Fused Pyrroles in Cholestane and Norcholestane Side Chains: Acaricidal and Plant Growth-Promoting Effects.

Herein, we describe the synthesis and characterization of fused pyrroles in cholestane and norcholestane side chains derived from kryptogenin and diosgenin, respectively. Both conventional and microwave heating techniques were used to synthesize the steroidal pyrroles from primary amines, with the microwave method producing the highest yields. In particular, the norcholestane pyrroles were tested as acaricides against the two-spotted spider mite (Tetranychus urticae Koch) under laboratory conditions and as plant growth promoters on habanero pepper (Capsicum chinense Jacq) under greenhouse conditions.

Medium-Chain Fatty Acids from Eugenia winzerlingii Leaves Causing Insect Settling Deterrent, Nematicidal, and Phytotoxic Effects.

Eugenia winzerlingii (Myrtaceae) is an endemic plant from the Yucatan peninsula. Its organic extracts and fractions from leaves have been tested on two phloem-feeding insects, Bemisia tabaci and Myzus persicae, on two plant parasitic nematodes, Meloidogyne incognita and Meloidogyne javanica, and phytotoxicity on Lolium perenne and Solanum lycopersicum. Results showed that both the hexane extract and the ethyl acetate extract, as well as the fractions, have strong antifeedant and nematicidal effects. Gas chromatography-mass spectrometry analyses of methylated active fractions revealed the presence of a mixture of fatty acids. Authentic standards of detected fatty acids and methyl and ethyl derivatives were tested on target organisms. The most active compounds were decanoic, undecanoic, and dodecanoic acids. Methyl and ethyl ester derivatives had lower effects in comparison with free fatty acids. Dose-response experiments showed that undecanoic acid was the most potent compound with EC50 values of 21 and 6 nmol/cm2 for M. persicae and B. tabaci, respectively, and 192 and 64 nmol for M. incognita and M. javanica, respectively. In a phytotoxicity assay, medium-chain fatty acids caused a decrease of 38-52% in root length and 50-60% in leaf length of L. perenne, but no effects were observed on S. lycopersicum. This study highlights the importance of the genus Eugenia as a source of bioactive metabolites for plant pest management.

Molecular Docking and Dynamics Simulation of Protein ß-Tubulin and Antifungal Cyclic Lipopeptides.

To elucidate interactions between the antifungal cyclic lipopeptides iturin A, fengycin, and surfactin produced by Bacillus bacteria and the microtubular protein ß-tubulin in plant pathogenic fungi (Fusarium oxysporum, Colletrotrichum gloeosporioides, Alternaria alternata, and Fusarium solani) in molecular docking and molecular dynamics simulations, we retrieved the structure of tubulin co-crystallized with taxol from the Protein Data Bank (PDB) (ID: 1JFF) and the structure of the cyclic lipopeptides from PubChem (Compound CID: 102287549, 100977820, 10129764). Similarity and homology analyses of the retrieved ß-tubulin structure with those of the fungi showed that the conserved domains shared 84% similarity, and the root mean square deviation (RMSD) was less than 2 Å. In the molecular docking studies, within the binding pocket, residues Pro274, Thr276, and Glu27 of ß-tubulin were responsible for the interaction with the cyclic lipopeptides. In the molecular dynamics analysis, two groups of ligands were formed based on the number of poses analyzed with respect to the RMSD. Group 1 was made up of 10, 100, and 500 poses with distances 0.080 to 0.092 nm and RMSDs of 0.10 to 0.15 nm. For group 2, consisting of 1000 poses, the initial and final distance was 0.1 nm and the RMSDs were in the range of 0.10 to 0.30 nm. These results suggest that iturin A and fengycin bind with higher affinity than surfactin to ß-tubulin. These two lipopeptides may be used as lead compounds to develop new antifungal agents or employed directly as biorational products to control plant pathogenic fungi.

Insect deterrent and nematicidal screening of microfungi from Mexico and anti-aphid compounds from Gliomastix masseei.

