The present work was conducted for two seasons (2010/2011-
2011/2012) in the Plant Protection Research Station at Qaha, Qalubiya
Governorate to study the effect of different sowing dates (Oct.30th ;
Nov.15thand Nov.30th) on the infestation of fenugreek plants
(Trigonella foenum graecum) with insect pests and find models for the
relationship between the accumulated heat units and seasonal
populations of fenugreek pests. The obtained results revealed seven
insect pests infesting fenugreek plants, two species on the leaves
(Liriomyza spp. and Bemisia tabaci) and five species on the terminal
buds (Acyrthosiphon pisum ; Aphis gossypii ; Aphis craccivora ;
Thrips tabaci and Phytonomus brunneipennis) in different sowing
dates and seasons. The seasonal populations of insect pests on
fenugreek plants had varied in the three sowing dates and seasons. In
addition, results showed that sowing fenugreek by mid-November
received lower infestation with insect pests than early and lately
sowing dates (Oct.30th & Nov.30th) and the proper date for sowing
fenugreek must be in the second half of November. On the other hand,
results showed varied relations for accumulated heat units (DegreeDays Units) and the mean numbers of seasonal populations of
fenugreek pests. Calculation the accumulated heat units for the
fenugreek insect pests confirmed the variability of seasonal
populations in different sowing dates and seasons. The 1st season has
highly accumulated heat units for most insect pests than the 2nd ones
and differences in the accumulated heat units ranged 7.5 -19.9% in the
two seasons. The larvae of leaf miner, Liriomyza spp. have varied
accumulated heat units mostly increased with 13.8% in 1st season than
the second ones. The accumulated heat units for B. tabaci were varied
(435- 542.7 D°) in the two seasons and the difference reached 19.9%.
There for, the insect don't occur during the season if the accumulated
heat units below than 435 D°. The aphid species have highly
accumulated heat units in the three sowing dates ranged 1003.3-1188.7
D° in the 1st season and 901.0 - 1099.3 D° in the 2nd one with
differences ranged 7.5 - 10.2%. Cotton thrips, T. tabaci has varied
accumulated heat units (782.7 - 891.7 D°) in the two seasons; the 1st
season has highly Degree-Days Units (DDD) than the 2nd one with
difference 12.2%. The clover leaf weevil P. brunneipennis has varied
accumulated heat units (603 - 715 D°) in the two seasons with difference 15.7%. The obtained results created beneficial
methodological developments for designing ecological zones maps for
distribution the insect pests over the country and designing dynamic
program for integrated pest management (IPM) under different
ecological conditions in Egypt.