Field-evolved resistance to chitin synthesis inhibitor insecticides by soybean looper, Chrysodeixis includens (Lepidoptera: Noctuidae), in Brazil

Soybean looper (SBL), Chrysodeixis includens (Walker), is an economically important soybean and cotton pest in Brazil. Here, we selected an SBL strain resistant to teflubenzuron using F2 screening, estimated the resistance allele frequency, characterized the inheritance of resistance, investigated fitness costs, evaluated patterns of cross-resistance, and determined the magnitude of resistance. The teflubenzuron-resistant strain (Teflu-R) was selected from field-collected populations with an estimated allele frequency of 0.1700. Estimated LC50 values were 0.010 and 363.61 μg a.i. cm-2 for the susceptible (Sus) and Teflu-R strains, respectively, representing a 36,361-fold resistance ratio (RR). The LC50 values of reciprocal crosses were 1.02 and 0.59 μg a.i. cm-2, suggesting that resistance is autosomally inherited. The low survival of reciprocal crosses (16 and 20%) on teflubenzuron-sprayed leaves indicates incomplete recessive resistance. The number of segregations influencing resistance was 2.72, suggesting a polygenic effect. The Teflu-R strain showed longer development periods as well as lower survival and population growth than the Sus strain, revealing fitness costs. The Teflu-R strain also showed high cross-resistancesto other chitin inhibitor insecticides, such as novaluron (RR = 6147-fold) and lufenuron (RR = 953-fold), but low cross-resistance to methoxyfenozide, flubendiamide, and indoxacarb (RR < 3.45-fold). On discriminatory concentrations of teflubenzuron and novaluron, populations of SBL showed survival rates from 15 to 52%, indicating field resistance to these insecticides. Our findings indicated that resistance to teflubenzuron in SBL is autosomal, recessive, polygenic, and associated with fitness cost. We also found a high cross-resistance to other benzoylphenylureas and a high frequency of resistance to this mode-of-action in SBL in Brazil.

Chitin synthesis inhibitors promote liver cancer cell metastasis via interfering with hypoxia-inducible factor 1α

Chitin synthesis inhibitors (CSIs), as alternatives to conventional insecticides, have been in worldwide demand in recent years. However, little attention has been paid to the potential ecological safety and health risks of CSIs, especially their abilities to interfere with nonsexual hormone receptors such as hypoxia-inducible factor 1α (HIF-1α). In this work, we conducted a systematic study regarding the influence of CSIs on HIF-1α-related liver cancer cell metastasis. The dual-luciferase reporter gene assay revealed that two of fourteen CSIs exhibited dose-response HIF-1α agonistic activities at noncytotoxic concentrations with relative luciferase activity (RLA) values of 25.6% for diflubenzuron (DFB) and 20.9% for triflumuron (TFM). Following this result, in vitro bioassays demonstrated that both DFB and TFM stimulated HepG2 cell migration and invasion. This action was associated with the varied expression levels of genes involved in epithelial-to-mesenchymal transition (EMT) activation and extracellular matrix (ECM) degradation, such as the upregulation of fibronectin (FN1) and matrix metalloproteinase-2 (MMP-2) and the suppression of E-cadherin (E-cad) and tissue inhibitor of metalloproteinases-2 (TIMP-2). Moreover, changes in these EMT and ECM phenotype markers were dramatically blocked by a HIF-1α inhibitor (KC7F2), which further verified the involvement of HIF-1α in CSI-induced HepG2 cell metastasis. For the first time, our findings reveal that CSIs play crucial roles in promoting the metastasis of human liver cancer cells and that HIF-1α is potentially responsible for these changes.

Lethal and sublethal effects of the chitin synthesis inhibitor chlorfluazuron on Bradysia odoriphaga Yang and Zhang (Diptera: Sciaridae)

Bradysia odoriphaga Yang and Zhang is the primary insect pest that affects Chinese chive in northern China. Nevertheless, very few studies have been conducted on the use of chitin synthesis inhibitors (CSIs) for the control of B. odoriphaga. Here, lethal and sublethal effects of the CSI chlorfluazuron on B. odoriphaga were studied to explore the use for integrated pest management (IPM) of B. odoriphaga. A contact and ingestion toxicity bioassay showed that chlorfluazuron was more active against B. odoriphaga than three other CSIs, with a 72h LC₅₀ of 0.1593mg/L. Treatment with the LC₅₀ dose of chlorfluazuron decreased both the intrinsic and finite rates of increase of B. odoriphaga, in addition to reproduction rate, survival rate, and fecundity, and the mean generation time, total preovipositional period and larval development duration were shortened, compared with those of the control and LC₁₀ groups. The mean generation time, total preovipositional period and larval development duration were all also markedly decreased by treatment with chlorfluazuron at the LC₁₀. Furthermore, chlorfluazuron inhibited the feeding of the final instar larvae for a short period. Glutathione S-transferase and microsomal mixed function oxidase activities increased after exposure to the chemical. These results showed that chlorfluazuron at the sublethal LC₅₀ treatment inhibited B. odoriphaga population growth, whereas the danger of causing rapid population growth by using a lower sublethal concentration was demonstrated with the sublethal LC₁₀ treatment. Therefore, chlorfluazuron should be used with caution in an IPM program for B. odoriphaga.