Fungal metabolites are promising alternatives for the development of biorational pesticides. In this sense, microfungi from tropical regions are valuable sources of natural compounds for pest management. With the aim of broadening the search for new eco-friendly products to manage plant pests, this study was carried out to evaluate the biological activity of 23 tropical fungal extracts on three species of phytophagous insects and a plant parasitic nematode. In addition, the active principles of the most effective extract were identified. The insect deterrent activity of fungal extracts was evaluated on the settling of aphids Myzus persicae and Rhopalosiphum padi, and on the feeding of lepidoptera larva Spodoptera littoralis; the nematostatic activity was evaluated on the mobility of Meloidogyne javanica. Active metabolites from Gliomastix masseei were identified by GC-MS techniques and by comparison with commercial standards. Results showed seven extracts with strong effect on the settling of M. persicae and R. padi (settling inhibition >80%). The calculated median of effective concentration (EC50) values ranged from 8 to 38µg/cm2 for the extracts of Clonostachys rosea and G. masseei, respectively. Bioassay-guided separation of the ethyl acetate extract of G. masseei revealed the presence of fatty acids and their derivatives, where methyl 9-octadecenoate was the most active compound with EC50 values of 16µg and 35µg/cm2 for M. persicae and R. padi, respectively. Extracts of C. rosea and G. masseei could be a promising option in the control of pest aphids in agriculture.

Isolation of Mexican Bacillus Species and Their Effects in Promoting Growth of Chili Pepper (Capsicum annuum L. cv Jalapeño).

The purpose of this work was to isolate and identify native bacteria from plants collected in the State of Yucatán, México with the ability to promote growth of chili pepper (Capsicum annuum L. cv Jalapeño). We identified nine bacterial isolates that belong to five species of Bacillus (i.e. Bacillus subtilis, B. flexus, B. cereus, B. megaterium and B. endophyticus) that produced indoleacetic acid (4.0-24.3 µg/mL) with solubilization index of 1.3-1.6. All the bacterial isolates were evaluated based on their ability to promote growth of chili pepper. Plants inoculated with B. subtilis ITC-N67 showed an increase in stem diameter and root volume, whereas inoculation with B. cereus ITC-BL18 increased the number of flower buds, fresh biomass of roots and total fresh biomass. Conversely, B. flexus ITC-P4 and B. flexus ITC-P22 showed deleterious effect on root volume and total biomass. In summary, our data showed that native B. cereus TC-BL18 and B. subtilis ITC-N67 have potential to be used as growth promoting microorganism for chili pepper, particularly in the state of Yucatán, México.

The rectal complex and Malpighian tubules of the cabbage looper (Trichoplusia ni): regional variations in Na+ and K+ transport and cation reabsorption by secondary cells.

In larvae of most Lepidoptera the distal ends of the Malpighian tubules are closely applied to the rectal epithelia and are ensheathed within the perinephric membrane, thus forming the rectal complex. The cryptonephric Malpighian tubules within the rectal complex are bathed in fluid within a functional compartment, the perinephric space, which is separate from the haemolymph. In this study, the scanning ion-selective electrode technique (SIET) was used to measure transport of Na(+) and K(+) across the rectal complex and across multiple regions of the Malpighian tubules of larvae of the cabbage looper Trichoplusia ni. Measurements were made in an intact preparation in which connections of the tubules upstream to the rectal complex and downstream to the urinary bladder and gut remained intact. SIET measurements revealed reabsorption of Na(+) and K(+) across the intact rectal complex and into the bath (haemolymph), with K(+) fluxes approximately twice as large as those of Na(+). Analyses of fluxes in larvae with empty guts, found in recently moulted larvae, versus those with full guts highlighted differences in the rates of K(+) or Na(+) transport within tubule regions that appeared morphologically homogeneous, such as the rectal lead. The distal rectal lead of larvae with empty guts reabsorbed K(+), whereas the same region secreted K(+) in tubules of larvae with full guts. SIET measurements of the ileac plexus also indicated a novel role for secondary (type II) cells in cation reabsorption. Secondary cells reabsorb K(+), whereas the adjacent principal (type I) cells secrete K(+). Na(+) is reabsorbed by both principal and secondary cells, but the rate of reabsorption by the secondary cells is approximately twice the rate in the adjacent principal cells.

