Synergism between ammonia, lactic acid and carboxylic acids as kairomones in the host-seeking behaviour of the malaria mosquito Anopheles gambiae sensu stricto (Diptera: Culicidae)

Host odours play a major role in the orientation and host location of blood-feeding mosquitoes. Anopheles gambiae Giles sensu stricto, which is the most important malaria vector in Africa, is a highly anthropophilic mosquito species, and the host-seeking behaviour of the females of this mosquito is guided by volatiles of human origin. Ammonia, lactic acid and several carboxylic acids are known to be present in the human odour blend. We investigated the effect of these compounds on naive female mosquitoes using a dual-port olfactometer. Ammonia was an attractant on its own, whereas lactic acid was not attractive. Carboxylic acids, offered as a mixture of 12 compounds, were repellent at the concentration tested. The addition of ammonia to the carboxylic acid mixture overruled the repellent effect of the latter. Combining ammonia with either lactic acid or the carboxylic acids did not enhance the attractiveness of ammonia alone. However, a synergistic effect was found when ammonia, lactic acid and the carboxylic acids were applied as a blend. Our findings indicate that An. gambiae s.s. relies on the combination of ammonia, lactic acid and carboxylic acids in its orientation to human hosts. The role of lactic acid in this tripartite synergism differs from that reported for the yellow fever mosquito Aedes aegypti.     

Ammonia as an attractive component of host odour for the yellow fever mosquito, Aedes aegypti

Behavioural responses of Aedes aegypti mosquitoes to ammonia were investigated in a modified Y-tube olfactometer. Ammonia was attractive in concentrations from 17 ppb to 17 ppm in air when presented together with lactic acid. Aqueous solutions of ammonia salts in concentrations comparable to those found in human sweat also increased the attractiveness of lactic acid. The role of lactic acid as an essential synergist for ammonia became further apparent by the fact that ammonia alone or in combination with carbon dioxide was not effective, even though the synergistic effect of carbon dioxide and lactic acid was corroborated. An extract from human skin residues, which attracts approximately 80% of the tested mosquitoes, contains both lactic acid and ammonia. The combination of these compounds, however, attracts no more than 45%, indicating that other components on human skin also play a role in host finding. Preparative liquid chromatography of the skin extract yielded three behaviourally active fractions which work together synergistically. Fraction III contains lactic acid as the effective principle; the compositions of the other two have not been clarified yet. The attractiveness of fraction I was augmented considerably when ammonia was added, whereas the effect of fraction II was not influenced by ammonia. These results suggests that ammonia is part of the effective principle of fraction II and contributes to the attractive effect of host odours.     

The effect of lactic acid on odour-related host preference of yellow fever mosquitoes.

In a behavioural study we have investigated the role of lactic acid for the host preferences of yellow fever mosquitoes (Aedes aegypti) by comparing the attractiveness of rubbings from the hands of different human individuals and extracts obtained from skin rubbings from different mammals (Bos primigenius f. taurus, Capra aegagrus f. hircus, Felis silvestris f. catus and Homo sapiens). Certain human individuals were consistently more attractive to mosquitoes than others. Addition of lactic acid markedly increased the degree of attractiveness of formerly less attractive human odour samples and they were preferred over those which were originally the most attractive. There was almost no response to animal odour samples. In contrast to human samples, which contain a high amount of lactate, this compound could not be detected in samples from animals. When skin emanations from animals were combined with lactic acid, however, as many mosquitoes responded to odour samples of B. primigenius f. taurus and C. aegagrus f. hircus as did to human odours. All these data demonstrate that olfactory-based host preference of the anthropophilic mosquito A. aegypti is to a large extent due to differences in the amount of lactic acid in the odour samples.     

