The work was conducted to clarify the efficiency of certain insecticides on the
population of whitefly B. tabaci and incidence of yellow leaf curl virus (TYLCV) in
tomato field. The experiment was carried out during Nili plantation of two
successive seasons at El-Fayoum governorate. The obtained data showed that the
alternate use of etofenprox /thiamethoxam; imidacloprid/ thiamethoxam;
acetamiprid/ etofenprox; single continuous application of etofenprox; etofenprox /
imidacloprid; acetamiprid/ imidacloprid; thiamethoxam/ acetamiprid; imidacloprid;
thiamethoxam and acetamiprid gave excellent initial mortality over 90% on the adult
stage of B. tabaci and incidence of tomato yellow leaf curl virus without significant
differences between treatments. Thimethoxam as soil drench proved to be the most
effective insecticide against adult and immature stages of whitefly, while
acetamiprid achieved the lowest mortality for these two stages as well as short
residual mortality. On the other hand, alternation of etofenprox / imidacloprid
showed the highest initial mortality on nymphs. Residue levels in tomato fruits were
also investigated at 30, 45 and 60 days after application of tested insecticides. For
imidacloprid residues were found in amounts nearly above maximum residue levels
MRLs 30 days while degraded to amounts below MRL by the progression of time to
45 and 60 days after application. Application of imidacloprid in alternate spray
program with thiamethoxam; etofenprox; acetamiprid resulted in residues below
MRL at the 3 preharvest intervals. Acetamiprid when used at the recommended rate
showed the residue of 0.36 mg/kg at early season and then decreased to 0.08 mg/kg
at late season. Alternate use of acetamiprid with thiamethoxam; etofenprox or
imidacloprid reduce MRLs in tomato fruits. The successive applications of
etofenprox alone at the recommended rate resulted in residues above MRL after 30
and 45 days and approximately near MRL at 60 days. On the other hand, the half
rate in alternative use with imidacloprid; acetamiprid or thiamethoxam showed
residues below MRL at all sampling intervals. Thiamethoxam when used in single
successive applications gave residues of 2.5, 1.9 and 1.5 mg/kg at the 3 preharvest
intervals, respectively