The Psychrotolerant Antarctic Fungus Lecanicillium muscarium CCFEE 5003: A Powerful Producer of Cold-Tolerant Chitinolytic Enzymes

Lecanicillium muscarium CCFEE 5003, isolated in Continental Antarctica, is a powerful producer of extracellular cold-tolerant enzymes. Chitin-hydrolyzing enzymes seems to be the principal extracellular catalytic activities of this psychrotolerant fungus. The production of chitinolytic activities is induced by chitin and other polysaccharides and is submitted to catabolite repression. The chitinolytic system of L. muscarium consists of a number of different proteins having various molecular weights and diverse biochemical characteristics, but their most significant trait is the marked cold-tolerance. L. muscarium and selected strains of the biocontrol agent of pathogenic fungi Trichoderma harzianum, have been compared for their ability to produce chitinolytic enzymes at different temperatures. At low temperatures the Antarctic strain was definitely much more efficient. Moreover, the fungus was able to exert a strong mycoparasitic action against various other fungi and oomycetes at low temperatures. The parasitic role of this organism appeared related to the production of cell wall degrading enzymes being the release of extracellular chitinolytic enzymes a key event in the mycoparasitic process. Due to the mentioned characteristics, L. muscarium could have an important role for potential applications such as the degradation of chitin-rich materials at low temperature and the biocontrol of pathogenic organisms in cold environments. For these reasons and in view of future industrial application, the production of chitinolytic enzymes by the Antarctic fungus has been up-scaled and optimised in bench-top bioreactor.

Termite (order Blattodea, infraorder Isoptera) baiting 20 years after commercial release

Termite baiting is now one of the two main management tools in developed countries after 20 years of commercial release. It has two main goals: to use small amounts of active ingredient and 'colony elimination', i.e. death of all individuals in the colony. We consider how well baiting has been evaluated from 100 studies in the scientific literature. Studies have included 15 active ingredients, 23 termite species and 16 countries, yet most studies have focused on the chitin synthesis inhibitor hexaflumuron, Reticulitermes and the United States. Baiting has mostly met its goals: typically about 0.5 g of active ingredient was used, and colony elimination achieved, albeit with rates varying from 0 to 100%, and sometimes supplemented with liquid insecticide. Baiting was most successful using chitin synthesis inhibitors against Reticulitermes and Coptotermes (Rhinotermitidae), in temperate locations, although colony elimination was usually inferred indirectly - mostly by termite absence from baits - and was often slow, from 25 to 450 days. Baiting has been less tested and less successful against higher termites in tropical locations, where they are most diverse and abundant. Future research may have to consider greater termite species diversity and other active ingredients to reduce control times in order to fulfil the potential of baiting.

Dietary lufenuron reduces egg hatch and influences protein expression in the fruit fly Bactrocera latifrons (Hendel)

Lufenuron (LFN), a chitin synthase inhibitor, impacts the fertility of Ceratitis capitata, Bactrocera dorsalis, B. cucurbitae, and B. latifrons. We posed the hypothesis that LFN curtails egg hatch in the solanaceous fruit fly, B. latifrons. In this study, newly emerged virgin adults were sexed and fed for 12 days with varying concentrations of LFN-laced agar diets until sexual maturation. Eggs were collected from 12-d-old adults and the egg hatch was assessed. Egg hatch decreased in adults reared on LFN-treated diets. LFN-treated media did not influence fertility after one gender was reared on experimental and the other on control media before mating. Exposure to LFN-treated medium after mating led to reduced egg hatch. We infer that LFN is not a permanent sterilant, and reduced egg hatch depends on continuous exposure to dietary LFN after mating. Proteomic analysis identified two differentially expressed proteins, a pheromone binding protein and a chitin binding protein, between adults maintained on LFN-treated and control diets. Expression of two genes encoding chitin synthase 2, and chitin binding protein, was altered in adults exposed to dietary LFN. LFN treatments also led to increased expression of two odorant binding proteins one in females and one in males. We surmise these data support our hypothesis and provide insight into LFN actions.

High resolution genetic mapping uncovers chitin synthase-1 as the target-site of the structurally diverse mite growth inhibitors clofentezine, hexythiazox and etoxazole in Tetranychus urticae

The acaricides clofentezine, hexythiazox and etoxazole are commonly referred to as 'mite growth inhibitors', and clofentezine and hexythiazox have been used successfully for the integrated control of plant mite pests for decades. Although they are still important today, their mode of action has remained elusive. Recently, a mutation in chitin synthase 1 (CHS1) was linked to etoxazole resistance. In this study, we identified and investigated a Tetranychus urticae strain (HexR) harboring recessive, monogenic resistance to each of hexythiazox, clofentezine, and etoxazole. To elucidate if there is a common genetic basis for the observed cross-resistance, we adapted a previously developed bulk segregant analysis method to map with high resolution a single, shared resistance locus for all three compounds. This finding indicates that the underlying molecular basis for resistance to all three compounds is identical. This locus is centered on the CHS1 gene, and as supported by additional genetic and biochemical studies, a non-synonymous variant (I1017F) in CHS1 associates with resistance to each of the tested acaricides in HexR. Our findings thus demonstrate a shared molecular mode of action for the chemically diverse mite growth inhibitors clofentezine, hexythiazox and etoxazole as inhibitors of an essential, non-catalytic activity of CHS1. Given the previously documented cross-resistance between clofentezine, hexythiazox and the benzyolphenylurea (BPU) compounds flufenoxuron and cycloxuron, CHS1 should be also considered as a potential target-site of insecticidal BPUs.

Behavioral and histological changes in the Formosan subterranean termite (Isoptera: Rhinotermitidae) induced by the chitin synthesis inhibitor noviflumuron

This study describes the behavioral and histological changes of the molting process in Coptotermes formosanus Shiraki caused by the chitin synthesis inhibitor noviflumuron. Termites exposed to noviflumuron initiated ecdysis as untreated individuals did; however, peristalsis contractions were weak and the expansion of the dorsal breach of the exoskeleton did not occur. Treated termites could not complete their molting process and died after the initiation of the ecdysis. Histological observations showed that the process of voiding the gut protozoa during premolting was not affected by the noviflumuron treatment. However, the formation of the new cuticle was disrupted resulting in the loss of integrity of the cuticle. The alteration of the cuticle was visible in the gizzard (foregut), the thoracic pleurons, and most of the exoskeleton. Muscles were partially able to reattach to the incompletely formed new cuticle, and muscle contractions resulted in tearing off the cuticle. Because the integrity of the newly formed cuticle was compromised by the noviflumuron treatment, we concluded that termites' death was caused primarily by the loss of hemolymph as a result of the damage done by the muscle contractions on the exoskeleton during the peristalsis. As the physiological homeostasis was disrupted, termites were too weak to shed their old cuticle, ultimately resulting in termite dying during the molting process.

