, M.Sc. Thesis, Faculty of Agriculture, Cairo University., 154p., 2011.
Experiments were conducted at Qalubia Governorate to study the population fluctuation of the two spotted spider mite Tetranychus urticae Koch infesting four watermelon cultivars; Aswan, Daytona, Molokai and Giza-1 and associated natural enemies; and their response to environmental factors (temperature and relative humidity) during two successive seasons 2009 and 2010. In addition, the susceptibility of four watermelon cultivars to mite infestation was estimated. Also, biology and life table parameters of T. urticae, Phytoseiulus persimilis (Athias-Henriot) and Neoseiulus californicus (McGregor) were studied. The efficiency of (biological and chemical) two control methods against T. urticae during the two seasons were conducted. The results revealed the following:-
Mite populations reached its peak during July and May in the first and second seasons, respectively, and infestation was lower in the first season and this might be due to early plantation in the second. The temperature and R.H. % positively affected population growth of T. urticae on Daytona and Molokai cultivars during the two seasons, while with natural enemies, it was insignificantly negative during the two successive seasons.
Aswan cultivar was the most highly susceptible recording average of 42.86 and 57.59 mite individuals/leaf during the two successive seasons, respectively, followed by the moderately infested cultivars (Daytona) recording 28.10 and 39.75 mite individuals. The lowest infestation was recorded on Molokai and Giza-1 cultivars, averaging 19.18 & 25.90 individuals/leaf for the former and 18.10 & 25.94 for the latter cultivar during the two successive seasons, respectively. Susceptibility of watermelon cultivars to infestation with T. urticae may be affected by plant leaf morphological structure and its chemical contents. The number of trichomes /cm2 of leaf averaged 647.8, 744.4, 1111.1 and 1296.7 for Aswan, Daytona, Molokai and Giza-1 respectively; the less number of trichomes the more mite infestation. Positive relationships occurred between mite infestation levels and total amino acids, free amino acids, nitrogen and total soluble sugars in watermelon cultivars, while negative relationships found with tannins and nearly shown with total phenolic compounds, total flavonoids and total carotenes.
Watermelon cultivars and temperatures affected the life table parameters and duration of developmental stage as well as adult longevity and female fecundity of T. urticae, P. persimilis and N. califomicus. Duration of female developmental stages being the shortest when rearing on leaves of Aswan cultivar at 30°C and the longest on leaves of Giza-1 cultivar at 25°C. Male showed similar trend as female with slightly shorter periods.
In biological control, Release of P. persimilis gave the highest reduction percentage with T. urticae movable stages, and the lowest reduction percentage with eggs during the two successive seasons. Also N. califomicus seemed to prefer eggs of T. urticae than movable stages compared with P. persimilis. In chemical control, the highest reduction percentages were recorded with Envidor 24%SC and the lowest reduction percentages were recorded with Endo 50% during the two successive seasons.
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