Toxicity of Catharanthus roseus (chichirica), Piper nigrum (black pepper) and Nicotiana tabacum (tobacco) to Periplaneta americana (American cockroaches)

This study tested the toxicity of chichirica (Catharanthus roseus), black pepper (Piper nigrum) and tobacco (Nicotiana tabacum) extracts to adult American cockroaches (Periplaneta americana) by means of topical application on their dorsal thorax. This was done to determine the percent mortality of cockroaches at different concentrations of the extracts. The 48 hr-LC50 was estimated using the trimmed Spearman-Karber analysis. The crude chichirica extract at concentrations 300, 500 and 1000 mg/ml did not show any toxicity to the cockroaches. Mortality was not observed forty-eight hours after the treatment. However, it was observed that crude extracts of black pepper and tobacco were toxic to cockroaches at 200, 400, 600 and 800 mg/ml concentration. Application of crude black pepper extract resulted to a percent mortality of 20% at 200 mg/ml concentration, 60 % at 400 mg/ml concentration, 65% at 600 mg/ml concentration and 70% at 800 mg/ml concentration. Application of crude tobacco extract resulted to a percent mortality of 20% at 200 mg/ml concentration, 33.3% at 400 mg/ml concentration, 51.7% at 600 mg/ml concentration and 73.3% at 800 mg/ml concentration. Percent mortality of cockroaches was noted to be directly proportional to the concentration of the extracts. The estimated 48 hr-LC50 value of crude black pepper was 357.61 mg/ml while the estimated 48 hr-LC50 value for crude tobacco was 540.08 mg/ml. Based on the 48 hr-LC50, crude black pepper extract appeared to be more toxic than crude tobacco extract to adult American cockroaches