Gene Editing and Genetic Control of Hemipteran Pests: Progress, Challenges and Perspectives

Whitefly-Plant Interactions: An Integrated Molecular Perspective

The rapid advances in available transcriptomic and genomic data and our understanding of the physiology and biochemistry of whitefly-plant interactions have allowed us to gain new and significant insights into the biology of whiteflies and their successful adaptation to host plants. In this review, we provide a comprehensive overview of the mechanisms that whiteflies have evolved to overcome the challenges of feeding on phloem sap. We also highlight the evolution and functions of gene families involved in host perception, evaluation, and manipulation; primary metabolism; and metabolite detoxification. We discuss the emerging themes in plant immunity to whiteflies, focusing on whitefly effectors and their sites of action in plant defense-signaling pathways. We conclude with a discussion of advances in the genetic manipulation of whiteflies and the potential that they hold for exploring the interactions between whiteflies and their host plants, as well as the development of novel strategies for the genetic control of whiteflies.

Mechanical Egg Activation and Rearing of First Instar Larvae of Sirex noctilio (Hymenoptera: Siricidae)

Egg activation is a cellular transition of an arrested mature oocyte into a developing embryo through a coordinated series of events. Previous studies in Hymenoptera have indicated that mechanical pressure can induce egg activation. In this study, we developed the first egg activation protocol for the haplodiploid insect pest, Sirex noctilio (Hymenoptera: Siricidae), from two climatically different regions in South Africa to demonstrate the broad applicability of the method. In addition, activated eggs were exposed to three treatments involving water, pine sawdust, and the fungal symbiont of S. noctilio, Amylostereum areolatum (Russulales: Amylostereaceae), to determine if the symbiotic fungus is a requirement for egg development in an artificial laboratory environment, as the symbiotic fungus has been hypothesised to be necessary for egg and early larval development in a natural environment. A rearing protocol was developed for the first instar larvae using a modified Anoplophora glabripennis (Coleoptera: Cerambycidae) artificial diet. A significant difference between the mean survival rates of activated eggs from the two different regions was observed. Amylostereum areolatum was shown to be unnecessary for egg survival and adversely affected egg eclosion in an artificial laboratory environment. The maximum larval survival duration on the artificial diet was 92 days. The egg activation and rearing protocol developed in this study enables opportunities for research on the physiology, ecology, symbioses, and genetics of S. noctilio, which can be exploited for new genetic pest management strategies.

The Roles of transformer-2 (tra-2) in the Sex Determination and Fertility of Riptortus pedestris, a Hemimetabolous Agricultural Pest

In most holometabolous insects, transformer-2 (tra-2) is an auxiliary gene required for sex determination, exerting a crucial role in regulating sexual differentiation; however, the study of tra-2 in hemimetabolous insects remains very sparse and limited to just a few species. In this study, we investigated the sequence and expression profile of the tra-2 gene in the bean bug, Riptortus pedestris, an agricultural pest belonging to the Heteroptera order. Three non-sex-specific splicing isoforms of Rptra-2 were found, Rptra-2293, Rptra-2284, and Rptra-2299, which shared most exons and exhibited similar expression throughout all stages of development, with particularly elevated levels in the embryo, ovary, and testis. RNAi knockdown experiments revealed that the suppression of Rptra-2 in nymphs led to abnormal females, characterized the formation of male-specific external genital, and also caused longer nymph duration. Knockdown of the expression of the Rptra-2 gene in newly emergent virgin females would cause ovarian arrest, and injecting the 8th-day virgin females with dsRptra-2 also caused a noticeable decline in the offspring numbers. Conversely, in dsRptra-2-treated males, the testes maintained normal morphology but experienced impaired reproductive capacity, attributed to diminished sperm viability. These findings highlight the crucial role of Rptra-2 in the sex determination and fertility of R. pedestris, providing valuable insights into the sex determination mechanisms of hemimetabolous insects.

CRISPR/Cas9-mediated knockout of NlCYP6CS1 gene reveals its role in detoxification of insecticides in Nilaparvata lugens (Hemiptera: Delphacidae)

BACKGROUND

The brown planthopper (Nilaparvata lugens) is one of the major rice insect pests in Asia. Recently, high levels of insecticide resistance have been frequently reported and cytochrome P450 monooxygenase (P450)-mediated metabolic detoxification is a common resistance mechanism in N. lugens. However, there has been no persuasive genetic method to prove the role of P450s in insecticide resistance in N. lugens.

