A rapid spectrophotometric method for the monitoring of embryonic development in Boophilus decoloratus (Koch, 1844) is described. The method is based on a quantitative assessment of guanine, the principal end-product of nitrogenous metabolism in ticks, which is gradually built up and stored in the rectal sac during embryonic development of the larvae. A study of the growth of tick embryos under constant temperature conditions and 6 different humidity conditions demonstrated that embryonic development was dependent on the water content of the eggs at the time of oviposition. When eggs lost more than 35% of their initial mass through evaporation, nitrogenous metabolism (as indicated by guanine production) was seriously affected and embryos died.
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