Report 
  Title  
  INSECTICIDE SUSCEPTIBITY of FIELD POPULATIONS of GERMAN COCKROACH STRAINS COLLECTED in HOTELS in MEXICO
  Key Words  
  Cockroaches, insecticide formulations, bioassay, resistance
  Author  
  Alejra Espinosa-Islas, J. Concepcion Rodriguez Maciel and Hussein Sanchez-Arroyo
  Abstract  
  The high level of resistance to organophosphate and pyrethroid insecticides by German cockroaches is due to multiple factors, including the scheduled use of them, and isolated populations. Resistance in field populations have been observed in some Mexican strains, in which control failure with cypermethrin formulations have been reported. However, in Mexico we lack studies regarding insecticide toxicity in the German cockroach. For assessing insecticide toxicity, LD was determined to four insecticide formulations 50 by topical application. Distilled water and acetone (50/50) were used as solvents. Four resistant German cockroach strains were collected in Ixtapa-Zihuatanejo, Gro. (two strains), Huatulco, Oax., and Mexico City. The Orlando susceptible strain was used as reference. All the strains showed high levels of resistance to the insecticides evaluated. LD were considerable high, compared with other studies where pure active 50 ingredients are used. Apparently, the solvents present in the formulation increased the insecticide toxicity. The most resistant strain showed a resistant ratio of 2100 for deltamethrin (Mexico City), 178.7 for clorpyrifos (Ixtapa II) , 46.4 for cypermethrin (Huatulco), and 12.2 for bendiocarb (Mexico City). Even when we may expect different LDs compared with experiments where the active ingredient is pure, 50 adequately correlated, the results with formulated insecticides could help to make decisions regarding the replacement of insecticides in practical situations.