Selecting biological control agents
Native range - experimental confirmation of host range
Applicants to the EPA must demonstrate the range of hosts that a new organism will exploit once released in New Zealand and assess the direct risks of those interactions. It is theoretically possible that the behaviour of the organism in the field in its native range could provide sufficient information to do this, but it is more likely that experimental evaluation of the organism's host range testing will be required to achieve this. The purpose of conducting host range tests on a potential biological control agent is to avoid introducing an agent that might cause significant economic or environmental damage while avoiding the unnecessary rejection of a potentially effective agent. Host-specificity testing remains the most important method for predicting the safety of both weed (Briese 2006) and arthropod (van Lenteren et al. 2006, van Lenteren et al. 2006) control agents.
Host-range studies to predict possible non-target effects of biological control agents for weeds were first conducted in the 1920's (McFadyen 1998). Based largely on a retrospective study of almost 50 years of such research, Wapshere (1974) proposed a strategy for evaluating the safety of organisms for biological weed control in which plants of decreasing relatedness are presented to the control agent until no further attack is observed. The pattern of attack revealed by this process defines the taxonomic limit (species, genus, etc) within which the host range lies. This hypothesis has become standard practice throughout the world for determining the fundamental host range of potential control agents for weeds. Wapshere's original paradigm has proven to be robust, and appears to be equally useful in predicting the host range of biotrophic pathogens (Morin and Edwards 2006).
There have been few examples recorded where these standardised procedures for estimating field host range of arthropod or fungal control agents have failed (Fowler et al. 2000, Pemberton 2000, Barton 2004). In New Zealand, a recent survey of the field host range of most of the agents introduced for the biological control of weeds indicated no cases where the recorded host-range was not, or could not have been predicted by appropriate application of centrifugal phylogenetic testing before the agents were released (Paynter et al. 2004).
Historically, testing of control agents for arthropod pest control has been restricted to checking that the parasitoid or predator attacks the target host, is not a hyperparasitoid of other natural enemy of the host, and does not attack biocontrol agents of other pests. van Driesche and Hoddle (2000) reviewed the techniques available at that time and recommended that the non-target species tested should include not only insects that are closely-related to the host, but also arthropods of special ecological or scientific interest even if distantly related, including biological control agents.
The process of determining the host range of a parasitoid experimentally is complicated by other issues, and sorting out the framework for predicting host range is a big theoretical issue (Bigler et al. 2006). Host range testing of parasitoids is conducted despite these constraints. van Driesche and Hoddle (2000) and Kuhlmann et al. (2005) list and discuss a range of programmes conducted over the last 24 years that have assessed the host range of parasitoids prior to release. While wider host-testing of parasitoids developed for arthropod control has been carried out in New Zealand since the 1970's (Hill et al. 1985), this has not been standard practice in other parts of the world. Recent New Zealand exemplars include Cameron and Walker (1989), Cameron et al. (1995), Stufkens et al. (1994), Cameron and Walker (1997), Barratt et al. (1997), Froud and Stevens (1998), ERMA New Zealand (2000), Charles (2001) and Berndt et al. (2007). Some recent testing programmes for control agents for weed control in New Zealand are described by Hill et al. (2001), Hill et al. (2001), Hill and Gourlay (2002) and Grosskopf et al. (2002).
The factors influencing host selection in natural enemies have already been reviewed in this section. The next two sections review how species are selected for testing, and the experimental techniques used to evaluate these influences on agent safety.
Barratt B.I.P., Evans A.A., Ferguson C.M., Barker G.M., McNeill M.R. and Phillips C.B. (1997). Laboratory nontarget host range of the introduced parasitoids Microctonus aethiopoides and Microctonus hyperodae (Hymenoptera: Braconidae) compared with field parasitism in New Zealand. Environmental Entomology 26: 694-702.
Barton J.E. (2004). How good are we at predicting the field host-range of fungal pathogens used for classical biological control of weeds? Biological control in agricultural IPM systems 31: 99-122
Berndt L.A., Mansfield S. and Withers T.M. (2007). A method for host range testing of a biological control agent for Uraba lugens. New Zealand Plant Protection 60: 286-290.
Bigler F., Babendreier D. and Kuhlmann U. (2006). Environmental impact of arthropod biological control: methods and risk assessment. Pp. 288. CABI Publishing, Delemont, Switzerland.
Briese D.T. (2006). Can an a priori strategy be developed for biological control? The case for Onopordum spp. thistles in Australia. Australian Journal of Entomology 45: 317-323
Cameron P.J. and Walker G.P. (1989). Status of introduced larval parasitoids of tomato fruitworm. Proceedings of the New Zealand Plant Protection Conference 42: 229-232
Cameron P.J. and Walker G.P. (1997). Host specificity of Cotesia rubecula and Cotesia plutellae, parasitoids of white butterfly and diamondback moth. Pp. 236-241 In: Proceedings of the 50th New Zealand Plant Protection Conference, M. O'Callaghan (Ed.) NZ Plant Protection Society Inc.
