Different development and fecundity between Spodoptera frugiperda USA and China populations, influenced by ecdysone-related genes.

The fall armyworm (FAW), Spodoptera frugiperda, is one of the most harmful plant pests in the world and is globally distributed from the American continent to the Asian region. The FAW USA population (Sf-USA) and China population (Sf-CHN), which belong to corn strain, showed different developmental periods and fecundity rates in lab conditions. Sf-USA had faster development and higher fecundity compared with Sf-CHN. To examine these differences, transcriptomic data from two FAW populations were analyzed and compared. Twelve gigabytes of transcripts were read from each sample and 21,258 differentially expressed genes (DEGs) were detected. DEGs with log2 fold change ≥ 2 were identified and compared in two populations. In comparison to the Sf-CHN, we discovered that 3471 and 3851 individual DEGs upregulated and downregulated, respectively. Comparing transcriptome profiles for differential gene expression revealed several DEGs, including 39 of ecdysone (E)-, 25 of juvenile hormone-, and 15 of insulin-related genes. We selected six of E-related genes, such as Neverland, Shade, Ecdysone receptor, Ecdysone-inducible protein 74 (E74), E75, and E78 from DEGs. Gene expressions were suppressed by RNA interference to confirm the physiological functions of the selected genes from Sf-USA. The Sf-USA showed developmental retardation and a decrease in fecundity rate by suppression of E-related genes. These findings show that biological characteristics between Sf-USA and Sf-CHN are influenced by E-related genes.

Prostaglandin E2 mediates chorion formation of the Asian tiger mosquito, Aedes albopictus, at late oogenesis.

Chorion-i.e., the eggshell-is formed during the late stage of oogenesis by follicular epithelium in the ovary. Although the endocrine signal(s) driving choriogenesis remain unclear in mosquitoes, this process in other insects has been suspected to involve the mediation of prostaglandins (PGs). This study tested the role of PG in the choriogenesis of the Asian tiger mosquito, Aedes albopictus, and its influence on controlling the expressions of genes associated with chorion formation by a transcriptome analysis. An immunofluorescence assay showed that PGE2 is localised in follicular epithelium. With the treatment of aspirin, an inhibitor of PG biosynthesis, at mid oogenesis, the PGE2 signal disappeared in the follicular epithelium led to significantly inhibited chorion formation along with a malformed eggshell. Ovary transcriptomes were assessed by RNASeq at the mid and late ovarian developmental stages. Differentially expressed genes (DEGs) exhibiting more than twofold changes in expression levels included 297 genes at mid stage and 500 genes at late stage. These DEGs at these two developmental stages commonly included genes associated with egg and chorion proteins of Ae. albopictus. Most chorion-associated genes were clustered in the 168 Mb region on a chromosome and exhibited significantly induced expressions at both ovarian developmental stages. The inhibition of PG biosynthesis significantly suppressed the expression of the chorion-associated genes while the addition of PGE2 rescued the gene expressions and led to recovery of choriogenesis. These results suggest that PGE2 mediates the choriogenesis of Ae. albopictus.

PGE2 mediation of egg development in Western flower thrip, Frankliniella occidentalis.

Eicosanoids mediate various insect physiological processes, including reproduction. Especially, the eicosanoid prostaglandin E2  (PGE2 ) is known to mediate oocyte development in some insects. The explosive reproductive potential of the Western flower thrips, Frankliniella occidentalis, damages various agricultural crops. However, little is known about the underlying physiological processes of egg development in this pest. This study found that treatment with aspirin (ASP) (a specific cyclooxygenase (COX) inhibitor) used to inhibit PGE2 biosynthesis during ovarian development significantly suppressed the reproduction of female F. occidentalis. However, the addition of PGE2 to ASP-treated females significantly rescued the suppressed reproduction. PGE2 was detected in growing ovarian follicles in an immunofluorescence assay. The hypothetical biosynthetic machinery of PGE2 was predicted from the F. occidentalis genome and included phospholipase A2  (PLA2 ), COX-like peroxidase (POX), and PGE2 synthase (PGES). Three specific PLA2 s were highly expressed in female adults during active oogenesis. Specific POX and PGES genes also showed high expression during active oogenesis. The adverse effect of ASP treatment on oogenesis was observed in follicle formation in the germarium where the follicle numbers in an ovariole were decreased, which resulted in hypotrophied ovaries. This impairment was rescued by the addition of PGE2 . ASP treatment also significantly inhibited chorion formation and suppressed gene expression associated with choriogenesis, which included chorion protein, mucin, and yellow while it did not inhibit vitellogenin gene expression. However, the addition of PGE2 induced the expression of the target genes suppressed by ASP treatment and rescued chorion formation. These results suggest that PGE2 mediated ovarian development by affecting follicle formation and choriogenesis in F. occidentalis.

Transcriptome analysis of female western flower thrips, Frankliniella occidentalis, exhibiting neo-panoistic ovarian development.

The western flower thrips, Frankliniella occidentalis, is one of the most devastating insect pests with explosive reproductive potential. However, its reproductive physiological processes are not well understood. This study reports the ovarian development and associated transcriptomes of F. occidentalis. Each ovary consisted of four ovarioles, each of which contained a maximum of nine follicles in the vitellarium. The germarium consisted of several dividing cells forming a germ cell cluster, presumably consisting of oocytes and nurse cells. The nurse cells were restricted to the germarium while the subsequent follicles did not possess nurse cells or a nutritive cord, supporting the neo-panoistic ovariole usually found in thysanopteran insects. Oocyte development was completed 72 h after adult emergence (AAE). Transcriptome analysis was performed at mid (36 h AAE) and late (60 h AAE) ovarian developmental stages using RNA sequencing (RNASeq) technology. More than 120 million reads per replication were matched to ≈ 15,000 F. occidentalis genes. Almost 500 genes were differentially expressed at each of the mid and late ovarian developmental stages. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that these differentially expressed genes (DEGs) were associated with metabolic pathways along with protein and nucleic acid biosynthesis. In both ovarian developmental stages, vitellogenin, mucin, and chorion genes were highly (> 8-fold) expressed. Endocrine signals associated with ovarian development were further investigated from the DEGs. Insulin and juvenile hormone signals were upregulated only at 36 h AAE, whereas the ecdysteroid signal was highly maintained at 60 h AAE. This study reports the transcriptome associated with the ovarian development of F. occidentalis, which possesses a neo-panoistic ovariole.