Residuals Efficacy of Thiamethoxam and Thiaclopride Soil Applications against Whitefly, Bemisia tabaci (Homoptera; Aleyrodidae) and Their Impact on Soil Microarthropods

Field studies were
carried out to investigate the efficacy of thiamethoxam (TMX) and thiaclopride
(THI) via three different types of soil against whitefly, Bemisia tabaci,
on tomato seedlings during two successive seasons. Physical and chemical
criteria were determined in each of soil type. Results revealed that, the soil
types were loamy sand (Al-Maamoura), silt loam (Bangar Al-Sokkar) and clay
(Abou-Homous). During 2016 and 2017, clay soil had the highest contents in
organic matter (3.43 and 3.48% respectively) and organic carbon (1.99 and 2.03%
respectively). The highest mean reduction percentages of whiteflytreated
with the TMX in loamy sand soil were 79.35 and 80.12% and in silt loam were
78.39 and 81.60% during 2016 and 2017comparing to clay soil. Likewise, THI had
the highest mean reduction percentages during 2016 and 2017 in loamy sand soil (78.06
and 79.88% respectively) and silt loam (77.12 and 78.56% respectively) compared
to clay soil. Residuals efficacy of TMX and THI extended to 15 days in loamy
sand and silt loam soils compared to 9 days in clay soil during the two seasons
and the season of 2016 respectively. During the season of 2017, THI had more
extension for a week in the three tested soils. Initial effects against
whitefly had a rapid onset on the 3^rd day post-treatments of TMX in
loamy sand and THI in silt loam and clay soils during the two seasons. Initial
effects delayed on the 9^th day post treatment of TMX in silt loam
soil during season of 2017and in clay soil during the two seasons.
Retardations, extended to the 9^th day of THI treatment in loamy sand
soil during the season of 2017. The efficiencies of TMX and THI via soils of
loamy sand and silt loam against whitefly were significantly more than clay
soil. Full recovery levels of
micro-arthropods revealed at the end of the 7^th week in all soil’s depths of loamy sand and silt
loam treated with TMX and in loamy sand soil treated
with THI during the two seasons. Treated areas of high OM -clay soil failed to reach the recovery levels.