Mechanisms of midgut remodeling: juvenile hormone analog methoprene blocks midgut metamorphosis by modulating ecdysone action

A short neuropeptide F analog (sNPF), III-2 may particularly regulate juvenile hormone III to influence Spodoptera frugiperda metamorphosis and development

Allatostatin (AS) or Allatotropin (AT) is a class of insect short neuropeptide F (sNPF) that affects insect growth and development by inhibiting or promote the synthesis of juvenile hormone (JH) in different insects. III-2 is a novel sNPF analog derived from a group of nitroaromatic groups connected by different amino acids. In this study, we found that III-2 showed high insecticidal activity against S. frugiperda larvae with a LC50 of 18.7 mg L-1. As demonstrated by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), III-2 particularly facilitated JH III and hindered 20E synthesis in S. frugiperda. The results of RNA-Seq and quantitative real-time polymerase chain reaction (qPCR) showed that III-2 treatment promoted the expression of key genes such as SfCYP15C1 in JH synthesis pathway and inhibited the expression of SfCYP314A1 and other genes in the 20E synthetic pathway. Significant differences were also observed in the expression of the genes related to cuticle formation. We report for the first time that sNPF compounds specifically interfere with the synthesis and secretion of a certain JH in insects, thus affecting the ecdysis and growth of insects, and leading to death. This study may provide a new plant conservation concept for us to seek the targeted control of certain insects based on specific interference with different JH.

Fenoxycarb exposure affects antiviral immunity and HaNPV infection in the cotton bollworm, Helicoverpa armigera

BACKGROUND

Application of insect growth regulators (IGR) is a good option for insect pest management because of their fewer adverse effects on humans and domestic animals. These compounds are capable of interfering with normal growth and development by mimicking the actions of hormones such as juvenile hormone (JH) or ecdysone. The effect of JH and its analogs on some aspects of insect immunity has been determined, yet their possible effects on antiviral immunity response has not been investigated yet. Considering the importance of antiviral response in viral replication, in this study the effects of the JH analog (JHA), fenoxycarb on the antiviral immunity pathway core genes [i.e. micro (mi)RNA, small interfering (si)RNA and apoptosis] of Helicoverpa armigera (Hubner) larvae were investigated. The effect of fenoxycarb on the susceptibility of the larvae to H. armigera nuclear polyhedrosis virus (HaNPV) also was assessed.

RESULTS

The results showed that the transcription level of miRNA (Dicer1, Ago1), siRNA (Dicer2, Ago2) and apoptosis (Caspase1, Caspase5) core genes in H. armigera larvae were decreased significantly after 24, 48 and 96 h feeding on a diet containing lethal and sublethal doses of fenoxycarb. Moreover, the mortality rate to HaNPV in the larvae treated with fenoxycarb increased compared to the control, leading to an increased replication of HaNPV.

CONCLUSION

Together, our results suggest that the antiviral immune system could be modulated by JHA and facilitate HaNPV replication in the larvae, increasing the mortality rate of the insect larvae. Understanding the effect of JHA on antiviral immunity is an important step toward the process of exploiting JHAs and viral pathogens to control insect pests. © 2022 Society of Chemical Industry.

Autophagy genes AMBRA1 and ATG8 play key roles in midgut remodeling of the yellow fever mosquito, Aedes aegypti

The function of two autophagy genes, an activating molecule BECN1 regulated autophagy (AMBRA1) and autophagy-related gene 8 (ATG8) in the midgut remodeling of Aedes aegypti was investigated. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis of RNA samples collected from the last instar larvae and pupae showed that these two genes are predominantly expressed during the last 12 h and first 24 h of the last larval and pupal stages, respectively. Stable ecdysteroid analog induced and juvenile hormone (JH) analog suppressed these genes. RNA interference (RNAi) studies showed that the ecdysone-induced transcription factor E93 is required for the expression of these genes. JH-induced transcription factor krüppel homolog 1 (Kr-h1) suppressed the expression of these genes. RNAi-mediated silencing of AMBRA1 and ATG8 blocked midgut remodeling. Histological studies of midguts from insects at 48 h after ecdysis to the final larval stage and 12 h after ecdysis to the pupal stage showed that ATG gene knockdown blocked midgut remodeling. AMBRA1 and ATG8 double-stranded (dsRNA)-treated insects retained larval midgut cells and died during the pupal stage. Together, these results demonstrate that ecdysteroid induction of ATG genes initiates autophagy programmed cell death during midgut remodeling. JH inhibits midgut remodeling during metamorphosis by interfering with the expression of ATG genes.

CRISPR-Cas9 Genome Editing Uncovers the Mode of Action of Methoprene in the Yellow Fever Mosquito, Aedes aegypti

Methoprene, a juvenile hormone (JH) analog, is widely used for insect control, but its mode of action is not known. To study methoprene action in the yellow fever mosquito, Aedes aegypti, the E93 (ecdysone-induced transcription factor) was knocked out using the CRISPR-Cas9 system. The E93 mutant pupae retained larval tissues similar to methoprene-treated insects. These insects completed pupal ecdysis and died as pupa. In addition, the expression of transcription factors, broad complex and Krüppel homolog 1 (Kr-h1), increased and that of programmed cell death (PCD) and autophagy genes decreased in E93 mutants. These data suggest that methoprene functions through JH receptor, methoprene-tolerant, and induces the expression of Kr-h1, which suppresses the expression of E93, resulting in a block in PCD and autophagy of larval tissues. Failure in the elimination of larval tissues and the formation of adult structures results in their death. These results answered long-standing questions on the mode of action of methoprene.

Ovomermis sinensis parasitism arrests midgut replacement by altering ecdysone and juvenile hormone in Helicoverpa armigera larvae

Many entomopathogens regulate the development of their insect hosts. However, the influence of mermithid nematodes on the development of their host remains unclear. In the current study, we provide insights into how Ovomermis sinensis parasitism affects the development of Helicoverpa armigera. We observed that O. sinensis arrests host development, as evidenced by the reduced body size and failure of Helicoverpa armigera to pupate. Moreover, midgut replacement of the host was significantly blocked by parasitism. Furthermore, juvenile hormone (JHIII) titers of the host were dramatically elevated by parasitism, but JH esterase (JHE) activities were strongly inhibited. By contrast, steroid hormone (20-hydroxyecdysone, 20E) titers of the host were significantly depressed by parasitism on days 4-6. The expression profiles of hormone-related genes in the host also showed similar patterns with the hormone titer. For this reason, rescue experiments were performed by injecting 20E and JHIII into developmentally arrested hosts. Notably, the midgut replacement of the host was rescued by the injection of 20E, whereas JHIII injection resulted in negative effects. Altogether, O. sinensis arrests H. armigera midgut replacement by reducing 20E and maintaining JH, thereby causing developmental arrests. Our study is the first report of the possible mechanism of mermithid nematodes in regulating insect development.