[Antifungal effect of phenolic and carotenoids extracts from chiltepin (Capsicum annum var. glabriusculum) on Alternaria alternata and Fusarium oxysporum]. / Efecto antifúngico de extractos fenólicos y de carotenoides de chiltepín (Capsicum annum var. glabriusculum) en Alternaria alternata y Fusarium oxysporum.

The effect of phenolic and carotenoid extracts from chiltepin fruits on mycelial growth and the inhibition of conidial germination of Alternaria alternata and Fusarium oxysporum were investigated in the present work. Phenolic extracts inhibited mycelial growth of A.alternata by 38.46%, and significantly reduced conidial germination on the fifth day after treatment to 92% in relation to control. No significant changes were observed in the inhibition of mycelial growth in Fusarium oxysporum; however, the number of germinated conidia was reduced, showing 85% inhibition five days after treatment in relation to control. Moreover, carotenoid extracts showed 38.5% inhibition of mycelial growth and 85.3% inhibition of conidial germination of A.alternata, five days after treatment. Carotenoid extracts showed less inhibition of mycelial growth (20.3%) in F.oxysporum, with respect to A.alternata; while there was greater inhibition of conidial germination (96%) on the fifth day after treatment. Phenolic and carotenoid extracts from chiltepin may be a promising alternative as a natural fungicide against fungi of agricultural importance.

A review of the impact of maize-legume intercrops on the diversity and abundance of entomophagous and phytophagous insects.

In many parts of the world, chemical pesticides are the primary method of pest control in maize (Zea mays L.) crops. Concerns about the negative consequences of chemical pesticide use on people's health and the environment, as well as the emergence of insecticide resistance, have accelerated attempts to discover alternatives that are effective, low-risk, and cost-effective. Maize-legume intercropping systems are known to have multiple benefits to agroecosystem functioning, including pest regulation. This review focuses on the influence of maize-legume intercropping systems on insect diversity and abundance as a mechanism for insect pest regulation in maize crops. First, this review combines knowledge of maize-legume intercrops, with a particular emphasis on the mechanism by which this practice attracts beneficial insects (e.g., predators, parasitoids) to reduce pest damage in intercropping systems. In addition, the pairings of specific legume species with the greatest potential to attract more beneficial insects and therefore reduce maize pests are also discussed. Finally, future research needs are also recommended. Findings are reviewed in the context of looking for long-term management strategies that can increase the adoption of integrated pest management programs in maize-based production systems.

Effects of the microbial metabolite destruxin A on ion transport by the gut and renal epithelia of Drosophila melanogaster.

Destruxins have been implicated in the infection process by entomopathogenic fungi and have been also found to be highly toxic when applied topically or ingested by different insect species. To gain insight into the mechanism of action of this toxin on insect internal organs, we have evaluated the effects of destruxin A on Drosophila melanogaster Malpighian tubules and gut tissues. Destruxin A was toxic when injected into adults; the calculated EC(50) was 0.11 mM. Destruxin A significantly inhibited fluid secretion rate by Malpighian tubules as well; the calculated IC(50) was 0.25 µM. The Na(+) concentration in the secreted fluid increased significantly when tubules were exposed to 0.25 µM destruxin A, whereas pH and the concentrations of Ca(2+) and K(+) did not change. In gut, there was no effect of destruxin on H(+) flux, but there was a significant decrease in K(+) and Ca(2+) absorption. The concentration of Ca(2+) and K(+) in the hemolymph of destruxin A-injected flies was not significantly different from those of control flies after 3 h. Taken together, these results show that destruxin A produces differential effects on ion transport by renal and gut tissues. © 2012 Wiley Periodicals, Inc.

