Abstract
The somatic effects of caffeine were studied by using a rapidly proliferating insect developmental system. The results show that caffeine is a potent growth inhibitor of housefly larvae. Puparium formation is also severely affected, which suggests a caffeine effect on hormone‐controlled responses. Pupal mortality is marked when larvae are treated with higher concentrations of caffeine. The results indicate that caffeine may have several target sites of action; these are briefly discussed.