Paradoxical growth of Candida albicans in the presence of caspofungin is associated with multiple cell wall rearrangements and decreased virulence

In the last decade, echinocandins have emerged as an important family of antifungal drugs because of their fungicidal activity against Candida spp. Echinocandins inhibit the enzyme β-1,3-d-glucan synthase, encoded by the FKS genes, and resistance to echinocandins is associated with mutations in this gene. In addition, echinocandin exposure can produce paradoxical growth, defined as the ability to grow at high antifungal concentrations but not at intermediate concentrations. In this work, we have demonstrated that paradoxical growth of Candida albicans in the presence of caspofungin is not due to antifungal degradation or instability. Media with high caspofungin concentrations recovered from wells where C. albicans showed paradoxical growth inhibited the growth of a Candida krusei reference strain. Cells exhibiting paradoxical growth at high caspofungin concentrations showed morphological changes such as enlarged size, abnormal septa, and absence of filamentation. Chitin content increased from the MIC to high caspofungin concentrations. Despite the high chitin levels, around 23% of cells died after treatment with caspofungin, indicating that chitin is required but not sufficient to protect the cells from the fungicidal effect of caspofungin. Moreover, we found that after paradoxical growth, β-1,3-glucan was exposed at the cell wall surface. Cells grown at high caspofungin concentrations had decreased virulence in the invertebrate host Galleria mellonella. Cells grown at high caspofungin concentrations also induced a proinflammatory response in murine macrophages compared to control cells. Our work highlights important aspects about fungal adaptation to caspofungin, and although this adaptation is associated with reduced virulence, the clinical implications remain to be elucidated.

Can a chitin-synthesis-inhibiting turfgrass fungicide enhance black cutworm susceptibility to a baculovirus?

BACKGROUND

Developmental resistance, i.e. reduced virulence and speed of kill of late instars, is a limiting factor in the use of baculoviruses for caterpillar control. Agrotis ipsilon multicapsid nucleopolyhedrovirus (AgipMNPV) is highly infective to young black cutworms, Agrotis ipsilon, but too slow-acting against late instars for effective curative control on golf courses or sports fields. Chitin-synthesis-inhibiting fungicides containing the active ingredient polyoxin-d are used to control fungal diseases in turfgrass, and similar compounds have been shown in the laboratory to synergize baculoviruses by disrupting peritrophic membrane function. This study tested whether applying the virus together with such a fungicide can synergize AgipMNPV activity against A. ipsilon in turfgrass.

RESULTS

The addition of a chitin synthesis inhibitor failed to increase AgipMNPV infectivity to A. ipsilon in the field. Rather, delayed and slightly reduced mortality from viral infection was seen when larvae fed on fungicide/virus-treated grasses as opposed to virus-only treatments. Choice tests revealed the fungicide residues to be a mild feeding deterrent.

CONCLUSION

Because polyoxin-d does not deactivate AgipMNPV, the two substances are compatible. However, combination applications of polyoxin-d and Agip MNPV on turfgrass might interfere with larval ingestion of a lethal virus dose, resulting in prolonged larval feeding in the field.

Two-generation effects of the chitin synthesis inhibitor, teflubenzuron, on the aquatic midge Chironomus riparius

Teflubenzuron, a chitin synthesis inhibitor was used in a two-generation test with Chironomus riparius (Insecta) to assess effects over a full life cycle from the first-instar larvae in the parental (P) generation until emergence in the subsequent F1 generation. Sediment spiked with teflubenzuron ranging from 10 to 390.6 μg/kg sediment dry weight (dw) was used. EC₅₀-values for fecundity and fertility were 112.7 and 74.5 μg/kg dw, respectively. Significant adverse effects were observed compared to the solvent control for emergence rate (P < 0.01) and also for developmental rate. No observed effect concentrations values were lower for emergence rate in the F1 generation (62.5 μg/kg dw) than in the P generation (100 μg/kg dw), demonstrating that the F1 generation was more affected than the P generation. Thus, this two-generation test may help detecting population level effects as an amendment to the risk assessment for chronic exposures to endocrine disrupting compounds.

Areawide field study on effect of three chitin synthesis inhibitor baits on populations of Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae)

Periodic sampling of 43 independent monitors, initially active with Formosan subterranean termite, Coptotermes formosanus Shiraki, or the eastern subterranean termite, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae), was conducted to evaluate the effects of cellulose baits containing one of three chitin synthesis inhibitors (CSIs)-diflubenzuron, hexaflumuron, or chlorfluazuron-on termite populations. Diflubenzuron at 0.1% active ingredient (AI, wt:wt) had no noticeable effect on termite populations. Chlorfluazuron (0.25% [AI]) significantly reduced termite populations in approximately 3 yr. Chlorfluazuron used after > 2-yr diflubenzuron treatment significantly reduced termite populations within months. This suggests diflubenzuron exposure increased the termite's sensitivity to chlorfluazuron accelerating population collapse. Hexaflumuron (0.5% [AI]) also reduced termite populations in approximately 2 yr. The process of removing most detectable termite populations from the approximately 160,000-m2 campus of the Southern Regional Research Center, New Orleans, LA, with CSIs baits required approximately 3 yr. Adjustments in the specific bait formulations and application procedures might reduce time to suppression. Establishment of new independent termite populations provides a mechanism to minimize the effects of baits. Remedial control measures around and under structures should be considered when implementing an area wide management strategy.

[The effects of chitin synthesis inhibitor, diflubenzuron on the larvae of Culex pipiens (L.) and Culiseta longiareolata (Macquart) (Diptera: Culicidae)]

OBJECTIVE

The aim of the present study was to detect effects of diflubenzuron on Culex pipiens and Culiseta longiareolata larvae, and determine the weekly mortality rate and most effective dose of diflubenzuron during the study.

