Silverleaf whitefly populations were first found in the San Joaquin Valley in July 1992. It is now established in the San Joaquin Valley, although losses in cotton have been minimal. This pest is able to successfully overwinter in the valley and utilizes a sequence of crop and weed hosts during the year. In 1993, populations of this pest were found in cotton fields in late July/Aug and densities increased and reached moderate levels in cotton in Sept. However, damage to cotton was minimal. In 1994, silverleaf whitefly populations occurred about 3 weeks earlier than in 1993 and infested cotton fields in June and built to fairly high densities in some fields. Some whitefly-inflicted damage occurred in cotton. Silverleaf whitefly populations in 1995 were at much lower densities than in 1994 and, in many ways, populations were more similar to the 1993 levels. Populations of this pest are apparently sensitive to unfavorable spring environmental conditions (degree-day accumulation and rainfall in the spring), which apparently inhibited build-up in 1995.