Survival Rate of the Neotropical Stingless Bees Nannotrigona perilampoides and Frieseomelitta nigra after Exposure to Five Selected Insecticides, under Controlled Conditions.

Insecticides used in agricultural pest management pose survival risks to the stingless bees that forage on crops in tropical and subtropical regions. In the present study, we evaluated, under laboratory conditions, the acute oral toxicity of five selected insecticides (dinotefuran, imidacloprid, flupyradifurone, spirotetramat, and cyantraniliprole) to two species of neotropical stingless bees: Nannotrigona perilampoides and Frieseomelitta nigra. At field recommended doses, dinotefuran, imidacloprid, and flupyradifurone caused the highest mortality in both bee species. These insecticides also caused the largest decrease in the survival rate when exposed to a 10-fold dilution of the field recommended doses. Notably, dinotefuran exerted a high effect even at 100-fold dilution (100% mortality). In contrast, cyantraniliprole had a low effect and spirotetramat was virtually nontoxic. These results suggest that some insecticides used to control sap-sucking insects may have a significant negative impact on the communities of stingless bees.

Determining relevant traits for selecting landrace accessions of Phaseolus lunatus L. for insect resistance.

Plant-insect interactions are a determining factor for sustainable crop production. Although plants can resist or tolerate herbivorous insects to varying degrees, even with the use of pesticides, insects can reduce plant net productivity by as much as 20%, so sustainable strategies for pest control with less dependence on chemicals are needed. Selecting plants with optimal resistance and photosynthetic traits can help minimize damage and maintain productivity. Here, 27 landrace accessions of lima beans, Phaseolus lunatus L., from the Yucatan Peninsula were evaluated in the field for morphological resistance traits, photosynthetic characteristics, insect damage and seed yield. Variation was found in physical leaf traits (number, area, and dry mass of leaves; trichome density, specific leaf thickness and hardness) and in physiological traits (photosynthetic rate, stomatal conductance, intercellular carbon, water-use efficiency, and transpiration). Five accessions (JMC1325, JMC1288, JMC1339, JMC1208 and JMC1264) had the lowest index for cumulative damage with the highest seed yield, although RDA analysis uncovered two accessions (JMC1339, JMC1288) with strong positive association of seed yield and the cumulative damage index with leaf production, specific leaf area (SLA) and total leaf area. Leaf traits, including SLA and total leaf area are important drivers for optimizing seed yield. This study identified 12 important morphological and physiological leaf traits for selecting landrace accessions of P. lunatus for high yields (regardless of damage level) to achieve sustainable, environmentally safe crop production.

Comparative toxicity of pesticides to stingless bees (Hymenoptera: Apidae: Meliponini).

Stingless bees are potential pollinators of commercial tropical crops and their use may increase in the short term. However, studies comparing the toxicity of pesticides to different individuals and species are lacking, making it difficult to evaluate their short- and long-term effects on colonies and populations of these insects. In this work, we tested the lethality of compounds from the main pesticide groups on stingless bees of the species Melipona beecheii Bennett, Trigona nigra Provancher, and Nannotrigona perilampoides Cresson. The LDo (in micrograms per bee) for each pesticide was calculated for callow workers and foragers of the three species as well as for gynes and drones of M. beecheii. The results showed that all species were highly susceptible to the evaluated compounds. Nicotinoid pesticides were the most toxic, followed in descending order by permethrin, diazinon, and methomyl. We found evidence of a relationship between the body weight of the species and their LD50 for permethrin and methomyl (r = 0.91 and 0.90, respectively) but not for diazinon (r = -0.089). An analysis of contingency tables showed that within each species, callow workers had higher mortalities than foragers (P < 0.01). In M. beecheii at similar pesticide dose more males died compared with females [chi2((0.0),1) = 10.16]. However, gynes were less resistant than workers [chi2((0.01),1)) = 8.11]. The potential negative consequences of pesticides to native stingless bees are discussed considering the reproductive biology of these insects. It is important to take actions to prevent damage to these key species for the ecology and agriculture of Mexico and Latin America

Identification of Insect-Deterrent Metabolites from Acremonium masseei strain CICY026, a Saprophytic Fungus from a Sinkhole in Yucatán.

