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Selecting biological control agents

Predicting direct non-target impacts

Exploration in the target home range

Some case studies

The natural host range of Coleoptera feeding on broom (Cytisus scoparius) was surveyed in Europe by Syrett and Emberson (1997) as part of a biocontrol programme for broom. Their aim was to obtain field data on host preferences of broom-feeding Coleoptera to assist in the selection of the most host-specific species for a biocontrol programme. They found nine species feeding on species in the same genus, but that two, Bruchidius villosus (F.)(Coleoptera: Chrysomelidae) and Exapion elongatissimum (Desbrochers)(Coleoptera: Brentidae) were considered to be essentially monophagous. Subsequently, after release in New Zealand it was found that B. villosus attacked the exotic non-target species tagasaste (Cytisus proliferus). Further studies in the native range showed that B. villosus aggregates on the earliest-flowering species, which in New Zealand is tagasaste, which flowers before broom (Sheppard et al. 2006). This study emphasised the value of native-range studies in understanding the role of phenological synchrony in ecological host-specificity.

Haye et al. (2005) retrospectively determined the ecological host range of the braconid Peristenus digoneutis Loan introduced into North America from Europe for control of Lygus spp. (Hemiptera: Miridae). Potential non-target mirids were collected from a wide range of environments in northern Germany. They found that the parasitoid was reared from seven non-target hosts in the same subfamily as the target host but no other subfamilies, and that overall parasitism in non-target species was never more than 1%. No-choice laboratory tests in North America suggested that native Lygus spp. were likely to be hosts but other non-target Miridae were not suitable hosts for P. digoneutis (Mason et al. 2011). Post-release studies in North America have shown that three non-target mirid species were attacked, but at very low levels. However, Peristenus relictus (Ruthe), another parasitoid of mirids was predicted to attack several other non-target species in the field (Mason et al. 2011). The authors noted that although a number of non-target hosts have been identified in the area of origin, and area of introduction, severe non-target effects are not necessarily indicated. They concluded that a complete host range evaluation should combine data from field collections in the area of origin, and laboratory data to avoid rejecting promising biological control agents.

A study of the natural host range of the tachinid Aphantorhaphopsis samarensis (Villeneuve) being considered for biocontrol of gypsy moth (Lymantria dispar L.) was carried out. The only known hosts from the literature were the lymantriids L. dispar and Orgyia recens (Hubner) (Fuester et al. 2001). Collections of potential hosts in Europe in areas where A. samarensis was abundant produced no records of additional hosts, or where pupae were found that resembled the parasitoid, no adult successfully emerged. Over a five year period about 850 larvae representing 54 species and 11 families of Lepidoptera, there were no records of parasitism by A. samarensis. Host specificity testing with North American Lepidoptera were consistent with the data obtained from Europe, and it was concluded that A. samarensis has a narrow host range and presents minimal threat to non-target species.

A review of the research carried out in the natural range of Rhinocyllus conicus (Fröl.) was carried out to determine whether the non-target impacts observed in the introduced range in North America on native thistles could have been predicted (Gassman and Louda 2001). Surveys in Europe over the period 1961 to 1982 showed that R. conicus larvae were found on species in the genera Carduus, Cirsium, Silybum and Onopordum, although a preference for Carduus was indicated. Initially differential phenology was thought to be responsible for geographical variability in host range, but later biotype differences in R. conicus were implicated, and a further theory about innate preference resulting from resource concentration was put forward. The latter two factors combined to convince biocontrol practitioners that there would be minimal non-target impact on native Cirsium species in North America. However, comprehensive post-release studies have shown that R. conicus has undoubtedly impacted on native Cirsium populations in North America. The authors suggest that the evidence from the natural range was sufficient to indicate that further tests were required before a decision to import R. conicus should have been made, and a full analysis of the scientific evidence was sufficient to predict that non-target impacts would occur. They concluded that pressure to address the weed problem, focus on non-target effects on economic plants, and the biotype argument led to the decision that was made.