RESULTS

Here, CRISPR/Cas9 system was used to disrupt the P450 gene NlCYP6CS1 to elucidate its role in insecticide resistance in field populations of N. lugens. We successfully constructed a homozygous strain (Nl6CS1-KO) with a 5-bp deletion and 1-bp insertion mutation of NlCYP6CS1. Compared with a background resistant strain (Nl-R), the susceptibility of knockout strain Nl6CS1-KO to imidacloprid, nitenpyram, thiamethoxam, dinotefuran, and pymetrozine was increased by 2.3-, 3.4-, 7.0-, 4.2- and 3.9-fold, respectively, but not significantly changed to triflumezopyrim, chlorpyrifos and buprofezin. Life table analysis demonstrated that the Nl6CS1-KO strain resembled the Nl-R strain in terms of egg and nymph developmental duration and adult lifespan, but differed from the Nl-R strain in the survival rate of eggs and nymphs, reproduction, and body weight.

CONCLUSIONS

Our study demonstrates the effect of functional deletion of NlCYP6CS1 on multiple insecticide resistance in N. lugens. For the first time, we applied CRISPR/Cas9 system to reveal the mechanism of insecticide resistance in N. lugens, which may shed light on similar studies in other hemipteran insects. © 2023 Society of Chemical Industry.

Genome editing of the vermilion locus generates a visible eye color marker for Oncopeltus fasciatus

Insects display a vast array of eye and body colors. Genes encoding products involved in biosynthesis and deposition of pigments are ideal genetic markers, contributing, for example, to the power of Drosophila genetics. Oncopeltus fasciatus is an emerging model for hemimetabolous insects, a member of the piercing-sucking feeding order Hemiptera, that includes pests and disease vectors. To identify candidate visible markers for O. fasciatus, we used parental and nymphal RNAi to identify genes that altered eye or body color while having no deleterious effects on viability. We selected Of-vermilion for CRISPR/Cas9 genome editing, generating three independent loss-of-function mutant lines. These studies mapped Of-vermilion to the X-chromosome, the first assignment of a gene to a chromosome in this species. Of-vermilion homozygotes have bright red, rather than black, eyes and are fully viable and fertile. We used these mutants to verify a role for Of-xdh1, ortholog of Drosophila rosy, in contributing to red pigmentation using RNAi. Rather than wild-type-like red bodies, bugs lacking both vermilion and xdh1 have bright yellow bodies, suggesting that ommochromes and pteridines contribute to O. fasciatus body color. Our studies generated the first gene-based visible marker for O. fasciatus and expanded the genetic toolkit for this model system.

Transcriptome and population structure of glassy-winged sharpshooters (Homalodisca vitripennis) with varying insecticide resistance in southern California

Background

Homalodisca vitripennis Germar, the glassy-winged sharpshooter, is an invasive insect in California and a critical threat to agriculture through its transmission of the plant pathogen, Xylella fastidiosa. Quarantine, broad-spectrum insecticides, and biological control have been used for population management of H. vitripennis since its invasion and subsequent proliferation throughout California. Recently wide-spread neonicotinoid resistance has been detected in populations of H. vitripennis in the southern portions of California’s Central Valley. In order to better understand potential mechanisms of H. vitripennis neonicotinoid resistance, we performed RNA sequencing on wild-caught insecticide-resistant and relatively susceptible sharpshooters to profile their transcriptome and population structure.

Results

We identified 81 differentially expressed genes with higher expression in resistant individuals. The significant largest differentially expressed candidate gene linked to resistance status was a cytochrome P450 gene with similarity to CYP6A9. Furthermore, we observed an over-enrichment of GO terms representing functions supportive of roles in resistance mechanisms (cytochrome P450s, M13 peptidases, and cuticle structural proteins). Finally, we saw no evidence of broad-scale population structure, perhaps due to H. vitripennis' relatively recent introduction to California or due to the relatively small geographic scale investigated here.

Conclusions

In this work, we characterized the transcriptome of insecticide-resistant and susceptible H. vitripennis and identified candidate genes that may be involved in resistance mechanisms for this species. Future work should seek to build on the transcriptome profiling performed here to confirm the role of the identified genes, particularly the cytochrome P450, in resistance in H. vitripennis. We hope this work helps aid future population management strategies for this and other species with growing insecticide resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08939-1.