Pre-harvest spray of neem (Azadirachta indica A. Juss) seed products andpirimiphos-methyl as a method of reducing field infestation of cowpeas by storagebruchids in the Nigerian Sudan savanna

The efficacy of neem seed oil (NSO) applied in water at the rate of 20 ml/land aqueous neem seed extract (ANSE) applied at the rate of 50 g/l, in reducingfield infestation of cowpeas by storage bruchids was compared with that ofpirimiphos-methyl (PMM) (Actinic 25 EC?) applied at the recommended rate of 2ml/1 to plants in 16 m-2 experimental plots in Maiduguri, northeastern Nigeria inthe cropping seasons of 2001 and 2002. Insecticides were applied twice, thrice orfour times at weekly, intervals to mature cowpea (var. IT89KD-374-57) pods. Theresults show that in the 2002 cropping season, two, three or four gays of NSO orANSE significantly reduced the number of eggs laid by bruchids on cowpea pods.In both cropping seasons, two sprays of any of the insecticides significantlyreduced the percentage of pods bearing bruchid eggs and/or the number of exitholes of F1 adult bruchids on pods in the 2001 season. In plots that received twosprays of the insecticides in 2002, PMM educed the number of eggs laid onthreshed cowpea seeds significantly more than ANSE. In the same year,significantly fewer adult bruchids emerged from seeds obtained from PMM-treatedpods that received two sprays than those from ANSE- treated pods that receiveda similar number of sprays of the 977 adult bruchids that emerged from shelledcowpea seeds in the 2001 cropping season, 28.6, 24.0, 29.6 and 17.7% emerged fromseeds obtained from unsprayed pods and pods sprayed with NSO, ANSE and PMM,respectively; 28.6, 20.2, 21.2 and 30.1% emerged from cowpea seeds obtained fromunsprayed pods and pods sprayed twice, thrice and four times, respectively. Ofthis number of adult bruchids, 28.2, 40.9, 28.0 and 2.8% were Callosobruchusrhodesianus, C. maculatus, Bruchidius atrolineatus and C. chinensis. Of the 1727adult bruchids that emerged in the 2002 cropping season, comparable figureswere 30.8, 26.1, 30.2 and 12.9% for unsprayed pods and pods sprayed with NSO,ANSE and PMM, respectively; 30.8, 22.3, 25.5 and 21.4% for unsprayed pods andpods sprayed twice, thrice and four times, respectively. Of this number, 16.3,29.5, 7.5 46.7 were C. rhodesianus, C. maculatus, B. atrolineatus and C. chinensis,respectively.