SELECTION OF A COWPEA WEEVIL (COLEOPTERA, BRUCHIDAE) BIOTYPE VIRULENTTO COWPEA WEEVIL RESISTANT LANDRACE TVU-2027

Studies of cowpea weevil, Callosobruchus maculatus (F.), larvae in see ds of resistant (cowpea land-ace) TVu 2027 and susceptible 'California Blackeye No. 5' (CB5) revealed that 10-15% of the cowpea weevil popul ation develop at the same rate in TVu 2027 as in CB5 seeds. When adult s having the same developmental rates on TVu 2027 as CB5 were selected and intercrossed for 8 generations, there was no significant differen ce in within-seed developmental time between the selected and unselect ed populations. Therefore, these rapidly developing individuals do not represent an emerging cowpea weevil biotype but may result from a cha nce avoidance of the resistance factor by individual cowpea weevil lar vae, coupled with seed-to-seed variation for the resistance factor. Ho wever, we were able to develop a cowpea weevil biotype virulent to TVu 2027 by selecting and intercrossing the most rapidly developing indiv iduals over 53 cowpea weevil generations. After 53 generations of sele ction the cowpea weevil biotype developed as rapidly in TVu 2027 seeds as did the unselected population in susceptible CB5 seeds. The biotyp e developed at the same rate on cowpea weevil-resistant KNS and KNW li nes as on TVu 2027, confirming that the basis of resistance is the sam e in all 3 lines. Also, biotype virulence to KNS and KNW suggests that the biotype can be used to identify cowpea lines with the TVu 2027 so urce of resistance.