METHODS

The lower and higher doses (0.016, 0.032, and 0.064 mg(ai)/cm(2)) than 0.05 mg(ai)/cm(2) which are brecommended for granular formulation of diflubenzuron by WHO (World Health Organization) was applied against 1st, 2nd, 3rd and 4th instars under laboratory conditions and mortality was recorded.

RESULTS

According to our data, diflubenzuron was more effective against early instars, and it was found most effective in the 4th and 3(th) week post-treatment in the application for Culex pipiens and Culiseta longiareolata larvae respectively. In addition, the most effective dose of diflubenzuron was obtained as 0.064 mg(ai)/cm(2) (LC50 > 4640 ppm, LC90 = 0.0034 ppm). Furthermore Culiseta longiareolata was more sensitive than Culex pipiens larvae.

CONCLUSION

Knowing the specific mortality rate of diflubenzuron in different mosquitoe species and larvae stages, plays an important role in determining the resistance against diflubenzuron.

Impact of five commercial baits containing chitin synthesis inhibitors on the protist community in Reticulitermes flavipes (Isoptera: Rhinotermitidae)

Eastern subterranean termite, Reticulitermes flavipes (Kollar), workers were continuously exposed to one of five chitin synthesis inhibiting (CSI) active ingredients and the protist community from the hindgut quantified biweekly for 21 d. The CSIs tested included commercially available formulations of diflubenzuron, hexaflumuron, lufenuron, noviflumuron, and novaluron. Results showed termites exposed to CSIs had a significant decrease (>or=30%) in the estimated total protist population after 3 d, regardless of treatment. Protist species impacted were Dinenympha fimbriata, D. gracilis, Microjoenia fallax, Pyrsonympha vertens, and Trichonympha agilis and could be indicative of weakened digestive homeostasis, but further studies are needed. We also provide evidence that lufenuron is highly toxic and discuss some of the implications this might have on termite management practices.

Laboratory evaluation of Flurox, a chitin synthesis inhibitor, on the termite, Microcerotermes diversus

Microcerotermes diversus (Silvestri) (Isoptera: Termitidae) is the most economically destructive termite in structures in southwest Iran. One sustainable control strategy that usually helps to reduce subterranean termite damage in buildings, is the use of insect growth regualtors in a suitable bait matrix that are safe to the user and the environment. In the laboratory assays described here, the delayed toxicity of Flurox, a chitin synthesis inhibitor, to M. diversus was evaluated under force-feeding and choice trials. Flurox induced worker and nymph mortality and incomplete ecdysis in nymphs of M. diversus under no-choice and two-choice feeding tests. These adverse effects may cause disruption of the caste balance in M. diversus, leading to the collapse of the colony. These assays determined concentrations of Flurox that can be used in bait formulations.

A chitin-like component in Aedes aegypti eggshells, eggs and ovaries

An insoluble white substance was prepared from extracts of eggshells of Aedes aegypti, the yellow fever mosquito and dengue vector. Its infrared and proton NMR spectra were similar to that of standard commercial chitin. This putative chitin-like material, also obtained from ovaries, newly laid and dark eggs, was hydrolyzed in acid and a major product was identified by HPLC to be glucosamine. The eggshell acid hydrolysate was also analyzed by ESI-MS and an ion identical to a glucosamine monoprotonated species was detected. The presence of chitin was also analyzed during different developmental stages of the ovary using a fluorescent microscopy technique and probes specific for chitin. The results showed that a chitin-like material accumulates in oocytes during oogenesis. Streptomyces griseus chitinase pre-treatment of oocytes greatly reduced the chitin-derived fluorescence. Chitinase activity was detected in newborn larvae and eggs prior to hatching. Feeding experiments indicated that the chitin synthesis inhibitor lufenuron inhibited chitin synthesis, either when mosquitoes were allowed to feed directly on lufenuron-treated chickens or when an artificial feeding system was used. Lufenuron inhibited egg hatch, larval development and reduced mosquito viability. These data demonstrate for the first time that (1) a chitin-like material is present in A. aegypti eggs, ovaries and eggshells; (2) a chitin synthesis inhibitor can be used to inhibit mosquito oogenesis; and (3) chitin synthesis inhibitors have potential for controlling mosquito populations.

Recent advances in antifungal agents

New antifungals are needed in the medicine because of more aggressive and invasive diagnostic and therapeutic methods used, rapid emergence of resistant and new opportunistic fungi, increasing number of patients suffering from immunosuppressive situations e.g., AIDS, transplantation, cancer, etc. Several classes of new antifungal agents are discussed here including some new members of known families. Voriconazole, posaconazole and ravuconazole, are novel triazoles that inhibit the ergosterol synthesis. These drugs overcome problems associated with the ineffectivity of fluconazole against some Aspergillus spp. or the variable bioavailability of itraconazole. Echinocandins (caspofungin, anidulafungin and micafungin) represent a new family of antifungal agents that inhibit 1,3-beta-glucan synthase. Nikkomycins targeting the chitin synthase, show activity against Histoplasma capsulatum and Blastomyces dermatitidis. Sordarin derivatives that block the fungal protein synthesis can be considered as a promising new class of antifungal agents for the treatment of Candida and Pneumocystis infections.

