All the new field populations collected were significantly more resistant to spiromesifen than the susceptible population, confirming the presence of resistance. Several populations showing high levels of resistance to spiromesifen (>10000-fold), exhibited crossresistance to spirotetramat, but resistance ratios were much lower (130-fold). The spiromesifen laboratory-selected strain was very resistant to spiromesifen (LC50 > 30000 mg L-1) and spirotetramat (LC50 = 368.1 mg L-1), but lacks any cross-resistance to other insecticides, thus providing options for resistance management. None of the synergists tested significantly restored the susceptibility of B. tabaci to either spiromesifen or spirotetramat.