Preparing the way for sterile insect release: Determination of false codling moth distribution across a landscape mosaic
Introduction
The false codling moth (FCM) (Thaumatotibia leucotreta (Meyrick), Lepidoptera: Tortricidae) is an indigenous pest of citrus fruit, and numerous other crops in sub-Saharan Africa (Newton, 1998, Reed, 1974, Schwartz, 1981, Stibick et al., 2007). It is an important phytosanitary insect, impacting negatively on the export of fresh citrus fruit to international markets (Hofmeyr et al., 2005). FCM is known to infest most types of citrus (Citrus spp.), with the Navel orange cultivar (Citrus sinensis (L.) Osbeck var Navel) being particularly prone to attack, largely due to the presence of a navel end which favours the oviposition of eggs (Schwartz, 1981, Newton, 1990). The efficacy of conventional insecticidal control is being compromised by appearance of insecticide resistance in FCM populations (Hofmeyr and Pringle, 1998), as well as residue restrictions imposed by export markets. Mating disruption, pest-specific granulovirus applications, sterile insect release (SIR) and the integration of the various suppression techniques, including strict orchard sanitation, are options that are currently being adopted (Hofmeyr and Pringle, 1998, Newton, 1998, Moore, 2012).
Little is known about FCM host preferences, or about its dispersal capacity. However, genetic studies suggest that FCM has low dispersal capability (Timm et al., 2010). The movement of FCM between various host types, including citrus orchards, and its ability to maintain a viable population in alternative host plants when there is no fruit available for infestation in citrus orchards has not been well investigated. Knowledge of these largely behavioural facets is important for planning an effective management strategy for FCM, especially SIR, the effectiveness of which would be potentially reduced should there be a substantial population of FCM in natural vegetation outside citrus orchards. In response, the aim of this study was to determine the spatial distribution of FCM at the landscape scale, so as to provide a platform for implementation of an area-wide control strategy that includes the SIR technique.
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Materials and methods
The study was conducted in the Citrusdal area, Western Cape Province, South Africa (S32°35.700′; E18°59.300′). The study area included the agriculturally intensive Olifants river valley, bordered on either side by montane natural fynbos vegetation (mostly Protea spp., Erica spp. and Restio spp.). The valley is ±70 km long, 7–10 km wide. This study site was chosen because of its suitability for the implementation of an SIR programme, being enclosed by mountain ranges and fairly isolated, with
Results
In the first season (April–November 2006), more FCM male individuals were sampled in mixed-variety citrus orchards, than in Navel or Valencia orange orchards (Fig. 1), while more individuals were sampled in Valencia than in Navel orange orchards. During the second season (March–October 2007), there were fewer differences in trap catches between citrus cultivars.
Male FCM flight activity within citrus peaked between May and July, with a smaller peak between September and mid-November (Fig. 2).
Discussion
There was much variation in the number of FCM male individuals sampled from one citrus orchard to another. This, at least in part, is due to variation in FCM management practices, quality of these management practices, as well as host value of the citrus cultivar. Interestingly, there was high abundance within Valencia orange orchards, a cultivar which has been regarded as a poor host for this species (Newton, 1998). This was probably due to the Valencia orange cultivar receiving less attention
Acknowledgements
Citrus Research International funded the project. We thank H and M Hofmeyr for technical support, and landowners for allowing access to sites. MJS acknowledges support from the National Research Foundation, South Africa.
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