An efficient conversion of carboxylic acids to one-carbon degraded aldehydes via 2-hydroperoxy acids

After the formation of dianions of a carboxylic acid with lithium diisopropylamide, oxygen was bubbled into the solution to produce 2-hydroperoxy acid. Then the reaction mixture was acidified with a 2 N HCl solution and subsequently elevated to 50 degrees C to afford the aldehyde with the loss of one carbon atom. Even saturated (C(10)-C(20)) and unsaturated (C(18:1)) carboxylic acids were converted into the odd aldehydes (C(9)-C(19), C(17:1)) in high yields. This conversion was found to be an efficient method for the preparation of carboxylic acids (Cn) to one-carbon degraded aldehydes (Cn-1) via 2-hydroperoxy acids.     

Behavioural mode of action of deet: inhibition of lactic acid attraction

Using the mosquito Aedes aegypti in a novel olfactometer that measures movement towards and away from a stimulus, we could not confirm that 'deet' is a repellent of mosquitoes. In the absence of a host, deet was an attractant and in the presence of a host, it was an inhibitor of attraction. This inhibition occurred in the gaseous phase and was therefore not the result of the physical properties of deet. We determined that L-lactic acid, a component of human sweat that is an attractant to mosquitoes, is the target of this inhibition, implying that lactic acid may be a bottleneck in the behavioural cascade preceding blood-sucking.     

Substrate specificity of regiospecific desaturation of aliphatic compounds by a mutant Rhodococcus strain

Substrate specificity of cis-desaturation of alipahtic compounds by resting cells of a mutant, Rhodococcus sp. strain KSM-MT66, was examined. Among substrates tested, the rhodococcal cells were able to convert n-alkanes (C13-C19), 1-chloroalkanes (C16 and C18), ethyl fatty acids (C14-C17) and alkyl (C1-C4) esters of palmitic acid to their corresponding unsaturated products of cis configuration. The products from n-alkanes and 1-chloroalkanes had a double bond mainly at the 9th carbon from their terminal methyl groups, and the products from acyl fatty acids had a double bond mainly at the 6th carbon from their carbonyl carbons.     

Behavioural responses of Anopheles gambiae sensu stricto to components of human breath, sweat and urine depend on mixture composition and concentration

Host-seeking behaviour of the anthropophilic malaria vector Anopheles gambiae sensu stricto (Diptera: Culicidae) is mediated predominantly by olfactory cues. Several hundreds of odour components have been identified from human emanations, but only a few have been proven to act as attractants or synergists in the host-seeking behaviour of female An. gambiae. In previous work, aromatics, alcohols and ketones in human odours were found to elicit electrophysiological activity in antennal olfactory neurons of female An. gambiae. However, the behavioural effects of these compounds have not been investigated. In this study, behavioural responses of female An. gambiae to components of human breath, urine and sweat at a series of concentrations, or a single concentration in the case of acetone, were examined in combination with ammonia and L-lactic acid in a dual-choice olfactometer. The results showed that at specific concentrations 4-ethylphenol, indole, 3-methyl-1-butanol and two ketones inhibited the attractive effect of a mixture of ammonia and lactic acid. Acetone on its own was not attractive; however, when combined with lactic acid, the binary mixture was attractive. When combined with ammonia, acetone inhibited the attractiveness exerted by ammonia alone. Dodecanol and dimethyldisulphide did not affect the attraction exerted by ammonia and lactic acid at any of the concentrations tested. By contrast, a human-specific armpit odour, 7-octenoic acid, augmented the attraction exerted by the combination of ammonia and lactic acid at a specific dosage.     

Substrate Specificity of Regiospecific Desaturation of Aliphatic Compounds by a Mutant Rhodococcus Strain

Substrate specificity of cis-desaturation of alipahtic compounds by resting cells of a mutant, Rhodococcus sp. strain KSM-MT66, was examined. Among substrates tested, the rhodococcal cells were able to convert n-alkanes (C13-C19), 1-chloroalkanes (C16 and C18), ethyl fatty acids (C14-C17) and alkyl (C1-C4) esters of palmitic acid to their corresponding unsaturated products of cis configuration. The products from n-alkanes and 1-chloroalkanes had a double bond mainly at the 9th carbon from their terminal methyl groups, and the products from acyl fatty acids had a double bond mainly at the 6th carbon from their carbonyl carbons.     

