RESUMEN
In Mexico, the use of repellents to prevent insects from landing and biting is a common practice. However, variation in the efficiency of natural and synthetic repellents has been observed. In this study, we evaluated the repellency and protection time of 16 synthetic and 13 natural-based commercial products against Aedes aegypti (L.) from an endemic dengue area (Jojutla, Morelos) in Central Mexico. The "arm exposure" cage test was used to assess the efficacy of the repellents. Tests were conducted by three adult volunteers. Results showed that DEET (N, N-Diethyl-3-methylbenzamide) repellents provided the highest protection and duration times against Ae. aegypti. However, low repellency and short-time protection was observed (when compared with the manufacturers' protection times). Natural-based products did not repel (either landing or biting) mosquitoes for >30 min. These results show that most of the repellent products did not provide satisfactory levels of personal protection against mosquito bites. Frequent reapplication of repellents (synthetic and natural-based) may compensate for their short duration of action. Repellent efficacy data must be integrated into the decision-making process for an optimal response to the local (or specific region) situation.
Asunto(s)
Aedes , Mordeduras y Picaduras de Insectos/prevención & control , Repelentes de Insectos , Mosquitos Vectores , Animales , Femenino , MéxicoRESUMEN
We evaluated the effect of 3 sublethal concentrations of Cd (as CdCl(2), 209.50, 104.75 and 52.38 microg/L) and Zn (as ZnCl(2), 283.88, 141.94 and 70.97 microg/L) separately and together on the population growth of the common Mexican brachionid rotifer Brachionus havanaensis using 1 x 10(6) cells/mL of Chlorella vulgaris as the algal diet. The LC(50) (24-h bioassay conducted in the absence of food) for B. havanaensis was 419.0 +/- 8.1 microg/L for Cd and 2271.0 +/- 404.4 microg/L for Zn. The effect of different concentrations of Cd or Zn on the population growth of B. havanaensis showed decreased population abundance with increasing levels of the metal concentration in the medium. However, for Cd even at the highest tested concentration (i.e., 50% LC(50), 209.5 microg/L), there was some increase in the abundance of B. havanaensis, although much lower than in controls. On the other hand, for Zn at highest tested concentration (i.e., 12.5% LC(50), 283.88 microg/L), the population of B. havanaensis showed little growth and remained close to the initial density. Under the conditions of mixed metal exposure, B. havanaensis did not grow at the highest tested concentrations of Cd+Zn combination. The rate of population increase (r) varied from 0.11 to 0.43 per day, depending on the heavy metal concentration. Statistically r was adversely influenced by the heavy metal concentration in the medium. Tests of multiple comparisons indicated that r at the lowest level of Cd or Zn (alone or mixed) was not significantly different from controls. Our data from the acute toxicity tests showed that Cd was 5 times more toxic than Zn to B. havanaensis but this difference was much reduced based on the chronic toxicity studies.