Evaluation of an in vitro bloodfeeding system for testing mosquito repellents.

Median effective doses and 95% effective doses of 9 commercial mosquito repellents were determined for the yellow fever mosquito, Aedes aegypti, in an in vitro bloodfeeding test system and on the human forearm. Results obtained in the 2 test systems did not differ significantly but, because of the inherent variability of repellent test data, did not always agree closely. Potential modifications of in vitro bloodfeeding test systems for increased accuracy, precision, and reliability are discussed.

Variation in the protection periods of repellents on individual human subjects: an analytical review.

Mosquito repellent test data from the literature were analyzed to estimate mean protection periods and among-subjects standard deviations. Standard deviations were a linear function of the means. Numbers of subjects needed to determine mean protection periods of 1-8 h with confidence limits of +/- 0.5, 1.0, 1.5, and 2.0 h at the 99 and 95% levels of confidence were computed from regression values of the standard deviation, and a table of sample sizes was constructed for use in planning repellent tests.

Responses of male and female mosquitoes to repellents in the World Health Organization insecticide irritability test system.

A study was conducted to compare responses of male and female Aedes aegypti (Linn.) and Aedes taeniorhynchus (Wiedemann) to 9 olfactory repellents in the World Health Organization insecticide irritability test system. An irritant insecticide (permethrin) and a control were included for comparison. Aedes aegypti exhibited significantly more takeoffs than Ae. taeniorhynchus, and female mosquitoes exhibited significantly more takeoffs than males. Permethrin induced significantly more takeoffs than the control, but olfactory repellents did not. Certain 2- and 3-factor interactions of test materials, species, and sexes were statistically significant. This study supports a previous conclusion that the World Health Organization test method does not measure contact repellency (irritancy) and olfactory repellency equally.

Effect of skin abrasions on the efficacy of the repellent deet against Aedes aegypti.

Abrasion of repellent-treated human skin affected the efficacy of a sustained-release insect repellent containing N,N-diethyl-3-methylbenzamide (deet) against bites of Aedes aegypti. Skin treated with repellent when abraded up to 30 times showed significantly lower protection than unabraded skin against mosquito bites for 10 h. The mean value of the kinetic coefficient of friction during skin abrasion by clothing (battle dress uniform fabric) for repellent-treated skin (0.159 +/- 0.003) was significantly higher than untreated skin (0.122 +/- 0.005). Repellent-treated skin appeared stickier than the untreated skin. An increase in the number of skin abrasions by clothing resulted in a reduced duration of protection against mosquito bites.

Evolution of repellent tolerances in representative arthropods.

Eight commercial insect repellents were tested against Ornithodoros parkeri (Acari: Argasidae), Dermacentor variabilis (Acari: Ixodidae), Aedes aegypti (Diptera: Culicidae), and Xenopsylla cheopis (Siphonaptera: Pulicidae). Patterns of tolerance to the test materials were distinctive for each test species. Levels of tolerance were coded as character state 0 (sensitive), 1 (intermediate), or 2 (tolerant) and mapped on a cladogram reflecting the accepted classification of the test species. Character state 0 was regarded as primitive, as indicated by the ontology of repellent tolerances in ticks. Aedes aegypti was least evolved and X. cheopis was most evolved in tolerance to repellents. Multiple parallelism of the arachnid and X. cheopis lines occurred in the evolution of the observed tolerances.

U.S. Army soldiers' perceptions of arthropod pests and their effects on military missions.

A survey was conducted to determine the effects of biting and stinging arthropods on military personnel, operations, and training. Nearly 70% of respondents reported experiencing problems attributable to arthropods. Arthropods obstructed movement and field position, prevented concealment and cover, disrupted maneuvers, and caused panic. Twenty percent of respondents reported attendance at sick call for treatment of bites or stings, and 4% were hospitalized or assigned to quarters. Median lost time was 2 days. Bee, wasp, and ant stings and spider and chigger bites were the most frequent causes of lost time. Additional training on biting and stinging arthropods, use of repellents and other personal protective measures, first aid for bites and stings, and conditions requiring medical attention is needed in field units to enhance mission performance and reduce time lost because of arthropods. Materials for treatment of bites and stings should be included in first-aid kits issued for field use.

Evaluation of controlled-release mosquito repellent formulations.