Orientation behaviour of the blood-sucking bug triatoma infestans to short-chain fatty acids: synergistic effect of L-lactic acid and carbon dioxide

The role of short-chain fatty acids in the host-seeking behaviour of Triatoma infestans larvae was investigated using a locomotion compensator. Several short-chain fatty acids were tested alone over a wide range of doses, or in combination with L-lactic acid (L-LA; 100 microg). Bugs showed no attractive response to single carboxylic acids, but when L-LA was added to airstreams carrying specific intensities of either propionic (C3; 100 microg), butyric (C4; 1 microg) or valeric acid (C5; 1 microg), these mixtures elicited an attractive response, evincing a synergistic effect. No orientation response was observed when caproic acid (C6) was offered with L-LA at the doses tested. Two blends were created: (1) C3, C4 and C5 combined at the effective doses when added with L-LA [C3C4C5 (1)], and (2) C3, C4 and C5 combined at a third of those intensities [C3C4C5 (2)]. Both blends were tested alone, with L-LA (100 microg), with a sub-threshold concentration of CO(2) (300 p.p.m. above the ambient level), and combined with both compounds together. Oriented responses of bugs were only observed with the blend (2) added with L-LA and with the combination of this lure with CO(2). This last combination evoked a behavioural response similar in intensity to that induced by a live mouse.     

An investigation of the use of recovered vegetable oil for the preparation of starch thermoplastics

The main components (90%) in recovered vegetable oil (RVO) are esters of higher carboxylic acids and glycerol (triglycerides) which consist of three fatty acids: oleic (C18:1, Z), palmitic (C16:0) and linoleic (C18:2, Z) in the ratio 2.8:1.4:1. RVO may provide a low cost new supply of unsaturated fatty acid chlorides. Modification of potato starch using the mixture of fatty acid chlorides derived from RVO and using acid chlorides of the two major pure component acids has been performed. Films were prepared from the starch esters and mechanical properties tested. Commercially available potato starch, modified to DS-value 1.5 with RVO-derived acyl chlorides, was thermoplastic with a maximum tensile strength of 1.4 MPa and an elongation at break of 54%.     

A novel attractant for Anastrepha ludens (Diptera: Tephritidae) from a Concord grape product

An attractant for Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: Tephritidae), was developed from a commercial product called Sabor Uva containing processed Concord grape juice. The principal volatile components of Sabor Uva aroma were identified and an aqueous mixture of 15 components that was gas chromatographically similar to Sabor Uva was prepared. This mixture was equivalent to Sabor Uva in attractiveness by using wind-tunnel bioassays. After deleting chemicals that did not contribute to attractiveness, and increasing the concentrations of the remaining chemicals, the final attractant contained propylene glycol (90,000 ppm, vol/vol), acetic acid (4500), methyl anthranilate (1800), ethyl 2-methylpropionate (670), and one or both of the esters ethyl 3-methylbutyrate (44) and 2-methylbutyl propionate (44), in aqueous solution. This mixture was approximately 1.8X as attractive as Sabor Uva by indirect comparison. Deletion of propylene glycol, acetic acid, methyl anthranilate, or ethyl 2-methylpropionate from the mixture significantly decreased attractiveness. Deletion of either of the other two esters seemed to diminish attractiveness although effects were not statistically significant. Deletion of water from the mixture significantly decreased attractiveness. We conclude that propylene glycol, acetic acid, methyl anthranilate, water, and at least one or as many as all three of the methyl-branched esters are essential for complete attractiveness.     

