Presence Of Repellents Research Articles

Interactions of DEET and Novel Repellents With Mosquito Odorant Receptors.

The carboxamide N,N-di-ethyl-meta-toluamide (DEET) is the most effective and widely used insect repellent today. However, drawbacks concerning the efficacy and the safety of the repellent have led to efforts to design new classes of insect repellents. Through quantitative structure-activity relationships, chemists have discovered two chemical groups of novel repellents: the acylpiperidines and the carboxamides, with the acylpiperidines generally more potent in biological assays. Although the exact mechanism of action of DEET and other repellents has not yet been thoroughly elucidated, previous research shows that the activity of insect odorant receptors are inhibited in the presence of repellents. The present electrophysiological study employs two-electrode voltage clamp with Xenopus laevis oocytes expressing AgOR2/AgOrco and AgOR8/AgOrco receptors to assess the effects of the novel repellents on Anopheles gambiae Giles (Insecta: Diptera: Culicidae) mosquito odorant receptors. The novel acylpiperidines and carboxamides reversibly inhibited (12-91%) odorant-evoked currents from both AgOR2/AgOrco and AgOR8/AgOrco receptors in a dose-dependent manner at all tested concentrations (30 μM to 1 mM). Furthermore, all the novel agents were more potent inhibitors of the receptors than DEET, with the acylpiperidines producing on average greater inhibition than the carboxamides. Interestingly, there was a correlation (r2 = 0.72) between the percentage inhibition of AgOR2/AgOrco receptor currents and protection times of the acylpiperidines. Our results add to existing evidence that the repellency of a compound is linked to its ability to disrupt the insect olfactory system and that the acylpiperidines could represent a class of more effective alternatives to the current gold standard, DEET.

Can trials of spatial repellents be used to estimate mosquito movement?

BackgroundKnowledge of mosquito movement would aid the design of effective intervention strategies against malaria. However, data on mosquito movement through mark-recapture or genetics studies are challenging to collect, and so are not available for many sites. An additional source of information may come from secondary analyses of data from trials of repellents where household mosquito densities are collected. Using the study design of published trials, we developed a statistical model which can be used to estimate the movement between houses for mosquitoes displaced by a spatial repellent. The method uses information on the different distributions of mosquitoes between houses when no households are using spatial repellents compared to when there is incomplete coverage. The parameters to be estimated are the proportion of mosquitoes repelled, the proportion of those repelled that go to another house and the mean distance of movement between houses. Estimation is by maximum likelihood.ResultsWe evaluated the method using simulation and found that data on the seasonal pattern of mosquito densities were required, which could be additionally collected during a trial. The method was able to provide accurate estimates from simulated data, except when the setting has few mosquitoes overall, few repelled, or the coverage with spatial repellent is low. The trial that motivated our analysis was found to have too few mosquitoes caught and repelled for our method to provide accurate results.ConclusionsWe propose that the method could be used as a secondary analysis of trial data to gain estimates of mosquito movement in the presence of repellents for trials with sufficient numbers of mosquitoes caught and repelled and with coverage levels which allow sufficient numbers of houses with and without repellent. Estimates from this method may supplement those from mark-release-recapture studies, and be used in designing effective malaria intervention strategies, parameterizing mathematical models and in designing trials of vector control interventions.

Chemotactic Response of Escherichia Coli to Repellents, CoCl2 and NiCl2

Negative chemotaxis refers to the motion of microorganisms away from harmful chemicals. Soft agarose gel assay has been traditionally used to characterize the response to various repellents. In this study, we use the “chemical-in-plug” method to quantify the motion of Escherichia coli in the presence of repellents, NiCl2 and CoCl2, over a broad range of concentrations. These experiments were complimented with drift velocity measurements of individual bacteria in controlled gradients using a capillary assay. The latter also revealed the tumbling frequency and steady state clockwise bias for varying concentrations of repellents thereby providing insight into adaptation to repellents. The experimental technique yielded the motion of the bacteria in space and time and further related the motion to the evolving concentration profile of the repellent. Results show that the bacteria exhibit logarithmic sensing to the repellents, i.e., the drift velocity of E.coli is proportional to the logarithmic concentration gradient suggesting Weber law. The predictions of a standard population based model agreed with the observed linear behavior when the binding of the repellent to the receptor was sub-sensitive. This was borne out by a low value of Hill coefficient (n<<1) used to describe the binding characteristics of the receptors. The analysis shows that the binding characteristics for the repellents was sub-sensitive in contrast to an ultra-sensitive response observed for attractants suggesting a negative cooperative behavior of receptors. The above experiments suggest that negative cooperativity allows the cells to respond to harmful chemicals without saturation even at high concentration.

