CRISPR-based genetic control strategies for insect pests

Genetic control strategies such as the sterile insect technique have successfully fought insect pests worldwide. The CRISPR(clustered regularly interspaced short palindromic repeats) technology, together with high-quality genomic resources obtained in more and more species, greatly facilitates the development of novel genetic control insect strains that can be used in area-wide and species-specific pest control programs. Here, we review the research progress towards state-of-art CRISPR-based genetic control strategies, including gene drive, sex ratio distortion, CRISPRengineered genetic sexing strains, and precision-guided sterile insect technique. These strategies’ working mechanisms,potential resistance development mechanisms, and regulations are illustrated and discussed. In addition, recent developments such as stacked and conditional systems are introduced. We envision that the advances in genetic technology will continue to be one of the driving forces for developing the next generation of pest control strategies.

Development of a RNAi-based release of insects carrying a dominant lethal (RIDL) system in Drosophila melanogaster

Since the first report of the release of insects carrying a dominant lethal （RIDL） strategy, RIDL strains have been constructed in species including fruit flies and mosquitoes. However, in many insects, identification of sterile and lethal genes needed to generate a RIDL strain is limited by the lack of molecular and genetic information. Here, we created RIDL strains of Drosophila melanogaster using RNA interference （RNAi） of the Pygopus （Pygo） gene, a key component of the Wingless/Wnt signaling pathway. In two transgenic lines, XDll and XD15, we verified lethality in the absence of tetracycline, but we were unable to demonstrate sex-specific lethality. We found that male XD15 adults maintained on medium without tetracycline had a longer lifespan than wild type. This RNAibased RIDL strain may therefore offer the advantages of a transgene that promotes the expression of two contrary actions at different life stages： lethality in larvae and prolonged lifespan in adults, actions that could work together to provide prolonged delivery of lethality by the RIDL system. Use of RNAi can facilitate the development and application of RIDL strategies in a wide range of species.

Wild bacterial probiotics fed to larvae of mass-reared Queensland fruit fly[Bactrocera tryoni(Froggatt)]do not impact long-term survival,mate selection,or locomotor activity

Queensland fruit fly[Bactrocera Uyoni(Froggatt),Diptera,Tephritidae]is the most devastating insect pest impacting Australian horticulture.The Sterile Insect Technique(SIT)is an important component of tephritid pest management programs.However,mass-rearing and irradiation(to render insects sterile)may reduce the fitness and performance of the insect,including the ability of sterile males to successfully compete for wild females.Manipulation of the gut microbiome,including the supplementation with bacterial probiotics shows promise for enhancing the quality of mass-reared sterile flies,however there are fewer published studies targeting the larval stage.In this study,we supplemented the larval stage of mass-reared B.tryoni with bacterial probiotics.We tested several individual bacteria that had been previously isolated and characterized from the gut of wild B.tryoni larvae including Asaia sp.,Enterobacter sp.,Lactobacillus sp.,Leuconostoc sp.We also tested a consortium of all four of these bacterial isolates.The fitness parameters tested included adult survival in field cages,laboratory mate selection of bacteria supplemented males by bacteria nonsupplemented females,and laboratory locomotor activity of adult flies.None of the bacterial probiotic treatments in the current study was significantly different to the control for field survival,mate selection or locomotor activity of adult B.Uyoni,which agree with some of the other studies regarding bacterial probiotics fed to the larval stage of tephritids.Future work is needed to determine if feeding the same,and/or other probiotics to adults,as opposed to larvae can positively impact survival,mating performance,mating competitiveness and locomotor activity of B.tryoni.The bacterial group(s)and function of bacterial species that increase fitness and competitiveness is also of interest to tephritid mass-rearing programs.

Domestication-related changes in sexual performance of Queensland fruit fly

In Sterile Insect Technique(SIT)programs,massive numbers of insects are reared,sterilized,and released in the field to impede reproduction of pest populations.The domestication and rearing processes used to produce insects for SIT programs may have significant evolutionary impacts on life history and reproductive biology.We assessed the effects of domestication on sexual performance of laboratory reared Queensland fruit fly,Bactrocera tryoni,by comparing an old(49 generations)and a young colony(5 generations).We evaluated mating propensity,mating latency,copula duration,sperm transfer,and ability to induce sexual inhibition in mates.Overall,both males and females from the old colony had greater mating propensity than those from the young colony.Copula duration was longer when females were from the old colony.There was no evidence of sexual isolation between the colonies as males and females from the two colonies had similar propensity to mate with flies from either colony.Males from the old colony transferred more sperm regardless of which colony their mate was from.Finally,males from both colonies were similarly able to induce sexual inhibition in their mates and were also similarly able to secure copulations with already-mated females.Positive effects of domestication on sperm transfer,coupled with maintained ability to induce sexual inhibition in mates and to secure copulations with previously mated females,highlights that domestication may have little effect,or even positive effects,on some aspects of sexual performance that may advantage mass-reared B.tryoni in SIT programs.