Cameron P.J., Walker G.P. and Keller M.A. (1995). Introduction of Cotesia rubecula, a parasitoid of white butterfly. Proceedings of the New Zealand Plant Protection Conference 48: 345-347
Charles J.G. (2001). Introduction of a parasitoid for mealybug biocontrol: a case study under new environmental legislation. New Zealand Plant Protection 54: 37-41
ERMA New Zealand (2000). Pseudaphycus maculipennis for the control of the obscure mealybug (Pseudococcus viburni). Evaluation and Review Report.
Fowler S.V., Syrett P. and Hill R.L. (2000). Success and safety in the biological control of environmental weeds in New Zealand. Austral Ecology 25: 553-562.
Froud K.J. and Stevens P.S., (1998). Parasitism of Heliothrips haemorrhoidalis and two non-target thrips by Thripobius semiluteus (Hymenoptera; Eulophidae) in quarantine. Pp. 526-529 In: Pest Management - Future Challenges. Proceedings of the 6th Australasian Applied Entomological Research Conference, M.P. Zalucki, R.A.I. Drew and G.G. White (Ed.) Brisbane Australia.
Grosskopf G., Smith L.A. and Syrett P. (2002). Host range of Cheilosia urbana (Meigen) and Cheilosia psilophthalma (Becker) (Diptera: Syrphidae), candidates for the biological control of invasive alien hawkweeds (Hieracium spp., Asteraceae) in New Zealand. Biological Control 24: 7-19
Hill R.L. and Gourlay A.H. (2002). Host-range testing, introduction, and establishment of Cydia succedana (Lepidoptera: Tortricidae) for biological control of gorse, Ulex europaeus L., in New Zealand. Biological Control 25: 173-186
Hill R.L., Cumber R.A. and Allan D.J. (1985). Parasitoids introduced to control larvae of the Noctuidae (Lepidoptera) in New Zealand (1968-1978). DSIR Entomology Division, 24 p.
Hill R.L., Markin G.P., Gourlay A.H., Fowler S.V. and Yoshioka E. (2001). Host range, release, and establishment of Sericothrips staphylinus Haliday (Thysanoptera: Thripidae) as a biological control agent for gorse, Ulex europaeus L. (Fabaceae), in New Zealand and Hawaii. Biological Control 21: 63-74
Hill R.L., Wittenberg R. and Gourlay A.H. (2001). Biology and host range of Phytomyza vitalbae and its establishment for the biological control of Clematis vitalba in New Zealand. Biocontrol Science and Technology 11: 459-473
Kuhlmann U., Schaffner U. and Mason P.G. (2005). Selection of non-target species for host specificity testing of entomophagous biological control agents. Pp. 566-583 In: Second International Symposium on Biological Control of Arthropods, Davos, Switzerland, 12-16 September, 2005, M.S. Hoddle (Ed.) United States Department of Agriculture, Forest Service, Washington.
McFadyen R.E.C. (1998). Biological control of weeds. Annual Review of Entomology 43: 369-393.
Morin L. and Edwards P.B. (2006). Selection of biological control agents for bridal creeper: a retrospective review. Australian Journal of Entomology 45: 287-291
Paynter Q.E., Fowler S.V., Gourlay A.H., Haines M.L., Harman H.M., Hona S.R., Peterson P.G., Smith L.A., Wilson-Davey, J.R.A., Winks, C.J. and Withers T.M. (2004). Safety in New Zealand Weed Biocontrol: A nationwide survey for impacts on non-target plants. New Zealand Plant Protection 57: 102-107
Pemberton R.W. (2000). Predictable risk to native plants in weed biological control. Oecologia 125: 489-494.
Stufkens M.W., Farrell J.A. and Popay A.J. (1994). Quarantine host range tests on two exotic parasitoids imported for aphid control. Pp. 149-153 In: Proceedings of the 47th New Zealand Plant Protection Conference.
van Driesche R.G. and Hoddle M.S. (2000). Classical arthropod biological control: assessing success, step by step. Pp. 39-75 In: Biological control: Measures of success, G.M. Gurr and S.D. Wratten (Ed.) Kluwer Academic Publishers, Dordrecht, The Netherlands
van Lenteren J.C., Bale J., Bigler F., Hokkanen H.M.T. and Loomans A.J.M. (2006). Assessing risks of releasing exotic biological control agents of arthropod pests. Annual Review of Entomology 51: 609-634.
van Lenteren J.C., Cock M.J.W., Hoffmeister T.S. and Sands D.P.A. (2006). Host specificity in arthropod biological control, methods for testing and interpreting the data. Pp. 38-63. CAB Publishing, Delemont.
Wapshere A.J. (1974). A strategy for evaluating the safety of organisms for biological weed control. Annals of Applied Biology 77: 201-211.
Habitats and agent mobility
Selecting test species