Caffeine effect on mortality and oviposition in successive generations of Aedes aegypti

OBJECTIVE: Previous experiments showed that caffeine blocks the development of Aedes aegypti (Diptera, Culicidae) in the larval stage, consequently inhibiting the production of adults. This study aimed at obtaining data suggestive of caffeine resistance by these mosquitoes. METHODS: Experiments were carried out in successive generations to assess adult production from eggs laid in previous generation and oviposition rate in every generation using 200 and 500 µg/mL caffeine. Tap water was used as control. Experiments were conducted in the city of São José do Rio Preto, Southeastern Brazil between 2002 and 2005. Statistical tests consisted of exploratory data analysis and smoothing algorithms. RESULTS: Increasing reduction in productivity of adults occurred among generations at both caffeine concentrations but the differences were only significant at 200µg/mL caffeine. As for the oviposition rate, there was a decrease in the mean number of eggs per female over generations at both caffeine concentrations. CONCLUSIONS: There was no evidence of caffeine resistance over generations. The study results corroborate caffeine as an alternative as an important Ae. Aegypti control agent to avoid resistance.

The parasitism of Ixodes luciae (Acari: Ixodidae) on marsupials and rodents in Peruvian Amazon

In this work the infestation with I. luciae on Didelphimorphia and Rodentia in different environments of Peruvian Amazon was studied. Didelphimorphia was represented by the family Didelphidae. Specimens belonging to Caluromys lanatus, Didelphis marsupialis, Marmosops sp.2, Metachirus nudicaudatus, Philander andersoni and Philander opossum were infested with adults I. luciae and one Micoureus sp. was infested with larvae. In Rodentia, the infestation with I. luciae nymphs was restricted to Hylaeamys perenensis, Hylaeamys yunganus and Oligoryzomys microtis, while one Oecomys bicolor (all Cricetidae) was infested with larvae of this species. The few larvae were found on rodents captured in primary forest. The only significant difference (P < 0.05) in prevalence of adult ticks on Didelphimorphia was between P. andersoni and M. nudicaudatus (chi-square distribution). Adult tick distribution was significant different in P. andersoni in comparison with M. nudicaudatus, P. opossum and D. marsupialis (Kruskal-Wallis test). No significant effect of month or environment was detected in relation to adult tick infestation on Didelphimorphia. The prevalence of nymphal infestation as well as tick distribution showed that H. perenensis and H. yunganus were significantly more prone to be infested with nymphs of I. luciae than O. microtis. Prevalence of nymph infestation was higher in primary and secondary forest than rural areas while abundance was higher in secondary forest when compared with rural areas (P < 0.05). Kruskal-Wallis test showed differences (P < 0.05) for nymphal infestation during December in relation to January, March, April and June. The natural cycle of I. luciae appeared to be continuous, bound to adult tick infestation on Philander and nymphal infestation on Hylaeamys in forested environs.

Effects of caffeine on learning and memory in rats tested in the Morris water maze

We studied some of the characteristics of the improving effect of the non-specific adenosine receptor antagonist, caffeine, using an animal model of learning and memory. Groups of 12 adult male Wistar rats receiving caffeine (0.3-30 mg/kg, ip, in 0.1 ml/100 g body weight) administered 30 min before training, immediately after training, or 30 min before the test session were tested in the spatial version of the Morris water maze task. Post-training administration of caffeine improved memory retention at the doses of 0.3-10 mg/kg (the rats swam up to 600 cm less to find the platform in the test session, P<=0.05) but not at the dose of 30 mg/kg. Pre-test caffeine administration also caused a small increase in memory retrieval (the escape path of the rats was up to 500 cm shorter, P<=0.05). In contrast, pre-training caffeine administration did not alter the performance of the animals either in the training or in the test session. These data provide evidence that caffeine improves memory retention but not memory acquisition, explaining some discrepancies among reports in the literature.