Carl E. Schreck

Mosquito density, biting rate and cage size effects on repellent tests.

Mosquito biting rates and the mean duration of protection (in hours) from bites (MDPB) of Aedes aegypti and Anopheles quadrimaculatus, using the repellent ‘deet’ (N,N‐diethyl‐3‐methylbenzamide) on a 50 cm2 area of healthy human skin, were observed in small (27 l), medium (≈65 l) and large (125 l) cages containing low, medium or high densities of mosquitoes: respectively, 640, 128 or 49 cm3 of cage volume per female. At the initial treatment rate of ≈ 0.4 μl/cm2 (1 ml of 25% deet in ethanol on 650 cm2 of skin), the MDPB for deet against Ae.aegypti ranged from 4.5 to 6.5 h and was significantly less (5.0 ± 0.8 h) in large cages compared with medium (6.2 ± 0.9 h) and small (6.2 ± 0.8 h) cages, regardless of the density. Against An.quadrimaculatus the MDPB for deet 0.4 μl/cm2 was 1.5–8.0 h, less in small (3.7 ± 2.3 h) and large (2.2 ± 1.1 h) cages at medium (3.7 ± 2.3 h) and high (2.5 ± 1.7 h) mosquito densities, and was longest in medium cages (6.2 ± 2.6 h) at low mosquito densities (5.8 ± 2.8 h). With equinoxial photoperiodicity (light on 06.00–18.00 hours) the biting rate was influenced by the time of observation (08.00, 12.00, 16.00 hours) for Ae.aegypti but not for An.quadrimaculatus. For both species, the biting rate was inversely proportional to mosquito density and the MDPB. The shortest MDPBs were obtained in large cages with high densities of mosquitoes and longest protection times occurred in medium sized cages with low mosquito densities.

Evaluations of permethrin-impregnated clothing and three topical repellent formulations of deet against tsetse flies in Zambia

ABSTRACT. Permethrin‐impregnated clothing and three topical repellent formulations of deet (diethyltoluamide) were field tested against natural populations of tsetse flies, mostly Glossina morsitans centralis Machado, in central Zambia. Volunteers wore different combinations of clothing impregnated with permethrin 0.125 mg ai/cm2 and repellents while riding in a vehicle that was driven slowly (4–6 km/h), with the windows and rear door open, through fly‐infested areas. The mean rate of tsetse bites was about twenty per 75 min for unprotected people. The treatment combination of permethrin‐impregnated clothing (blue cotton coveralls) and either of two controlled‐release deet formulations on exposed skin of face and arms provided 91% mean protection, but this was not significantly better (P>0.05) than wearing deet repellent alone (76–87% protection). No significant differences of protection were observed between the three repellent treatments, although the two controlled‐release formulations (intended to be more persistent) were applied at approximately half the dosage of the standard 75% deet. Wearing permethrin‐impregnated coveralls alone provided relatively poor protection (34%) for the untreated and exposed skin of head and hands. However, olive drab mesh jackets treated with permethrin reduced the tsetse biting rate by 75%.

Synthesis and Mosquito Repellent Properties of 2,2‐Dialkyl‐ and 2‐Alkyl‐4,4‐dimethyl‐N‐acetyloxazolidines

Nineteen novel N-acetyl-2,2-dialkyloxazolidines (2) and N-acetyl-2-alkyl-4,4-dimethyloxazolidines (3) were synthesized from commercially available carbonyl compounds and ethanolamine or 2-amino-2-methyl-1-propanol. Their bioactivity against laboratory-reared mosquitoes was compared in patch tests to known N-acetyl-2-alkyloxazolidines (1) and N,N-diethyl-m-toluamide (deet insect repellent). Isomeric composition measurements by [ 13 C]NMR spectroscopy favoured the Z rotational isomer for samples of 2 (91-96% Z) and the E rotational isomer for samples of 3 (66-71% E), in agreement with molecular mechanics calculations on rotational isomers of model oxazolidines. Samples of 1 were previously shown to exist in solution mostly as the Z isomer (60-70% Z). Within the optimal molecular weight range for these experimental chemicals, the duration of repellency against Aedes aegypti (L.), Anopheles quadrimaculatus Say and Anopheles albimanus Wiedemann generally followed the order : 1 > 2 > deet > 3. Bioassay data are discussed in relation to the equilibrium populations of rotational isomers for substituted N-acetyloxazolidines.

Comparison of Four Cinchoninates, an Oxetanone, and Two Standard Skin Repellents against Aedes Aegypti and Stomoxys Calcitrans

Five compounds (50% solutions in ethanol) were evaluated as skin repellents against caged Aedes aegypti (L.) and Stomoxys calcitrans (L.) by comparing the protection times obtained with the protection times obtained with 2 standard repellents, deet (25% solution in ethanol) and dimethyl phthalate (50% solution in ethanol). Against mosquitoes, the deet was significantly more effective than the candidate compounds or than dimethyl phthalate, and dimethyl phthalate was equal in effectiveness to the 4 cinchoninates and was less effective than 4-pentyl-2-oxetanone, which had a disagreeable odor. In the tests with Stomoxys calcitrans, 4-pentyl-2-oxetanone as a 50% solution in ethanol was more effective than deet and the other repellents; also, ethyl 3-ethylcinchoninate and butyl 3-methylcinchoninate as 50% solutions were about as effective as deet, buy ethyl 3-methylcinchoninate was only about half as effective as deet, and propyl 3-methylcinchoninate and dimethyl phthalate were the least effective.

Separation of cis and trans isomers from a mosquito repellent, CIC-4, via semi-preparative high-performance liquid chromatography and the repellent effect of each☆

Abstract CIC-4 (1,1,4,5,6,7,8,8a-octahydro-3H-2-benzopyran-3-one) is a fused bicyclic lactone which acts as a non-contact insect repellent for Aedes aegypti at 1% concentration in 95% aqueous ethanol when applied topically to rhesus monkeys. Chromatographic and spectroscopic analyses of a synthetic sample indicated the presence of cis-and trans-fused isomers. To supply each isomer for the assessment of mosquito repellent efficacy on humans, we developed a semi-preparative high-performance liquid chromatographic separation technique for the isomer separation. A column of 5-μm silica was used for isolating milligram quantities of each isomer. By this method, each isomer was obtained in > 95% gas-liquid chromatographic (GLC)-purity for biological evaluation. Supporting GLC and electron impact and chemical ionization gas chromatography-mass spectrometric data are also presented for each isomer. Biological evaluation on the human arm using Anopheles quadrimaculatus, Aedes aegypti, and Anopheles albimanus as the test species was effective in determining relative repellency to the standard N,N-diethyl-3-methyl-benzamide