Simulated field evaluation of the efficacy of two formulations of diflubenzuron, a chitin synthesis inhibitor against larvae of Aedes aegypti (L.) (Diptera: Culicidae) in water-storage containers

Tablet (40 mg a.i./tablet) and granular (2% a.i.) formulations of diflubenzuron, a chitin synthesis inhibitor, insect growth regulator, were evaluated for larvicidal efficacy against the larvae of Aedes aegypti (L.) in water-storage containers under field conditions in Thailand. Each formulation was applied to 200-1 clay jars at 5 different dosages (0.02, 0.05, 0.1, 0.5 and 1 mg/l a.i.). The jars were covered with solid celocrete sheets and placed in the shade under a roof. Another experiment was also carried out using 3 different dosages (0.1, 0.5 and 1 mg/l) where half the water in each treated jar and the control was removed and refilled weekly. Each treatment was replicated four times. The treatments were challenged by adding 25 3rd instar larvae/jar weekly. Assessments were made of each treatment through emergence inhibition (%EI) by removing and counting pupal skins one week after larval addition. Using these assessment techniques, a high degree of larvicidal efficacy (96-100%EI) was achieved with 4 dosages (0.05, 0.1, 0.5 and 1 mg/l) of both (tablet and granular) formulations for a period of 23 weeks post-treatment. The efficacy of the lowest dosage (0.02 mg/l) of tablet and granular formulations lasted for 21 and 22 weeks post-treatment, respectively. Under the conditions of water removal and weekly refilling, a high degree of larvicidal efficacy (96-100%El) at the 3 dosages was obtained with the tablet formulation 18 to 21 weeks post-treatment, whereas the efficacy of the granular formulation persisted 15 to 23 weeks post-treatment depending on the dosage. This study clearly demonstrates a high level of residual activity with both formulations of diflubenzuron against larvae of Ae. aegypti in water-storage containers. Considering environmental factors and water-use conditions, it is likely that dosages of 0.05 to 0.1 mg a.i./l are effective dosages providing long-lasting control for 3 to 4 months in the field.

Laboratory evaluation of five chitin synthesis inhibitors against the colorado potato beetle, Leptinotarsa decemlineata

Results of laboratory experiments are reported that tested the effects of five chitin synthesis inhibitors, diflubenzuron, cyromazine, lufenuron, hexaflumuron and triflumuron. on second instars of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Crysomelidae), originally collected from potato fields of Bostanabaad, a town 66 km southeast of Tabriz, Iran. In bioassays, the larvae were fed potato leaves dipped in aqueous solutions containing chitin synthesis inhibitors. The mortalities and abnormalities of the treated larvae were recorded 72 hours after treatments. LC(50) values were 58.6, 69.6, 27.3, 0.79 and 81.4 mg ai/ L for diflubenzuron, cyromazine, lufenuron, hexaflumuron and triflumuron, respectively. Compared with phosalone, which is one of the common insecticides used for controlling this pest in Iran, lufenuron and hexaflumuron seem to be much more potent, and if they perform equally well in the field, they would be suitable candidates to be considered as reduced risk insecticides in management programs for L. decemlineata due to much wider margin of safety for mammals and considerably fewer undesirable environmental side effects.

Enhancement of the biological activity of nucleopolyhedrovirus through disruption of the peritrophic matrix of insect larvae by chlorfluazuron

The enhancement of Spodoptera litura (F.) nucleopolyhedrovirus (SlNPV) activity using the chitin synthesis inhibitor chlorfluazuron was investigated. When tested against fifth-instar S. litura larvae, chlorfluazuron produced synergistic effects at doses of 0.05 and 0.025 microg per insect, and additive effects at doses of 0.1 and 0.2 microg. Furthermore, the time required for SlNPV to kill larvae was significantly reduced by chlorfluazuron at all doses tested. The activity and killing speed of Autographa californica (Spey) nucleopolyhedrovirus (AcMNPV) against third-instar Spodoptera exigua (Hübner) larvae were similarly improved by chlorfluazuron at a dose of 0.05 microg per larva. Furthermore, the growth of S. exigua was significantly retarded by chlorfluazuron. Environmental scanning electron microscopy (ESEM) showed that the peritrophic matrices (PMs) of S. litura exposed to chlorfluazuron alone, or the combination treatment, were markedly disrupted. Obvious ruptures on the outer surfaces of the PM were observed, which potentially facilitated the passage of virions through the matrix.

In vitro and in vivo Effects of Lufenuron on Dermatophytes Isolated from Cases of Canine and Feline Dermatophytoses*

Lufenuron is a benzyl-urea phenol compound that inhibits chitin synthesis and is used as an insecticide. Its efficacy in the therapy of dermatophytosis in dogs and cats was evaluated in several clinical studies, with contradictory results. We assessed the in vitro susceptibility of dermatophytes isolated from dogs and cats to lufenuron, and the clinical response of skin lesions to the drug. Dermatophyte cultures isolated from clinical cases were exposed to lufenuron by three different methods: direct application and application of whole blood or subcutaneous tissue samples obtained from a lufenuron-treated healthy dog. No inhibition of dermatophyte growth was observed in any of the samples after 1 week of incubation. Eight dogs and six cats with skin lesions were included in the in vivo survey. Results indicated that six of seven skin lesions that were diagnosed as being caused by dermatophytes did not respond to lufenuron whereas six of seven skin lesions that were not caused by dermatophytes improved. We concluded that lufenuron, in the way it was administered in this study, had no inhibitory activity on dermatophytes in vitro or in vivo and its clinical use as an anti-fungal agent is questionable. An immunomodulatory effect of the drug is, however, possible.

The effects of four insect growth-regulating (IGR) insecticides on honeybee (Apis mellifera L.) colony development, queen rearing and drone sperm production

This study assessed the effects of exposure to IGRs on the long-term development of the honeybee colony, viability of queens and sperm production in drones and integrated the data into a honeybee population model. Colonies treated with diflubenzuron resulted in a short-term reduction in the numbers of adult bees and brood. Colonies treated with fenoxycarb declined during the season earlier and started the season slower. The number of queens that successfully mated and laid eggs was affected in the fenoxycarb treatment group but there were no significant differences in the drone sperm counts between the colonies. An existing honeybee population model was modified to include exposure to IGRs. In the model, fenoxycarb reduced the winter size of the colony, with the greatest effects following a June or an August application. Assuming a 'larvae per nurse bee' ratio of 1.5 for brood rearing capability, the reduction in winter size of a colony following a fenoxycarb application was at its worst about 8%. However, even if only those bees reared within 2 weeks of the IGR being applied are subject to premature ageing, this might significantly reduce the size of over-wintering colonies, and increase the chance of the bee population dwindling and dying in late winter or early spring.

