Population Density, Economic Threshold and Injury Levels of Tetranychus urticae and Petrobia tritici Infesting Wheat Plants at Sharkia and Beheira Governorates, Egypt

Assessment of the economic damage threshold (ETL) and economic injury level (EIL) of the two tetranychid Tetranychus urticae and Petrobia tritici infested wheat (Giza 168) were studied during 2016/2017 season at Sharkia and Beheira governorates. Also, the population density of both mite species were estimated. Results cleared that the values of (ETL) were less than (EIL) level. The (ETLs) values of T. urticae on wheat plants at Beheira and Sharkia (as x1 &x2 peaks results) ranged 4-4.33 and 4.33-10 individuals /leaf, while the (EIL)values ranged 4.33-5 and 10.3313.33 individuals /leaf in the two localities, respectively. In the same trend the ETLs of P.tritici on wheat plants at Sharkia and Beheira (as x1 &x2 peaks results) ranged 3.33-4.00 and 3.33 individuals. /leaf, while the EILs ranged 5-5.33 and 3.67-5.33 Individuals / leaf in the two localities, respectively. In addition, the results of population density of the two-mite species showed that, there were two peaks for each species at the two localities. Statistical analysis detected a positive insignificant correlation between the population of the two mite species and average temperature while it was insignificantly negative with average of R.H. %. The relatively high effect as partial regression (E.V. %) for tested climatic factors of 5.18% was recorded for average temperature on P.tritici at Sharkia governorate, while the relatively high multiple correlation for the two tested climatic factors together was 17.07% recorded on P. tritici at Beheira governorate.