Biocontrol introduction
Target pest: Sitona obsoletus (Coleoptera: Curculionidae) = Sitona lepidus, clover root weevil
Agent introduced: Microctonus aethiopoides European biotypes (Hymenoptera: Braconidae)
Imported:
2000
Import source:
Europe (see 'Import notes' section for details).
Import notes:
Goldson et al. (2001) - in the European summer of 2000, approximately 8,500 Sitona lepidus [subsequently reclassified as S. obsoletus] were collected from 15 locations in 11 European countries, and parasitoids reared out and identified, initially in Montpellier, France, and later at North Wyke, Devon, England. All ecotypes of M. aethiopoides were found to develop readily in S. obsoletus and between September and November 2000 four shipments, totalling 1,599 parasitised weevils, were sent from North Wyke to New Zealand containment for culturing and analysis. These yielded 267 M. aethiopoides pupae, from which 204 adults were reared. By November 2000, six ‘ecotypes’ of M. aethiopoides had been established in containment at Lincoln, Canterbury. These were from (with the numbers in brackets indicating the number of parental pairs each population could be traced back to by May 2001) Aberystwyth (Wales) (2), Athenry (Ireland) (1), Heggenes (Norway) (3), Mikkeli (Finland) (1), Montpellier (France) (2) and North Wyke (England) (3). In addition, ‘hybrids’ were established from North Wyke/Brasov (Romania) (2), Mikkeli/Pordenone (Italy) (2), Mikkeli/Wigtown (Scotland) (1) and Montpellier/Nancy (France) (3).
Released:
2006 [Only the biotype from Ireland was released - see Microctonus aethiopoides Irish biotype entry. Also, see Goldson et al. (2003) and Goldson et al. (2005) in 'General comments' section below for rationale.]
Release details:
See Microctonus aethiopoides Irish strain entry.
Establishment:
See Microctonus aethiopoides Irish strain entry.
Impacts on target:
See Microctonus aethiopoides Irish strain entry.
Impacts on non-targets:
Goldson et al. (2005) - host range testing for M. aethiopoides European biotype was carried out in quarantine in New Zealand with strains from Wales, Ireland and Romania [see ‘Import notes’ section]. However, the Irish strain, found to be parthenogenetic, was used predominantly in the testing. Potential non-target host weevils tested were five native species in tribes closely related to the tribe to which S. obsoletus belongs and four introduced species released in New Zealand as weed biocontrol agents. European M. aethiopoides was able to develop in the native weevils Irenimus aequalis, Nicaeana cervina, Catoptes cuspidatus, Protolobus porculus and Steriphus variabilis with parasitism rates of 13, 28, 2, 7 and 8%, respectively. These levels were significantly less than those in the corresponding S. obsoletus controls (69%). These results suggest that in the field I. aequalis and N. cervina could probably support successive generations of European M. aethiopoides while C. cuspidatus is very unlikely to. Protobolus porculus and S. variabilis may support some parasitoid development but this is unlikely to be at a level that would significantly affect the host population densities. Of the introduced weevils tested low levels of development were found in the nodding thistle biocontrol agent Rhinocyllus conicus (1%), and the gorse biocontrol agent Exapion ulicis (7%). In comparison, development levels of M. aethiopoides Morrocan biotype (released in New Zealand as a biocontrol of Sitona discoideus) in these two hosts in this study were 23% and 12% respectively. Rhinocyllus conicus, but not E. ulicis, is known to be attacked in the field in New Zealand by Moroccan M. aethiopoides. These results suggest neither of these biocontrol agents are likely to be field hosts for European M. aethiopoides. In conclusion, this study indicates that while European M. aethiopoides is capable of successfully parasitising non-target species, rates of parasitism were less than its Moroccan counterpart and it is likely to have fewer hosts [see Barratt et al. (1997) information in the Microctonus aethiopoides Moroccan biotype entry]; therefore, should the parthenogenetic biotype from Ireland be released in New Zealand its ecological impacts are likely to be less severe than those already imparted by the Moroccan M. aethiopoides.
General comments:
Goldson et al. (2003) - hybridisation trials between a European strain of M. aethiopoides (a parasitoid of S. obsoletus) and a Moroccan strain (widespread in New Zealand and an effective biocontrol of lucerne weevil, Sitona discoideus, but ineffective against S. obsoletus) showed that while these strains have notable host differences they are not reproductively isolated. Results showed a progressive decline in efficacy between the initial crossing of European females with Moroccan males and ensuing strain hybrids. Therefore, a strain introduced into New Zealand to control S. obsoletus could cross with the Moroccan strain, significantly reducing effectiveness of M. aethiopoides against both S. obsoletus and S. discoideus.
Goldson et al. (2005) - fortunately, the population imported from Ireland [see ‘Import notes’ section] has been found to be parthenogenetic, so this variant offers promise as a biocontrol agent for S. obsoletus [avoiding the possibility of hybridisation with the Moroccan biotype of M. aethiopoides released against Sitona obsoletus - see Goldson et al. (2003) above].
References
Goldson SL, McNeill MR, Proffitt JR (2003). Negative effects of strain hybridisation on the biocontrol agent Microctonus aethiopoides. New Zealand Plant Protection 56: 138-142 https://journal.nzpps.org/index.php/nzpp/article/view/6055/5883
Goldson SL, McNeill MR, Proffitt JR, Barratt BIP (2005). Host specificity testing and suitability of a European biotype of the braconid parasitoid Microctonus aethiopoides as a biological control agent against Sitona Lepidus (Coleoptera: Curculionidae) in New Zealand. Biocontrol Science and Technology 15(8): 791-813 https://doi.org/10.1080/09583150500136444
Goldson SL, Phillips CB, McNeill MR, Proffitt JR and Cane RP (2001). Importation to New Zealand Quarantine of a candidate biological control agent of clover root weevil. New Zealand Plant Protection 54: 147-151 https://journal.nzpps.org/index.php/nzpp/article/view/3756/3584
