Old strategies with a new twist: sterile insect rearing for pest and disease control
With an increasing human population, it is vital to develop techniques for maximizing crop yields. Insect pest control is an important part of this process. There are several approaches, such as use of pesticides or transgenic plants producing insect repellent. Each of these techniques has its advantages and disadvantages. For example, some pesticides may also be toxic to humans.
Another technique that has been successfully used in the past is called the “sterile insect technique” (SIT). This technique consists of the release of reproductively sterile males, which will compete with the normal males for mates. Females that mate with these sterile males do not produce offspring resulting in a reduction of the total population. This technique has been successfully used in the past to eradicate screwworm flies from the island of Curaçao in Venezuela and also controlling their populations in the USA and Mexico. This technique has also been used for reducing the transmission of African sleeping sickness by controlling tse tse fly populations in Africa and to mosquitoes. An advantage of this technique is that the release of sterile insects cannot give rise to a transgenic population in the wild, thus reducing potential problems.
While SIT has been proven to be effective at suppressing the populations of insect pests it has, in the past, relied on DNA-damaging agents to induce sterilization, which usually made these males weak and consequently, limited effectiveness of the technique. Moreover, identification of sterile males from a mixed population is time-consuming and thus lowers the practicality of this technique. In a study (Kandul et al., 2019) from Omar S Akbari’s laboratory at the university of San Diego, CA, the authors developed a new technology that allows a lab to both generates sterile males and also eliminates all female flies at the same time, in order to ease the process of sterile male selection. Through a CRISPR-Cas9 approach, the authors were able to eliminate different genes involved both in female viability and in male sterility. The CRISPR-Cas9 approach utilizes the Cas9 enzyme in conjunction with specific guide RNA sequences that target the enzyme to cut specific sites of DNA and create the desired mutant. An advantage of this approach is that it utilizes a binary system in that the Cas9 component of the system is expressed in one of the parental lines, and the guide RNA expressed in the other parental line. These isolated components do not create mutants or affect the fitness of the fly. It is thus possible to maintain a vast healthy parental population in order to easily create many sterile males. After testing 10 genes for each of these categories, they selected β-Tubulin mutants and the sex determination gene sex lethal. The knockdown of sex lethal proved to be an additional improvement since prospective female flies become intersex sterile males, thereby effectively doubling the population of sterile male flies.
Overall, this technique that has been developed in fruit flies can be readily applied to agricultural pests and insects that transmit disease, in order to lower their number and concomitant impact on human related activities and health.
Citation: Kandul, N. P. et al. (2019) ‘Transforming insect population control with precision guided sterile males with demonstration in flies’, Nature Communications. Springer US, 10(1), p. 84. doi: 10.1038/s41467-018-07964-7.
Another technique that has been successfully used in the past is called the “sterile insect technique” (SIT). This technique consists of the release of reproductively sterile males, which will compete with the normal males for mates. Females that mate with these sterile males do not produce offspring resulting in a reduction of the total population. This technique has been successfully used in the past to eradicate screwworm flies from the island of Curaçao in Venezuela and also controlling their populations in the USA and Mexico. This technique has also been used for reducing the transmission of African sleeping sickness by controlling tse tse fly populations in Africa and to mosquitoes. An advantage of this technique is that the release of sterile insects cannot give rise to a transgenic population in the wild, thus reducing potential problems.
While SIT has been proven to be effective at suppressing the populations of insect pests it has, in the past, relied on DNA-damaging agents to induce sterilization, which usually made these males weak and consequently, limited effectiveness of the technique. Moreover, identification of sterile males from a mixed population is time-consuming and thus lowers the practicality of this technique. In a study (Kandul et al., 2019) from Omar S Akbari’s laboratory at the university of San Diego, CA, the authors developed a new technology that allows a lab to both generates sterile males and also eliminates all female flies at the same time, in order to ease the process of sterile male selection. Through a CRISPR-Cas9 approach, the authors were able to eliminate different genes involved both in female viability and in male sterility. The CRISPR-Cas9 approach utilizes the Cas9 enzyme in conjunction with specific guide RNA sequences that target the enzyme to cut specific sites of DNA and create the desired mutant. An advantage of this approach is that it utilizes a binary system in that the Cas9 component of the system is expressed in one of the parental lines, and the guide RNA expressed in the other parental line. These isolated components do not create mutants or affect the fitness of the fly. It is thus possible to maintain a vast healthy parental population in order to easily create many sterile males. After testing 10 genes for each of these categories, they selected β-Tubulin mutants and the sex determination gene sex lethal. The knockdown of sex lethal proved to be an additional improvement since prospective female flies become intersex sterile males, thereby effectively doubling the population of sterile male flies.
Overall, this technique that has been developed in fruit flies can be readily applied to agricultural pests and insects that transmit disease, in order to lower their number and concomitant impact on human related activities and health.
Citation: Kandul, N. P. et al. (2019) ‘Transforming insect population control with precision guided sterile males with demonstration in flies’, Nature Communications. Springer US, 10(1), p. 84. doi: 10.1038/s41467-018-07964-7.