Juvenile hormone-induced histone deacetylase 3 suppresses apoptosis to maintain larval midgut in the yellow fever mosquito

SignificanceJuvenile hormone (JH), a sesquiterpenoid, regulates many aspects of insect development, including maintenance of the larval stage by preventing metamorphosis. In contrast, ecdysteroids promote metamorphosis by inducing the E93 transcription factor, which triggers apoptosis of larval cells and remodeling of the larval midgut. We discovered that JH suppresses precocious larval midgut-remodeling by inducing an epigenetic modifier, histone deacetylase 3 (HDAC3). JH-induced HDAC3 deacetylates the histone H4 localized at the promoters of proapoptotic genes, resulting in the suppression of these genes. This eventually prevents programmed cell death of midgut cells and midgut-remodeling during larval stages. These studies identified a previously unknown mechanism of JH action in blocking premature remodeling of the midgut during larval feeding stages.

FMRF-related peptides in Aedes aegypti midgut: neuromuscular connections and enteric nervous system

FMRFamide-related peptides (FaRPs) are a class of neuropeptides that participate in a variety of physiological processes in invertebrates. They occur in nerves of stomatogastric ganglia and enteroendocrine cells of the insect digestive tract, where they may control muscle functions. However, their direct involvement in muscle function has never been shown in situ. We studied the relationship between FaRPs and midgut muscle during larval-pupal transition of the mosquito Aedes aegypti. In late L4, FaRP-positive neuronal extensions attach to the bundles of the external circular muscle layer, and muscle stem cells start to undergo mitosis in the internal circular layer. Thereafter, the external muscle layer degenerates, disappearing during early pupal development, and is completely absent in the adult mosquito. Our results indicate that FaRP-based neural signals are involved in the reorganization of the muscle fibers of the mosquito midgut during the larval-pupal transition. In addition to confirming FaRP involvement in muscle function, we show that the mosquito midgut muscles are largely innervated, and that circular and longitudinal muscle have specific neuron bodies associated with them.

Stage-specific action of juvenile hormone analogs

The discovery of juvenile hormones (JH) and their synthetic analogs (JHA) generated excitement and hope that these compounds will replace first- and second-generation insecticides that have not so desirable environmental and human safety profiles. However, JHAs used commercially during the past four decades did not meet these expectations. The recent availability of advanced molecular and histological methods and the discovery of key players involved in JH action provided some insights into the functioning of JHA in a stage and species-specific manner. In this review, we will summarize recent findings and stage-specific action of JHA, focusing on three commercially used JHA, methoprene, hydroprene and pyriproxyfen and economically important pests, the red flour beetle, Tribolium castaneum, and the tobacco budworm, Heliothis virescens, and disease vector, the yellow fever mosquito, Aedes aegypti.

20-Hydroxyecdysone (20E) signaling as a promising target for the chemical control of malaria vectors

With the rapid development and spread of resistance to insecticides among anopheline malaria vectors, the efficacy of current World Health Organization (WHO)-approved insecticides targeting these vectors is under threat. This has led to the development of novel interventions, including improved and enhanced insecticide formulations with new targets or synergists or with added sterilants and/or antimalarials, among others. To date, several studies in mosquitoes have revealed that the 20-hydroxyecdysone (20E) signaling pathway regulates both vector abundance and competence, two parameters that influence malaria transmission. Therefore, insecticides which target 20E signaling (e.g. methoxyfenozide and halofenozide) may be an asset for malaria vector control. While such insecticides are already commercially available for lepidopteran and coleopteran pests, they still need to be approved by the WHO for malaria vector control programs. Until recently, chemicals targeting 20E signaling were considered to be insect growth regulators, and their effect was mostly studied against immature mosquito stages. However, in the last few years, promising results have been obtained by applying methoxyfenozide or halofenozide (two compounds that boost 20E signaling) to Anopheles populations at different phases of their life-cycle. In addition, preliminary studies suggest that methoxyfenozide resistance is unstable, causing the insects substantial fitness costs, thereby potentially circumventing one of the biggest challenges faced by current vector control efforts. In this review, we first describe the 20E signaling pathway in mosquitoes and then summarize the mechanisms whereby 20E signaling regulates the physiological processes associated with vector competence and vector abundance. Finally, we discuss the potential of using chemicals targeting 20E signaling to control malaria vectors.

Evaluation of inhibitor of apoptosis genes as targets for RNAi-mediated control of insect pests

Apoptosis has been widely studied from mammals to insects. Inhibitor of apoptosis (IAP) protein is a negative regulator of apoptosis. Recent studies suggest that iap genes could be excellent targets for RNA interference (RNAi)-mediated control of insect pests. However, not much is known about iap genes in one of the well-known insect model species, Tribolium castaneum. The orthologues of five iap genes were identified in T. castaneum by searching its genome at NCBI (https://www.ncbi.nlm.nih.gov/) and UniProt (https://www.uniprot.org/) databases using Drosophila melanogaster and Aedes aegypti IAP protein sequences as queries. RNAi assays were performed in T. castaneum cell line (TcA) and larvae. The knockdown of iap1 gene induced a distinct apoptotic phenotype in TcA cells and induced 91% mortality in T. castaneum larvae. Whereas, knockdown of iap5 resulted in a decrease in cell proliferation in TcA cells and developmental defects in T. castaneum larvae which led to 100% mortality. Knockdown of the other three iap genes identified did not cause a significant effect on cells or insects. These data increase our understanding of iap genes in insects and provide opportunities for developing iap1 and iap5 as targets for RNAi-based insect pest control.

CREB-binding protein regulates metamorphosis and compound eye development in the yellow fever mosquito, Aedes aegypti

Juvenile hormones (JH) and ecdysone coordinately regulate metamorphosis in Aedes aegypti. We studied the function of an epigenetic regulator and multifunctional transactivator, CREB binding protein (CBP) in A. aegypti. RNAi-mediated knockdown of CBP in Ae. aegypti larvae resulted in suppression of JH primary response gene, Krüppel-homolog 1 (Kr-h1), and induction of primary ecdysone response gene, E93, resulting in multiple effects including early metamorphosis, larval-pupal intermediate formation, mortality and inhibition of compound eye development. RNA sequencing identified hundreds of genes, including JH and ecdysone response genes regulated by CBP. In the presence of JH, CBP upregulates Kr-h1 by acetylating core histones at the Kr-h1 promoter and facilitating the recruitment of JH receptor and other proteins. CBP suppresses metamorphosis regulators, EcR-A, USP-A, BR-C, and E93 through the upregulation of Kr-h1 and E75A. CBP regulates the expression of core eye specification genes including those involved in TGF-β and EGFR signaling. These studies demonstrate that CBP is an essential player in JH and 20E action and regulates metamorphosis and compound eye development in Ae. aegypti.

