Resistance of Callosobruchus maculatus (Fab.) to pirimiphos methyl in three zones in Nigeria.

Abstract

The influence of climate on the resistance of Callosobruchus maculatus Fab. to pirimiphos methyl from three Geographical Zones in Nigeria was investigated in the laboratory at 32 ± 2 oC and 70 ± 5 % relative humidity. Samples of cowpea seeds infested with C. maculatus were obtained from twelve locations spread across savannah forest (northern boundary), rain forest and mangrove forest (southern boundary). Survival rates of 20 bruchids from each location were observed for two hours using 0.1 ml, 0.2 ml, 0.3 ml, 0.4 ml and 0.5 ml of pirimiphos methyl (Actellic ® 25EC). Two age groups of the bruchids (1-day old and 7-day old adults) were treated separately to study the age influence on their resistance and samples were replicated three times. Low survival rates were observed in both age groups of C. maculatus from all the locations when treated with 0.4 ml and 0.5 ml of pirimiphos methyl. The 7- day old adults showed resistance to 0.3 ml treatment while the 1-day old adults had low survival rate at this treatment. Resistance in 1-day old C. maculatus increased gradually in samples from the mangrove forest and peaked at the edge of the rain forest before gradually decreasing towards the savannah forest at 0.3 ml treatment. Seven-day-old adults treated with 0.4 ml showed some level of resistance in two central locations within the rain forest when compared to all other locations. Incidentally these two locations fall within cities where awareness for the use of insecticide might be high.