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.

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.

Mathematical models of the effectiveness and persistence of mosquito repellents.

Two models of the effectiveness and persistence of mosquito repellents on the skin were developed from published functions and data. The probit plane model, Y = a + b1X1 + b2X2, relates the response (Y, in probits) of the mosquito test population to the log dose (X1) of repellent applied and the test period, or elapsed time from the time of application (X2). The exponential decay model, Z = X1 + (b2/b1)X2, estimates the repellent residue (log-1 Z) from X1 and X2. The models were validated with original data from tests of deet (N,N-diethyl-3-methylbenzamide) and ethyl hexanediol (2-ethyl-1,3-hexanediol) on the forearm against the yellow fever mosquito, Aedes aegypti. The probit plane model was evaluated as Y = 8.83 + 1.56 X1-0.69X2 for deet and Y = 8.67 + 1.68X1 - 0.92X2 for ethyl hexanediol when X1 is in log mg/cm2 and X2 is in hours. The exponential decay model was evaluated as Z = X1 - 0.45X2 for deet and Z = X1 - 0.55X2 for ethyl hexanediol. The decay constant (lambda) and half-life (t1/2) were estimated as 1.03 hr-1 and 0.67 hr for deet and 1.26 hr-1 and 0.55 hr for ethyl hexanediol from the slope parameter (b2/b1) of the decay model. Applicable correlation coefficients, standard errors and confidence limits are given. The introduction of these models of the pharmacodynamics of mosquito repellents is a step toward establishing a rational basis for the research, development, testing and evaluation of repellents and for their regulation by the government.(ABSTRACT TRUNCATED AT 250 WORDS)