Biocontrol introduction
Target pest: Chrysodeixis eriosoma (Lepidoptera: Noctuidae), green looper or silver Y moth
Agent introduced: Copidosoma floridanum (Hymenoptera: Encyrtidae) = Litomastix maculata
Imported:
1969
Import source:
Victoria, Australia
Import notes:
Cameron et al. (1989) - ten Chrysodeixis argentifera larvae parasitised with C. floridanum were collected in Victoria, Australia and shipped to Nelson, New Zealand in March 1969. At the time of importation the parasitoids were identified as Litomastix sp. [see Cameron et al. (1989) entry in the ‘General comments’ section for taxonomic details]. The emerging parasitoids were reared in quarantine and released. With confirmed establishment at Auckland in 1973 a large-scale breeding programme was initiated for further releases.
Released:
1969
Release details:
Cameron et al. (1989) - the individuals imported in 1969 were reared in quarantine and the resulting material was released in 1969 at Nelson, South Island and in 1970 at Auckland and Hamilton in the North Island and Lincoln (Canterbury) in the South Island. Following establishment in the field in 1973 a large-scale breeding programme led to releases at more than 100 sites throughout the Auckland and Wellington provinces in the North Island and in Christchurch in the South Island. In 1979 further releases were made in Christchurch.
Establishment:
Cameron et al. (1989) - establishment was confirmed at Auckland in 1973 and subsequently established quickly throughout the North Island and in the Nelson province but establishment was not confirmed in Christchurch until 1982.
Impacts on target:
Cameron et al. (1989) - Copidosoma floridanum achieves very high levels of parasitism in late-summer/early-autumn in situations where hosts are present throughout the year but is poorly synchronised with C. eriosoma in late-winter/early-spring. For example, a 1982 publication reported 30% parasitism of the first spring generation (early-October to early-December), 70% in the second main generation (early/mid-December to late-January) and between 84 and 100% in the third to fifth generations (early-March onwards, including the overwintering fifth generation). In more disturbed sites represented by commercial crops, much lower levels of parasitism have been recorded (between 8 and 72% in various crops and regions at various times of year). Because the greatest impact of C. floridanum on C. eriosoma is delayed until midsummer and because the parasitoid also prolongs the life of the most damaging stage of the pest and increases its food consumption significantly (by over 70%) it is unclear at present whether the importation of C. floridanum has been beneficial.
Impacts on non-targets:
Roberts (1986) - there is some evidence to suggest that native Trichogrammatoidea species attacking eggs of C. eriosoma and other pest noctuids might have been eliminated as a parasite of C. eriosoma from the Auckland region by C. floridanum. In the summer of 1975, Trichogrammatoidea parasitism of C. eriosoma eggs was recorded at 96.4% at both Paihia (Northland) and Auckland. Between 1976 and 1979, only six of 556 C. eriosoma eggs [1.1%] collected in the Auckland regions were parasitised by Trichogrammatoidea, and none of 961 C. eriosoma eggs observed in the field at Mahurangi [in the northern part of the Auckland region] showed the characteristic blackening of Trichogrammatoidea parasitism. If Trichogrammatoidea have been displaced by C. floridanum as parasites of C. eriosoma in the Auckland region, and, as the data hints, both Trichogrammatoidea and C. floridanum are both capable of 95% parasitism of C. eriosoma, there is a possible situation where parasites killing the pest at the egg stage have been replaced by an egg-larval parasite that does not kill the host until it has consumed 72.9% more than an unparasitised caterpillar and infinitely more than an egg. The data regarding the replacement of Trichogrammatoidea by C. floridanum is not conclusive and contains some puzzles (for example, explaining the parasitism rate drop from 96.4% in one year in one part of Auckland to 1.1% in the following few years elsewhere in Auckland), but there is room for concern.
General comments:
Cameron et al. (1989) - this parasitoid was imported as Litomastix sp. and initially identified as Litomastix maculata, a name recently synonymised with Copidosoma floridanum.
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.
Roberts LIN (1986). The practice of biological control - implications for conservation, science and the community. The Weta 9(2): 76-84