Micromycetes from unexplored sources represent an opportunity to discover novel natural products to control insect pests. With this aim, a strain of Acremonium masseei CICY026 isolated from a tropical sinkhole was identified, cultured on fermented rice, and its ethyl acetate extract (EAE) was evaluated against three serious phytophagous insects (Bemisia tabaci, Myzus persicae, and Rhopalosiphum padi). DNA from A. masseei CICY026 was used to confirm its identity. EAE caused settling inhibition (SI) of M. persicae and R. padi (67.5% and 75.3%, respectively). Bioassay-guided fractionation of the active EAE led to the isolation of a novel metabolite, named hexahydroacremonintriol (1), and of acremonin A glucoside (2). The structures of 1 and 2 were determined using IR, one- and two-dimensional NMR, HRMS, and confirmed by theoretical data. The aphid M. persicae was noticeably sensitive to 1 and 2 (SI: 55.6% and 67.2%, respectively), whereas R. padi was only slightly affected by 1 (SI: 59%). This new knowledge about mycobiota from these special sinkhole ecosystems will inform the development of new biorational pesticides.

Backyards: typology and contribution to food security in Mexico / Quintais: tipologia e contribuição para a segurança alimentar no México

Backyards are family settings adjacent to the house, characterized mainly by being small-scale and diversified productive spaces. The research typologically characterized the backyards and their contribution to family food security in La Concordia municipality, Chiapas, Mexico. The research was descriptive and mixed, quantitative, and qualitative, and semi-structured interviews were applied to 130 families. For the typification, 21 variables were used, and the statistical techniques of Factorial Analysis and Clusters were applied. The cases studied were classified, according to the relevance of their production and contribution to food security, into two general groups: a) a group of backyards that is more productive and contributes to food security, which in turn includes three subtypes of backyards that differ from each other by their profile towards vegetable or poultry production for subsistence, and/or pigs as a form of savings; b) a group of less productive backyards in which other management strategies for food security are assumed and differ from each other by the level of expulsion of labor force and types of families, nuclear or extended. Poultry and plant species for multiple uses was the most frequently characteristic, regardless of the type of backyard.

Os quintais são ambientes familiares adjacentes à casa, caracterizados principalmente por serem espaços produtivos de pequena escala e diversificados. A pesquisa teve como objetivo caracterizar tipologicamente os quintais e sua contribuição para a segurança alimentar familiar no município de La Concordia, Chiapas, México. A pesquisa foi descritiva e mista, quantitativa e qualitativa, na qual foram aplicadas entrevistas semiestruturadas a 130 famílias. Para a tipificação foram utilizadas 21 variáveis e aplicadas as técnicas estatísticas de Análise Fatorial e Clusters. Os casos estudados foram classificados, de acordo com a relevância de sua produção e contribuição para a segurança alimentar, em dois grupos gerais: a) um grupo de quintais mais produtivos e que contribuem para a segurança alimentar, que por sua vez inclui três subtipos de quintais que diferem entre si pelo seu perfil para a produção de hortaliças ou aves para subsistência, e/ou suínos como forma de poupança; b) conjunto de quintais menos produtivos em que se assumem outras estratégias de gestão da segurança alimentar e diferem entre si pelo nível de expulsão de mão de obra e tipos de famílias, nucleares ou extensas. Aves e espécies vegetais de uso múltiplo foi a característica mais encontrada, independente do tipo de quintal.

Transepithelial transport of salicylate by the Malpighian tubules of insects from different orders.

