Characterisation of Lepidoptera species associated with Macadamia in South Africa

Abstract

Lepidoptera is the second largest insect order, following Coleoptera, with approximately 180_000 species of moths and butterflies described to date. The destructive larval stage, along with their abundance and distribution, has made members from Lepidoptera some of the most damaging insects to agriculture and forestry. Lepidopteran larvae feed mostly on foliage, but may also feed on roots, seeds, flowers, fruits, branches and woody stems, with various sources of timber, fodder, fabric and food serving as hosts. Yield losses resulting from lepidopteran feeding can be devastating, with associated costs oftentimes extensive.

Macadamia is one of the hundreds of host species associated with lepidopteran damage. South Africa is currently the largest producer of macadamia nuts worldwide, with Mpumalanga, KwaZulu-Natal and Limpopo serving as the three main production regions. In South Africa, four Lepidoptera have been reported as pests of macadamia, namely Thaumatotibia batrachopa (Meyrick, 1908) (Tortricidae), Thaumatotibia leucotreta (Meyrick, 1913) (Tortricidae), Ectomyelois ceratoniae (Zeller, 1839) (Pyralidae) and Cryptophlebia peltastica (Meyrick, 1921) (Tortricidae). The species composition of these four nut borers and the associated kernel losses from each is largely unresolved.

The work presented in this dissertation focused on lepidopteran pests of macadamia, with an emphasis on species present in South Africa. Information on lepidopteran pests was synthesized, a survey of the lepidopteran larvae present in macadamia nuts between 2017 and 2019 in orchards located in Mpumalanga, KwaZulu-Natal and Limpopo was conducted, population structure of T. batrachopa was analysed and diagnostic tools were developed for T. batrachopa, T. leucotreta, E. ceratoniae and C. peltastica. Various artificial diets and laboratory conditions for the rearing of T. batrachopa were evaluated, and life cycle duration, life stage descriptions, percentage mortality and sex ratio of T. batrachopa were considered.

Chapter 1 of this dissertation provides an overview of literature pertaining to Lepidoptera, with a focus on those associated with macadamia. Information such as the diversity, distribution and host range of lepidopteran pests of macadamia is summarised and the availability of phenology and population studies regarding these species is evaluated. This chapter also considers the species reported as pests in South African macadamia orchards and the products registered for control of these pests.

Chapter 2 of this dissertation focuses on the identification of significant lepidopteran pests in South African macadamia orchards and the development of rapid diagnostic tool for the purpose of optimising control regimes. Identification of lepidopteran species present in macadamia nuts from the three main growing regions between 2017 and 2019 was achieved through the use of mtDNA COI sequence data. These data were also used to determine the phylogenetic relationships between these species and other closely related species and/or species previously associated with macadamia worldwide. Furthermore, the population genetic structure of T. batrachopa was characterised using mtDNA COI sequence data generated in this study. Finally, species-specific PCRs for T. batrachopa and T. leucotreta were developed and a PCR-RFLP assay was designed to identify T. batrachopa, T. leucotreta, E. ceratoniae and C. peltastica.

Chapter 3 of this dissertation aims to evaluate the success of various artificial diets and laboratory conditions for the rearing of T. batrachopa. At present, a sustainable rearing protocol and artificial diet for T. batrachopa have not been determined. This chapter also considers the duration of each life stage, life stage descriptions, percentage mortality and sex ratio of T. batrachopa.