Bioecology of lepidopteran pests of Macadamia integrifolia in South African production areas

MSc (Integrated Pest Management), North-West University, Potchefstroom Campus

South Africa is the largest exporter of macadamia nuts in the world. Larvae of the Lepidoptera nut borer complex causes economic damage to macadamia in South Africa. Larvae damage both young developing and old hard nuts which then drop from trees and may be unsuitable for processing. The Lepidoptera species that constitute the nut borer complex in South Africa are Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), Thaumatotibia batrachopa (Meyrick) (Lepidoptera: Tortricidae), Cryptophlebia peltastica (Meyrick) (Lepidoptera: Tortricidae) and Ectomyelois ceratoniae (Zeller) (Lepidoptera: Pyralidae). Mixed populations of these species are often reported in macadamia orchards in South Africa. Previous surveys of the nut borer complex in Limpopo and Mpumalanga showed that the species complex may change within and between seasons. Limited information is available on the nut borer, both within smaller regions in provinces, as well as in areas such as KwaZulu-Natal. The aims of this study were to determine the moth flight patterns, population structure, phenology, and relative abundance of larvae of the nut borer complex over a growing season at Barberton in the Mpumalanga province of South Africa. In this study, pheromone traps were used to monitor moth numbers during one growing season and nuts were sampled to determine the identity and quantify of larval numbers inside nuts at weekly intervals for 21 weeks after commencement of macadamia flowering at this locality. Identification of larvae was done using both morphological and molecular methods. A rapid assessment of the species complex was also done by means of an area-wide survey at five localities outside of the Barberton area, including the two sites in KwaZulu-Natal. Three of the moth species were captured by means of pheromone traps at Barberton. According to moth catches, T. leucotreta dominated T. batrachopa, with these two species making up 69 % and 27 % of the trap catches, respectively. No E. ceratoniae moths were captured in pheromone traps. Peak moth flight numbers were recorded 12-16 weeks after commencement of flowering. Significant bycatches of T. batrachopa were made in the traps put out for C. peltastica, and vica versa. Larval infestations, which included E. ceratoniae, varied during the season and was dominated by T. leucotreta, followed by T. batrachopa, E. ceratoniae and C. peltastica. Four other Lepidoptera species were also recorded at Barberton but at very low numbers. These were: Lobesia vanillana (de Joannis), Nola imitate (Son) (Nolidae), Janseodes melanospila (Guenée) (Erebidae), and Ariathisa sp. (Noctuidae). In the area wide survey, all the species of the borer complex were collected, except for C. peltastica. The most diverse nut borer complex was recorded at Levubu and Nelspruit. Thaumatotibia batrachopa was recorded in three of the areas, including KwaZulu-Natal while T. leucotreta was only recorded in Mpumalanga and Limpopo. Ectomyelois ceratoniae was recorded in Mpumalanga and Limpopo as well as in one locality in KwaZulu-Natal where it was also the only species that was collected from fallen nuts. Monitoring data such as this can be used in decision making regarding the application of various pest management practices. This study highlights the discrepancy between pheromone trap catches and larval numbers and that trap captures do not provide an accurate indication of the larval community composition and the time of infestation.

Masters