The organic anion salicylate is a plant secondary metabolite that protects plants against phytophagous insects. In this study, a combination of salicylate-selective microelectrodes and a radioisotope tracer technique was used to study the transepithelial transport of salicylate by the Malpighian tubules of 10 species of insects from five orders. Our results show that salicylate is transported into the lumen of the Malpighian tubules in all the species evaluated, except Rhodnius prolixus. The transepithelial transport of salicylate by the Malpighian tubules of Drosophila simulans, Drosophila erecta, Drosophila sechellia, and Acheta domesticus was saturable, Na(+)-dependent and inhibited by alpha-cyano-4-hydroxycinnamic acid. This transport system resembles that previously found in tubules of Drosophila melanogaster. In contrast, transepithelial transport of salicylate by Malpighian tubules of Tenebrio molitor, Plagiodera versicolora, Aedes aegypti, and Trichoplusia ni was unaffected by Na(+)-free bathing saline. The presence of both salicylate and salicylate metabolites in the secreted fluid samples from the Malpighian tubules of A. domesticus, R. prolixus, T. molitor, and T. ni indicates that insect Malpighian tubules may both transport and metabolize salicylate. The highest capacities to rid the hemolymph of salicylate were found in T. molitor, P. versicolora and Drosphila spp. Our results suggest that transport of salicylate by the Malpighian tubules might contribute to elimination of this organic anion from the hemolymph, particularly in some species that encounter high levels of organic anion in the diet.

Maize legume intercropping systems in southern Mexico: A review of benefits and challenges / Sistemas consorciados de milho no sul do México: uma revisão dos benefícios e desafios

Intercropping is the process of planting two or more crops simultaneously in the same field in order to provide greater ecosystem services (i.e. services related to sustainable land and water use, climate change mitigation, and ecosystem restoration). In southern Mexico, the cereal-legume intercropping is a traditional cropping practice that is declining overtime. This paper provides a literature review of the potential benefits and constraints of a maize-legume intercropping for small-scale farms in southern Mexico. This review explored and elucidated the different ecosystem services delivered by maize-legume intercropping systems. This information will help farmers know how to make a better use of cereal-legume intercropping systems to increase maize yields, improve their socioeconomic conditions, and enhance conservation agricultural practices in southern Mexico.

Consórcio é o processo de plantar duas ou mais safras simultaneamente no mesmo campo, a fim de fornecer maiores serviços de ecossistema (ou seja, serviços relacionados ao uso sustentável da terra e da água, mitigação das mudanças climáticas e restauração do ecossistema) para as lavouras. No sul do México, o consórcio cereal-leguminosa é uma prática tradicional de cultivo que está diminuindo com o tempo. Este artigo fornece uma revisão da literatura sobre os benefícios e limitações potenciais do consórcio milho-leguminosa para fazendas de pequena escala no sul do México. Esta revisão foi escrita para explorar e elucidar os diferentes serviços ecossistêmicos fornecidos por sistemas consorciados de milho e leguminosa. Essas informações ajudarão os agricultores a saber como fazer um melhor uso dos sistemas consorciados de cereais e leguminosas para aumentar a produtividade do milho, melhorar sua subsistência socioeconômica e melhorar as práticas agrícolas de conservação no sul do México.

Characterization of salicylate uptake across the basolateral membrane of the malpighian tubules of Drosophila melanogaster.

