The sweetpotato whitefly Bemisia tabaci(Hemiptera:Aleyrodidae)is an extremely polyphagous insect pest that causes significant crop losses in Israel and worldwide.B.tabaci is a species complex of which the B and Q biotypes are the most widespread and damaging worldwide.The change in biotype composition and resistance to insecticide in Israel was monitored during the years 2008-2010 to identify patterns in population dynamics that can be correlated with resistance outbreaks.The results show that B biotype populations dominate crops grown in open fields,while Q biotype populations gradually dominate crops grown in protected conditions such as greenhouses and nethouses,where resistance outbreaks usually develop after several insecticide applications.While in previous years,Q biotype populations were widely detected in many regions in Israel,significant domination of the B biotype across populations collected was observed during the year 2010,indicating the instability of the B.tabaci population from one year to another.Reasons for the changing dynamics and the shift in the relative abundance of B.tabaci biotype,and their resistance status,are discussed. The sweetpotato whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is an extremely polyphagous insect pest that causes significant crop losses in Israel and worldwide. B. tabaci is a species complex of which the B and Q biotypes are the most widespread and damaging worldwide. Change in biotype composition and resistance to insecticide in Israel was monitored during the years 2008-2010 to identify patterns in population dynamics that can be correlated with resistance outbreaks.The results show that B biotype populations dominate crops grown in open fields, while Q Communities grown in open fields. dominate crops grown in protected conditions such as greenhouses and nethouses, where resistance outbreaks are commuted after several insecticide applications. Whilst in last years, Q biotype populations were widely detected in many regions in Israel, significant domination of the B biotype across populations collected was observed during the year 2010, indicating the instability of the B.tabaci popul ation from one year to another. Reasons for the changing dynamics and the shift in the relative abundance of B. tabaci biotype, and their resistance status, are discussed.