Eight polymer and 9 microcapsule formulations of deet were tested on laboratory rabbits against Aedes aegypti and Anopheles albimanus. Several formulations were significantly more effective than simple (unformulated) deet at the same strength for periods up to 24 h. Best results were obtained with a polymer formulation containing a high molecular weight fatty acid and 3 microcapsule formulations containing lanolin, gum arabic, gelatin, tannic acid, stearic acid, polypropylene glycol, water, and a commercial lotion in the microcapsule and carrier fractions.

Evaluation of the laboratory rabbit model for screening topical mosquito repellents.

The laboratory rabbit was evaluated as a model for screening topical mosquito repellents, using data obtained in tests of deet (N,N-diethyl-3-methylbenzamide) against Aedes aegypti on humans and rabbits. Host-specific differences in the action of the test material were quantified by multiple regression analysis. The test material was less effective but more persistent in tests on rabbits, and responses of the mosquito test population were more variable.

Evaluation of the laboratory mouse model for screening topical mosquito repellents.

Eight commercial repellents were tested against Aedes aegypti 0 and 4 h after application in serial dilution to volunteers and laboratory mice. Results were analyzed by multiple regression of percentage of biting (probit scale) on dose (logarithmic scale) and time. Empirical correction terms for conversion of values obtained in tests on mice to values expected in tests on human volunteers were calculated from data obtained on 4 repellents and evaluated with data obtained on 4 others. Corrected values from tests on mice did not differ significantly from values obtained in tests on volunteers. Test materials used in the study were dimethyl phthalate, butopyronoxyl, butoxy polypropylene glycol, MGK Repellent 11, deet, ethyl hexanediol, Citronyl, and dibutyl phthalate.

Studies on the inheritance of repellent tolerances in Aedes aegypti.

Two laboratory strains and 6 inbred strains of Aedes aegypti were tested against deet, ethyl hexanediol, dimethyl phthalate, and Indalone. Reciprocal crosses and backcrosses of 2 inbred strains were tested against deet only. Results obtained were compatible with a quantitative genetic model in which the effects of the factors involved were multiplicative. Certain inbred strains differed significantly from cognate laboratory and/or inbred strains in tolerance to one or more test materials. Heritability in the broad sense (H2) was estimated at 0.05 for deet, 0.22 for ethyl hexanediol, 0.48 for dimethyl phthalate, and 0.51 for Indalone. Partial dominance was observed in the inheritance of tolerance to deet.

Role of repellents in vector control and disease prevention.

Repellents are an inexpensive and practical means of protection against nuisance and disease vector arthropods in conjunction with or when other control measures are not feasible. Appropriate selection of skin and/or clothing repellents along with proper wear of clothing can provide adequate protection from biting arthropods, and are available in a wide variety of forms including lotions, creams, foams, soaps, aerosols, sticks, and towellettes. A coordinated effort among different research groups associated with advances in the science of insect repellents such as mode of action information, doses of repellents to generate threshold level responses and controlled release delivery mechanisms, may help in understanding the mechanisms by which repellents work. This in turn may revolutionize the development of repellents for personal protection and their use in vector control.

Compatibility of army face paint and insect repellent formulation.

The compatibility studies of a new controlled-release repellent formulation (NSN 6840-01-284-3982, insect repellent personal application) and a new camouflage face paint (NSN 6850-01-262-0635) indicated that the repellent did not interfere with the use of face paints when repellent was applied first, and the face paints did not reduce the effectiveness of the repellent against mosquitoes.

Laboratory observations on mating and leklike aggregations in Lutzomyia longipalpis (Diptera: Psychodidae).

The mating behavior of the sand fly, Lutzomyia longipalpis, was studied under laboratory conditions. Male sand flies landed on the bodies of anesthetized mice, where they exhibited leklike displays such as wing fanning, parading, and aggression. Lek behavior was more frequent in older males, and dominance hierarchies were established. Male sand flies at leks copulated more frequently than male sand flies at other locations in the cage. Females mated by older males produced more eggs than did females mated by younger males; however, there was no difference in the number of larvae produced.

Controlled release repellent formulations on human volunteers under three climatic regimens.

Two controlled-release repellent formulations containing 33% (3M) and 42% (Biotek) deet and an Army repellent containing 75% deet were evaluated in 3 different climatic regimens (tropical forested, tropical open and basic hot environments). The 3 repellents provided similar protection for different time periods after application under all 3 climates against Aedes aegypti, Ae. taeniorhynchus and Anopheles stephensi whereas there was no difference in protection period against An. albimanus.