Knockout of juvenile hormone receptor, Methoprene-tolerant, induces black larval phenotype in the yellow fever mosquito, Aedes aegypti

Juvenile hormone (JH) analogs are used to control mosquitoes. However, both larval development and action of JH analogs are not well studied in these insects because RNA interference does not work well. A multiple single guide RNA-based CRISPR/Cas9 genome-editing method was used to knockout the methoprene-tolerant gene (Met, a JH receptor). The Met knockout larvae showed precocious development of pupal cuticle and expression of pupal/adult genes involved in the synthesis and melanization of cuticle and blood meal digestion. The methods developed here could help to overcome the major hurdle in functional genomics studies in Aedes aegypti and facilitate advances in understanding larval development and mode of action of JH analogs.

The yellow fever mosquito, Aedes aegypti, vectors human pathogens. Juvenile hormones (JH) control almost every aspect of an insect’s life, and JH analogs are currently used to control mosquito larvae. Since RNA interference does not work efficiently during the larval stages of this insect, JH regulation of larval development and mode of action of JH analogs are not well studied. To overcome this limitation, we used a multiple single guide RNA-based CRISPR/Cas9 genome-editing method to knockout the methoprene-tolerant (Met) gene coding for a JH receptor. The Met knockout larvae exhibited a black larval phenotype during the L3 (third instar larvae) and L4 (fourth instar larvae) stages and died before pupation. However, Met knockout did not affect embryonic development or the L1 and L2 stages. Microscopy studies revealed the precocious synthesis of a dark pupal cuticle during the L3 and L4 stages. Gene expression analysis showed that Krüppel homolog 1, a key transcription factor in JH action, was down-regulated, but genes coding for proteins involved in melanization, pupal and adult cuticle synthesis, and blood meal digestion in adults were up-regulated in L4 Met mutants. These data suggest that, during the L3 and L4 stages, Met mediates JH suppression of pupal/adult genes involved in the synthesis and melanization of the cuticle and blood meal digestion. These results help to advance our knowledge of JH regulation of larval development and the mode of action of JH analogs in Ae. aegypti.

Identification of target genes for RNAi-mediated control of the Twospotted Spider Mite

RNA interference (RNAi) is being developed for the management of pests that destroy crops. The twospotted Spider Mite (TSSM), Tetranychus urticae is a worldwide pest due to its unique physiological and behavioral characteristics including extraordinary ability to detoxify a wide range of pesticides and feed on many host plants. In this study, we conducted experiments to identify target genes that could be used for the development of RNAi-based methods to control TSSM. Leaf disc feeding assays revealed that knockdown in the expression genes coding for proteins involved in the biosynthesis and action of juvenile hormone (JH) and action of ecdysteroids [Methoprene-tolerant (Met), retinoid X receptor β, farnesoic acid O-methyltransferase, and CREB-binding protein] caused 35-56% mortality. Transgenic tobacco plants expressing hairpin dsRNA targeting Met gene were generated and tested. About 48% mortality was observed in TSSM raised on transgenic tobacco plants expressing dsMet. These studies not only broaden our knowledge on understanding hormone action in TSSM but also identified target genes that could be used in RNAi-mediated control of TSSM.

Vector Control and Insecticidal Resistance in the African Malaria Mosquito Anopheles gambiae

Mosquito-borne diseases (including malaria) belong among the leading causes of death in humans. Vector control is a crucial part of the global strategy for management of mosquito-associated diseases, when insecticide use is the most important component in this effort. However, drug and insecticide resistance threaten the successes made with existing methods. Reduction or elimination of malaria is not possible without effective mosquito control. This article reviews current strategies of intervention in vector control to decrease transmission of disease and covers current relevant knowledge in molecular biology, biochemistry, and medicinal chemistry.

Role of Broad-Complex (Br) and Krüppel homolog 1 (Kr-h1) in the Ovary Development of Nilaparvata lugens

Ovarian development plays an important role in the life history of insects and is crucial for control of the insect population. The metamorphosis of an insect is precisely regulated by the interaction of the juvenile hormone and ecdysone. To understand the role of NlBr and NlKr-h1 in ovary development, we used RNA interference (RNAi) to down-regulate the expression of Broad-Complex (Br) and Krüppel homolog 1 (Kr-h1), two important down-stream transcription factors of juvenile hormone and ecdysone signaling. We further investigated their effects on metamorphosis and ovary development. The results showed that both NlBr and NlKr-h1 are induced by ecdysone. The down-regulation of NlBr and NlKr-h1 alone or together by RNAi is more effective than the topical application of ecdysone on the number of ovarioles, suggesting the necessity of NlBr and NlKr-h1 in determining the number of ovarioles. The ovarian grade was significantly increased/decreased by the topical application of ecdysone and down-regulation of NlBr and NlKr-h1. The pre-oviposition period was also increased. When NlBr and NlKr-h1 were down-regulated together, the ovary grade was not significantly different compared to the control (dsGFP), indicating that the development of the ovary is under the control of both NlBr and NlKr-h1. The interaction between the NlBr and NlKr-h1 on the number of ovarioles and the development of the ovary indicates cross-talk between both juvenile hormone and ecdysone signaling at the transcription level in the brown planthopper. Both genes are nuclear transcription factors and may regulate signaling via down-stream genes. These results would help to both enhance the current understanding of the regulatory mechanism of the interaction between juvenile hormone and ecdysone signaling pathways during ovarian development and to design chemicals to control pests.

Diversity and Transmission of Gut Bacteria in Atta and Acromyrmex Leaf-Cutting Ants during Development

The social Hymenoptera have distinct larval and adult stages separated by metamorphosis, which implies striking remodeling of external and internal body structures during the pupal stage. This imposes challenges to gut symbionts as existing cultures are lost and may or may not need to be replaced. To elucidate the extent to which metamorphosis interrupts associations between bacteria and hosts, we analyzed changes in gut microbiota during development and traced the transmission routes of dominant symbionts from the egg to adult stage in the leaf-cutting ants Acromyrmex echinatior and Atta cephalotes, which are both important functional herbivores in the New World tropics. Bacterial density remained similar across the developmental stages of Acromyrmex, but Atta brood had very low bacterial prevalences suggesting that bacterial gut symbionts are not actively maintained. We found that Wolbachia was the absolute dominant bacterial species across developmental stages in Acromyrmex and we confirmed that Atta lacks Wolbachia also in the immature stages, and had mostly Mollicutes bacteria in the adult worker guts. Wolbachia in Acromyrmex appeared to be transovarially transmitted similar to transmission in solitary insects. In contrast, Mollicutes were socially transmitted from old workers to newly emerged callows. We found that larval and pupal guts of both ant species contained Pseudomonas and Enterobacter bacteria that are also found in fungus gardens, but hardly or not in adult workers, suggesting they are beneficial only for larval growth and development. Our results reveal that transmission pathways for bacterial symbionts may be very different both between developmental stages and between sister genera and that identifying the mechanisms of bacterial acquisition and loss will be important to clarify their putative mutualistic functions.

