Ecology and field biology of the sorghum chafer, Pachnoda interrupta (Olivier) (Coleoptera: Scarabaeidae) in Ethiopia

摘要

Studies on sorghum chafer (Pachnoda interrupta) were conducted under field condition for two consecutive years (2005 to 2006) to determine the biology and ecology of the beetle. Average oviposition rate by a single female was 1.28 eggs per day for a period of 11 days. In general, eggs hatched within 4 to 22 days with a mean of 15.7 days, after which larval and pupal stages lasted a mean of 59.8 and 18.3 days, respectively. The highest rate of oviposition was recorded during the first four days after mating and none after the eleventh day. A total of 156 and 236 sites or samples were investigated from nine habitats (under tree in forest, under tree in crop fields, in a crop fields, border of crop fields, grazing land, riverside, manure heaps, termite mound and cattle dung in homestead) to identify breeding and hibernating areas of the beetles. Fertile humus and moist light soil under the shade of various tree species in the forest and along the riverside were found to be the potential breeding and hibernating areas of the beetles. Metal boards were used and arranged to east wards, where the sources of flights were expected. During June 2005 outbreak, a total of 1770 beetles with equal sex proportion were caught within 15 days from 36 passive metal board traps, with the beetles’ infestation being first recorded near the Afar border. Monitoring of flight direction at the time of the outbreak using these metal board traps showed no significant difference in beetle catches among different directions (north, south, east and west). In conclusion, the beetles could breed in areas where the previous outbreak did not occur; importantly, the beetle hibernated in fertile and moist soils near river bed of all areas of outbreak.