Host specificity testing and suitability of the parasitoidMicroctonus hyperodae (Hym.: Braconidae, Euphorinae) as a biological control agent ofListronotus bonariensis (Col.: Curculionidae) in New Zealand

Abstract

The behaviour of the parasitoid Microctonus hyperodae Loan was studied under quarantine conditions to determine its likely host range in New Zealand. The species was imported from South America as a potential biological control agent of Argentine stem weevil, Listronotus bonariensis (Kuschel).The study involved systematic evaluation of the parasitoid's behaviour when exposed to 24 non-host weevil species ; all but three of these were native to New Zealand. Of those tested, four were found to sustain some M. hyperodae development. However, further examination showed that in all but one species, Irenimus aequalis (Broun), parasitoid development was impeded, with up to 50 % of the larvae becoming encapsulated. Overall, those weevil species that were attacked produced only 19 % of the parasitoids derived from L. bonariensis controls.As an adjunct to this quarantine study, a review of the habitats of the native weevil and target pest populations indicated that refugia would probably exist for native alpine species.L aequalis was not considered to be threatened by M. hyperodae as this weevil has benefited from the advent of European agricultural systems to the extent that it is now recognised as a minor pest. In view of its relatively oligophagous behaviour, the parasitoid was recommended as suitable for release. KEY-WORDS :Microctonus hyperodae, New Zealand, host range, habitat separation.

Host specificity testing and suitability of a European biotype of the braconid parasitoidMicroctonus aethiopoidesas a biological control agent againstSitona lepidus(Coleoptera: Curculionidae) in New Zealand

“…In order to provide stringent evaluation of biological control 'safety', non-target test species are generally exposed to as much pressure as possible from candidate control agents through the use of no-choice tests. This provides maximum estimates of likely host range (e.g., Goldson et al 1992;Barratt et al 1997b). Furthermore, measurement of the incidence of complete parasitoid larval development in non-target hosts, as indicated by the emergence of prepupae, is a useful estimator of the ability of non-target hosts to permit at least some inter-generational development of the parasitoid.…”

Methods Used to Assess Non-target Effects of Invertebrate Biological Control Agents of Arthropod Pests

“…If only a few replicates are carried out in host specificity tests, the potential variability of the agent may not be accounted for, which may lead to false positives or negatives. For instance, 1--3 replicates were conducted by Goldson et al (1992) and Neale et al (1995), although groups of up to 50 female parasitoids were introduced for each replicate (see Table 1). The reasoning of using groups of the agent was that variability of the data decreases.…”

The value of parasitoids in biological control

“…Such effort may take two forms: another biological control agent can be introduced, and/or conditions can be changed to allow optimisation of existing control systems. The details of such activities are beyond the scope of this contribution but in brief may comprise such considerations as ecotypic effects (e.g., Caltagirone 1985;Goldson et al 1992), allomone/ kairomones (e.g., Lewis et al 1975), crop modification, food plants for beneficial insects (e.g., Shahjahnan 1974), cultural practices, and the maintenance of refugia (e.g., Ali & Reagan 1985).…”

“…This has increased the requirement for host-specific agents that will not threaten potentially at-risk nontarget species. Therefore, fewer species of natural enemies are likely to be suitable for use, and these must now be carefully scrutinised for possible ecological side effects (e.g., Goldson & Phillips 1991;Goldson et al 1992). Parasitoids have already made a large contribution to existing biological control programmes in New Zealand (e.g., Goldson et al 1990) and, in view of the requirements described above, the limited host range of many koinobiontic (Haeselbarth 1979) parasitoid species suggests that they are likely to become even more valuable to future efforts.…”