Evaluation of various carbon substrates for the biosynthesis of polyhydroxyalkanoates bearing functional groups by Pseudomonas putida

The ability of Pseudomonas putida to synthesize polyhydroxyalkanoate (PHA) from 36 different carboxylic acids containing various functional groups was examined. This bacterium did not utilize short carboxylic acids (C(4)-C(6)) containing bromine, methoxy, ethoxy, cyclohexyl, phenoxy, and olefin groups as the sole carbon substrate. No polymer was isolated from the cells grown with carboxylic acids bearing hydroxyl, amino, para-methoxyphenoxy, and para-ethoxyphenoxy groups regardless of the carbon substrate chain lengths used even when they were cofed with nonanoic acid. Of all the carbon substrates evaluated, only 6-para-methylphenoxyhexanoic acid, 8-para-methylphenoxyoctanoic acid, 8-meta-methylphenoxyoctanoic acid, 10-undecenoic acid, and 10-undecynoic acid supported both growth and the production of PHA containing the corresponding functional groups by P. putida. The present results indicate that the carbon availability of P. putida for growth and PHA production is significantly different from that of P. oleovorans.     

The effects of allatectomy and juvenile hormone replacement on the development of host-seeking behaviour and lactic acid receptor sensitivity in the mosquito Aedes aegypti

Host-seeking behaviour in newly emerged Aedes aegypti (L.) females is not expressed immediately after adult eclosion but develops gradually over a period of approximately 3-4 days. This development is accompanied by an apparent maturation of the antennal chemosensory afferent neurons involved in the detection of the airborne host attractant lactic acid. Since these events coincide in time with juvenile hormone-dependent previtellogenic ovarian growth and since the expression of other reproduction-associated behaviour has previously been shown to be dependent on juvenile hormone, the effects of juvenile hormone removal and replacement on the development of host-seeking behaviour and the response characteristics of the lactic acid-sensitive receptors were investigated. No effect of juvenile hormone removal by allatectomy or juvenile hormone replacement or augmentation by topical application of the juvenile hormone mimic methoprene was found. It was concluded that this hormone is not involved in the appearance of host-seeking behaviour or the apparent maturation of the lactic acid receptors that occurs during early imaginal life.     

Analysis of corynomycolic acids and other fatty acids produced by Corynebacterium lepus grown on kerosene.

The saponifiable carboxylic acids of the extracellular product of Corynebacterium lepus grown on kerosene have been isolated and characterized. About 25% of these acids were a mixture of simple, saturated fatty acids ranging from C13 to C24 and including both even and odd homologues. The distribution of these acids was bimodal, with maxima at C15 and C21. The other 75% of the acids was a mixture of corynomycolic acids [R1--CH(OH)--CH(R2)--COOH] ranging from C28 to C43. The R1 alkyl fragments varied from C16 to C25, and R2 fragments varied from C6 to C14. Both even and odd corynomycolic acid homologues were observed, and the distribution had a single pronounced maximum at C32 and C33. Bacterial utilization of the carboxylic oxidation products of the kerosene substrate is suggested to account for the wide distribution in chain length of these saturated fatty acids and for the observation of both even and odd homologues.     

Sweaty skin: an invitation to bite?

Anopheles gambiae sensu stricto and Aedes aegypti have a preference for human blood, which determines their importance as vectors of pathogens responsible for human diseases. Volatile organic chemicals are the principal cues by which humans are being located. Human sweat contains components that are attractive to anthropophilic mosquito species, and variation in sweat composition causes differential attractiveness to mosquitoes within and between individuals and also between humans and other mammals. Characteristics of skin glands and skin microbiota define the odorous organic compounds emitted by sweat, thereby the degree of attractiveness of the host to mosquitoes. Carboxylic acids in particular appear to characterize humans. Thus sweat-associated human volatiles are probably the primary determinant factor in the host preference of anthropophilic mosquitoes.     