Developmental Expression of Ecdysone-Related Genes Associated With Metamorphic Changes During Midgut Remodeling of Silkworm Bombyx mori (Lepidoptera:Bombycidae)

Steroid hormone 20-hydroxyecdysone is known as the systemic regulators of insect cells; however, how to impact the fate and function of mature and stem cells is unclear. For the first time, we report ecdysone regulatory cascades in both mature midgut cell and stem cell fractions related to developmental events by using histological, immunohistochemical, biochemical and gene expression analysis methods. Ecdysone receptor-B1 (EcR-B1) and ultraspiracle 1 (USP-1) mRNAs were detected mainly in mature cells during programmed cell death (PCD). Lowered E75A and probably BR-C Z4 in mature cells appear to provide a signal to the initiation of PCD. E74B, E75B and BR-C Z2 seem to be early response genes which are involved in preparatory phase of cell death. It is likely that βFTZ-F1, E74A and BR-C Z1 are probably associated with execution of death. EcR-A and USP2 mRNAs were found in stem cells during remodeling processes but EcR-B1, USP1 and E74B genes imply an important role during initial phase of metamorphic events in stem cells. BHR3 mRNAs were determined abundantly in stem cells suggesting its primary role in differentiation. All of these results showed the determination the cell fate in Bombyx mori (Linnaeus) midgut depends on type of ecdysone receptor isoforms and ecdysone-related transcription factors.

Dynamics and regulation of glycolysis-tricarboxylic acid metabolism in the midgut of Spodoptera litura during metamorphosis

Significant changes usually take place in the internal metabolism of insects during metamorphosis. The glycolysis-tricarboxylic acid (glycolysis-TCA) pathway is important for energy metabolism. To elucidate its dynamics, the mRNA levels of genes involved in this pathway were examined in the midgut of Spodoptera litura during metamorphosis, and the pyruvate content was quantified. The expression patterns of these genes in response to starvation were examined, and the interaction between protein phosphatase 1 (PP1) and phosphofructokinase (PFK) was studied. The results revealed that the expression or activities of most glycolytic enzymes was down-regulated in prepupae and then recovered in some degree in pupae, and all TCA-related genes were remarkably suppressed in both the prepupae and pupae. Pyruvate was enriched in the pupal midgut. Taken together, these results suggest that insects decrease both glycolysis and TCA in prepupae to save energy and then up-regulate glycolysis but down-regulate TCA in pupae to increase the supply of intermediates for construction of new organs. The expression of all these genes were down-regulated by starvation, indicating that non-feeding during metamorphosis may be a regulator of glycolysis-TCA pathway in the midgut. Importantly, interaction between PP1 and PFK was identified and is suggested to be involved in the regulation of glycolysis.

Ultrastructural analysis of apoptosis and autophagy in the midgut epithelium of Piscicola geometra (Annelida, Hirudinida) after blood feeding

Cell death in the endodermal region of the digestive tract of the blood-feeding leech Piscicola geometra was analyzed using light and transmission electron microscopes and the fluorescence method. Sexually mature specimens of P. geometra were bred under laboratory conditions and fed on Danio rerio. After copulation, the specimens laid cocoons. The material for our studies were non-feeding juveniles collected just after hatching, non-feeding adult specimens, and leeches that had been fed with fish blood (D. rerio) only once ad libitum. The fed leeches were prepared for our studies during feeding and after 1, 3, 7, and 14 days (not sexually mature specimens) and some weeks after feeding (the sexually mature). Autophagy in all regions of the endodermal part of the digestive system, including the esophagus, the crop, the posterior crop caecum (PCC), and the intestine was observed in the adult non-feeding and feeding specimens. In fed specimens, autophagy occurred at very high levels--in 80 to 90 % of epithelial cells in all four regions. In contrast, in adult specimens that did not feed, this process occurred at much lower levels--about 10 % (esophagus and intestine) and about 30 % (crop and PCC) of the midgut epithelial cells. Apoptosis occurred in the feeding adult specimens but only in the crop and PCC. However, it was absent in the non-feeding adult specimens and the specimens that were collected during feeding. Moreover, neither autophagy nor apoptosis were observed in the juvenile, non-feeding specimens. The appearance of autophagy and apoptosis was connected with feeding on toxic blood. We concluded that autophagy played the role of a survival factor and was involved in the protection of the epithelium against the products of blood digestion. Quantitative analysis was prepared to determine the number of autophagic and apoptotic cells.

Juvenile hormone regulates Aedes aegypti Krüppel homolog 1 through a conserved E box motif

Juvenile hormone (JH) plays important roles in regulation of many physiological processes including development, reproduction and metabolism in insects. However, the molecular mechanisms of JH signaling pathway are not completely understood. To elucidate the molecular mechanisms of JH regulation of Krüppel homolog 1 gene (Kr-h1) in Aedes aegypti, we employed JH-sensitive Aag-2 cells developed from the embryos of this insect. In Aag-2 cells, AaKr-h1 gene is induced by nanomolar concentration of JH III, its expression peaked at 1.5 h after treatment with JH III. RNAi studies showed that JH induction of this gene requires the presence of Ae. aegypti methoprene-tolerant (AaMet). A conserved 13 nucleotide JH response element (JHRE, TGCCTCCACGTGC) containing canonical E box motif (underlined) identified in the promoter of AaKr-h1 is required for JH induction of this gene. Critical nucleotides in the JHRE required for JH action were identified by employing mutagenesis and reporter assays. Reporter assays also showed that basic helix loop helix (bHLH) domain of AaMet is required for JH induction of AaKr-h1. 5' rapid amplification of cDNA ends method identified two isoforms of AaKr-h1, AaKr-h1α and AaKr-h1β, the expression of both isoforms is induced by JH III, but AaKr-h1α is the predominant isoform in both Aag-2 cells and Ae. aegypti larvae.

