The Host Status of Lemons for the False Codling Moth,Thaumatotibia leucotreta(Meyrick) (Lepidoptera: Tortricidae) with Particular Reference to Export Protocols

Abstract

The South African citrus industry is dependent on export of fresh fruit to many markets around the world, with approximately 70 % of South Africa’s citrus crop being exported (CGA 2013). The false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), is recorded as a pest of citrus fruit in southern Africa (Newton 1998; Grout & Moore 2015). As a result of its endemism to sub-Saharan Africa (Moore 2002), certain export markets of importance for the South African citrus industry, such as Peoples Republic of China, U.S.A. and South Korea, regulate it as a quarantine pest. Control of the pest in the field can be highly effective, using a suite of integrated control options, applied with diligent management (Moore & Hattingh 2012). These can succeed in reducing T. leucotreta infestation by 97 % or more (Moore et al. 2015). Such an integrated system, using the sterile insect technique as the mainstay of the programme, has succeeded in reducing moth catches by 99 %, fruit infestation by 96 % and export rejections by 89 % in the Western Cape Province of South Africa, since the inception of the programme in 2007 (Barnes et al. 2015). Despite the potential efficacy of such control strategies, some export markets still require mandatory post-harvest cold treatment of citrus fruit as a phytosanitary risk mitigation measure for T. leucotreta (SA-DAFF 2014). The cold treatment developed for T. leucotreta by Myburgh (1965) entails maintenance of the fruit at temperatures below 0 °C for 22 days. Such treatment is not only costly to apply, but there is a high risk of the fruit developing chilling injury (Lafuente et al. 2003; Cronje 2007). Some citrus fruit types are able to tolerate such cold treatment, if carefully managed (Lafuente & Zacarias 2006). However, some other citrus types are highly sensitive to cold damage and this cold treatment is not a feasible risk mitigation measure for commercial export of these types (Lafuente & Zacarias 2006). Lemons are highly sensitive to cold damage and cannot withstand exposure to temperatures below 0 °C for 22 days (Underhill et al. 1999; Lafuente & Zacarias 2006). Although standalone postharvest quarantine treatments, such as cold treatment, are still the most commonly used phytosanitary risk mitigation measure (Paull & Armstrong 1994), a range of alternative options, including non-host status, are increasingly being adopted (Liquido et al. 1995; Aluja et al. 2004; Follett & Neven 2006; Follett & Hennessey 2007; Pringle et al. 2015). Pringle et al. (2015) indicated that there are no definitions of host status of fruit specifically for tortricid pests, but referred to the following definitions that Aluja & Mangan (2008) applied to host status for Tephritidae: a natural host is one that is infested under totally natural field conditions. A non-natural host (or conditional host) is not known to be infested under natural field conditions, but there is experimental evidence that it can be infested and produce reproductive adults under laboratory (artificial) conditions. A non-host is one in which development cannot be completed. Pringle et al. (2015) also applied the following definitions provided by NAPPO (2008): a conditional host may be a host or non-host depending on suitability of conditions (e.g. stage of maturity, other physiological conditions or physical conditions), whereas a natural non-host does not become infested in nature. Most importantly, Pringle et al. (2015) followed NAPPO (2008) in its guidelines on determination of host status from natural infestation by evaluating infestation during the export harvest season, as a mandatory requirement in determining host status for phytosanitary purposes, regardless of data from field cage, greenhouse or laboratory trials. This approach to establishing host status was adopted by Armstrong (1991), who declared Sharwil avocados non-hosts (when attached to the tree) for oriental fruit fly, Bactrocera dorsalis (Hendel), and Mediterranean fruit fly, Ceratitis capitata (Wiedemann), after inspection of 114 000 fruit