Field measurement of soil water repellency and its impact on water flow under different vegetation

AbstractNumerous recent laboratory studies have shown that vegetation can influence soil water flow by inducing very low levels of water repellency. In this study we extended on this previous research by developing a field-based test using a miniature infiltrometer to assess low levels of water repellency from physically based measurements of liquid flow in soil. The field-based test was verified through a simple laboratory experiment and then applied to determine the impact of vegetation and antecedent soil water content. The soil hydraulic properties determined were hydraulic conductivity, sorptivity, as well as the persistence and index of water repellency. Tests were conducted following a dry spell and wet spell on (1) forest soil (0 cm depth), (2) glade soil (0 cm depth) and (3) glade soil (50 cm depth). It was found that both the persistence and index of water repellency, R, decreased in the order as follows: forest soil &gt; glade soil (0 cm) &gt; glade soil (50 cm) for both dry and wet spell. The range of values of R was 0.28 (wettable) to 360 (highly water repellent), which affected hydraulic conductivity k r(−2 cm). R increased and hence k r(−2 cm) decreased in the order: forest soil &lt; glade soil (0 cm) &lt; glade soil (50 cm) for both the dry and wet spell. There were clear interactions between vegetation and changes to water flow caused by presence of repellency.

Assessing onion thrips behaviour in the presence of repellent and attractant volatile odours

Assessing onion thrips behaviour in the presence of repellent and attractant volatile odours

Prefeeding Behavior of the Crucifer Flea Beetle, Phyllotreta cruciferae, on Host and Nonhost Crucifers

The prefeeding behaviours of adult crucifer flea beetles, Phyllotreta cruciferae (Coleoptera: Chrysomelidae: Alticinae), were determined on seedlings of the host plant, Brassica napus, and compared to behaviors on seedlings of the nonhost crucifers, Crambe abyssinica, Sinapis alba, and Camelina sativa. Three stages of prefeeding behaviour, i.e., acclimation, stimulation, and initial feeding, were distinguished through observation of filmed beetles. Both antennal and tarsal chemoreceptors are important in determination of host plant quality by the crucifer flea beetle. The results of this study suggest that the sequence of prefeeding behaviors plays a crucial role in the onset of feeding. Differences in time spent on plant tissue and the frequency and duration of prefeeding behaviors provide insight into possible mechanisms of resistance to flea beetles in the non-Brassica crucifers. The nonpreferred hosts C. abyssinica and S. alba contain deterrent phytochemicals that partially inhibit feeding. These deterrent compounds appear to be volatile in nature in S. alba but nonvolatile in C. abyssinica. CFB resistance in the nonhost C. sativa may result from either the presence of repellent or the absence of stimulatory volatile phytochemicals.

Variable diets and changing taste in plant-insect relationships.

The host ranges of phytophagous insects are determined to a large degree by plant chemistry. Specialist insects are often closely associated with plants that produce characteristic chemicals, which may act as attractants or stimulants to aid in finding or recognizing a host. Generalist insects are generally believed to rely on the presence of repellents or deterrents to ensure avoidance of unsuitable plants. However, the chemistry of any plant can be highly variable, as a result of growth characteristics, genetic variation, or environmental factors. Such variable chemistry may provide windows of opportunity for nonadapted insects to utilize a plant or for a plant to become resistant to a normally adapted herbivore. Differences in insect responses to plant constituents may also result from genetic variation or environmental factors. In particular, dietary experience has been found to influence the ability of insects to taste plant chemicals that may serve as signals of suitability or unsuitability. Certain dietary constituents appear to suppress the development of taste sensitivity to deterrents in an insect, whereas the presence of specific stimulants in the diet may result in the development of dependence on these compounds. These findings further emphasize the fact that the dynamics of plant biochemistry along with plasticity in the sensory system of insects might be expected to play a major role in the evolution of new plant-insect relationships.

Preferência alimentar de Dione juno juno (Cramer) por genótipos de maracujazeiro e avaliação do uso de extratos aquosos

Avaliou-se a preferência alimentar de lagartas de Dione juno juno (Cramer) por genótipos de maracujazeiro, utilizando-se discos foliares, em condições de laboratório, e lagartas de primeiro e de quarto ínstar, em testes com e sem chance de escolha, com os seguintes materiais: Passiflora alata, P. setacea, P. coccinea, P. cincinnata, P. nitida, e os híbridos P. edulis x P. giberti, P. edulis x P. alata e P. alata2 x P. macrocarpa. Usando-se extrato aquoso de folhas (liofilizado recomposto) procurou-se determinar a presença de repelente, estimulante ou deterrente nos genótipos P. edulis e P. alata. Avaliou-se também a técnica de uso de extrato impregnado em discos de papel filtro e de ágar, em várias concentrações. Os resultados evidenciaram que P. alata, P. setacea, P. nitida e P. alata2 x P. macrocarpa são resistentes a D. juno juno e que essa resistência é do tipo não-preferência para alimentação; que folhas de P. alata2 x P. macrocarpa apresentam elevado poder de repelência ao inseto; no extrato de P. alata ocorre algum composto com forte ação repelente ou restringente de alimentação; que para a discriminação da preferência para alimentação de lagartas de D. juno juno por genótipos de maracujazeiro, pode ser utilizado ágar impregnado com 0,04 ml de extrato aquoso de folhas.

