Food preference, population dynamics and bacterial harborage of the german cockroach Blattella germanica L. in Bangkok markets

Abstract

The 48-h-staved male and female German cockroaches were given choices among eight food items such as bread, sugar, banana, potato, peanut, cheese, pork, and cat food. The amount of food eaten was recorded using the Rodgers’s index for indicating the food preference of the cockroaches. The male German cockroaches significantly preferred banana and potato whereas the female cockroaches significantly preferred only banana. Additionally, the female cockroaches also significantly preferred peanut, sugar, and cat food more than the males. The foraging time of the German cockroach occurred at nighttime with two peaks of feeding activity. The first peak occurred during 07.00-10.00 pm, then, the second peak occurred during 04.00-05.00 am. A study on the population dynamics of the German cockroach was monitored in twelve Bangkok markets from March 2005 to March 2006. The selected market areas were conducted monthly during the study period. The two highest peaks of the German cockroach were conducted monthly during the study period. The two highest peaks of the German cockroach were in July and August whereas the two lowest peaks of the cockroach were in December and January. The highest catch of the German cockroach was the large nymphal stage (th 5[superscript=th] and 6[superscript=th] instars). The highest number of the German cockroaches was in a poor sanitary market in low population density zone of Bangkok whereas none of the German cockroach was caught from a good sanitary market in high population density zone of bangkok. Moreover, the cockroaches caught from the groceries were significantly higher than the butcher shops and vegetable shops in the twelve Bangkok markets. Aerobic and facultative anaerobic bacteria were isolated from 2 parts of the German and the American cockroaches, the external cuticles and the middle guts. The German cockroach hosted 21 species of bacteria whereas the American cockroach hosted 26 species. The serious pathogens in this study were Bacillus cereus, Staphylococcus aureus and Salmonella Arizona. The opportunistic pathogens such as pseudomonas aeruginosa were found in all markets. Additionally Escherichia coli, and indicator of environmental surveillance as a measurement of human and warm-blooded animal fecal contamination, was also isolated from all markets. The bacterial species isolated from the cockroaches from poor sanitary markets was significantly higher than from good sanitary markets. The similarity coefficient of the bacterial species between the German and the American cockroaches investigated in twelve Bangkok markets were ranged from 0.87 to 1.00. The results indicate that the both kinds of cockroaches carried the similar bacterial species. Insecticidal residues in the living German cockroach were analyzed by High Performance Liquid Chromatography. The highest concentration of insecticidal residue in the living cockroach samples was cypermethrin, followed by 3-phenoxybenzoic acid, and cyfluthrin, respectively. The highest residue concentrations of cypermethrin, 3-phenoxybenzoic acid, and cyfluthrin were detected from a good sanitary market in low population density zone of Bangkok. This suggests that cypermethrin and cyfluthrin resistances may have been developing in the German cockroach populations after being treated by the repetitious insecticides.