Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) population ecology in citrus orchards: the influence of orchard age Submitted in fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY at RHODES UNIVERSITY by Sonnica Albertyn December 2017 ABSTRACT 1 Anecdotal reports in the South African citrus industry claim higher populations of false codling moth (FCM), Thaumatotibia (Cryptophlebia) leucotreta (Meyr) (Lepidoptera: Tortricidae), in orchards during the first three to five harvesting years of citrus planted in virgin soil, after which, FCM numbers seem to decrease and remain consistent. Various laboratory studies and field surveys were conducted to determine if, and why juvenile orchards (four to eight years old) experience higher FCM infestation than mature orchards (nine years and older). In laboratory trials, Washington Navel oranges and Nova Mandarins from juvenile trees were shown to be significantly more susceptible to FCM damage and significantly more attractive for oviposition in both choice and no-choice trials, than fruit from mature trees. Although fruit from juvenile Cambria Navel trees were significantly more attractive than mature orchards for oviposition, they were not more susceptible to FCM damage. In contrast, fruit from juvenile and mature Midnight Valencia orchards were equally attractive for oviposition, but fruit from juvenile trees were significantly more susceptible to FCM damage than fruit from mature trees. Artificial diets were augmented with powder from fruit from juvenile or mature Washington Navel orchards at 5%, 10%, 15% or 30%. Higher larval survival of 76%, 63%, 50% and 34%, respectively, was recorded on diets containing fruit powder from the juvenile trees than on diets containing fruit powder from the mature trees, at 69%, 57%, 44% and 27% larval survival, respectively. Bioassays were conducted to determine if differences in plant chemistry between fruit from juvenile and mature trees will have an impact on the susceptibility FCM to entomopathogenic nematodes (EPN), entomopathogenic fungi (EPF) and Cryptophlebia leucotreta granulovirus (CrleGV). No significant differences in the susceptibility of larvae reared on diets containing 15% fruit powder from juvenile and mature trees to EPN and EPF were recorded. Mortality of neonate larvae was significantly lower when placed on diets containing 15% fruit powder from mature trees (45% mortality) than diets containing 15% fruit powder from juvenile trees (61% mortality), after larvae ingested the lowest virus concentration tested, being 2 x104 OBs/ml. Data collected from field surveys showed significantly lower egg parasitism, virus infection of larvae and EPF occurrence in juvenile orchards than mature orchards. Egg parasitism was between 11% and 54% higher in mature orchards than juvenile orchards, with the exception of Mandarins during 2015, where egg parasitism was slightly higher in juvenile orchards, but not significantly so. A significantly higher proportion of larvae retrieved from mature 2 orchards (7% of larvae) were infected with CrleGV than larvae retrieved from juvenile orchards (4% of larvae). A significantly higher occurrence of EPF was recorded in non-bearing and mature orchards, with 40% and 37% occurrence respectively, than in juvenile orchards, with 25% occurrence recorded. EPF occurrence in juvenile orchards increased significantly by 16% to 32% from the first to the third year of sampling. In contrast to results recorded in laboratory trials, similar or higher pest pressure in juvenile orchards than mature orchards did not always result in significantly higher levels of FCM damage under field conditions. FCM damage in juvenile orchards may have been lower than expected, as greater extremes of temperature and lower humidity were recorded in juvenile orchards, which would increase larval mortality. Results of this study showed that juvenile and mature orchards are significantly different and should be managed differently. 3 ACKNOWLEDGEMENTS I wish to express my sincere appreciation to the following persons and institutions: My supervisors, Prof Martin Hill and Dr Sean Moore for their guidance, interest and constructive comments throughout the course of this study. Prof Julie Coetzee for guidance on statistical analysis. Wayne Kirkman, Mathew Goddard, Claire Love, Mellissa Peyper, Sean Thackeray, Dr John Opoku-debhrah, Zongezile Zondi, Zamazima Njili and Zoleka Marwanqana for technical assistance. Dr Candice Coombes and Dr Tamryn Marsberg for identifying entomopathogenic fungi and Prof Antoinette Malan for identifying entomopathogenic nematodes. River Bioscience (Pty) Ltd for supplying the required life stages of false codling moth when needed. The owners and managers of Riverbend Farm, Miskruier Farm, Buffelsbos Farm, Woodridge Farm, Halaron Farm and Douglasdale Farm for allowing me to use their citrus orchards for trials and for their willingness to assist me when needed. Citrus Research International, National Research Foundation and Rhodes University and for funding the project My family and friends, especially my husband for support throughout. 4 TABLE OF CONTENTS ABSTRACT.....................................................................................................1 ACKNOWLEDGEMENTS............................................................................ 4 TABLE OF CONTENTS................................................................................5 TABLES........................................................................................................ 10 FIGURES....................................................................................................... 13 CHAPTER 1 ................................................................................................. 17 General Introduction.................................................................................. 17 1.1 Introduction.................................................................................................17 1.2 Insect Pest Ecology....................................................................................18 1.3 Plant insect interactions.................................................................................21 1.4 Natural enemy interactions........................................................................... 25 1.5 False codling moth.........................................................................................29 1.5.1 Classification and taxonomy...................................................................... 29 1.5.2 Biology and morphology............................................................................ 30 1.5.3 Distribution and host range........................................................................ 32 1.5.4 Economic importance and damage........................................................... 33 1.5.5 Control methods.........................................................................................34 1.5.5.1 Monitoring.............................................................................................34 1.5.5.2 Chemical control...................................................................................35 1.5.5.3 Biological control..................................................................................36 1.5.5.3.1 Parasitoids.....................................................................................37 1.5.5.3.2 Predators........................................................................................38 1.5.5.3.3 Entomopathogenic nematodes...................................................... 38 1.5.5.3.4 Entomopathogenic fungi................................................................ 39 1.5.5.3.5 Viruses...........................................................................................41 1.5.5.4 Cultural control.....................................................................................42 1.5.5.5 Mating disruption..................................................................................42 1.5.5.6 Attract and Kill......................................................................................43 1.5.5.7 Sterile insect technique ...................................................................... 43 1.5.5.8 Post harvest control ............................................................................ 44 5 1.6 Aim of the study............................................................................................45 CHAPTER 2 ................................................................................................. 47 False codling moth oviposition preferences and host susceptibility: the influence of orchard age....................................................................47 2.1 Introduction .................................................................................................... 47 2.2 Materials and Methods .................................................................................. 49 2.2.1 Fruit collection.............................................................................................49 2.2.2 Internal fruit quality tests............................................................................ 49 2.2.3 Nutritional content of Washington Navel oranges......................................50 2.2.4 Washington Navel volatile profile............................................................... 50 2.2.5 False codling moth cultures......................................................................