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Pest management for durable eucalypts

By T J Murray & H. Lin, June 2017.

Download SWP-T029 (pdf)

Executive summary

One of the more unexpected and important results from the phenology study summarised here, was that only one generation of P. charybdis was observed in each of the two years monitored. This contrasts with two generations usually observed in the North Island. In the North Island the second generation occurs in late summer (February/March) and can be partially reduced due to the actions of two species of egg parasitoids. Given P. charybdis appears to have only one generation in the Marlborough study area, it is possible the phenology of these egg parasitoids is similarly affected, which may reduce their effectiveness and biological control agents and would be worthy of investigation.

Robust developmental data, including developmental thresholds, development duration and stage specific mortality were successfully obtained for all stages of P. charybdis. In combination with environmental data from the field sites, these will be used to create population models for P. charybdis in the Marlborough region. These data will be combined with results obtained from another part of durable eucalypt pest management programme, on growth impact of defoliation, to help inform models for predicting damaging population numbers as part of IPM monitoring.

Clear differences were seen in the incidence and severity of natural insect pest damage sustained by different E. boasistoana families. This indicates there is variation, which if heritable, could provide a basis for selecting for pest tolerance. Interestingly, all except the southern provenance E. bosistoana families sustained less or similar levels of overall and chewing damage compared to the single E. globoidea family assessed as a representative monocalypt. Of the four feeding guilds assessed, chewers inflicted the greatest damage, as expected, and mining damage was relatively minimal. The least tolerant families were more easily identified than the most tolerant and represented the four families from the southernmost provenance, as well as family 128 from Bungonia. Generally, families 108 followed by 125 and 129 show the greatest tolerance, with high proportions of trees sustaining incidental or no damage from the different feeding guilds. Other families were more difficult to rank due to greater variability between the individual trees assessed, but all showed some apparently tolerant individuals which will be investigated further.

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