Expression Analysis Reveals the Association of Several Genes with Pupal Diapause in Bactrocera minax (Diptera: Tephritidae)

Population-specific thermal responses contribute to regional variability in arbovirus transmission with changing climates

Temperature is increasing globally, and vector-borne diseases are particularly responsive to such increases. While it is known that temperature influences mosquito life history traits, transmission models have not historically considered population-specific effects of temperature. We assessed the interaction between Culex pipiens population and temperature in New York State (NYS) and utilized novel empirical data to inform predictive models of West Nile virus (WNV) transmission. Genetically and regionally distinct populations from NYS were reared at various temperatures, and life history traits were monitored and used to inform trait-based models. Variation in Cx. pipiens life history traits and population-dependent thermal responses account for a predicted 2.9°C difference in peak transmission that is reflected in regional differences in WNV prevalence. We additionally identified genetic signatures that may contribute to distinct thermal responses. Together, these data demonstrate how population variation contributes to significant geographic variability in arbovirus transmission with changing climates.

Advantages of diapause in Anastatus japonicus Ashmead mass production on eggs of the Chinese oak silkworm, Antheraea pernyi

BACKGROUND

Anastatus japonicus Ashmead, a biological control agent utilized in China to control fruit bugs and forest caterpillars, is efficiently raised on large Chinese oak silkworm (Antheraea pernyi) eggs. Here, we investigated the biological parameters of non-diapaused and diapaused Anastatus japonicus after long-term storage within eggs of the host, Antheraea pernyi, under laboratory conditions.

RESULTS

Diapaused mature larvae of Anastatus japonicus were more cold-tolerant than non-diapaused mature larvae, as reflected by a lower supercoiling point, lower freezing point, and higher survival rate at cold temperatures. Diapause induction enhanced the lifespan, fecundity and oviposition period of Anastatus japonicus than non-diapaused Anastatus japonicus when refrigerated for 6 months. However, after 12 months of refrigeration, the fecundity and oviposition period of Anastatus japonicus were significantly reduced with and without diapause. No difference in the progeny sex ratio of Anastatus japonicus was observed between diapause-induction treatment and those of non-diapaused. With the extension of refrigeration period from 6 months to 12 months, the lifespan, fecundity and oviposition period of Anastatus japonicus which were treated with diapause induction showed a sharp decrease. No significantly difference in the lifespan, fecundity and oviposition period of Anastatus japonicus was observed between diapause-induction treatment and those of non-diapaused when refrigerated for 12 months.

CONCLUSION

These results suggest that the induction of diapause is an applicable technique to achieve mass production of Anastatus japonicus in long-term storage using eggs of the factitious host Antheraea pernyi, without compromising the quality of the parasitoid. The refrigeration period of diapaused Anastatus japonicus should not exceed 6 months. © 2023 Society of Chemical Industry.

Identification and expression profiles of gustatory receptor genes in Bactrocera minax larvae (Diptera: Tephritidae): Role of BminGR59f in larval growth

Insects employ various types of gustatory receptors (GRs) to identify nutrient-rich food and avoid toxic substances. The larval gustatory system is the critical checkpoint for food acceptance or rejection. As a specialist herbivore, the larvae of Bactrocera minax feed only on unripe citrus fruits. However, how larvae use GRs to check and adapt to the secondary metabolites in unripe citrus fruits remains unknown. In this study, we first performed developmental expression profiles showing that most BminGRs genes were highly expressed in 1st and 2nd instar larvae and that tissue-specific expression indicated high expression of most BminGRs genes in the mouthparts of 2nd instar larvae. Furthermore, we found that silencing BminGR59f by RNA interference (RNAi) affected the growth of 2nd instar B. minax larvae. Hesperidin and naringin were screened as ligands of BminGR59f via RNAi and cell calcium imaging, and the combination of these two flavones increased the body weight of larvae. In summary, we identified a novel gustatory perception pattern in B. minax for detecting hesperidin and naringin, which boosted the growth of B. minax larvae. These results shed light on how specialist herbivores detect and adapt to host metabolites in adverse environments depending on larval GRs.