Mechanisms of Carboxylic Acid Attraction in Drosophila melanogaster

Sour is one of the fundamental taste modalities that enable taste perception in animals. Chemoreceptors embedded in taste organs are pivotal to discriminate between different chemicals to ensure survival. Animals generally prefer slightly acidic food and avoid highly acidic alternatives. We recently proposed that all acids are aversive at high concentrations, a response that is mediated by low pH as well as specific anions in Drosophila melanogaster. Particularly, some carboxylic acids such as glycolic acid, citric acid, and lactic acid are highly attractive to Drosophila compared with acetic acid. The present study determined that attractive carboxylic acids were mediated by broadly expressed Ir25a and Ir76b, as demonstrated by a candidate mutant library screen. The mutant deficits were completely recovered via wild-type cDNA expression in sweet-sensing gustatory receptor neurons. Furthermore, sweet gustatory receptors such as Gr5a, Gr61a, and Gr64a-f modulate attractive responses. These genetic defects were confirmed using binary food choice assays as well as electrophysiology in the labellum. Taken together, our findings demonstrate that at least two different kinds of receptors are required to discriminate attractive carboxylic acids from other acids.     

Very long-chain phenylpropyl and phenylbutyl esters from Taxus baccata needle cuticular waxes

The cuticular wax of Taxus baccata L. needles was found to contain four different classes of long-chain esters that were identified by various chemical transformations with product assignment employing GC-MS. Homologous series of (1) 3-(4'-hydroxyphenyl)-propyl esters of C(20)-C(36) fatty acids, (2) 4-(4'-hydroxyphenyl)-2-butyl esters of C(18)-C(28) fatty acids, (3) 3-(3',4'-dihydroxyphenyl)-propyl esters of C(20)-C(32) fatty acids, and (4) 4-(3',4'-dihydroxyphenyl)-2-butyl esters of C(18)-C(28) fatty acids were identified. The four compound classes amounted to 0.1-3.6 micro g/cm(2) of needle surface area, corresponding to 0.2-7.6% of the wax mixture, respectively. While both phenylpropyl ester series had a maximum for the homolog containing tetracosanoic acid, in the phenylbutyl esters homologs containing eicosanoic and docosanoic acids predominated.     

不同居群无患子果实组成比较研究

无患子是一种广泛分布于我国南方的乔木,本文针对不同居群无患子全果的物理组成、种仁油脂及氨基酸组成等方面进行比较研究.福建无患子种仁含油率最高,达到42.8％;四川无患子种子含油率最高,达到13.7％.无患子油脂的脂肪酸碳链长度为C16～C24,其中C16～C20的脂肪酸均占92％以上,不饱和脂肪酸79％～85％.种仁氨...     

Determination of monoenoic fatty acid double bond position by permanganate-periodate oxidation followed by high-performance liquid chromatography of carboxylic acid phenacyl esters

This investigation was carried out to develop methods for a reverse-phase, high-performance liquid chromatography analysis of the monocarboxylic and dicarboxylic acids produced by permanganate-periodate oxidation of monoenoic fatty acids. Oxidation reactions were performed using [U-14C]oleic acid and [U-14C]oleic acid methyl ester in order to measure reaction yields and product distributions. The 14C-labeled oxidation products consisted of nearly equal amounts of monocarboxylic and dicarboxylic acid (or dicarboxylic acid monomethyl ester), with few side products (yield greater than 98%). Conversion of the carboxylic acids to phenacyl esters proceeded to completion. HPLC of carboxylic acid phenacyl esters was performed using a C18 column with a linear solvent gradient beginning with acetonitrile/water (1/1) and ending with 100% acetonitrile. Excellent resolution was achieved for all components of a mixture of C5 through C12 monocarboxylic acid phenacyl esters and C6 through C11 dicarboxylic acid phenacyl esters. Resolution was also achieved for all components of a mixture of C5 through C12 monocarboxylic acid phenacyl esters and C6 through C11 dicarboxylic acid monomethyl, monophenacyl esters. The resolution obtained by HPLC demonstrates that, for a wide range of monoenoic fatty acids, both products of a permanganate-periodate oxidation can be identified on a single chromatogram. Free fatty acids and fatty acid methyl esters were analyzed with equal success. Neither the oxidation nor the esterification reaction caused detectable hydrolysis of methyl ester. The method is illustrated for free acids and methyl esters of 14:1 (cis-9), 16:1 (cis-9), 18:1 (cis-6), 18:1 (cis-9), and 18:1 (cis-11).