SUSCEPTIBILITY OF THREE MAIZE CULTIVARS TO APHID INFESTATION AND EFFECT OF POTASSIUM FERTILIZER LEVELS ON APHID

Susceptibility of the three maize cultivars (Cross 10, Bashair 13 and Watania 4)
to aphid infestation was evaluated at EI-Mansoura district, Dakahlia Governorate
throughout 2002 and 2003 seasons. The obtained results cleared that the
population of cereal (Rhopalosiphum maidis (Fitch) and Rhopalosiphum padi L.)
and cotton (Aphis gossypii (Glover)) aphids on each cultivar recorded one peak during
each season of study. The initial infestation and population density of aphids were
varied according to aphid species. However, R. maidis infestation started earlier in
comparison with R. padi 3nd A. gossypii, respectively.
The Cross 10 cultivar was comparatively susceptible to aphid infestation and
harboured high numbers of R. maidis followed by Bashair 13 and Watania4 cultivars
during the two study seasons. In case of R. padi the same trend was found where
Cross 10 harboured higher numbers of 733 and 759 individuals during the two
study seasons. On the contrary, A. gossypii recorded differed result where the
highest number of 386 individuals found on Bashair cultivar during 2003 season.
The potassium fertilization Significantly influenced aphid populations.
However, the highest aphid numbers (143.9 and 66.4 individuals) recorded at zero
level of potassium, while the lowest numbers (70.9 and 25.07 individuals) recorded
at higher potassium level 150 kg/fadd. for R. maidis and R. padi. Host preferability
may be due to the variance in epidermal cells thickness which varied from 5.29 to
6.14 micron as response to the variance on potassium levels from zero to 150
kg/fadd.