The organic anion salicylate is a plant secondary metabolite that can protect plants against herbivores. Transport of salicylate across the basolateral membrane of the Malpighian tubules of Drosophila melanogaster was studied using a radioisotope tracer technique. The uptake of [(14)C]salicylate by the Malpighian tubules was active, saturable and Na(+)-dependent; the maximum uptake rate (J(max)) and the half saturation concentration (K(t)) were 12.6 pmoltubule(-1)min(-1) and 30.7micromoll(-1), respectively. In contrast to organic anion transport by vertebrate renal tissues, salicylate uptake was not trans-stimulated by glutarate (0.01-1.0 mmoll(-1)) or cis-inhibited by high concentrations (5 mmoll(-1)) of various alpha-keto acids (glutaric acid, alpha-ketoglutaric acid, succinic acid, and citric acid). Changes in basolateral membrane potential or physiologically relevant changes in bathing saline pH did not affect the rate of [(14)C]salicylate uptake. Ring-structure monocarboxylic acids (benzoic acid, nicotinic acid, gentisic acid, unlabelled salicylic acid, alpha-cyano-4-hydroxycinnamic acid, probenecid, fluorescein, and P-aminohippuric acid) strongly inhibited [(14)C]salicylate uptake rate. In contrast, short-chain monocarboxylic acids had little (butyric acid) or no effect (lactic acid, pyruvic acid, and propionic acid). Our results suggest that salicylate uptake across the basolateral membrane of D. melanogaster Malpighian tubules is mediated by a non-electrogenic, alpha-cyano-4-hydroxycinnamic acid-sensitive, Na(+):salicylate cotransport system.

Screening of Yucatecan plant extracts to control Colletotrichum gloeosporioides and isolation of a New Pimarene from Acacia pennatula.

Screening of seven Yucatecan plant extracts to look for fungicidal activity for the control of Colletotrichum gloeosporioides was carried out. Bioassay-directed purification of the root extract of one of the most active plants, Acacia pennatula, resulted in the isolation of the new compound 15,16-dihydroxypimar-8(14)-en-3-one (1), which in the in vitro bioassay "agar dilution" was shown to have growth, sporulation, and germination inhibition activity. Nuclear magnetic resonance spectroscopic techniques were used to elucidate its structure.

The insect excretory system as a target for novel pest control strategies.

The insect excretory system plays essential roles in osmoregulation, ionoregulation and toxin elimination. Understanding the mechanisms of fluid and ion transport by the epithelial cells of the excretory system provides a foundation for development of novel pest management strategies. In the present review, we focus on two such strategies: first, impairment of osmoregulation by manipulation of diuretic or antidiuretic signaling pathways and second, interference with toxin elimination by inhibition of toxin transport systems.

Secretion of Na(+), K(+) and fluid by the Malpighian (renal) tubule of the larval cabbage looper Trichoplusia ni (Lepidoptera: Noctuidae).

The Malpighian (renal) tubules play important roles in ionic and osmotic homeostasis in insects. In Lepidoptera, the Malpighian tubules are structurally regionalized and the concentration of Na(+) and K(+) in the secreted fluid varies depending on the segment of tubule analyzed. In this work, we have characterized fluid and ion (Na(+), K(+), H(+)) transport by tubules of the larval stage of the cabbage looper Trichoplusia ni; we have also evaluated the effects of fluid secretion inhibitors and stimulants on fluid and ion transport. Ramsay assays showed that fluid was secreted by the iliac plexus but not by the yellow and white regions of the tubule. K(+) and Na(+) were secreted by the distal iliac plexus (DIP) and K(+) was reabsorbed in downstream regions. The fluid secretion rate decreased>50% after 25µM bafilomycin A1, 500µM amiloride or 50µM bumetanide was added to the bath. The concentration of K(+) in the secreted fluid did not change, whereas the concentration of Na(+) in the secreted fluid decreased significantly when tubules were exposed to bafilomycin A1 or amiloride. Addition of 500µM cAMP or 1µM 5-HT to the bath stimulated fluid secretion and resulted in a decrease in K(+) concentration in the secreted fluid. An increase in Na(+) concentration in the secreted fluid was observed only in cAMP-stimulated tubules. Secreted fluid pH and the transepithelial electrical potential (TEP) did not change when tubules were stimulated. Taken together, our results show that the secretion of fluid is carried out by the upper regions (DIP) in T. ni Malpighian tubules. Upper regions of the tubules secrete K(+), whereas lower regions reabsorb it. Stimulation of fluid secretion is correlated with a decrease in the K(+)/Na(+) ratio.