title: Mating competitiveness of sterile genetic sexing strain males (GAMA) under laboratory and semi-field conditions: Steps towards the use of the Sterile Insect Technique to control the major malaria vector Anopheles arabiensis in South Africa.
abstract: BACKGROUND
  Anopheles arabiensis Patton is primarily responsible for malaria transmission in South Africa after successful suppression of other major vector species using indoor spraying of residual insecticides. Control of An. arabiensis using current insecticide based approaches is proving difficult owing to the development of insecticide resistance, and variable feeding and resting behaviours. The use of the sterile insect technique as an area-wide integrated pest management system to supplement the control of An. arabiensis was proposed for South Africa and is currently under investigation. The success of this technique is dependent on the ability of laboratory-reared sterile males to compete with wild males for mates. As part of the research and development of the SIT technique for use against An. arabiensis in South Africa, radio-sensitivity and mating competitiveness of a local An. arabiensis sexing strain were assessed.
  
  
  METHODS
  The optimal irradiation dose inducing male sterility without compromising mating vigour was tested using Cobalt 60 irradiation doses ranging from 70-100 Gy. Relative mating competitiveness of sterile laboratory-reared males (GAMA strain) compared to fertile wild-type males (AMAL strain) for virgin wild-type females (AMAL) was investigated under laboratory and semi-field conditions using large outdoor cages. Three different sterile male to fertile male to wild-type female ratios were evaluated [1:1:1, 5:1:1 and 10:1:1 (sterile males: fertile, wild-type males: fertile, wild-type females)].
  
  
  RESULTS
  Irradiation at the doses tested did not affect adult emergence but had a moderate effect on adult survivorship and mating vigour. A dose of 75 Gy was selected for the competitiveness assays. Mating competitiveness experiments showed that irradiated GAMA male mosquitoes are a third as competitive as their fertile AMAL counterparts under semi-field conditions. However, they were not as competitive under laboratory conditions. An inundative ratio of 10:1 induced the highest sterility in the representative wild-type population, with potential to effectively suppress reproduction.
  
  
  CONCLUSIONS
  Laboratory-reared and sterilised GAMA male An. arabiensis at a release ratio of 3:1 (3 sterile males to 1 wild, fertile male) can successfully compete for insemination of wild-type females. These results will be used to inform subsequent small-scale pilot field releases in South Africa.
authors.affiliation: Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Private Bag X4, Sandringham, Johannesburg, South Africa. gmunhenga@yahoo.com.|Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. gmunhenga@yahoo.com.
authors.forename: Givemore
authors.initials: G
authors.lastname: Munhenga
authors.affiliation: Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Private Bag X4, Sandringham, Johannesburg, South Africa. basilb@nicd.ac.za.|Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. basilb@nicd.ac.za.
authors.forename: Basil D
authors.initials: BD
authors.lastname: Brooke
authors.affiliation: Insect Pest Control Laboratory, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, International Atomic Energy Agency, Vienna, Austria. j.gilles@iaea.org.
authors.forename: Jeremie R L
authors.initials: JR
authors.lastname: Gilles
authors.affiliation: iThemba LABS (Laboratory for Accelerator Based Sciences), Somerset West, South Africa. jps@tlabs.ac.za.
authors.forename: Kobus
authors.initials: K
authors.lastname: Slabbert
authors.affiliation: Special Pathogens Unit, Center for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Private Bag X4, Sandringham, Johannesburg, South Africa. alank@nicd.ac.za.
authors.forename: Alan
authors.initials: A
authors.lastname: Kemp
authors.affiliation: Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Private Bag X4, Sandringham, Johannesburg, South Africa. leonardda@nicd.ac.za.|Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. leonardda@nicd.ac.za.
authors.forename: Leonard C
authors.initials: LC
authors.lastname: Dandalo
authors.affiliation: Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Private Bag X4, Sandringham, Johannesburg, South Africa. oliverw@nicd.ac.za.|Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. oliverw@nicd.ac.za.
authors.forename: Oliver R
authors.initials: OR
authors.lastname: Wood
authors.affiliation: Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Private Bag X4, Sandringham, Johannesburg, South Africa. leaner@nicd.ac.za.|Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. leaner@nicd.ac.za.
authors.forename: Leanne N
authors.initials: LN
authors.lastname: Lobb
authors.affiliation: Scientific Services, South African National Parks, Private Bag X402, Skukuza, South Africa. danny.govender@sanparks.org.|Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, South Africa. danny.govender@sanparks.org.
authors.forename: Danny
authors.initials: D
authors.lastname: Govender
authors.affiliation: Conservation Management, Kruger National Park, Private Bag X402, Skukuza, South Africa. marius.renke@sanparks.org.
authors.forename: Marius
authors.initials: M
authors.lastname: Renke
authors.affiliation: Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Diseases, Private Bag X4, Sandringham, Johannesburg, South Africa. lizettek@nicd.ac.za.|Wits Research Institute for Malaria, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa. lizettek@nicd.ac.za.
authors.forename: Lizette L
authors.initials: LL
authors.lastname: Koekemoer
mesh_terms: D000818:Animals; D000852:Anopheles / Q000502:physiology* / Q000528:radiation effects; D003037:Cobalt Radioisotopes; D007246:Infertility; D008297:Male; D009032:Mosquito Control / Q000379:methods*; D012726:Sexual Behavior, Animal; D013019:South Africa; D016019:Survival Analysis
chemical_list: D003037:Cobalt Radioisotopes