Juvenile hormone prevents 20-hydroxyecdysone-induced metamorphosis by regulating the phosphorylation of a newly identified broad protein

The steroid hormone 20-hydroxyecdysone (20E) initiates insect molting and metamorphosis. By contrast, juvenile hormone (JH) prevents metamorphosis. However, the mechanism by which JH inhibits metamorphosis remains unclear. In this study, we propose that JH induces the phosphorylation of Broad isoform Z7 (BrZ7), a newly identified protein, to inhibit 20E-mediated metamorphosis in the lepidopteran insect Helicoverpa armigera. The knockdown of BrZ7 in larvae inhibited metamorphosis by repressing the expression of the 20E response gene. BrZ7 was weakly expressed and phosphorylated during larval growth but highly expressed and non-phosphorylated during metamorphosis. JH regulated the rapid phosphorylation of BrZ7 via a G-protein-coupled receptor-, phospholipase C-, and protein kinase C-triggered pathway. The phosphorylated BrZ7 bound to the 5'-regulatory region of calponin to regulate its expression in the JH pathway. Exogenous JH induced BrZ7 phosphorylation to prevent metamorphosis by suppressing 20E-related gene transcription. JH promoted non-phosphorylated calponin interacting with ultraspiracle protein to activate the JH pathway and antagonize the 20E pathway. This study reveals one of the possible mechanisms by which JH counteracts 20E-regulated metamorphosis by inducing the phosphorylation of BrZ7.

Methoprene effects on survival and reproductive performance of adult female and male Aedes aegypti

Methoprene is a juvenile hormone analog commonly used for the control of mosquito larvae. It acts through interference with normal metamorphosis, resulting in mortality prior to and during adult emergence. Methoprene is not commonly used for the control of adult mosquitoes, due to an absence of acute effects. Here, we have evaluated for chronic effects caused by the exposure of adult Aedes aegypti mosquitoes to methoprene. We applied methoprene to adults, both through 1) topical application to the abdomen and 2) as an aerosol, examining for treatment effects on ovary development, adult longevity, and fecundity. The results demonstrate that relatively high doses are required to affect adult survivorship. In contrast, significant impacts on both fecundity and egg hatch were observed in females treated at the lower dosages. We discuss the results in relation to autocidal strategies for mosquito control in which the release of fecund females is to be avoided.

Degeneration and cell regeneration in the midgut of Podisus nigrispinus (Heteroptera: Pentatomidae) during post-embryonic development

Cell death, proliferation, and differentiation in some developmental stages of insects have been studied in the midgut of ametabolous, which undergo only continuous growth, and holometabolous, which undergo complete metamorphosis. However, in hemimetabolous insects, evolutionarily intermediate between ametabolous and holometabolous, midgut reorganization during the post-embryonic development has been poorly studied. The present study evaluates the post-embryonic development of the midgut of a hemimetabolous insect, Podisus nigrispinus, to test the hypothesis that these insects have programmed cell death and proliferation followed by differentiation of regenerative cells during midgut growth from nymphs to adult. The morphometrical data showed a 6-fold increase in midgut length from the first instar nymph to the adult, which did not result from an increase in the size of the midgut cells, suggesting that the growth of the midgut occurs by an increase in cell number. Cell death was rarely found in the midgut, whereas proliferation of regenerative cells occurred quite frequently. The growth of the midgut of P. nigrispinus appears to result from the proliferation of regenerative cells present in the epithelium; unlike ametabolous and holometabolous insects, the midgut of P. nigrispinus does not undergo extensive remodeling, as shown by the low frequency of digestive cell death.

Different pattern of Galleria mellonella jhbp gene expression in high five and Sf9 cells

Juvenile hormone binding protein (JHBP) is the key element of the system that transmits hormone signals to target tissues. Recently, we found that the core promoter of the jhbp gene is strongly under the control of the TATA box and the transcription start site. In this report, we have shown that the jhbp promoter contains distal regulatory elements whose functionality clearly depends on the particular cell environment and that the scope of research from one cell line is insufficient to generalize the conclusions of the analysis. Cf1/Usp (where Usp is ultraspiracle protein previously known as Cf1, chorion factor 1) elements suppressed transcription of the reporter gene in the High Five cell line but not in the Sf9 cell line. However, upstream from all three Cf1/Usp elements there is a DNA sequence, containing the Zeste element, which activates jhbp in both systems. We found that juvenile hormone strongly inhibited the activity of the jhbp promoter in the Sf9 cell line, whereas it did not have an effect in the High Five cell line. A second key hormone that controls insect development--20-hydroxyecdysone, was also found to suppress the transcription of jhbp. This is the first report describing how these two hormones affect jhbp gene expression in different cell lines.

The juvenile hormone signaling pathway in insect development

The molecular action of juvenile hormone (JH), a regulator of vital importance to insects, was until recently regarded as a mystery. The past few years have seen an explosion of studies of JH signaling, sparked by a finding that a JH-resistance gene, Methoprene-tolerant (Met), plays a critical role in insect metamorphosis. Here, we summarize the recently acquired knowledge on the capacity of Met to bind JH, which has been mapped to a particular ligand-binding domain, thus establishing this bHLH-PAS protein as a novel type of an intracellular hormone receptor. Next, we consider the significance of JH-dependent interactions of Met with other transcription factors and signaling pathways. We examine the regulation and biological roles of genes acting downstream of JH and Met in insect metamorphosis. Finally, we discuss the current gaps in our understanding of JH action and outline directions for future research.

Efficacy, fate, and potential effects on salmonids of mosquito larvicides in catch basins in Seattle, Washington

We investigated the efficacy, fate, and potential for direct effects on salmonids of 4 common mosquito larvicides (Mosquito Dunks and Bits (AI: Bacillis thuringiensis var. israelensis, [Bti]), VectoLex WSP (AI: Bacillus sphaericus [Bs], VectoLex CG [AI: Bs], and Altosid Briquets [AI: s-methoprene]) in Seattle, WA, during 3 summers. During efficacy trials in 2006, all treatments resulted in a rapid reduction in number of mosquito pupae (Mosquito Dunks and Bits and VectoLex WSP) or emergence success (Altosid Briquets). VectoLex CG was chosen for city-wide application in 2007 and 2008. The average counts of pupae within round-top basins remained significantly below the control average for 11 wk in 2007, whereas efficacy in grated-top basins was short-lived. In 2008 the average counts of pupae within grated-top basins remained significantly below the control average for 10 wk. Altosid XR was also effective in reducing adult emergence within grated basins in 2008. In 2007 and 2008, frequent precipitation events made the evaluation of efficacy difficult due to reductions in pupae across control and treated basins. Four separate analyses of VectoLex products revealed that the product was a combination of Bs and Bti. Both Bs and Bti were detected in 3 urban creeks connected to treated basins in 2007 and 2008. Laboratory toxicity test results suggest that concentrations of Bs and Bti detected in each of the watersheds pose little direct hazard to juvenile salmonids.