Attraction of mosquitoes to diethyl methylbenzamide and ethyl hexanediol.

Studies by prior workers have shown that insect repellents can act as attractants when present as low concentrations, deposits or residues. In the present study deet and ethyl hexanediol were tested in 2-fold serial doses from 1.9 X 10(-9) to 1.6 X 10(-2) mg/cm2 on the forearms of volunteers against colonized Anopheles albimanus, Aedes aegypti and Ae. taeniorhynchus. Both compounds were significantly repellent at the high end of the dose range, as expected. Neither was significantly attractant to An. albimanus in low doses. However, deet was significantly attractant to Ae. aegypti in the dose range 7.6 X 10(-9) to 1.2 X 10(-4) mg/cm2 and to Ae. taeniorhynchus in the dose ranges 1.9 X 10(-9) to 3.1 X 10(-8) mg/cm2 and 2.0 X 10(-6) to 2.5 X 10(-4) mg/cm2. Ethyl hexanediol was significantly attractant to Ae. taeniorhynchus in the dose range 1.9 X 10(-9) to 6.2 X 10(-5) mg/cm2. Based on these results and prior work of V.G. Dethier and C.N.E. Ruscoe, a model sequence of the effects of chemicals on insects with increasing dose was developed. It was concluded that the labels of commercial repellents should be amended to include instructions to wash off or reapply the repellent when it is no longer effective.

Resistance of permethrin to weathering in fabrics treated for protection against mosquitoes (Diptera: Culicidae).

Two different methods of treating cotton and nylon-cotton fabrics with permethrin were evaluated for protection from mosquito bites after laboratory weathering. Cotton fabric treated by the individual dynamic absorption method provided consistently better protection than cotton fabric treated by the aerosol method. The nylon-cotton fabric provided similar protection regardless of the treatment method. After weathering, the toxic effects of both types of permethrin-treated fabrics treated by both methods diminished much more rapidly than did the repellent effect. Low residual amounts of permethrin in the fabrics provided 85% protection from bites against Aedes aegypti (L.) and 93% protection against Anopheles stephensi Liston. Permethrin-treated fabrics were effective in providing protection from mosquito bites for long periods, even after exposure to weathering, and appear to be an effective means of reducing nuisance effects and disease transmission by mosquitoes.

Mutagenic potential of permethrin in the Drosophila melanogaster (Diptera: Drosophilidae) sex-linked recessive lethal test.

When permethrin was tested for mutagenicity in Drosophila melanogaster Meigen with the sex-linked recessive lethal test, it was nonmutagenic under conditions of this study. The frequencies of spontaneous mutation for permethrin and the negative control were 0.135% and 0.133%, respectively; the spontaneous mutation frequency for positive control was 12.6%. The difference between the mutation frequency of permethrin and the negative control was not significant.

Efficacy of diethyl methylbenzamide (deet) against Aedes dorsalis and a comparison of two end points for protection time.

The repellent deet (N,N-diethyl-3-methylbenzamide) was tested against the mosquito Aedes dorsalis in a coastal salt marsh in California. The experimental design incorporated a multiple regression model, sequential treatments and a proportional end point (95%) for protection time. The ED95 (95% effective dose) and 4-h ED95 were estimated at 0.05 mg/cm2 and 0.09 mg/cm2, respectively. The 0.05 mg/cm2 protection time and 0.10 mg/cm2 protection time were estimated at 0.2 h and 4.4 h. The decay constant and half-life were estimated at 0.17 h-1 and 4.1 h. The design and analysis of repellent field trials are discussed.

A field trial of ethyl hexanediol against Aedes dorsalis in Sonoma County, California.

The repellent ethyl hexanediol (2-ethyl-1,3-hexanediol) was tested against the mosquito Aedes dorsalis in a coastal salt marsh in California. The experimental design incorporated a linear regression model, sequential treatments and a proportional end point (95%) for protection time. The protection time of 0.10 mg/cm2 ethyl hexanediol was estimated at 0.8 h. This time is shorter than that obtained previously for deet (N,N-diethyl-3-methylbenzamide) against Ae. dorsalis (4.4 h).