Genetic biocontrol of pest insects by overexpression of endogenous toxic seminal fluid proteins

As insecticide usage is declining in favour of more sustainable pest management strategies, genetically modified organisms are being engineered to achieve highly targeted pest population suppression. With techniques such as reducing the reproductive potential of the population through the release of sterile or reproductively isolated individuals, or by introducing heritable transgenes which reduce the fitness of carrier offspring, genetic biocontrol technologies primarily achieve population suppression by their negative impact on population dynamics rather than directly causing harm. As such, genetic biocontrol programs require at least a generation to produce a reduction in the target population, making them largely incapable of the rapid response necessary to mitigate the damage from disease vector or agricultural pest outbreaks. Several proteins in the seminal fluid of male Drosophila melanogaster and other insects have been found to reduce the lifespan of mated females, including Acp62F, Acp70A, and CG10433. We hypothesised that dCas9-VPR could be used to drive overexpression of these toxic proteins in the male’s reproductive tract, which could be applied to develop a novel genetic biocontrol technology using sterile males which increase mated female mortality. D. melanogaster were engineered to express dCas9-VPR and sgRNA under accessory-gland specific promoters, and using label-free quantitative proteomics we observed statistically significant increase of CG10433 above basal levels, a ~20-fold increase of Acp62F above negative controls but not wild type males, and no upregulation of Acp70A. Transgenic males were completely infertile, suggesting a reduction in sperm quality. However, no significant difference in female lifespan or fertility was observed between those mated to transgenic males and controls. These results suggest either that dCas9-VPR transcriptional activation cannot achieve the requisite overexpression of toxic seminal fluid proteins necessary to further reduce mated female lifespan, or that the increased expression does not result in more protein to be transferred to the females.