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.