Risk assessment |
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An over-riding requirement for classical biological control of GWSS in French Polynesia is safety and a demand for minimal to non-existent non-target impacts. Particular attention has been paid to the identification and assessment of risk to non-target native fauna, in particular, native Cicadellids |
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Cicadellids of the Society Islands |
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Surveys and preparation of an inventory of native species collected from the Society Islands has been initiated to reduce the possibility that overlooked indigenous species could be inadvertently put at risk in French Polynesia. Three native species of cicadellids had been described from Society Islands before this program commenced. During our surveys, 24 species from 12 genera have been collected. Some collected species are undescribed native species and in need of detailed studies, others were exotic cicadellids that have invaded French Polynesia. |
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- Taxonomic studies |
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Gonatocerus ashmeadi is a specialized parasitoïd that attacks cicadellid eggs in the tribe Proconiini. Hence introduction of G. ashmeadi in French Polynesia is considered low risk for native cicadellids as surveys have clearly indicated that there are no indigenous representatives in the tribe Proconiini that may be potential hosts for G. ashmeadi. |
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- Morphological study |
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All known hosts of G. ashmeadi are cicadellids of moderately large size (1.5-2cm in length) laying fairly large eggs (2.5- 3 mm in length) that occur in clusters or masses. All cicadellids found in Society Islands are small and appear to lay their eggs singly and not in clusters or masses. The largest native species, T. tahitiensis, is typically between 6- 10 mm in length. Native cicadellids are considered to be at low risk of attack by G. ashmeadi. |
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Non-target impact studies conducted on cicadellids native to California have demonstrated that the risk of G. ashmeadi attacking non-target species depends greatly of the egg laying habit of these species. Cicadellids laying their eggs singly and on young stems, or leaves are not attacked by G. ashmeadi. Our studies indicates that six species of native cicadellids of Society Islands lay their eggs in stems, and 13 on leaves, and no native species produce egg masses typical of GWSS. Thus, these 18 species (out of the 24 surveyed) are considered to be at low risk of attack by G. ashmeadi. |
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Compared egg-laying biology of GWSS (big eggs in mass above) and a native cicadellid (single small egg on leaf below) |
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- Conclusions |
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From these findings, it appears unlikely that G. ashmeadi will attack and develop in eggs of native non-target cicadellids inhabiting the Society Islands. But some uncertainty exists since the inventory of native cicadellid species and the risk assessment study were not fully completed at the time of the release decision. However, all data collected up to the time the release decision was made strongly indicated low risk was posed by G. ashmeadi to native cicadellid species. |
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