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

BackgroundAnopheles 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.MethodsThe 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)].ResultsIrradiation 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.ConclusionLaboratory-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.

Vitellogenin expression in the oilseed rape pest Meligethes aeneus

“…Identification of females and males in a pest species can give great value to the development of new control methods and understanding, for example, the seasonal pattern of oviposition might be important for pest control. Sex‐specific control methods, are well known, for example, sterile insects in malaria control (Munhenga et al ., ) or pheromone traps for lepidopteran pests (Megido et al ., ), which minimize the mating success. Sex‐linked insecticide resistance is known from the housefly and Colorado potato beetle (Hawthorne, ; Rinkevich et al ., ; Hojland et al ., ), but is more the exception than the rule in insecticide resistance.…”

Laboratory rearing of Anopheles arabiensis: impact on genetic variability and implications for Sterile Insect Technique (SIT) based mosquito control in northern Sudan

“…Mating competitiveness experiments showed that irradiated male mosquitoes are fertile as wild counterparts under semi-field conditions. However, they were not as competitive under laboratory conditions [14]. …”

“…Broadly speaking, comparisons of the genetics of colony populations and field populations is important particularly in genetic control trials because population genetic make-up can affect physiological and behavioural fitness traits, and hence the efficacy of the genetic control methods [8–10]. The fitness of Anopheles arabiensis male populations in SIT trials in northern and south Africa, showed that prolonged colonization, irradiation, and transportation do not impede mating vigour and competitiveness of male mosquitoes [11–14]. Colonization of An.…”

Development of a genetic sexing strain of Anopheles arabiensis for KwaZulu‐Natal, South Africa

“…Two local A. arabiensis laboratory strains were used to develop the GSS strain. The first strain (GAMA) was developed by the introgression of the Sudanese A. arabiensis GSS ANO IPCL1 males (carrying the dieldrin resistance rdl gene on the Y chromosome) with A. arabiensis females colonized from material collected in 2010 from the Kruger National Park (Munhenga et al ., ). The GAMA strain had not been purified for the rdl gene for a number of generations prior to this study.…”

“…Over the past 6 years, extensive baseline studies on the population dynamics of wild target A. arabiensis populations have been carried out in the Kruger National Park and northern KZN, culminating in the identification of a pilot release site (Munhenga et al ., , ). In addition, mating competitiveness of representative laboratory strains has been established (Munhenga et al ., ). Apart from this baseline information, there are other aspects of the SIT programme that require optimization before pilot releases can be done.…”