Evo-devo of wing colour patterns in beetles

Pleiotropic effects of Ebony on pigmentation and development in the Asian multi-coloured ladybird beetle, Harmonia axyridis (Coleoptera: Coccinellidae)

Melanin plays a pivotal role in insect body pigmentation, significantly contributing to their adaptation to diverse biotic and abiotic environmental challenges. Several genes involved in insect melanin synthesis showed pleiotropic effects on insect development and reproduction. Among these, the N-β-alanyl dopamine synthetase gene (Ebony) is integral to the pigmentation process. However, the full spectrum of its pleiotropic impacts is not yet thoroughly understood. In this study, we identified and characterised the HaEbony gene in the Asian multi-coloured ladybird beetle (Harmonia axyridis) and found that HaEbony gene is a conserved gene within the Coleoptera order. We aimed to further explore the multiple roles of HaEbony in the physiology and behaviour in H. axyridis. The CRISPR/Cas9 system was applied to generate multiple HaEbony knockout allele (HaEbony+/-), showing nucleotide deletion in the G0 and G1 generations. Remarkably, the resultant HaEbony+/- mutants consistently displayed darker pigmentation than their wild-type counterparts across larval, pupal and adult stages. Furthermore, these HaEbony+/- individuals (G0) demonstrated an enhanced predatory efficiency, evidenced by a higher number of aphids consumed compared to the wild type. A significant finding was the reduced egg hatchability in both G0 and G1 generations of the HaEbony+/- group, highlighting a potential reproductive fitness cost associated with HaEbony deficiency. In conclusion, our study not only sheds light on the multifaceted roles of HaEbony in H. axyridis but also highlights the potential of employing CRISPR/Cas9-targeted modifications of the Ebony gene. Such genetic interventions could enhance the environmental adaptability and predatory efficacy of ladybirds, presenting a novel strategy in biological control application.

Silencing tyrosine hydroxylase or dopa decarboxylase gene disrupts cuticle tanning during larva-pupa-adult transformation in Henosepilachna vigintioctopunctata

BACKGROUND

The 28-spotted potato ladybird, Henosepilachna vigintioctopunctata, is a notorious defoliator of many solanaceous and cucurbitaceous plants. Tyrosine hydroxylase (TH) and dopa decarboxylase (DDC) are responsible for cuticle tanning pathway in insects.

RESULTS

We identified HvTH and HvDDC in H. vigintioctopunctata, and found that high levels of them were accumulated just before or right after molting. Injection of dsHvTH or feeding 3-iodo-tyrosine (3-IT) at the third instar larval stage repressed tanning of the larval cuticle, reduced larval feeding, inhibited larval growth, and consequently caused 100% of larval mortality. Knockdown of HvDDC at the third instar larval stage hardly affected the coloration of larval head, and partially inhibited pigmentation of larval bodies and around 80% of the HvDDC RNAi larvae developed into albino pupae and adults. Moreover, depletion of HvTH or HvDDC at the fourth instar larval stage resulted in albino pupae and adults. The HvTH or HvDDC hypomorph adults fully or partially failed to remove the larval/pupal exuviae, possessed pale and abnormal wings, and poorly tanned heads and bodies, and eventually, struggled for several days without feeding on leaves before death.

CONCLUSION

These results show that TH and DDC play key roles in larval and adult cuticle tanning and development in H. vigintioctopunctata. Also, these findings suggest that dopa- and dopamine-originated pigments are essential for larval and adult feeding behavior and the molting process during emergence. © 2022 Society of Chemical Industry.

Melanin Synthesis Pathway Interruption: CRISPR/Cas9-mediated Knockout of dopa decarboxylase (DDC) in Harmonia axyridis (Coleoptera: Coccinellidae)

CRISPR/Cas9 technology is a very powerful genome editing tool and has been used in many insect species for functional genomics studies through targeted gene mutagenesis. Here, we successfully established CRISPR/Cas9 research platform in Asian multi-colored ladybird beetle, Harmonia axyridis, an important natural enemy in biological control. In this study, one pivotal gene dopa decarboxylase (DDC) in melanin synthesis was targeted by CRISPR/Cas9 to generate mutants in H. axyridis by CRISPR/Cas9 technology. Our results showed that injection of single guide RNA of the DDC and Cas9 protein into preblastoderm eggs induced one insertion and four deletion (indels) mutant H. axyridis. Mutations of HaDDC gene generated 25% mutant rate with melanin missing phenotype in larva, pupa,l and adult stage. The predation ability of the fourth instar larvae has no significant difference between wild (control) and mutant H. axyridis (G0), while these mutant fourth instar larvae had longer developmental period than that of the wild type. Consequently, the total predation of the fourth instar larvae was significantly increased in H. axyridis mutants comparing with the wild type. These results indicated that the success of CRISPR/Cas9 gene editing in H. axyridis. The gene editing platform in H. axyridis would facilitate the gene function research and promote special strain of predatory ladybird beetle generation.

The Molecular Properties and Roles of Pannier in Harmonia axyridis's Metamorphosis and Melanin Synthesis

The GATA transcription factor Pannier is identified as the major regulatory gene in color pattern formation in the Asian multi-colored ladybird beetle (Harmonia axyridis). however, the mechanisms of Pannier in regulating melanin synthesis and development in H. axyridis remain elusive. In this study, we identified and characterized Pannier in H. axyridis (HaPnr) and showed it to have two alternative spliced variants named HaPnr-α and HaPnr-β. Analyses of developmental stage expression patterns revealed that HaPnr, HaPnr-α and HaPnr-β were constitutively expressed throughout all developmental stages. To examine the role of HaPnr in H. axyridis development, RNA interference was performed in late larvae (the fourth instar) and early pupae (the first day of pupa stage). The transcript levels of HaPnr were effectively suppressed after the injection of double-stranded RNA of HaPnr (dsHaPnr). The fourth instar larvae injected with dsHaPnr reduced the pupation rates to only 61.50%, compared with 88.5% in the dsGFP-injected group. The un-pupated larvae gradually died after 1 week, and visually unaffected pupae emerged into abnormal adults with malformed hind wings and melanin absent from the cuticle. These abnormal adults gradually died 10 days after eclosion. However, when early pupae were injected with dsHaPnr, the normal eclosion rate was achieved at 88.41% on day 6 after the injection. In addition, these successful eclosion adults also showed an absence of melanin in the cuticle, but they could mate normally and have normal fecundity as compared with the control. We further demonstrated that the suppression of HaPnr-α or HaPnr-β individually did not affect the pupation and eclosion process. The suppression of HaPnr-α expression resulted in elytra melanin decreasing in both the conspicua and the succinea subgroup in H. axyridis. Even though the suppression of HaPnr-β expression only affected the melanin synthesis in the succinea subgroup, it significantly prolonged the time taken for melanin synthesis to occur in the conspicua subgroup in H. axyridis. These results indicate that HaPnr plays an essential role in insect development, especially during their metamorphosis, and also support our hypothesis that HaPnr could regulate melanin synthesis in H. axyridis under the combined action with its two splicing variants, HaPnr-α and HaPnr-β.