Applying for general release or release with controls
The biological characteristics of populations vary. Where variation expresses itself as a consistent and measurable difference between populations, these can sometimes be called biotypes – a subset of individuals that are morphologically similar to but physiologically different from other members of the species. Form, strain, ecotype or variant are similar terms, and the difference between a biotype and a sub-species is not always clear.
Biological control agents introduced to a new country are normally collected in the home range of the pest from one or a small range of source populations. This limited gene pool becomes the founding population for a wide range of environmental conditions in the new environment. Being aware of the variation that exists within a species, and selecting the appropriate source of the control agent can be important to maximising the chance that the control agent will succeed in its new environment, and that its host range can be predicted accurately.
In biological control, there can be biotypes for host range, environmental limits, phenology, and even in breeding systems. A new strain of Microctonus aethiopoides was released in New Zealand recently for the control of clover root weevil. See Biocontrol of clover root weevil [http://www.epa.govt.nz/new-organisms/popular-no-topics/Pages/biocontrol-of-clover-root-weevil.aspx]. A Moroccan biotype of the species had been released in New Zealand years earlier to control the related Sitona discoideus, but this strain did not effectively attack the clover root weevil. Other biotypes in Europe attacked the weevil, but research showed mating between the two biotypes produced hybrids with poor efficacy against target hosts, and given that the Moroccan biotype attacked several native weevil genera in New Zealand, there were serious reservations about introducing the European biotype. Concerns were overcome with the identification of a parthenogenetic strain of European M. aethiopoides from Ireland, which has little risk of hybridisation, and a narrower host range than the Moroccan biotype (Goldson et al. 2003, Gerard et al. 2006, McNeill et al. 2006.
Strain differences may explain the attack of Cydia succedana (a control agent for gorse) on Lotus when it was released in New Zealand, a phenomenon that was not predicted by safety-testing (Fowler et al. 2003). It is now acknowledged good practice in New Zealand to introduce control agents for weeds from a population or biotype equivalent to that used for safety-testing research.
Fowler S.V., Gourlay A.H., Hill R.L. and Withers T. (2003). Safety in New Zealand weed biocontrol: a retrospective analysis of host-specificity testing and the predictability of impacts on non-target plants. Pp. 265–270 in Proceedings of the XI International Symposium on Biological Control of Weeds, Canberra, Australia, 2003, J.M. Cullen, D.T. Briese, D.J. Kriticos, W.M. Lonsdale, L. Morin and J.K. Scott (Ed.).
Gerard P.J., McNeill M.R., Barratt B.I.P. and Whiteman S.A. (2006). Rationale for release of the irish strain of Microctonus aethiopoides for biocontrol of clover root weevil. New Zealand Plant Protection 59: 285-289.
Goldson S.L., McNeill M.R. and Proffitt J.R. (2003). Negative effects of strain hybridisation on the biocontrol agent Microctonus aethiopoides. New Zealand Plant Protection 57: 138-142.
McNeill M.R., Proffitt J.R., Gerard P.J. and Goldson S.L. (2006). Collections of Microctonus aethipopoides Loan (Hymenoptera: Braconidae) from Ireland. New Zealand Plant Protection 59: 290-296.
Natural host range