Gassmann et al. (2008) carried out field surveys in Europe to identify herbivorous arthropods which were genus-specific to the buckthorn species Rhamnus cathartica and Frangula alnus for biocontrol in North America. They identified 21 genus-specific herbivores and 17 apparently monophagous species amongst the herbivorous fauna of buckthorn, and discussed the feeding strategies of these in relation to selecting potential biological control agents.

In New Zealand the braconid Microctonus aethiopoides Loan was introduced to control Sitona discoideus Gyllenhal, but post-release studies have shown that nine genera of non-target species are attacked in the field (), and retrospective laboratory host range tests have shown that nine genera were attacked (five in common). The same parasitoid was introduced in to Australia, and surveys to date have shown that only one native species (single record) was attacked (Barratt et al. 2005). M. aethiopoides was introduced from Moroccan populations to both Australia and New Zealand, but the known natural host range includes only two genera of weevils, Sitona and Hypera. Recent investigations in the natural range, Morocco, and in Australia where the previous record of non-target parasitism was found, were carried out to determine whether M. aethiopoides is indeed restricted to these two genera in Morocco, or whether in fact the natural host range is much broader.

Over 600 weevils comprising 47 species were collected in Morocco, but only four species were found to contain parasitoid larvae consistent with M. aethiopoides. These were Sitona discoideus, which was the species most abundantly collected, but also parasitised was Charagmus gressorius (F.), C. griseus and Hypera postica (Gyllenhal).

Sampling in Australia was also designed to optimise collection of potential non-target hosts of M. aethiopoides. However, no further records of non-target parasitism were detected after collecting about 350 specimens of weevils comprising 13 species from and near lucerne at the site in NSW where the single incidence of non-target parasitism had been found previously.


Barratt B.I.P., Oberprieler R.G., Ferguson C.M. and Hardwick S. (2005). Parasitism of the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) and non-target weevils by Microctonus aethiopoides Loan (Hymenoptera: Braconidae) in south-eastern Australia, with an assessment of the taxonomic affinities of non-target hosts of M. aethiopoides recorded from Australia and New Zealand. Australian Journal of Entomology 44: 192-200.

Fuester R.W., Kenis M., Swan K.S., Kingsley P.C., López-Vaamonde C. and Hérard F. (2001). Host Range of Aphantorhaphopsis samarensis (Diptera: Tachinidae), a larval parasite of the gypsy moth (Lepidoptera: Lymantriidae). Environmental Entomology 25: 332-340.

Gassman A. and Louda S.M. (2001). Rhinocyllus conicus: initial evaluation and subsequent ecological impacts in North America. Pp. 147-183 In: Evaluating indirect ecological effects of biological control, E. Wajnberg, J.K. Scott and P.C. Quimby (Ed.) CABI Publishing, Wallingford, Oxon., UK.

Gassmann A., Tosevski I. and Skinner L. (2008). Use of native range surveys to determine the potential host range of arthropod herbivores for biological control of two related weed species, Rhamnus cathartica and Frangula alnus. Biological Control 45: 11-20

Haye T., Goulet H., Mason P.G. and Kuhlmann U. (2005). Does fundamental host range match ecological host range? A retrospective case study of a Lygus plant bug parasitoid. Biological Control 35: 55-67.

Mason P.G., Broadbent A.B., Whistlecraft J.W. and Gillespie D.R. (2011). Interpreting the host range of Peristenus digoneutis and Peristenus relictus (Hymenoptera: Braconidae) biological control agents of Lygus spp. (Hemiptera: Miridae) in North America. Biological Control 57: 94-102.

Sheppard A., Haines M.L. and Thomann T. (2006). Native-range research assists risk analysis for non-targets in weed biological control: the cautionary tale of the broom seed beetle. Australian Journal of Entomology 45: 292-297

Syrett P. and Emberson R.M. (1997). The natural host range of beetle species feeding on broom Cytisus scoparius (L.) Link (Fabaceae) in south-west Europe. Biocontrol Science and Technology 7: 309-326