Sexual ecology of transgenic mosquitoes Stegomyia (Aedes) aegypti

Aedes aegypti is the main vector of the virus that causes dengue fever and its more severe form dengue hemorrhagic fever. As traditional control methods have been unable to prevent its global re-emergence as a significant threat to human health, the development of new control methods is gaining importance. One possibility is a genetics-based control strategy modelled on the traditional sterile insect technique (SIT). The RIDL system (Release of Insects carrying a Dominant Lethal) is such an approach, and has been engineered in Ae. aegypti with tetracycline-dependent repression of a dominant lethal gene construct. This thesis examines some of the aspects of Aedes aegypti mating ecology and behaviour that are relevant for the implementation of SIT-based control programmes, focusing on the competitive fitness of the genetically modified males. The transformed mosquitoes differed from unmodified mosquitoes with a similar genetic background with regard to several life history traits. Though the modified mosquitoes pupated earlier - which may be useful in the mass-rearing of such insects - most of the differences suggest reduced competitive performance of the modified males. These included reduced larval survival, adult longevity, insemination capacity and flight ability. In caged mating trials the modified males were less competitive than their wild type counterparts in direct competition for females. Genetically modified mosquitoes were generally smaller than unmodified mosquitoes reared at high larval densities, highlighting the value of optimising rearing conditions as females preferentially selected larger males for mating. Females exhibited no propensity to re-mate over several gonotrophic cycles, unless they had been mated to sperm-depleted males, in which case secondary insemination was common. In conclusion, genetic manipulation reduced the performance of mosquitoes. However, their competitive disadvantage could be compensated for by high over-flooding ratios upon release. Therefore, accurate estimates of competitive ability, as presented in this thesis, are essential if this control strategy is to prove successful

A Possible Mechanism for the Suppression of Plasmodium berghei Development in the Mosquito Anopheles gambiae by the Microsporidian Vavraia culicis

BACKGROUND: Microsporidian parasites of mosquitoes offer a possible way of controlling malaria, as they impede the development of Plasmodium parasites within the mosquito. The mechanism involved in this interference process is unknown. METHODOLOGY: We evaluated the possibility that larval infection by a microsporidian primes the immune system of adult mosquitoes in a way that enables a more effective anti-Plasmodium response. To do so, we infected 2-day old larvae of the mosquito Anopheles gambiae with one of 4 isolates of the microsporidian Vavraia culicis and reared one group as an uninfected control. Within each treatment, we fed half the adult females on a mix of P. berghei ookinetes and blood and inoculated the other half with a negatively charged CM-25 Sephadex bead to evaluate the mosquitoes' melanisation response. CONCLUSIONS: The microsporidian-infected mosquitoes were less likely to harbour oocysts (58.5% vs. 81.8%), harboured fewer oocysts (8.9 oocysts vs. 20.7 oocysts) if the malaria parasite did develop and melanised the Sephadex bead to a greater degree (73% vs. 35%) than the controls. While the isolates differed in the number of oocysts and in the melanisation response, the stimulation of the immune response was not correlated with either measure of malaria development. Nevertheless, the consistent difference between microsporidian-infected and -uninfected mosquitoes--more effective melanisation and less successful infection by malaria--suggests that microsporidians impede the development of malaria by priming the mosquito's immune system

Cost of Mating and Insemination Capacity of a Genetically Modified Mosquito Aedes aegypti OX513A Compared to Its Wild Type Counterpart

The idea of implementing genetics-based insect control strategies modelled on the traditional SIT is becoming increasingly popular. In this paper we compare a genetically modified line of Aedes aegypti carrying a tetracycline repressible, lethal positive feedback system (OX513A) with its wild type counterpart with respect to their insemination capacities and the cost of courtship and mating. Genetically modified males inseminated just over half as many females as the wild type males during their lifetime. Providing days of rest from mating had no significant effect on the total number of females inseminated by males of either line, but it did increase their longevity. Producing sperm had a low cost in terms of energy investment; the cost of transferring this sperm to a receptive female was much higher. Continued mating attempts with refractory females suggest that males could not identify refractory females before investing substantial energy in courtship. Although over a lifetime OX513A males inseminated fewer females, the number of females inseminated over the first three days, was similar between males of the two lines, suggesting that the identified cost of RIDL may have little impact on the outcome of SIT-based control programmes with frequent releases of the genetically modified males

Comparison of Life History Characteristics of the Genetically Modified OX513A Line and a Wild Type Strain of Aedes aegypti

The idea of implementing genetics-based insect control strategies modelled on the traditional SIT (Sterile Insect Technique), such as RIDL (Release of Insects carrying a Dominant Lethal), is becoming increasingly popular. In this paper, we compare a genetically modified line of Aedes aegypti carrying a tetracycline repressible, lethal positive feedback system (OX513A) with a genetically similar, unmodified counterpart and their respective responses to increasing larval rearing density using a constant amount of food per larva. The parameters that we examined were larval mortality, developmental rate (i.e., time to pupation), adult size and longevity

Sexual ecology of transgenic mosquitoes Stegomyia (Aedes) aegypti

Aedes aegypti is the main vector of the virus that causes dengue fever and its more severe form dengue hemorrhagic fever. As traditional control methods have been unable to prevent its global re-emergence as a significant threat to human health, the development of new control methods is gaining importance. One possibility is a genetics-based control strategy modelled on the traditional sterile insect technique (SIT). The RIDL system (Release of Insects carrying a Dominant Lethal) is such an approach, and has been engineered in Ae. aegypti with tetracycline-dependent repression of a dominant lethal gene construct. This thesis examines some of the aspects of Aedes aegypti mating ecology and behaviour that are relevant for the implementation of SIT-based control programmes, focusing on the competitive fitness of the genetically modified males. The transformed mosquitoes differed from unmodified mosquitoes with a similar genetic background with regard to several life history traits. Though the modified mosquitoes pupated earlier - which may be useful in the mass-rearing of such insects - most of the differences suggest reduced competitive performance of the modified males. These included reduced larval survival, adult longevity, insemination capacity and flight ability. In caged mating trials the modified males were less competitive than their wild type counterparts in direct competition for females. Genetically modified mosquitoes were generally smaller than unmodified mosquitoes reared at high larval densities, highlighting the value of optimising rearing conditions as females preferentially selected larger males for mating. Females exhibited no propensity to re-mate over several gonotrophic cycles, unless they had been mated to sperm-depleted males, in which case secondary insemination was common. In conclusion, genetic manipulation reduced the performance of mosquitoes. However, their competitive disadvantage could be compensated for by high over-flooding ratios upon release. Therefore, accurate estimates of competitive ability, as presented in this thesis, are essential if this control strategy is to prove successful.EThOS - Electronic Theses Online ServiceBiotechnology and Biological Sciences Research CouncilGBUnited Kingdo

Efficacy of melanization response in control mosquitoes and mosquitoes infected by one of four isolates of <i>V. culicis</i>.

<p>Each point represents the mean proportion of a Sephadex bead melanized by a mosquito. The vertical lines represent the standard errors of the means and the horizontal, dotted line shows the mean of the controls. Again, the numbers in the bars indicate the number of mosquitoes sampled.</p

The association between the melanization response and the success of infection by <i>P. berghei</i>.

<p>Each point shows the mean within a block of the control or the microsporidian-infected mosquitoes (where the four isolates were pooled), and the horizontal and vertical lines show the standard errors of the estimates. (a) Association between the melanization response and the proportion of mosquitoes harbouring at least one oocyst 10 days after bloodfeeding. (b) Association between the melanization response and the mean number of oocysts.</p