[Residue and efficacy study of neonicotinoids (Imidacloprid , Acetamiprid ,Thiamethoxam) used on greenhouse tomato to control whitefly]

Neonicotinoids, new insecticide group, highly effective against sucking insects and hugely integrated in the world insecticides market. The present study was carried out to evaluate the efficacy of three neonicotinoid insecticides against cotton whitefly Bemisia tabaci (Genn.) on green house tomato plants, and the residues of these neonicotinoids in tomato fruits after number of applications. The experiments were conducted under greenhouse conditions and carried out at the coastal area (Lattakia). All three insecticides Imidacloprid (24.5g ai/100Liter), Acetamiprid (10 g ai/100Liter) and Thiamethoxam (10g ai/100Liter) proved to be efficient against whiteflies Adults and nymphs (the studied life stages). All three neonicotinoids showed the best control to nymphs comparing to adults. Thiamethoxam demonstrated the best control of whiteflies to Imidacloprid and Acetamiprid respectively, especially after the intervals 5 and 7days after treatment (the last studied interval) when all three insecticides were significantly different in control to whiteflies with. In the periods up to 3 days after treatment Thiamethoxam and Imidacloprid had no significant differences between them with Thiamethoxam being superior to Imidacloprid and both of them significantly superior to Acetamiprid showing efficacy% of (81.03, 76.17, 66.25) respectively in controlling nymphs and (70.12, 68.91, 61.22) in controlling adults. In the coming intervals (5, 7 DAT) Thiamethoxam showed the best persistence in efficacy and were significantly different to Imidacloprid which was significantly different to Acetamiprid as well with efficacy% after 7 days (65.18, 60, 50.1) ) respectively in controlling nymphs and (60.85, 53.96, 49.21) in controlling adults. The second study carried out to investigate the accumulation of residues of Imidacloprid, Acetamiprid and Thiamethoxam caused by multiple applications on tomato fruits. Residues were studied after 4, 6 and 8th treatments, and samples were taken directly after spraying and up to the 10th day after spraying. All three insecticides residues proved not to accumulate significantly by number of treatments starting from the 4th one and they lightly differed. Imidacloprid residues dissipated the most rapidly among the three other insecticides with a percentage about 91% in 10 days from the initial deposit (2.125± 0.03 mg/kg) with a half-life of (1.32±0.03) days, and the calculated safety period was (6.89±0.2)days as much as twice of the recommended safety period 3 days. 95 Acetamiprid residues proved to degrade about 45% in 3 days then slowly to 58% in 10 days from the initial deposit (0.652± 0.031 mg/kg) with a half-life of (1.79±0.07) days and the calculated safety interval according to the proposed MRL 0.1mg/kg was (57.69±0.3) days and the calculated safety interval according to the proposed MRL 5 mg/kg was (1.15±0.1) days more than the recommended safety period 1 day. Thiamethoxam residues dissipated lightly about 13.5% in the first 24 hours then rapidly to 53.34% after the 3rd DAT and degraded about 72% in 10 days from the initial deposit (0.723±0.032) mg/kg with a half-life of (1.54±0.03) days and the calculated safety interval according to the proposed MRL 0.2 mg/kg was (12.24±0.3) days more than the recommended safety period 3 days