Field Efficacy, Sub-lethal, and Biochemical Effects of Certain Biorational Insecticides Against the New Intruder, Spodoptera frugiperda in Bani-Suef, Upper Egypt.

Frequent inspections on sorghum and maize crops during seasons of 2021 and 2022 in some regions in Bani-Suef governorate, Egypt, discovered unprecedented invasions of Spodoptera frugiperda (J. E. Smith). Accordingly, our study on Beauveria bassiana and spinetoram was supporter to the Food and Agriculture Organization's tendency in adopting biorational insecticides against S. frugiperda in Egypt. Exposure toxicity of LC25 values at 48 h of B. bassiana were 2.7 × 106 and 5.2 × 106 conidia mL-1 and spinetoram were 0.019 and 0.048 mg L-1 against the 2nd and 4th instar larvae laboratory strain of S. frugiperda, respectively. Sub-lethal effects (LC25) were accomplished on biological parameters against both instar larvae. LC25 of B. bassiana reduced adult emergency (89.91 and 91.05%) more than spinetoram (75.99 and 79.49%) against the 2nd and 4th instar larvae, respectively. The 2nd instar larvae exposed to LC25 of B. bassiana suppressed female fecundity (0.00 eggs) more than spinetoram (19.74 eggs). Enzymatic activity of lipase in hemolymph, fat bodies, and mid-gut of the 4th instars at 48 h showed significant drop in B. bassiana more than spinetoram. Glutathione-S-transferase (GST) levels in hemolymph for both insecticides were equal and exceeded the control. Fat bodies and mid-gut possessed the highest GST activity in B. bassiana followed by spinetoram and the control. Residual efficacy of spinetoram exceled B. bassiana at their field rates under semi-field condition in Bani-Suef along the two seasons of maize crop against both instars. Eventually, B. bassiana alongside spinetoram could afford good control especially on early instar larvae of S. frugiperda.

Proliferative and preparative cell divisions in wing discs of the last larval instar are regulated by different hormones and determine the size and differentiation of the wing of Bombyx mori.

Through investigating the two different enhanced cell division stages, we tried to clarify the switch from the growth to differentiation in the wing disc of the last larval instar of Bombyx mori. The response to insulin and 20E in vitro was stage specific. Bmmyc expression in V1 wing discs showed differences after being cultured with and without insulin. Bmmyc expression in V5 wing discs also showed differences after being cultured with and without 20E. Cell cycle-related genes, BmE2F1 and BmcycE, were upregulated with insulin or 20E in cultured wing discs of V1 or V5, respectively. Bmwnt1 and Bmras1 showed upregulation with 20E in cultured wing discs. Bmwnt1 showed upregulation with insulin in cultured wing discs, but Bmras1 did not show clear upregulation with insulin treatment. In contrast, Bmdpp showed upregulation with insulin, but did not show clear upregulation with 20E. The addition of PI3K or TOR inhibitors inhibited the upregulation of Bmmyc expression that was upregulated with insulin or 20E. The upregulation of Bmmyc and Bmwnt1 with insulin or 20E was inhibited with the addition of Myc or Wnt inhibitors, respectively. Genes related to matrix metalloprotease showed upregulation with 20E, and the upregulation was inhibited by the addition of Myc or Wnt inhibitors. From the present results, we concluded that cell division during the feeding stage occurred through PI3K/TOR cascade, and that at the wandering stage occurred through ecdysone and PI3K/TOR cascade; the former is for growth and the latter for differentiation.

Cuticular protein genes showing peaks at different stages are probably regulated by different ecdysone responsive transcription factors during larval-pupal transformation.

We aimed to explain the reason and function of the successive expression of ecdysone-responsive transcription factors (ERTFs) and related cuticular protein (CP) genes during transformation from larva to pupa. The regulation of the expression of CP genes by ERTFs was examined by in vitro wing disc culture and reporter assay using a gene gun transduction system. Two CP genes that showed expression peaks at different stages-BmorCPG12 at W3L and BmorCPH2 at P0 stage-were selected and examined. Reporter constructs conveying putative BHR3, ßFTZ-F1, BHR39, and E74A binding sites of BmorCPG12 and BmorCPH2 showed promoter activity when introduced into wing discs. In the present study, we showed the functioning of the putative BHR3 and E74A binding sites, together with putative ßFTZ-F1 binding sites, on the activation of CP genes, and different ERTF binding sites functioned in one CP gene. From these, we conclude that BHR3, ßFTZ-F1, and E74A that are successively expressed bring about the successive expression of CP genes, resulting in insect metamorphosis. In addition to this, reporter constructs conveying putative BHR39 binding sites of BmorCPG12 and BmorCPH2 showed negative regulation.

Expression profiles of cuticular protein genes in wing tissues during pupal to adult stages and the deduced adult cuticular structure of Bombyx mori.

We aimed to clarify the regulation of cuticular protein (CP) gene expression and the resulting insect cuticular layers by comparing the expression pattern of CP genes and related ecdysone-responsive transcription factor (ERTF) genes, the coding amino acid sequences of CP genes, and histological observation. The expression of CP and ERTF genes during pupal and adult stages was examined via qPCR. The number of CP genes expressed during pupal and adult stages decreased as compared to that during prepupal to pupation stages, particularly in CPRs. The peaks of transcripts were observed at P5, P6, P9, A0, and A1. The order of the ERTF and CP genes expression resembled that at prepupal and pupation stages, suggesting the relatedness of ERTFs with the same CP genes at both stages. Moreover, the order of expression of CP genes resembled that in prepupal to pupation stages, by which we presumed the spaces of CPs in the epicuticle, outer-exocuticle, inner-exocuticle, endocuticle layer.

Expression of matrix metalloproteinase genes during basement membrane degradation in the metamorphosis of Bombyx mori.

The present study was conducted to clarify the involvement of the basement membrane (BM) in insect metamorphosis through analysis of the expression profile of two types of metalloproteinase (MMP and ADAMTS) genes in several organs, their ecdysone involvement, and the histological change of BM. BM was observed around wing sac and in the wing cavity and around fat bodies at the W0 stage but disappeared after the W3 stage, and wing discs evaginated and fat body cells scattered after the W3 stage. The disappearance of the BM of midgut and silk glands was not observed after the W3 stage, but degenerated epithelium cells in the midgut and shrunken cells in the silk gland were observed after the W3 stage. BmMMP1 showed a peak at P0 in the wing discs, fat bodies, midgut, and silk gland. BmMMP2 showed a broad peak around pupation in the wing discs, fat bodies, midgut, and silk gland. BmADAMTS-1 showed enhanced expression at W2 in the wing discs, fat bodies, midgut, and hemocyte, while BmADAMTS-L showed enhanced expression at W3 in the fat bodies, midgut, silk gland, and hemocyte. After pupation, they showed a different expression in different organs. All of four genes were induced by 20-hydroxyecdysone in wing discs in vitro. The present results suggested the involvement of MMPs and ADAMTS in the BM digestion and the morphogenesis of organs during Bombyx metamorphosis.