Mites on plums in Lebanon. 11- Fluctuations of their population density and abundance on plum trees in Baalbek

A study on the fluctuations of population density of mites and their abundance was carried out during March-November, 1986 in a plum orchard nontreated with pesticides in Baalbeck (Bekaa). The most prevalent mites were: the almond gall budmite, Acalitus Phlococoptes (Nal.) Eriophidae); the big-beaked plum mite, Diptacus gigantorhynchus (Nal.) (Rhyncaphytopidae); the yellow spider mite, Eotetranychus carpini (Oudm.) (Tetranychidae); Zetzellia talhouki Dosse (Stigmaeide), Typhlodromus invectus (Chant) (Phytoseiidae) and a tydeid mite, Pronematinae sp. The population density of the yellow spider mite and the tydeid, Pronematinae sp. increased significantly during September-October. The abundance of tetrapodilid mites started to decrease on the third week of August. The population density and abundance of the predators, Zetzellia talhouki and Typhlodromous invectus were relatively balanced during May-October and reached the peak at 23 June (more than 100 individuals/100 leaves). The rise of minimum temperature above 6 deg C in April was an important factor inducing mites to leave their hibernation places and move on plum leaves. The decrease of temperatures below 0 deg C and the leaf-fall during November induced mites to move into overwintering niches, and the decrease of relative humidity below 30% during summer showed a negative effect on the development of tetranychid mites. It was found that there is a negative but not significant correlation at a probatiliby of P=95% between the abundance of: (i) Zetzellia talhouki and both the yellow spider mite and Pronematinae sp. (ii) the tetrapodilid mites and both the yellow spider mite and Pronematinae sp., whilst the correlation was positive and significant between the abundance of: (i) phytoseiid mites and both tetrapodilids at P=95%, and the yellow spider mite at P=98%, (ii) Z. talhouki and the tetrapodilids at P=99% (iii) tydeid mites Pronematinae sp. and the yellow spider mite at P=98