The role of autophagy in the midgut epithelium of Eubranchipus grubii (Crustacea, Branchiopoda, Anostraca)

Eubranchipus grubii (Crustacea, Branchiopoda, Anostraca) is an omnivorous filter feeder whose life span lasts no more than 12 weeks. Adult males and females of E. grubii were used for ultrastructural studies of the midgut epithelium and an analysis of autophagy. The midgut epithelium is formed by columnar digestive cells and no regenerative cells were observed. A distinct regionalization in the distribution of organelles appears - basal, perinuclear and apical regions were distinguished. No differences in the ultrastructure of digestive cells were observed between males and females. Autophagic disintegration of organelles occurs throughout the midgut epithelium. Degenerated organelles accumulate in the neighborhood of Golgi complexes, and these complexes presumably take part in phagophore and autophagosome formation. In some cases, the phagophore also surrounds small autophagosomes, which had appeared earlier. Fusion of autophagosomes and lysosomes was not observed, but lysosomes are enclosed during autophagosome formation. Autophagosomes and autolysosomes are discharged into the midgut lumen due to apocrine secretion. Autophagy plays a role in cell survival by protecting the cell from cell death.

20-hydroxyecdysone upregulates apoptotic genes and induces apoptosis in the Bombyx fat body

During insect metamorphosis, obsolete larval tissues are removed by programed cell death (PCD), mainly apoptosis and autophagy, which is directed by the molting hormone, 20-hydroxyecdysone (20E) and the 20E-triggered transcriptional cascade. Here, we investigated how 20E regulates apoptosis at the transcriptional level in the fat body of the silkworm, Bombyx mori. As detected by TdT-mediated dUTP Nick-End Labeling (TUNEL), apoptosis weakly occurred during the fourth larval molting, decreased to undetected levels during the early fifth instar, and gradually increased from day 4 of fifth instar to the wandering stage to the prepupal stage. Meanwhile, as determined by quantitative real-time PCR, eight genes involved in apoptosis, including Apaf-1, Nedd2 like1, Nedd2 like2, ICE1, ICE3, ICE5, Arp, and IAP, were highly expressed during molting and pupation, when the 20E titer is high. Injection of 20E into day 2 of fifth instar larvae significantly induced apoptosis and upregulated apoptotic genes after 6 h of treatment, and in vitro treatment of larval fat body tissues with 20E upregulated all the eight apoptotic genes. Moreover, RNAi knockdown of USP, a component of the 20E receptor complex EcR-USP, at the early-wandering stage reduced apoptosis and downregulated apoptotic genes after 24 h of treatment. Taken together, we infer that 20E upregulates apoptotic genes and thus induces apoptosis in the Bombyx fat body during larval molting and the larval-pupal transition.

Nutrient limitation results in juvenile hormone-mediated resorption of previtellogenic ovarian follicles in mosquitoes

Juvenile hormone (JH) is a central hormonal regulator of previtellogenic development in female Aedes aegypti mosquitoes. JH levels are low at eclosion and increase during the first day after adult emergence. This initial rise in JH is essential for female reproductive maturation. After previtellogenic maturation is complete, the mosquito enters a 'state-of-arrest' during which JH synthesis continues at a slower pace and further ovary development is repressed until a blood meal is taken. By examining the relationships between juvenile hormone, follicular resorption and nutrition in A. aegypti, we were able to define a critical role of JH during the previtellogenic resting stage. The rate of follicular resorption in resting stage mosquitoes is dependent on nutritional quality. Feeding water alone caused the rate of follicular resorption to reach over 20% by day 7 after emergence. Conversely, feeding a 20% sucrose solution caused resorption to remain below 5% during the entire experimental period. Mosquitoes fed 3% sucrose show rates of resorption intermediate between water and 20% sucrose and only reached 10% by day 7 after emergence. Follicular resorption is related to JH levels. Ligated abdomens separated from a source of JH (the corpora allata) showed an increase in resorption comparable to similarly aged starved mosquitoes (16%). Resorption in ligated abdomens was reduced to 6% by application of methoprene. The application of methoprene was also sufficient to prevent resorption in intact mosquitoes starved for 48 h (14% starved vs. 4% starved with methoprene). Additionally, active caspases were localized to resorbing follicles indicating that an apoptotic cell-death mechanism is responsible for follicular resorption during the previtellogenic resting stage. Taken together, these results indicate that JH mediates reproductive trade-offs in resting stage mosquitoes in response to nutrition.

Exogenous JH and ecdysteroid applications alter initiation of polydnaviral replication in an endoparasitoid wasp, Cotesia plutellae (Braconidae: Hymenoptera)

Polydnaviruses are a group of double-stranded DNA viruses and are symbiotically associated with some ichneumonoid wasps. As proviruses, the replication of polydnaviruses occurs in the female reproductive organ at the pupal stage. This study analyzed the effects of two developmental hormones, juvenile hormone (JH) and ecdysteroid, on the viral replication of Cotesia plutellae bracovirus (CpBV). All 23 CpBV segments identified contained a conserved excision/rejoining site ('AGCTTT') from their proviral segments. Using quantitative real-time PCR based on this excision/rejoining site marker, initiation of CpBV replication was determined to have occurred on day 4 on the pupal stage. Pyriproxyfen, a JH agonist, significantly inhibited adult emergence of C. plutellae, whereas RH5992, an ecdysteroid agonist, had no inhibitory effect. Although RH5992 had no effect dose on adult development, it significantly accelerated viral replication. The results of immunoblotting assays against viral coat proteins support the effects of the hormone agonists on viral replication.

The juvenile hormone analogue methoprene up-regulates the Ha-RNA-binding protein

RNA-binding proteins (RBPs) associate with RNA in cells to form ribonucleoprotein (RNP) complexes. The RBPs are involved in various aspects of RNA metabolism, but their roles in the juvenile hormone (JH) signaling pathway are not well known. An RNA-binding protein (Ha-RBP) was obtained from Helicoverpa armigera, a lepidopteran insect, which could be up-regulated by the juvenile hormone analogue methoprene at the mRNA level. Immunohistochemistry showed that Ha-RBP was mainly distributed in cells where protein synthesis was active, and its knockdown decreased the protein levels of JH-responsive genes. Immunocytochemistry showed that Ha-RBP was located in both the nucleus and the cytoplasm of normal cells, and methoprene could promote the translocation of Ha-RBP from the nucleus to the cytoplasm. This process was mediated by the JH receptor candidate HaMet but not by the ultraspiracle protein (USP). The knockdown of HaMet by RNAi decreased the expression of Ha-RBP and blocked its translocation from the nucleus to the cytoplasm. Together these findings indicate that Ha-RBP is involved in the juvenile hormone signaling pathway and Met mediates JH signaling by regulating Ha-RBP translocation from nucleus to cytoplasm, which may allow Ha-RBP to modify protein translation.

