Field infestation of Faidherbia (Acacia) albida (Del.) A. Chew. pods by stored product Coleoptera in the Nigerian savanna and effect of infestation on nutrient quality

A 6-month survey of the insect pest complex infesting the pods of the leguminous tree,Faidherbia (Acacia) albida, as well as their natural enemies, was conducted in Maiduguri located in the Sudan savanna and in Magumeri located in the Sahel savanna areas of north-eastern Nigeria, from January to June, 1999. The effect of infestation on the nutrient quality of the pods which are used as animal feed by livestock farmers was also evaluated. A total of 791 adult pest beetles, all belonging to the families Bruchidae and Tenebrionidae, were collected during the study. Of these,Bruchidius atrolineatus (55•1%), Acanthoscelides obtectus (29•2%) and Caryedon serratus (7•8%) belonging to the family Bruchidae, together, were the more dominant species. Tribolium castaneum (7•8%) was the only representative of the family Tenebrionidae. The proportion of the pods collected from the Sudan savanna (Maiduguri) that were infested with beetles (91•6%) was significantly higher than that collected from the Sahel savanna (Magumeri)(85•9%). Of the 87 adult parasitic wasps collected during the study,Hyposoter sp. belonging to the family Ichneumonidae was the most dominant (67•8%), and the family Braconidae comprising Bracon hebetor (17•24%) and Iphiaulax sp. (14•94%) constituted 32•2% of the total number of parasitic wasps. The parasitoids were unable to keep the populations of the pest beetles in check. Results of the proximate analysis showed that the crude protein, ether extract and crude fibre decreased significantly (p<0•05) with increasing severity of infestation while the nitrogen-free extract increased with increasing severity of infestation. The ash content was significantly higher in the heavily infested pods than in the moderately/mildly infested pods or in the uninfested pods. To enhance the utilization of acacia pods for livestock feeding during the dry season, it is concluded that more studies are needed to develop effective ways of protecting pods in the field and preserving them in storage against infestation by pest beetles.