Bioassays repellency

More recendy the cis and trans isomers of the mosquito repellent CIC-4, a mixture of citroneUa isomers, have been separated by preparative hplc and bioassayed for effectiveness (23). Chiral-phase capillary gas chromatography and mosquito repellent activity of some oxazoUdine derivatives of (+)-and ( —)-citroneUal have been studied to find stmcture—activity relationships (24). Several 2-aLkyl- -acetyloxahdines have been synthesized and tested against mosquitoes, with further efforts using nmr to determine the rotational isomers of the more active N-acetyl-2,2-dimethyloxazohdine (25). 

Bioassay of alternate molecular forms supports the view that the ORs are capable of resolving isomeric distinctions in neutral (non-biological) odourants. Stereochemical pairs of odours were tested for differential sensitivities in the blind subterranean mole rat (Spalax ehrenbergi). The subjects responded to one enantiomer, but not to its stereoisomer. Both sexes were attracted to the odour of R-(-)-carvone but unresponsive to S-(+)-carvone in contrast, males and females were repelled by the odour of (+)-citronellol, but not by (-)-citronellol (Heth et al., 1992). The lack of responsiveness by mole rats could be central due to lack of salience, or peripheral due to hyposmia/anosmia for one isomer. Both carvones have distinct odours for the human nose. 

In Alloxysta victrix, 6-methylhept-5-en-2-one 16, which is produced by both males and females, was identified as potentially attractive to the males and slightly repellent to the females in Y-tube olfactometer assays [60]. In this study, the activity was also dependent on prior exposure of the insects to the compound. Naive insects responded more strongly than previously exposed ones. This underscores a second difficulty in the bioassay-guided identification of parasitoid hymenopteran pheromones the responses are very dependent on the context and on prior exposure. Learning has been demonstrated in several species of parasitic hymenoptera [61-65]. 

The problem is much more difficult when the defensive compounds are distributed throughout the insect body and no clues are available as to which type of compounds are present. In this case, a H NMR spectrum on the insect total extract will usually not be helpful, and a reliable bioassay is needed to follow the biological activity through the fractionation process. Repellency bioassays using ants [9] or spiders [10] have been successfully used for this purpose. Chemotaxonomy can also be very helpful, as taxonomically related insects tend to produce the same kind of defensive chemicals. Thus, once the latter have been identified for a few species, the study of other species belonging to the same group is usually much simplified. A good example is provided by coc-... 

Numerous additional examples of the evaluation of plant essential oils as insect repellents exist in the literature however, rarely are bioassay-guided fractionations performed to determine the constituents responsible for the activity of these plant essential oils. When attempts are made to identify active constituents, they are often of a non-systematic manner and usually focus on those constituents that are commercially available or the major constituents. Such approaches have the potential of missing unusual or novel structural types which could be highly active compounds with the potential for commercial development. 

Of the three compounds isolated, piplaroxide and demethoxypiplartine (Fig. 7) demonstrated significant activity in a laboratory bioassay measuring repellency to the leafcutter ant Atta cephalotes. 

A listing of compounds evaluated in the laboratory as cockroach repellents summarizes 872 synthetic compounds out of 901 bioassayed from 1953 to 1974 (43). Fencholic acid [512-77-6] (3-isopropyl-l-methylcyclopentanecarboxylic acid) has been used as a standard repellent in tests conducted by placing 20 cockroaches in a glass crystallizing dish without food and water and offering them a choice of two cardboard shelters, one of which was treated with 1 or 2 ml, of a 1% solution of the candidate in acetone. Counts were made daily for seven days. 

As shown by bioassays, the karyorelictid ciliate Loxodes striatus may release toxin-containing yellow-brown extrusomes, which repel predators such as Dileptus (Ciliata) and Stenostomum (Turbellaria).32... 

The results of the boll weevil antifeedant bioassays with anthrani-lic acid, gentisic acid, senecioic acid, cinnamaldehyde and cinnamic acid are presented in Table II. Camphor was not bio-assayed due to its extreme volatility. However camphor is a known moth repellent (8) and is probably a boll weevil antifeedant since the fraction from which it was isolated was active. 

Here we review our research results concerning zoospore attractants, repellents, cytotoxins and inhibitors of zoospore motility together with bioassay systems to survey chemical regulators toward zoospores. The first part of this review described some new findings on the effects of host-specific plant signals on chemotaxis and differentiation of oomycete zoospores. The potential role and mode of action of nonhost secondary... 

Compounds 19 and 20 along with some acylated phosphatidic derivatives in addition to 1,2-dioleoylphosphatidic acid, were tested using the particle bioassay [83]. Commercially available l-oleoyl-2-lysophosphatidic acid (21) possessed repellent activity which was enhanced by monomethylation. When A. cochlioides zoospores were pre-treated with an excess of the natural stimulant N-frans-feruloyltyramine (19), and then exposed to Chromosorb W AW particles coated with various test compounds, it was found that 1 -oleoyl-2-lysophosphatidic (21, 100 ppm) and its monomethyl ester (22) (10 ppm), as well as the natural repellent 1-linoleoyl-2-lysophosphatidic acid monomethyl ester (20, 30 ppm), effectively inhibited zoospore motility [83], However, l-oleoyl-2-lysophosphatidic acid dimethyl ester (23) and 1,2-dioleoylphosphatidic acid tested with and without the stimulant (19) showed neither repellent nor motility inhibitory activity. The bioassay revealed that compounds possessing repellent activity are monoacylated phosphatidic acid derivatives containing at least one hydroxy group on the phosphoryl unit [83]. 

Endocrine disrupters (e.g., bisphenol A) are supposed to be the pollutants in our environment and pose a serious concern in human health. The minute amount of these compounds in our environment is difficult to detect mainly due to lack of a simple and sensitive bioassay method. In the present study, the estrogenic and repellent activities of known estrogenic compounds revealed to be correlated. The particle bioassay method is very simple and... 

For many years, the U.S. Department of Agriculture conducted a research program to identify attractants and repellents by bioassaying plant extracts and synthetic compounds, many related to known plant compounds. Attractants for the Mediterranean fruit fly, oriental fruit fly, and Japanese beetle and many others were selected as the result of these programs and widely used. 

In view of the reported deterrent activities of Solenopsis and Monomorium venoms under field conditions (1, IJ., 12), it seemed worthwhile to evaluate the comparative repellencies to ants of some of these venom-derived alkaloids. In this investigation, the deterrency of these nitrogen heterocycles to a variety of ant species was determined by using a feeding bioassay in which the reactions of hungry ant workers to alkaloid-treated food were quantified Selection of a variety of aggressive ant species... 

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