mitochondrial (COI) and nuclear (ITS) markers found no evidence of hybridisation between the two sub-species of the parasitoid in its introduced range. [Note though, that specimens from the introduced range used in the study did not include insects from New Zealand; only South Africa, Chile, Argentina and Australia.]
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
Hurley BP, Fitza KNE, Wingfield MJ, Slippers B. (2020). Sequence data reflect the introduction pathways of the Sirex woodwasp parasitoid, Ibalia leucospoides (Ibaliidae, Hymenoptera). Agricultural and Forest Entomology 22(2): 129-135 https://doi.org/10.1111/afe.12367
