No abstract

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.

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 3 rd instar larvae of Culex pipiens laboratory colony. The results revealed that M. anisoplia e showed maximum larval mortality (88%) with the lowest lethal time (LT 50 ) (22.6 hrs) at 10 8 spores/ml followed by B. bassiana (73.33%) with LT 50 (38.35 hrs), while P. lilicanus showed minimum percent mortality (65%) with highest LT 50 (51.5 hrs). The median lethal concentration (LC 50 ) values were found to be 1.027 × 10 5 spores/ml for M. anisopliae , 1.24 × 10 6 spores/ml for B. bassiana , while it was 8.453 × 10 6 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. anisoplia e proved its superior virulent effect as a bio-control agent against Cx. pipiens.

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.

Dipterous insects cause serious public health problems for both humans and animals (Linthicum, 2012). In Egypt, Culex pipiens (Diptera: Culicidae), has been investigated and declared as a vector of several diseases (El-Zayyat et al., 2017). It transmits Rift valley fever virus (Dodson et al., 2017), Japanese encephalitis (Chancey et al., 2015), Wuchereria bancrofti accredited for human lymphatic filariasis transmission (Joseph et al., 2011), and West Nile virus (Bassal et al., 2017). Culex pipiens was incriminated as the filarial vector in Egypt (El-Naggar et al., 2017) and has been recorded by all governorates without exception (Abdel-Shafi et al., 2016). Traditional insecticides were used to control mosquitoes (Killeen et al., 2017) but introduced problems in the environment by leaving undesirable residues in food, toxicological implications to human health, increased cost and handling hazards (Bonner and Alvanja, 2017). Flies have developed a certain level of resistance to most available insecticides ARTICLE INFO