Target pest: Mythimna separata (Lepidoptera: Noctuidae), cosmopolitan armyworm
Agent introduced: Cotesia ruficrus (Hymenoptera: Braconidae) = Apanteles ruficrus
Cumber et al. (1977) - strains of Cotesia ruficrus [as Apanteles ruficrus] were supplied from Pakistan in 1971 by the Commonwealth Institute of Biological Control at Rawalpindi. These strains were different from the strain already present in New Zealand [see the Cumber et al. (1977)/Cameron et al. (1989) entry in the âGeneral commentsâ section]. Field-collected larvae of Agrotis spp. were held in Pakistan until the emerging parasitoid larvae had spun cocoons, which were air-freighted to New Zealand. During April and May some 950 individual cocoons from 20 clusters were received. These produced approximately 500 adults. The culture was reared in New Zealand on Agrotis ipsilon prior to releases.
Cumber et al. (1977) - approximately 4,000 mass-parasitised larvae were distributed at 10 sites in Northland and in the north of the Auckland region in October-November 1971. However, most parasitoids were released as adults after an opportunity to feed and mate. Approximately 40,000 adults were released between December 1971 and March 1972 at 108 sites; four sites were in Nelson in the South Island, the rest were in the northern North Island (Northland, Auckland, Coromandel and the northern part of Waikato).
Cumber et al. (1977) - sampling of maize in the Helensville-Riverhead districts of the Auckland region during January to March 1973 showed that parasitism of M. separata larvae by C. ruficrus was sometimes greater than 80%. During the following winter, samples of larvae from roadside herbage also showed a high percentage of parasitism. The parasitoid became common on maize in the northern North Island in 1973, being found up to 50km from the nearest release sites. Surveys in 1974-75 showed that C. ruficrus had become established throughout the North Island.
Cameron et al. (1989) - following release of the Pakistan strain/s, C. ruficrus established immediately on M. separata and was recovered in a survey of noctuid larvae in 1975-76 from Agrotis ipsilon and Chrysodeixis eriosoma.
Impacts on target:
Cumber et al. (1977) - sampling of maize in the Helensville-Riverhead districts of the Auckland region during January to March 1973 showed that parasitism of M. separata larvae by C. ruficrus was sometimes greater than 80% and that larval populations of the pest were much reduced. The widespread establishment of C. ruficrus throughout the North Island by 1974-75 resulted in a marked reduction in use of insecticides. The Pakistan strains of C. ruficrus are clearly far more efficient than the resident strain [see the Cumber et al. (1977)/Cameron et al. (1989) entry in the âGeneral commentsâ section]. Minor local outbreaks of M. separata may still occur but the pest will never show a resurgence of the epidemic form which was common.
Cameron et al. (1989) - prior to the release of the Pakistan strain of C. ruficrus, a study in the south of the North Island showed a mean level of parasitism of M. separata of 36%, with the resident strain of C. ruficrus responsible for 46% of the parasitism. Subsequent to the release of the Pakistan strain of C. ruficrus, this strain was found to be well established on M. separata with very high rates of parasitism, and parasitism of M. separata was almost exclusively caused (greater than 95%) by C. ruficrus. Prior to the release of the Pakistan strain, large areas of grain crops (mostly maize) and pasture were sprayed for control of M. separata; following its establishment, chemical control is rarely necessary. Cotesia ruficrus has been heralded as an outstanding example of classical biological control and estimates of its annual monetary benefit to New Zealand are NZ$4.5-10 million. While reduction in M. separata outbreaks has been substantial, they still occur, favoured by the presence of weeds in a crop. Recent work suggests the reduction in food consumption by M. separata larvae parasitised by C. ruficrus may make more of a contribution to the biocontrol of the pest than the ability of C. ruficrus to reduce its abundance.
Cameron et al. (1993) - Cotesia ruficrus is categorised as exerting âsubstantialâ control (defined as âother control measures are only occasionally requiredâ) over M. separata.
Impacts on non-targets:
Cameron et al. (1993) - Cotesia ruficrus was reared on four cosmopolitan noctuid pest species as well as the native noctuid pest species, Graphania mutans. This is an example of a biocontrol programme where acceptance of native species as hosts was considered to be advantageous to the potential establishment and success of the agent.
Cumber et al. (1977), Cameron et al. (1989) - a strain of Cotesia ruficrus was already present in New Zealand, and known to parasitise Mythimna separata, prior to the introduction of the Pakistan strain/s of C. ruficrus. [Cumber et al. (1977) say that the resident strain of C. ruficrus had âestablished fortuitously in New Zealandâ, while Cameron et al. (1989) call it âan indigenous strainâ.]
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
Cumber RA, Allan DJ, Helmore L (1977). Introduction and successful establishment in New Zealand of further strains of Apanteles ruficrus Haliday (Hymenoptera: Braconidae) to combat Pseudaletia (Mythimna) separata (Walk.) (Lepidoptera: Noctuidae). New Zealand Journal of Agricultural Research 20(2): 255-258