Disruption of reproductive activity of Coptotermes formosanus (Isoptera: Rhinotermitidae) primary reproductives by three chitin synthesis inhibitors

Effects of the chitin synthesis inhibitors (CSIs) diflubenzuron, hexaflumuron, and lufenuron on the Formosan subterranean termite, Coptotermes formosanus Shiraki, primary reproductives were studied in the laboratory. Incipient colonies were established by collecting and pairing C. formosanus alates and placing them in dishes containing an artificial diet. Three groups of 56 colonies each were fed with a diet containing 10 ppm of one of each of the CSIs and were compared with a control group fed with an untreated diet. All eggs oviposited by treated young queens failed to hatch at the end of 6 mo. Estimated queen fecundity was significantly lower in the lufenuron treatment compared with the control group. Fecundity of hexaflumuron-treated queens did not differ significantly from that of queens from the control group and the other treatments. Adult mortality was significantly higher in the diflubenzuron and lufenuron treatments than in the control group at the end of 6 mo., but not in the hexaflumuron treatment. All the pairs died within 8 mo. in the diflubenzuron and lufenuron treatments, even after treatment was suspended at the end of 6 mo. Mortality in the hexaflumuron treatment was significantly higher than in the control group by the end of 9 mo. The three CSIs tested eliminated reproduction in C. formosanus by preventing egg hatching and induced adult mortality. Possible mechanisms by which CSIs induce termite adult death are discussed.

Effects of flucycloxuron, a chitin synthesis inhibitor, on reproductive events and thickness of chorion in mealworms

Flucycloxuron (FCX), a benzoylphenylurea derivative, was evaluated on Tenebrio molitor. The compound was incorporated into the diet and administrated to newly emerged females at various doses (2, 5 and 10 mg/kg). FCX was found to affect several reproductive events such as the duration of preovipostion and oviposition period, the fecundity, the viability of eggs and the duration of embryonic development, respectively. Morphological study of ovaries showed that FCX reduced both oocytes number, the ovaries weight and the size and the volume of the basal oocyte during the sexual maturation. In addition, it reduced the thickness of chorion from freshly laid eggs. However, electron microscopic study revealed that this compound had no significant effect on the fine structure of chorion. Finally, measurements of ovarian ecdysteroids production by an enzyme immunoassay indicated a reduction in the hormonal amounts recorded.

Potential drug targets in cyst-wall biosynthesis by intestinal protozoa

Given that resistance to antiprotozoal drugs exists and is likely to increase and given that currently no reliable treatments exist for some of these infections, efforts to find new targets for chemotherapy must be continued. In the case of cyst-forming pathogenic protozoa, one such target might be encystment pathways and cyst-wall assembly. Information is increasing on protozoan encystment and, as it does, we can begin to answer the question of whether targeting it for chemotherapy is a viable drug strategy. Currently, there are significant efforts to understand encystment in Giardia and Entamoeba, and potential targets are being discovered as work on their encystment mechanisms progress. We know with certainty now that Giardia and Entamoeba cyst walls contain unique proteins and polysaccharides which differ from those of their hosts and thus make them potentially interesting targets for a variety of chemotherapeutic attacks. Although we lack detailed information about the other protozoan cyst formers, enough evidence exists for Giardia and Entamoeba that it seems prudent to screen them with some of the antifungal drugs, especially those that target mannoproteins, chitin synthesis, and beta (1, 3) glucan synthesis to ascertain if they target elements in these protozoan pathways that are similar to those found in fungi.

Chitin synthesis as target for antifungal drugs

Human mycoses have become a threat to health world-wide. Unfortunately there are only a limited number of antimycotic drugs in use. Promising targets for drugs specific against fungi are those affecting chitin synthesis. Chitin is absent in vertebrates, and is essential for fungal wall integrity. A thorough knowledge of the mechanism of chitin synthesis is required to design specific inhibitors. We review here our current understanding of the process, and the most promising drugs that inhibit it. Chitin is made by chitin synthases requiring specific microvesicles, the chitosomes, for intracellular transport. Fungi contain several chitin synthases, some of which may be essential at a certain stage. This phenomenon is important to take into account for drug design. The most widely studied chitin synthase inhibitors are polyoxins and nikkomycins that probably bind to the catalytic site of chitin synthases. These are not equally susceptible to the drugs. In Saccharomyces cerevisiae the order of sensitivity is: Chs3p>Chs1p>Chs2p. Main problems for their succesful use in vivo are: low permeability, and different susceptibility of fungal species, and variable responses in animal models. Chemical modifications have been proposed to make more potent derivatives. Other synthetic or natural compounds are also promising as possible inhibitors, but their properties are less well known. Rational drug design has proceeded only on the basis of existing inhibitors, because the structure of the active site of chitin synthase is unknown. Undoubtedly, determination of this, and the biosynthetic mechanism will reveal unexpected drug targets in the future.

Microbial natural products as a source of antifungals

The vast number and variety of chemotherapeutic agents isolated from microbial natural products and used to treat bacterial infections have greatly contributed to the improvement of human health during the past century. However, only a limited number of antifungal agents (polyenes and azoles, plus the recently introduced caspofungin acetate) are currently available for the treatment of life-threatening fungal infections. Furthermore, the prevalence of systemic fungal infections has increased significantly during the past decade. For this reason, the development of new antifungal agents, preferably with novel mechanisms of action, is an urgent medical need. A selection of antifungal agents in early stages of development, produced by micro-organisms, is summarized in this review. The compounds are classified according to their mechanisms of action, covering inhibitors of the synthesis of cell wall components (glucan, chitin and mannoproteins), of sphingolipid synthesis (serine palmitoyltransferase, ceramide synthase, inositol phosphoceramide synthase and fatty acid elongation) and of protein synthesis (sordarins). In addition, some considerations related to the chemotaxonomy of the producing organisms and some issues relevant to antifungal drug discovery are also discussed.