Temperature and Photoperiodic Response of Diapause Induction in Anastatus japonicus, an Egg Parasitoid of Stink Bugs

Simple Summary

Anastatus japonicus Ashmead is an important egg parasitoid wasp and natural enemy of Tessaratoma papillosa. It is commercially used in biological control, and has effectively suppressed T. papillosa population for decades in China. In practice, medium temperature in spring always induces diapause in A. japonicus, leading to the delay of adult emergence and missing the best chance to control the pest. Accurately regulating the development of A. japonicus is a key technique for the production of biocontrol agents and field release applications. In this study, responsible environmental factors for the induction of diapause in A. japonicus were investigated. A short photoperiod and medium temperature led to diapause in A. japonicus. Second–third instar larva are the most sensitive stages to diapause stimuli. Diapausing mature larvae had a significantly higher survival rate after 180 days storage at 10 °C than that of nondiapausing mature larvae. Taken together, results suggest methods that could be exploited in the developmental regulation, field-release pretreatment technology, and long-term storage of A. japonicus.

Abstract

Anastatus japonicus Ashmead is a widely used biological control agent against stink bugs that can be successfully reared using the large eggs of the Chinese silkworm. In this study, environmental factors responsible for the induction of diapause in A. japonicus were investigated on host eggs of the Chinese silkworm. A. japonicus exhibited a facultative, mature larval diapause within its host eggs. Second–third instar larva are the most sensitive stages to diapause stimuli. The accumulation of diapause stimuli during all the larval stages maximized the diapause response. A short photoperiod of 10L:14D and temperature of 17 °C led to the occurrence of the highest diapause response, while a long photoperiod (14L:10D) and low temperatures (11 and 14 °C) prevented the diapause. A specific exposure period was required to reach high diapause incidence. Diapausing mature larvae had a significantly higher survival rate after 180 days storage at 10 °C than that of nondiapausing mature larvae. Taken together, results suggest methods that could be exploited in the developmental regulation, field-release pretreatment technology, and long-term storage of A. japonicus.

Mechanism of the growth and development of the posterior silk gland and silk secretion revealed by mutation of the fibroin light chain in silkworm

Silkworm, as a model organism, has very high economic value due to its silk secretion ability. Although a large number of studies have attempted to elucidate the mechanism of silk secretion, it remains unclear. In this study, the fibroin light chain (Fib-L) gene of silkworm was subjected to CRISPR/Cas9 editing, which yielded premature termination of translation at 135 aa. Compared with those of the wild type, the posterior silk glands (PSGs) of the homozygous mutants on the third day of the fifth instar showed obvious premature degeneration. Comparative transcriptome and proteomic analyses of the PSGs of wild-type individuals, heterozygous mutants and homozygous mutants were performed on the fourth day of the fifth instar. A GO enrichment analysis showed that the differentially expressed genes (DEGs) between homozygous mutants and wild-type individuals were enriched in cytoskeleton-related terms, and a KEGG enrichment analysis showed that the upregulated DEGs between homozygous mutants and wild-type individuals were enriched in the phagosome and apoptosis pathways. These results indicated that apoptosis was activated prematurely in the PSGs of homozygous mutants. Furthermore, autophagy and heat shock response were activated in the PSGs of homozygous mutants, as demonstrated by an analysis of the DEGs related to autophagy and heat shock. A comparative proteomic analysis further confirmed that autophagy, apoptosis and the heat shock response were activated in the PSGs of homozygous mutants, which led to premature degradation of the PSGs. These results provide insights for obtaining a more in-depth understanding of the mechanism of silk secretion in silkworms.

Comparative proteomics provides insights into diapause program of Bactrocera minax (Diptera: Tephritidae)

The Chinese citrus fly, Bactrocera minax, is a notorious univoltine pest that causes damage to citrus. B. minax enters obligatory pupal diapause in each generation to resist harsh environmental conditions in winter. Despite the enormous efforts that have been made in the past decade, the understanding of pupal diapause of B. minax is currently still fragmentary. In this study, the 20-hydroxyecdysone solution and ethanol solvent was injected into newly-formed pupae to obtain non-diapause- (ND) and diapause-destined (D) pupae, respectively, and a comparative proteomics analysis between ND and D pupae was performed 1 and 15 d after injection. A total of 3,255 proteins were identified, of which 190 and 463 were found to be differentially abundant proteins (DAPs) in ND1 vs D1 and ND15 vs D15 comparisons, respectively. The reliability and accuracy of LFQ method was validated by qRT-PCR. Functional analyses of DAPs, including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, and protein-protein interaction (PPI) network construction, were conducted. The results revealed that the diapause program of B. minax is closely associated with several physiological activities, such as phosphorylation, chitin biosynthesis, autophagy, signaling pathways, endocytosis, skeletal muscle formation, protein metabolism, and core metabolic pathways of carbohydrate, amino acid, and lipid conversion. The findings of this study provide insights into diapause program of B. minax and lay a basis for further investigation into its underlying molecular mechanisms.