Steroid receptor co-activator is required for juvenile hormone signal transduction through a bHLH-PAS transcription factor, methoprene tolerant

Metamorphosis in insects is regulated by juvenile hormone (JH) and ecdysteroids. The mechanism of 20-hydroxyecdysone (20E), but not of JH action, is well understood. A basic helix-loop-helix (bHLH)-Per-Arnt-Sim (PAS) family member, methoprene tolerant (Met), plays an important role in JH action. Microarray analysis and RNA interference (RNAi) were used to identify 69 genes that require Met for their hydroprene-regulated expression in the red flour beetle, Tribolium castaneum. Quantitative real time PCR analysis confirmed microarray data for 13 of the 16 hydroprene-response genes tested. The members of the bHLH-PAS family often function as heterodimers to regulate gene expression and Met is a member of this family. To determine whether other members of the bHLH-PAS family are required for the expression of JH-response genes, we employed RNAi to knockdown the expression of all 11 members of the bHLH-PAS family and studied the expression of JH-response genes in RNAi insects. These studies showed that besides Met, another member of this family, steroid receptor co-activator (SRC) is required for the expression of 15 JH-response genes tested. Moreover, studies in JH responsive Aag-2 cells revealed that Aedes aegypti homologues of both Met and SRC are required for the expression of the JH-response gene, kr-h1, and SRC is required for expression of ecdysone-response genes. These data suggest the steroid receptor co-activator plays key roles in both JH and 20E action suggesting that this may be an important molecule that mediates cross-talk between JH and 20E to prevent metamorphosis.

Analysis of molecular markers for metamorphic competency and their response to starvation or feeding in the mosquito, Aedes aegypti (Diptera: Culicidae)

The nutritional condition of fourth instar larvae of the yellow fever mosquito, Aedes aegypti, governs female longevity and egg production, both are key determinants of pathogen transmission. As well, nutrition provisions larval growth and development and attains its greatest pace in the last larval instar in preparation for metamorphosis to an adult. These developmental processes are regulated by a complex endocrine interplay of juvenile hormone, neuropeptides, and ecdysteroids that is nutrition sensitive. We previously determined that feeding for only 24h post-ecdysis was sufficient for fourth instar Ae. aegypti larvae to reach critical weight and accumulate sufficient nutritional stores to commit to metamorphosis. To understand the genetic basis of metamorphic commitment in Ae. aegypti, we profiled the expression of 16 genes known to be involved in the endocrine and nutritional regulation of insect metamorphosis in two ways. The first set is a developmental profile from the beginning of the fourth instar to early pupae, and the second set is for fourth instars starved or fed for up to 36 h. By comparing the two sets, we found that seven of the genes (AaegCYP302, AaegJHE43357, AaegBrCZ4, AaegCPF1-2, AaegCPR-7, AaegPpl, and AaegSlif) were expressed during metamorphic commitment in fourth instars and in fed but not starved larvae. Based on these results, the seven genes alone or in combination may serve as molecular indicators of nutritional and metamorphic status of fourth instar Ae. aegypti larvae and possibly other mosquito species in field and laboratory studies to gauge sub-lethal effects of novel and traditional cultural or chemical controls.

Cloning and functional expression of Rh50-like glycoprotein, a putative ammonia channel, in Aedes albopictus mosquitoes

Evidence has shown that female mosquitoes can deaminate more than 80% of the ingested bloodmeal protein amino acids, and thus lead to a massive amount of ammonia production. Ammonia transport is a critical step for detoxifying ammonia in organisms. Here we characterized a putative ammonia channel gene, Rhesus (Rh) 50 glycoprotein, from Aedes albopictus (AalRh50) and determined the difference of its expression profile in different tissues at both message and protein levels as well as its response to a blood meal. We showed that AalRh50 shares a low identity with E. coli ammonia transporter (EcoAmtB), but higher identities with human RhBG and Drosophila Rh50 genes. The analysis of ammonia-conductance sites indicates that AalRh50 has residue substitutions of S237L (equivalent to S219 in AmtB) in the external vestibule, F127I (equivalent to F107 in AmtB) in the pore entrance, and S281N (equivalent to S263 in AmtB) in the internal vestibule, which could alter or reduce ammonia-conductance activity. The results from quantitative real-time-PCR and immunohistochemistry revealed that AalRh50 is expressed at significantly higher levels in the head, Malpighian tubules, and thorax of the non-blood-fed females, suggesting that AalRh50 might play roles in maintaining normal neurotransmitter metabolism, acid-base balance, and flight energy production in different tissues of mosquitoes at the non-blood-fed condition. A blood meal significantly increases AalRh50 expression in midgut, fat body, and Malpighian tubules from 3 or 6 to 24h post feeding, indicating that AalRh50 plays an important role in detoxification of excess systemic ammonia of female adults during the gonotrophic cycle.

Fine structure of the midgut epithelium in two Archaeognatha, Lepismachilis notata and Machilis hrabei (Insecta), in relation to its degeneration and regeneration

In two archaeognathans, Lepismachilis notata and Machilis hrabei, the midgut epithelium and processes of its regeneration and degeneration have been described at the ultrastructural level. In both analysed species, the midgut epithelium is composed of epithelial and regenerative cells (regenerative nests). The epithelial cells show distinct regionalization in organelles distribution with the basal, perinuclear, and apical regions being distinguished. Degeneration of epithelial cells proceeds in a necrotic way (continuous degeneration) during the entire life of adult specimens, but just before each moult degeneration intensifies. Apoptosis has been observed. Regenerative cells fulfil the role of midgut stem cells. Some of them proliferate, while the others differentiate into epithelial cells. We compared the organisation of the midgut epithelium of M. hrabei and L. notata with zygentoman species, which have just been described.

Genome-wide regulation of innate immunity by juvenile hormone and 20-hydroxyecdysone in the Bombyx fat body

Background

Insect innate immunity can be affected by juvenile hormone (JH) and 20-hydroxyecdysone (20E), but how innate immunity is developmentally regulated by these two hormones in insects has not yet been elucidated. In the silkworm, Bombyx mori, JH and 20E levels are high during the final larval molt (4 M) but absent during the feeding stage of 5^th instar (5 F), while JH level is low and 20E level is high during the prepupal stage (PP). Fat body produces humoral response molecules and hence is considered as the major organ involved in innate immunity.