[Experimental study on bacteriostasis of chitosan and sodium hyaluronate]

OBJECTIVE

To compare the effect and coverage of bacteriostasis of chitosan and sodium hyaluronate.

METHODS

Each of the five bacteria, Proteus mirabilis, Escherichia coli, Candida albicans, Pseudomonas aeruginosa, Staphylococcus aureus, was cultivated for 33 tubes of broth culture. Leaving three tubes each group as control group, ploidy diluted concentration of high relative molecular weight chitosan, low relative molecular weight chitosan and sodium hyaluronate were added respectively in the broth culture. All the tubes were cultivated for 18 hours at 37 degrees C with homeothermia. Then the growth of bacteria was observed.

RESULTS

The minimal inhibitory concentrations (MIC) of high relative molecular weight chitosan were: Proteus mirabilis 0.031%, Escherichia coli 0.063%, Candida albicans 0.063%, Pseudomonas aeruginosa 0.063%, Staphylococcus aureus 0.063%; and the MIC of low relative molecular weight chitosan were: Proteus mirabilis 0.125%, Escherichia coli 0.025%, Candida albicans 0.25%, Pseudomonas aeruginosa 0.25%, Staphylococcus aureus 0.125%; bacteria grew well in each tube of sodium hyaluronate group and control group.

CONCLUSION

The above results show that sodium hyaluronate has no bacteriostasis, while chitosan has bacteriostasis on broad spectrum and high relative molecular weigh: chitosan has stronger effect.

Control of Ctenocephalides felis on dogs and cats using the insect growth regulator (or chitin synthesis inhibitor) lufenuron Program, in Egypt

Lufenuron, the chitin synthesis inhibitor (Program, Novartis-Switzerland) was given orally at doses of 10-mg/kg b/w to dogs and 30-mg/kg b/w to cats every four weeks (monthly) for the treatment of experimental flea infestations. Three to four weeks after the last infestation, Lufenuron had effectively controlled the Ct. felis infestation of dogs and cats as the drug prevented the development of the offspring of adult female fleas feeding on animals. Flea populations were absent or very low and remained so until the end of the study, 91 days after the first treatment.

Chitin synthesis and inhibition: a revisit

Chitin is an abundant biologically important aminopolysaccharide composed of N-acetyl-D-glucosamine units. Individual polymers, which are synthesized intracellularly by chitin synthase (CS), a membrane-bound glycosyl transferase, are translocated across the plasma membrane and coalesce to form rigid crystallites. These crystallites, inter alia, are integral parts of septa and cell walls in yeast and filamentous fungi, respectively, and of cuticles in invertebrates, notably crustaceans and insects. Despite decades of intensive research, many events associated with the complexity of chitin formation and deposition are still obscure, or only partially understood. The list includes the hormonal control of CS at the transcriptional and translational levels as well as the post-translational CS packaging; trafficking and guidance of CS clusters to proper sites in the cells and their intricate insertion into the plasma membranes; activation of the catalytic step and its control or modulation; and translocation of chitin chains across cell membranes, their orientation, fibrillogenesis and association with other extracellular structural components such as polysaccharides (fungi) and cuticular proteins (insects). Also the precise biochemical lesions inflicted by CS inhibitors, such as the acylurea insect growth regulators, are largely unclear. The recent isolation and sequencing of insect CS genes should help in elucidating various aspects of chitin biochemistry and inhibition. In particular, the large number of transmembrane segments, characteristic of the insect CS, are speculated to be involved in chitin translocation and are expected to shed light on the mode of action of acylurea insecticides.

[Kinetics of in vitro drug release from chitosan and N-alkyl chitosan membranes]

By using the so-called "lag-time" method, we studied the effect of membrane thickness(h), initial drug concentration(Co) and flow rate(V) on the difusion coefficient(D) of model drug in membranes. The experiment indicates that D increases as h and v increase; D Keeps constant when C0 changes; Under the same condition, the D value of N-alkyl chitosan membrane is bigger than that of pure chitosan membrane.

Laboratory evaluation of lufenuron on immature stages of potato tuber moth (Lepidoptera: Gelechiidae)

The effects of the chitin synthesis inhibitor lufenuron against potato tuber moth, Phthorimaea operculella (Zeller), eggs were determined by topically exposing different age groups of eggs (1-4 d old) to treated potato tubers (Solanum tuberosum L.) under laboratory conditions. Larval hatch from both treated (4 and 12 g [AI]/100 liter) and untreated tubers was >95%, but mortality of first instars was high in treated tubers (>90%) compared with untreated tubers. Examination of the treated tubers showed that most of the larvae were unable to penetrate or cause any noticeable damage to the potato tubers. However, the few first instars that survived were able to penetrate the tubers and continue their development to the pupal or adult stages. At 12 g (AI)/100 liter, adult emergence was <2% and most of the emerged adults had morphological deformities such as reduced wing size and they were unable to free themselves from the pupal sacs. These data suggest that topical application of lufenuron to eggs before larval hatch would reduce the amount of damage caused by potato tuber moth as part of integrated pest management program.

Use of orally administered chitin inhibitor (lufenuron) to control flea vectors of plague on ground squirrels in California

The efficacy of orally administered lufenuron, a chitin inhibitor, to control fleas on California ground squirrels, Spermophilus beecheyi (Richardson), was evaluated during a 2-yr study in Santa Barbara County, CA. Results demonstrated that use of a host-targeted feed cube containing lufenuron was effective in significantly reducing the burden of Oropsylla montana (Baker) and Hoplopsyllus anomalus (Baker) fleas on ground squirrels. A flea index that indicated a mean number of fleas per squirrel of 10.0 decreased to 1.3 after 2 treatments in season 1, and to 0.7 and 0.2 after the 3rd and 4th treatments, respectively, in season 2. A cost comparison of this new method compared with a traditional reactive, emergency, insecticide-based plague control program demonstrated a cost reduction of approximately 90%. The results of this study indicated that a lufenuron feed cube was an effective, cost-saving, and proactive technique for controlling fleas on California ground squirrels, and thus reducing the risk of disease transmission in plague endemic regions.

