The Field Biology of Sorghum Chafer: its Temporal Occurrence and Overseasoning Habits

Abstract

The investigation was initiated to study the temporal occurrence of the different life stages and inter-seasonal habits of sorghum chafer (Pachnoda interrupta Olivier) at three major outbreak areas located in the northeastern part of Central Ethiopia. Adult flight was monitored by trapping while events such as behavior over the dry season, oviposition, and larval occurrence were studied by regular soil sampling and field observations. P. interrupta is a univoltine insect; but the adults had two flight periods. The first flight period was September/October and the second June/July. The size of the beetle population in flight in both occasions had no significant correlation with rainfall and temperature. Adult P. interrupta stayed in diapause in the soil for 7 - 8 months from November to the following June/July. Eggs, larvae and pupae were recovered from July to the beginning of October. The mortality rate among adults was generally low during the dry season (October-June). Two parasitoids, Adapsilia latipennis (Walker) (Diptera: Pyrgptidae) and Eutrixopsis sp. (Diptera: Tachnidae), were identified attacking adult P. interrupta. Entomopathogenic fungi Beauveria sp. and Metarrhizium sp. were isolated from both adults and larvae. Unidentified bacterial/viral pathogens were also causing severe mortality in the larva. Total mortality as high as 96% was observed among larvae collected from one of the study sites, Werer.