Results

A genome-wide microarray analysis of Bombyx fat body isolated from 4 M, 5 F and PP uncovered a large number of differentially-expressed genes. Most notably, 6 antimicrobial peptide (AMP) genes were up-regulated at 4 M versus PP suggesting that Bombyx innate immunity is developmentally regulated by the two hormones. First, JH treatment dramatically increased AMP mRNA levels and activities. Furthermore, 20E treatment exhibited inhibitory effects on AMP mRNA levels and activities, and RNA interference of the 20E receptor EcR-USP had the opposite effects to 20E treatment.

Conclusion

Taken together, we demonstrate that JH acts as an immune-activator while 20E inhibits innate immunity in the fat body during Bombyx postembryonic development.

Quantitative analysis of replication and tropisms of Dengue virus type 2 in Aedes albopictus

Dengue virus serotype 2 (DENV-2) RNA replication profiles and tropisms were studied by using quantitative RT-PCR (q-RTPCR) in intrathoracically infected Aedes albopictus. The virus RNA replication profiles were diverse in mosquito organs. In fat body, brain, salivary gland, and malpighian tubes, it peaked at 8, 23, 23, and 27 days post-infection, respectively, and then, all declined. In midgut, it increased all the time and had no trend of decline. In ovary, it had no apparent increase. Subsequent Western blotting of DENV-2 E protein had similar results. Using ribosomal protein 7 (rpS7) as an internal control, we found that, in salivary gland, brain, fat body, and midgut, the average DENV-2 RNA levels (DENV-2 RNA/rpS7 mRNA) were 1,028, 464, 5.6, and 6.2, respectively; in malpighian tubes, it was 1, and in ovary, it was far less than 1. These results suggest that infection profiles and tropism of DENV-2 RNA in Ae. albopictus organs are significantly different.

Mode of action of methoprene in affecting female reproduction in the African malaria mosquito, Anopheles gambiae

BACKGROUND

One of the most studied actions of juvenile hormone (JH) is its ability to modulate ecdysteroid signaling during insect development and metamorphosis. Previous studies in mosquitoes showed that 20-hydroxyecdysone (20E) regulates vitellogenin synthesis. However, the action of JH and its mimics, e.g. methoprene, on female reproduction of mosquitoes remains unknown.

RESULTS

Here, a major malaria vector, Anopheles gambiae Giles, was used as a model insect to study the action of methoprene on female reproduction. Ecdysteroid titers and expression profiles of ecdysone-regulated genes were determined before and after a blood meal. An ecdysteroid peak was detected at 12 h post blood meal (PBM). The maximum expression of ecdysone-regulated genes, such as ecdysone receptor (EcR), hormone receptor 3 (HR3) and vitellogenin (Vg) gene, coincided with the ecdysteroid peak. Interestingly, topical application of methoprene at 6 h PBM delayed ovarian development and egg maturation by suppressing the expression of ecdysone-regulated genes in female mosquitoes.

CONCLUSION

The data suggest that ecdysteroid titers are correlated with Vg synthesis, and methoprene affects vitellogenesis by modulating ecdysteroid action in A. gambiae.

Developmental regulation of glycolysis by 20-hydroxyecdysone and juvenile hormone in fat body tissues of the silkworm, Bombyx mori

20-Hydroxyecdysone (20E) and juvenile hormone (JH) control a variety of physiological events during insect development and metamorphosis. To understand how 20E and JH developmentally regulate energy metabolism in insects, we performed a genome-wide microarray analysis of fat body tissues isolated from the silkworm, Bombyx mori. Many genes involved in energy metabolism, including genes in the glycolytic pathway, were down-regulated during molting and pupation, when 20E levels are high. Notably, 20E treatment exhibited inhibitory effects on key glycolytic enzyme mRNA levels and activities, and RNA interference of the 20E receptor EcR-USP had the opposite effects to 20E treatment. Meanwhile, JH treatment stimulated both mRNA levels and activities of the key glycolytic enzymes, presumably via antagonizing the 20E action. Taken together, we conclude that 20E acts as a general blocker for glycolysis in the Bombyx fat body during molting and pupation, whereas the physiological role of JH is contrast with 20E during molting.

Accumulated organic debris in catch basins improves the efficacy of S-methoprene against mosquitoes in Toronto, Ontario, Canada

To control West Nile Virus in the greater Toronto area of Ontario, Canada, S-methoprene (Altosid XRbriquets 2.1% AI) is applied each year to storm water catch basins. Because the efficacy of the XRbriquets to reduce adult mosquito populations had not been evaluated locally and was influenced by organic debris in a pilot study, we compared the efficacy of the briquets in 17 sediment and debris-filled catch basins versus 20 catch basins that were vacuumed free of debris. Emergence rates approached 100% in the 5 untreated control catch basins. Emergence rates were significantly lower, and S-methoprene was detected more often and at higher levels, in debris-filled basins versus cleaned catch basins. Overall, 20% of pupae emerged from clean catch basins versus only 3% from debris-filled ones, the difference between treatments becoming significant after 26 days. S-methoprene and total organic carbon concentrations in the catch basins were positively correlated (P < 0.001). We hypothesize that S-methoprene is binding to the organic fraction in the water and sediment in the debris-filled basins, prolonging S-methoprene doses, which are reflected in lower mosquito emergence rates.

Regulation of midgut growth, development, and metamorphosis

The insect midgut is an important site of entry for pathogens and insect control agents. This review focuses on recent information related to midgut epithelial growth, metamorphosis, and repair as a defense against pathogens. The roles of stem cell mitogens and differentiation factors are described. Included is a discussion of apoptosis and autophagy in the yellow body. Sloughing, also described, protects the midgut from virus infections and bacterial toxins through death and replacement of affected cells. The mechanisms by which the repair process reduces the effectiveness of pest control strategies are discussed. Primary tissue culture methods also are described, and their value in understanding the mechanisms by which biologically based insecticides work is discussed.

Ecdysteroid hormone action

Several reviews devoted to various aspects of ecdysone research have been published during the last few years. Therefore, this article concentrates mainly on the considerable progress in ecdysone research observed recently, and will cover the results obtained during the last 2 years. The main emphasis is put on the molecular mode of ecdysteroid receptor-mediated hormone action. Two examples of interaction with other hormonal signalling pathways are described, namely crosstalk with juvenile hormone and insulin. Some selected, recently investigated examples of the multitude of hormonal responses are described. Finally, ecological aspects and some practical applications are discussed.