A two years study, from November, 1995 to October, 1997 populationstudy was carried out on trees of three orange varieties at Sharkia Governorate to
evaluate the population densities of the citrus rust mite, Phyllocoptruta oleivora
(Ashmead) throughout different months of the year, and also to determine the
preference of this mite species to infest different directions and levels of trees.
Highest infestation to leaves occurred in July, 1996 on Balady and Navel
varieties (2235 and 2903 individuals/100 leaves, respectively) and in June, 1996 on
Valencia variety (1961 individuals), and on June 1997 on Balady, Valencia and Navel
varieties (1659, 1407 and 2021 individuals/100 leaves, respectively). While on citrus
fruits, highest peak of population abundance occurred in August (12307 & 13365, 9405
& 12605 ari 17420 & 14705 individuals/lO leaves in 1996 & 1997 on Balady, Valencia
and Navel varieties, respectively). Starting from August to December, the population
densities of R oleivora individuals decreased on leaves and were higher on indicating
moving of the mite individuals from leaves to fruits during this period.
In both years of study, leaves and fruits of Navel orange variety were the
heaviest infested, followed by Balady variety, while those of Valencia variety harboured
the lowest overall mean of population densities to proof as the least prolonged variety.
On different tree directions and levels of Balady variety, the east direction and
lower level of trees harboured the highest population densities of P. oleivora
individuals. While, on the contrary, the southern direction and upper parts of trees
were the least infested. That was attributed to higher relative humidity and suitable
temperature on the former location, and lower %RH and unsuitable temperature on
the latter one.