Laboratory selection pressure was implemented to
the adults  of  cowpea Aphis craccivora  ( Koche ) 
as well as adults  of  whitefly 
Bemisia tabaci (Gennadius) collected from Behira field-strain to
build up resistance toward confidor (imidacloprid)  insecticide. The level of selection pressure
was carried out using LC₂₅ and LC₅₀ values  of tested compound . After 15 generations, the
level of resistance to confidor (imidacloprid) was 73.78 folds  for B. tabaci and 78.40 fold  for A. craccivora. The two strains
showed cross-resistance to primiphos-methyl (actilic) (9.64 and 7.04 fold) for B-tabaci
and A. craccivora  respectively,
while these strains showed high resistance to lambda-cyhalothrin (karate) and
diafenthiuron ( polo) with 73.90 and 33.73 fold for A. craccivora   respectively and it was 50.41 and 19.07 fold
for B. tabaci  respectively.