BACKGROUND: Calliptamus italicus L. is a major pest in Xinjiang grassland. The diapause overwintering strategy is one of the important reasons for the large population of this pest. This study investigated the function of the genes associated with the release of diapause (DIB, JHE and CAM) in Calliptamus italicus by RNA interference (RNAi) technology to aid in its biological control.
RESULTS: The expression levels of DIB and its downstream-associated genes (EcR and FTZ-F1) in the eggs injected with dsDIB for 12 h decreased by 96.6%, 55.8% and 81.8%, respectively. Diapause began to terminate on day 3, and development was almost complete on day 6. However, the head was significantly smaller. The expression levels of JHE and its downstream-associated genes (JHEH and VgR) at 48 h after dsJHE treatment decreased by 76.5%, 85.6% and 85.9%, respectively. The termination of diapause occured on day 3 of incubation. The development was basically complete on day 6, but the yolk had been incompletely absorbed. The expression of CAM and its downstream-associated genes (CAMK4 and MYL) at 24 h after dsCAM treatment decreased by 42.4%, 95.3% and 82.7%, respectively. Diapause termination was completed on day 4 for incubation, and development was abnormal on day 6. The absorption of yolk was incomplete.
CONCLUSIONS: DIB, JHE and CAM can delay the diapause termination of Calliptamus italicus eggs to different degrees and can be developed as potential target genes for its biological control. © 2024 Society of Chemical Industry.

Baculovirus infection can prevent the pupation of insects. Juvenile hormone (JH) plays a vital role in regulating insect molting and metamorphosis. However, the molecular mechanism of baculovirus preventing the pupation of larvae by regulating the Juvenile hormone (JH) pathway is still unclear. In this study, we found that the Mamestra brassicae multiple nucleopolyhedroviruses (MbMNPV) infection prolonged the larval stage of fourth instar Helicoverpa armigera (H. armigera) by 0.52 d and caused an increase in JH titer. To identify the genes that contribute to the JH increase in H. armigera-MbMNPV interaction, we analyzed mRNA expression profiles of the fat bodies of H. armigera infected by MbMNPV. A total of 3637 differentially expressed mRNAs (DE-mRNAs) were filtered out through RNA-seq analysis. These DE-mRNAs were mainly enriched in Spliceosome, Ribosome biogenesis in eukaryotes, Aminoacyl-tRNA biosynthesis, Mismatch repair, and RNA degradation signaling pathway, which are related to the virus infection. Real-time PCR was used to verify the RNA sequencing results. To find out which genes caused the increase in JH titer, we analyzed all the DE-mRNAs in the transcriptome and found that the JHE and JHEH genes, which were related to JH degradation pathway, were down-regulated. JHE and JHEH genes in the larvae of MbMNPV-infected group were significantly down-regulated compared with the control group by RT-qPCR. We further proved that the JH is degraded by JHE in H. armigera larvae by RNAi, ELISA, RT-qPCR and bioassay, while the hydrolysis of JH by JHEH in H. armigera larvae can almost be ignored. Knocking down of HaJHE promoted the expression of the JH receptor gene Met and the downstream gene Kr-h1, and the replication of MbMNPV. This study clarified that JH is mainly degraded by JHE in H. armigera larvae. The MbMNPV infection of H. armigera larvae leads to the increase of JH titer by inhibiting the expression of JHE. The increase in JH titer promotes the expression of the JH receptor gene Met and the downstream gene Kr-h1, which prevents the pupation of H. armigera, and promotes MbMNPV replication. This study provides new insights into H. armigera and MbMNPV interaction mechanisms.

The existence, nature, and physiological consequences of genetic variation for juvenile hormone esterase (JHE) activity was studied in the wing-polymorphic cricket, Gryllus firmus. Hemolymph (blood) JHE activity was sixfold lower in nascent short-winged (SW) females, relative to nascent long-winged (LW) females during the last juvenile stadium (stage). Morph-associated genetic variation for JHE activity had two causes, variation in loci: (1) regulating whole-organism enzyme activity; and (2) controlling the degree to which JHE is secreted into the blood Reduced JHE activity in nascent SW-selected individuals was associated with reduced in vivo juvenile hormone catabolism. This suggests that variation in JHE activity during juvenile development may have important physiological consequences with respect to the regulation of blood levels of juvenile hormone and consequent specification of wing morph. This is the first definitive demonstration of genetic variation for hormonal metabolism in any insect and a genetic association between hormone metabolism and the subsequent expression of morphological variation (wing morph). However, we have not yet firmly established whether these associations represent causal relationships In contrast to the clear association between JHE activity and wing morph development, we observed no evidence indicating that variation in JHE activity plays any direct or indirect role in causing the dramatic differences in ovarian growth between adult wing morphs. Variation in JHE activity also does not appear to be important in coordinating the development of wing morph with the subsequent expression of reproductive differences between adult morphs. Finally genetic variation for the developmental profiles of JHE activity during juvenile and adult stages are remarkably similar in three Gryllus species. This suggests that genetic correlations between JHE activities during different periods of development, which underlie these activity profiles, have been conserved since the divergence of the three Gryllus species.

Forkhead box O (FOXO) functions as the terminal transcription factor of the insulin signaling pathway and regulates multiple physiological processes in many organisms, including lifespan in insects. However, how FOXO interacts with hormone signaling to modulate insect growth and development is largely unknown. Here, using the transgene-based CRISPR/Cas9 system, we generated and characterized mutants of the silkworm Bombyx mori FOXO (BmFOXO) to elucidate its physiological functions during development of this lepidopteran insect. The BmFOXO mutant (FOXO-M) exhibited growth delays from the first larval stage and showed precocious metamorphosis, pupating at the end of the fourth instar (trimolter) rather than at the end of the fifth instar as in the wild-type (WT) animals. However, different from previous reports on precocious metamorphosis caused by juvenile hormone (JH) deficiency in silkworm mutants, the total developmental time of the larval period in the FOXO-M was comparable with that of the WT. Exogenous application of 20-hydroxyecdysone (20E) or of the JH analog rescued the trimolter phenotype. RNA-seq and gene expression analyses indicated that genes involved in JH degradation but not in JH biosynthesis were up-regulated in the FOXO-M compared with the WT animals. Moreover, we identified several FOXO-binding sites in the promoter of genes coding for JH-degradation enzymes. These results suggest that FOXO regulates JH degradation rather than its biosynthesis, which further modulates hormone homeostasis to control growth and development in B. mori In conclusion, we have uncovered a pivotal role for FOXO in regulating JH signaling to control insect development.