Chitin oligosaccharide synthesis by rhizobia and zebrafish embryos starts by glycosyl transfer to O4 of the reducing-terminal residue

Lipochitin oligosaccharides are organogenesis-inducing signal molecules produced by rhizobia to establish the formation of nitrogen-fixing root nodules in leguminous plants. Chitin oligosaccharide biosynthesis by the Mesorhizobium loti nodulation protein NodC was studied in vitro using membrane fractions of an Escherichia coli strain expressing the cloned M. loti nodC gene. The results indicate that prenylpyrophosphate-linked intermediates are not involved in the chitin oligosaccharide synthesis pathway. We observed that, in addition to N-acetylglucosamine (GlcNAc) from UDP-GlcNAc, NodC also directly incorporates free GlcNAc into chitin oligosaccharides. Further analysis showed that free GlcNAc is used as a primer that is elongated at the nonreducing terminus. The synthetic glycoside p-nitrophenyl-beta-N-acetylglucosaminide (pNPGlcNAc) has a free hydroxyl group at C4 but not at C1 and could also be used as an acceptor by NodC, confirming that chain elongation by NodC takes place at the nonreducing-terminal residue. The use of artificial glycosyl acceptors such as pNPGlcNAc has not previously been described for a processive glycosyltransferase. Using this method, we show that also the DG42-directed chitin oligosaccharide synthase activity, present in extracts of zebrafish embryos, is able to initiate chitin oligosaccharide synthesis on pNPGlcNAc. Consequently, chain elongation in chitin oligosaccharide synthesis by M. loti NodC and zebrafish DG42 occurs by the transfer of GlcNAc residues from UDP-GlcNAc to O4 of the nonreducing-terminal residue, in contrast to earlier models on the mechanism of processive beta-glycosyltransferase reactions.

Resistance to the insecticides lufenuron and propoxur in natural populations of Drosophila melanogaster (Diptera: Drosophilidae)

Lufenuron is a newly marketed benzoylphenyl urea chitin-synthesis inhibitor insecticide that is effective against certain insects, including Drosophila melanogaster (Meigen). Resistance to this class of insecticides is not widespread in pest insect populations and, for the resistance that has been reported, the genetic basis is not understood. In previous work, natural population strains of D. melanogaster from 2 widely separated locations in the United States were found to be as much as 100 times more resistant to lufenuron when compared with laboratory strains. It was postulated that this resistance is the result of cross-resistance that evolved to an earlier, widely used insecticide. In the current study we examined cross-resistance of selected D. melanogaster strains to propoxur, a likely candidate carbamate insecticide that has been extensively used during the past 3 decades. However, no correlation between resistance to lufenuron and propoxur was found. Strains were selected to represent a range of dates of establishment (1936-1996) from natural populations to laboratory culture. Examination of these strains showed susceptibility to propoxur in long-established laboratory strains, but resistance in recently established strains. Susceptibility to lufenuron was also high in long-established strains and apparently slowly decreased in natural populations until approximately equal to 5 yr ago, when it decreased more rapidly. These results suggest that if this loss in susceptibility results from agricultural chemical usage, then these chemicals can significantly affect a non-target insect.

The effect of chitin synthesis inhibitors on the development of Brugia malayi in Aedes aegypti

Two chitin synthesis inhibitors (CSIs) viz., triflumuron and hexaflumuron interfere++ with the development of Brugia malayi in Aedes aegypti (a black-eyed Liverpool strain). The development of B. malayi was slow in both the treated populations and the infection rate, infectivity rate and L3 load per mosquito decreased significantly (P < 0.001) in comparison with untreated controls. Hexaflumuron was found to be more inhibiting than triflumuron.

Compounds active against cell walls of medically important fungi

A number of substances that directly or indirectly affect the cell walls of fungi have been identified. Those that actively interfere with the synthesis or degradation of polysaccharide components share the property of being produced by soil microbes as secondary metabolites. Compounds specifically interfering with chitin or beta-glucan synthesis have proven effective in studies of preclinical models of mycoses, though they appear to have a restricted spectrum of coverage. Semisynthetic derivatives of some of the natural products have offered improvements in activity, toxicology, or pharmacokinetic behavior. Compounds which act on the cell wall indirectly or by a secondary mechanism of action, such as the azoles, act against diverse fungi but are usually fungistatic in nature. Overall, these compounds are attractive candidates for further development.

Inhibition of chitin synthesis in the cell wall of Coccidioides immitis by polyoxin D

The cell walls of both growth phases of Coccidioides immitis were studied by light and electron microscopy and biochemical procedures in an effort to assess the role of chitin in the fungus. Inhibition of normal chitin synthesis in the spherule by exposure to several concentrations of polyoxin D (PD) led to multiple morphological effects. Exposure of the mycelial phase to significantly higher levels of the compound had no morphological effect, as determined by autoradiography and light and electron microscopy. However, when equal masses of both morphological phases were treated with PD and pulsed with labeled N-acetylglucosamine, there was a greater relative (percent) reduction of incorporation of label in PD-treated mycelia compared with that of spherules. Nevertheless, the treated and untreated mycelia incorporated severalfold more counts than did corresponding spherules. The results suggest that chitin is important in maintaining the structural integrity of the spherule phase, but the role of chitin in the mycelial phase is less clear.

Stoffwechselprodukte von mikroorganismen. 154. Mitteilung. Nikkomycin, ein neuer hemmstoff der chitinsynthese bei pilzen

From the fermentation broth of Streptomyces tendae Tü 901 a substance was isolated which inhibits the growth of several fungi. The new antibiotic affects the chitchin biosynthesis. Its structure was identified by mass spectrometry of the products obtained after chemical degradation. Nikkomycin is a nucleoside-peptide antibiotic consisting of uracil, an amino hexuronic acid and a new amino acid containing a pyridin ring.