Studies of the Mechanisms Involved in Host Finding And
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STUDIES OF THE MECHANISMS INVOLVED IN HOST FINDING AND MATING BEHAVIOUR OF THE AFRICAN COFFEE WHITE STEM BORER, MONOCHAMUS LEUCONOTUS (PASCOE) (COLEOPTERA: CERAMBYCIDAE) Dumisani Kutywayo A thesis submitted in partial fulfilment of the requirements of the University of Greenwich for the Degree of Doctor of Philosophy August 2015 To My Mother and Late Father ii ABSTRACT The African coffee white stem borer, Monochamus leuconotus (Coleoptera: Cerambycidae) is a serious pest of Arabica coffee in Zimbabwe and other African countries. Very was known about the chemical ecology of M. leuconotus prior to the initiation of the studies described in this thesis. The objectives of this work were to investigate the mating behaviour in order to look for evidence of the existence of chemical interactions between conspecific beetles and host plants. Mating behaviour and daily activity patterns of adult M. leuconotus were characterised under laboratory and semi- field conditions. Mating was initiated after the male encountered a searching female and touched her with antennae or tarsi. The activities of feeding, walking, mounting and copulation were mostly done during daylight hours with the exception of oviposition, which occurred at night. Laboratory bioassays conducted to determine whether contact pheromones played a role in mate recognition showed that males were able to complete the full sequence of behavioural activities involved in mating with both live and dead conspecific females. Males did not respond to dead females washed with hexane, and the responses could be partially restored by recoating the washed females with the hexane washings, indicating that cuticular hydrocarbons are important for recognition of sex and species. A laboratory bioassay was developed for evaluating the olfactory response of M. leuconotus to different cues. Females responded positively to coffee leaves, coffee bark scrapings and the synthetic male-specific compound of M. leuconotus dispensed in a sachet while males responded positively to coffee bark and to a combination of coffee leaves and the synthetic male-specific compound dispensed in a vial. Field trapping trials were conducted in Zimbabwe using live insect baits and the synthetic male-specific compound of M. leuconotus dispensed in polyethylene sachet and vials and different trap designs. Significant numbers of beetles were captured in traps baited with the male-specific compound, and numbers caught were further increased when certain host-plant volatiles were added, particularly (R)-(-)-linalool and methyl salicylate. Intercept panel traps and MK2 rat traps were effective in retaining insects caught. Floral surveys conducted around coffee fields to identify alternative host plants did not give conclusive evidence on the existence of alternative host plants although suspected coffee stem borer symptoms of attack were observed on previously reported alternative host plants. Feeding and oviposition studies suggested that female M. leuconotus feed mostly on Rubiaceae and preferred to lay eggs on Coffea arabica, G. ternifolia, V. infausta and K. venosa. The implications of the findings in relation to possible application of chemical ecology in management of M. leuconotus are discussed. iv ACKNOWLEDGEMENTS I would like to thank all those who have contributed to the success of this work. In particular, I would like to salute my main supervisor, Prof. David Hall for agreeing to be my mentor and living up to it up to the final stages. I would also like to recognize the support of my second supervisor Prof. Steve Torr for the encouragement and direction in data processing not forgetting the ever-accessible Dudley Farman for IT and overall support. At the Coffee Research Station, Zimbabwe, my colleagues Meeting Mbangani, Abel Chemura, Samuel Maronga, Sarah Chikerede, Tapiwa Foroma, Julius Mathende and the late Simba Maesera deserve special mention for their assistance in collection of insects in the field and maintaining a positive interest as the study progressed. My friend at ARDA Katiyo, Dennis Siduna deserves a special mention for his assistance in monitoring the traps while Chris Chapano helped in identifying plants during the surveys in search of alternative host plants. My colleagues in the Coffee White Stem Borer project at CABI namely, Dr. Sean Murphy, Dr. George Oduor, Dr. Noah Phiri and Mr. Morris Akiri encouraged me throughout while similar support came from Mr. Caleb Dengu formerly of the CFC and Dr. Dennis Seuidieu of the ICO. My fellow students at NRI namely, Jo Sarfor and Freddy van Hulst provided me with unlimited support. This thesis would not have been complete without the generous financial support from the Common Fund for Commodities and the Natural Resources Institute. v TABLE OF CONTENTS DECLARATION .............................................................................................................. III ABSTRACT ..................................................................................................................... IV ACKNOWLEDGEMENTS ................................................................................................ V TABLE OF CONTENTS .................................................................................................. VI ABBREVIATIONS ........................................................................................................ XVI GLOSSARY OF TERMS USED ................................................................................. XVII CHAPTER 1 GENERAL INTRODUCTION ................................................................ 1 1.1. BACKGROUND TO CURRENT WORK .............................................................. 1 1.2. THE COFFEE WHITE STEM BORER, Monochamus leuconotus (Pascoe) ........ 1 1.2.1 Classification .................................................................................................... 1 1.2.2 Description of M. leuconotus ............................................................................ 2 1.2.3 Life history ........................................................................................................ 4 1.2.4 Economic significance ..................................................................................... 5 1.2.5 Alternative host plants of M. leuconotus .......................................................... 5 1.2.6 Oviposition and larval development of M. leuconotus ...................................... 7 1.2.7 Current management practices for M. leuconotus ........................................... 7 1.3. GENERAL REVIEW OF SEMIOCHEMICALS ..................................................... 8 1.3.1 Semiochemicals ............................................................................................... 8 1.3.2 Allelochemicals ................................................................................................ 8 Kairomones ............................................................................................................................ 9 Synomones ............................................................................................................................. 9 Other categories of allelochemicals ..................................................................................... 10 1.3.3 Pheromones ................................................................................................... 10 Sex pheromones ................................................................................................................... 11 Aggregation pheromones .................................................................................................... 11 vi Alarm pheromones ............................................................................................................... 11 Trail pheromones ................................................................................................................. 12 Epideictic pheromones ......................................................................................................... 12 1.3.4 Insect movement in response to stimuli ......................................................... 12 Attraction and Repulsion ...................................................................................................... 13 Baits/Lures............................................................................................................................ 13 1.4. INSECT DETECTION OF ODOUR SOURCES ................................................. 13 1.5. PHEROMONE IDENTIFICATION ...................................................................... 15 1.5.1 Overview of procedure ................................................................................... 15 1.5.2 Proof of pheromone existence ....................................................................... 15 1.5.3 Collection of chemical .................................................................................... 16 1.5.4 Pheromone Identification ............................................................................... 16 Separation ............................................................................................................................ 16 Bioassays .............................................................................................................................. 17 Analysis and identification ................................................................................................... 18 1.5.5 Pheromone synthesis in the laboratory .........................................................