Phytochemical Investigation of Three Cystoseira Species and Their Larvicidal Activity Supported with In Silico Studies.

Culex pipiens mosquitoes are transmitters of many viruses and are associated with the transmission of many diseases, such as filariasis and avian malaria, that have a high rate of mortality. The current study draws attention to the larvicidal efficacy of three methanolic algal extracts, Cystoseira myrica, C. trinodis, and C. tamariscifolia, against the third larval instar of Cx. pipiens. The UPLC-ESI-MS analysis of three methanol fractions of algal samples led to the tentative characterization of twelve compounds with different percentages among the three samples belonging to phenolics and terpenoids. Probit analysis was used to calculate the lethal concentrations (LC50 and LC90). The highest level of toxicity was attained after treatment with C. myrica extract using a lethal concentration 50 (LC50) of 105.06 ppm, followed by C. trinodis (135.08 ppm), and the lowest level of toxicity was achieved by C. tamariscifolia (138.71 ppm) after 24 h. The elevation of glutathione-S-transferase (GST) and reduction of acetylcholine esterase (AChE) enzymes confirm the larvicidal activity of the three algal extracts. When compared to untreated larvae, all evaluated extracts revealed a significant reduction in protein, lipid, and carbohydrate contents, verifying their larvicidal effectiveness. To further support the observed activity, an in silico study for the identified compounds was carried out on the two tested enzymes. Results showed that the identified compounds and the tested enzymes had excellent binding affinities for each other. Overall, the current work suggests that the three algal extractions are a prospective source for the development of innovative, environmentally friendly larvicides.

Virulence of entomopathogenic fungi against Culex pipiens: Impact on biomolecules availability and life table parameters.

Culex pipiens mosquitoes considered as vectors for many arboviruses such as the West Nile virus and encephalitis virus showing a global impact on human health. The natural management of the aquatic stages of this pest is crucial for maintaining an insecticide-free and sustained environment. The present work focused on studying the biological and biochemical effects of the entomopathogenic fungi: Metarhizium anisopliae, Beauveria bassiana, and Paecilomyces lilicanus, against 3rd instar larvae of Culex pipiens laboratory colony. The results revealed that M. anisopliae showed maximum larval mortality (88%) with the lowest lethal time (LT50) (22.6 hrs) at 108 spores/ml followed by B. bassiana (73.33%) with LT50 (38.35 hrs), while P. lilicanus showed minimum percent mortality (65%) with highest LT50 (51.5 hrs). The median lethal concentration (LC50) values were found to be 1.027 × 105 spores/ml for M. anisopliae, 1.24 × 106 spores/ml for B. bassiana, while it was 8.453 × 106 spores/ml for P. lilicanus. A reduction in female fecundity, number of hatched eggs, pupation and adult emergence percentage were recorded. The biochemical analysis of the treated larvae revealed different quantitative decrease in total soluble proteins, lipids, and carbohydrate hydrolyzing enzymes compared to control. Histopathological effects of fungal infection upon insect cuticles, muscles, and midgut were investigated. Based on the obtained results, M. anisopliae proved its superior virulent effect as a bio-control agent against Cx. pipiens.

Correction: Methyl Farnesoate Plays a Dual Role in Regulating Drosophila Metamorphosis.

[This corrects the article DOI: 10.1371/journal.pgen.1005038.].

Methyl farnesoate plays a dual role in regulating Drosophila metamorphosis.

Corpus allatum (CA) ablation results in juvenile hormone (JH) deficiency and pupal lethality in Drosophila. The fly CA produces and releases three sesquiterpenoid hormones: JH III bisepoxide (JHB3), JH III, and methyl farnesoate (MF). In the whole body extracts, MF is the most abundant sesquiterpenoid, followed by JHB3 and JH III. Knockout of JH acid methyl transferase (jhamt) did not result in lethality; it decreased biosynthesis of JHB3, but MF biosynthesis was not affected. RNAi-mediated reduction of 3-hydroxy-3-methylglutaryl CoA reductase (hmgcr) expression in the CA decreased biosynthesis and titers of the three sesquiterpenoids, resulting in partial lethality. Reducing hmgcr expression in the CA of the jhamt mutant further decreased MF titer to a very low level, and caused complete lethality. JH III, JHB3, and MF function through Met and Gce, the two JH receptors, and induce expression of Kr-h1, a JH primary-response gene. As well, a portion of MF is converted to JHB3 in the hemolymph or peripheral tissues. Topical application of JHB3, JH III, or MF precluded lethality in JH-deficient animals, but not in the Met gce double mutant. Taken together, these experiments show that MF is produced by the larval CA and released into the hemolymph, from where it exerts its anti-metamorphic effects indirectly after conversion to JHB3, as well as acting as a hormone itself through the two JH receptors, Met and Gce.

Wnt signaling cross-talks with JH signaling by suppressing Met and gce expression.

Juvenile hormone (JH) plays key roles in controlling insect growth and metamorphosis. However, relatively little is known about the JH signaling pathways. Until recent years, increasing evidence has suggested that JH modulates the action of 20-hydroxyecdysone (20E) by regulating expression of broad (br), a 20E early response gene, through Met/Gce and Kr-h1. To identify other genes involved in JH signaling, we designed a novel Drosophila genetic screen to isolate mutations that derepress JH-mediated br suppression at early larval stages. We found that mutations in three Wnt signaling negative regulators in Drosophila, Axin (Axn), supernumerary limbs (slmb), and naked cuticle (nkd), caused precocious br expression, which could not be blocked by exogenous JHA. A similar phenotype was observed when armadillo (arm), the mediator of Wnt signaling, was overexpressed. qRT-PCR revealed that Met, gce and Kr-h1expression was suppressed in the Axn, slmb and nkd mutants as well as in arm gain-of-function larvae. Furthermore, ectopic expression of gce restored Kr-h1 expression but not Met expression in the arm gain-of-function larvae. Taken together, we conclude that Wnt signaling cross-talks with JH signaling by suppressing transcription of Met and gce, genes that encode for putative JH receptors. The reduced JH activity further induces down-regulation of Kr-h1expression and eventually derepresses br expression in the Drosophila early larval stages.

Drosophila Met and Gce are partially redundant in transducing juvenile hormone action.

The Drosophila Methoprene-tolerant (Met) and Germ cell-expressed (Gce) bHLH-PAS transcription factors are products of two paralogous genes. Both proteins potentially mediate the effect of juvenile hormone (JH) as candidate JH receptors. Here we report that Met and Gce are partially redundant in transducing JH action. Both Met and gce null single mutants are fully viable, but the Met gce double mutant, Met(27) gce(2.5k), dies during the larval-pupal transition. Precocious and enhanced caspase-dependent programmed cell death (PCD) appears in fat body cells of Met(27) gce(2.5k) during the early larval stages. Expression of Kr-h1, a JH response gene that inhibits 20-hydroxyecdysone (20E)-induced broad (br) expression, is abolished in Met(27) gce(2.5k) during larval molts. Consequently, expression of br occurs precociously in Met(27) gce(2.5k), which may cause precocious caspase-dependent PCD during the early larval stages. Defective phenotypes and gene expression changes in Met(27) gce(2.5k) double mutants are similar to those found in JH-deficient animals. Importantly, exogenous application of JH agonists rescued the JH-deficient animals but not the Met(27) gce(2.5k) mutants. Our data suggest a model in which Drosophila Met and Gce redundantly transduce JH action to prevent 20E-induced caspase-dependent PCD during larval molts by induction of Kr-h1 expression and inhibition of br expression.