Seed Selection by the Red Imported Fire Ant (Hymenoptera: Formicidae) in the Laboratory

Ninety–sixspecies and varieties of seeds in 28 families were presented to laboratory colonies of Solenopsis invicta Buren. Small seeds were moved and subsequently damaged more often than large seeds. Although generally more resistant to damage, some species with large seeds such as com, Zea mays L., were susceptible to S. invicta damage. Seed coats protected some seed species from ant damage. Presence of repellent and attractant surface chemical swas also demonstrated for some seeds. Although chemicals could be extracted from seeds that could be considered attractive, some seeds appeared to be protected from S. invicta predation by repellents (predation means the seed is damaged so extensively that it can no longer germinate). Many species of seeds were susceptible to some degree of S. invicta predation, and most were transported to new locations. We also soaked seeds, which in general increased their susceptibility to predation, although seed removal was reduced. Seeds that were beginning to germinate were difficult to characterize: some germinated seeds were more susceptible to predation, but other germinated seeds were less susceptible to predation. Of resistant and susceptible seeds, Fabaceae seeds were most resistant and Labiatae seeds were most susceptible to S. invicta movement and damage. Seeds may play an important role as a food resource for S. invicta , and, as a result, S. invicta may be serious seed predators and competitors of animals for which seeds represent an important resource.

A Model for Transmembrane Signalling by the Aspartate Receptor Based on Random-cassette Mutagenesis and Site-directed Disulphide Cross-linking

Extracellular information is transduced by transmembrane receptors into the inside of the cell across a membrane barrier. To understand the molecular basis of transmembrane signalling, we replaced the transmembrane segment 2 (TM2) of the Escherichia coliaspartate receptor, Tar, with random sequences that are 21 amino acid residues in length and consist of Arg, Gly, Ser, Cys, Val, Leu, Ile and Phe at each position. From this ensemble for recombinant molecules, functional receptors were recovered as clones that could bind aspartate and transmit a signal to the intracellular domain.Restricted average hydrophobicity values were observed for functional transmembrane domains, and support the observation that transmembrane segments typically havehydrophobicity values greater than 1.6. However, non-functional transmembrane domains with greater hydrophobicity than 1.6 indicate that hydrophobicity is not a sole determinant for its function. Fourier transform analysis of the functional TM2 sequences suggest that the transmembrane segment has an α-helical structure with three distinct faces. Cross-linking of the faces to transmembrane segment 1 (TM1) mimics the “locked” signalling phenotypes of the wild-type receptor. The results are consistent with a model in which TM2 rotates in the plane of the lipid bilayer, and the rotation becomes locked at one face of the α-helix in the presence of attractant and at another face in the presence of repellent. This dynamic movement of the transmembrane domain may be a common signalling mechanism of homologous membrane receptor molecule such as the insulin receptor. Random-cassette mutagenesis and disulphde cross-linking provide powerful strategies for examining the structure and function of transmembrane segments.

Resistance in Soybeans to the Mexican Bean Beetle: II. Reactions of the Beetle to Resistant Plants1

Mexican bean beetles (Epilachna varivestis Mulsant) displayed differential preference reactions when fed foliage from resistant soybean (Glycine max (L.) Merrill) genotypes PI 229358, PI 227687, and PI 171451. These reactions included reduced longevity and fecundity in adults and weight loss and high mortality in larvae. These symptoms appeared similar to starvation and hypothetically resulted from reduced consumption of resistant foliage by the insects.Larvae tended to fall from plants of the genotypes PI 229358 and PI 171451 possibly because lack of feeding stimulants or presence of repellents caused high larval movement and leaf surfaces provided poor footing for the insects.

The Status and Termite Durability of Northern Cypress Pine

SUMMARY The cypress pine which occurs naturally over wide areas of the Northern Territory and adjacent islands is being grown successfully in plantations. The taxonomic status of this tree is reviewed briefly and it is treated as a tropical ecotype of Callitris columellaris, and referred to as northern cypress pine. The significance of northern cypress pine in the forestry programme of the Northern Territory is discussed with particular reference to future demands for termite resistant timber. Laboratory tests with two species of Coptotermes showed the heartwood timber of northern cypress pine to have a high natural termite durability, comparable with that of white cypress pine. This durability, which is considered to be due to the presence of repellent or deterrent substances in the timber, is equally high in both plantation and naturally grown trees.

The Specificity of the Tobacco Hornworm, Protoparce Sexta, to Solanaceous Plants1

Oviposition and feeding of the tobacco hornworm arc almost entirely restricted to plants of the family Solinaceae. Oviposition appears to be initiated by olfactory stimuli widely distributed in this plant family, and consequently it, is largely suppressed in the absence of host plants or after excision of the antennae. Both in the field and laboratory, the moths preferred tomato foliage over other solanaceous plants for oviposition. Larval feeding appears to be governed by gustatory stimuli common to plants of this family. On certain ones, such as Nicandra and Petunia , feeding and growth are limited by the presence of repellents or toxins. Some limited feeding occurred on certain nonsolanaceous plants after various periods of starvation.