Mageda Mohammed Mofleh
General Commission for Scientific Agricultural Research-
Lattakia Research Center
Faculty of Agriculture, Tishreen University
A study on the population dynamics of Tetranychus urticae was conducted through two seasons 2007-2008 in the Syrian coastal region. It was found that its activity starts on Ricinus communis plants and reaches the highest peak in the first week of May, then the population decreases at the end of May. In June the population rose again, and reaches the peak in July. In middle of August the numbers of T. urticae started to decline and disappear in late November in the study region. The activity and numbers of associated predators are dependent on the presence of the prey.
Many predators of T. urticae were found in the coastal region. The most important host plants were determined for the predators of T. urticae in the coastal region, and they were eleven host plants.
Temperature plays a key role in the time needed for development of the average fecundity of the spider mite Tetranychus urticae and the predator Phytoseiulus persimilis. Development time of Tetranychus urticae was 10.9±0.59 days at temperature 25±2°C and 8.15±0.5 days at 30±2°C. Development time of Phytoseiulus persimilis was 6.2 ±0.15 and 5.7 ±0.3 days under the same temperature, respectively. The average fecundity of P. persimilis was 45.2±5.3 and 39.1±4.1 eggs/female when the predator was fed on eggs, but when P. persimilis feed on eggs and immature stages the average fecundity was 52.6±5.9 and 44.8±6.03 eggs/female on 25±2°C and 30±2°C. The average fecundity of T. urticae was 106.5±27.6 and 96.4 ±20.5 eggs\female at the two temperatures, respectively.
The predatory mite Phytoseiulus persimilis was able to control the spider mite Tetranychus urticae in a greenhouse during 2006-2007 after releasing the predator in rate 1:10 (predator : prey).
Life tables studies were conducted on Tetranychus urticae and two of its predators (P. persimilis, S. gilvifrons) at two different temperatures (25 ±2 °C) and (30 ±2 °C). The ages of individuals (x) reached 23 and 18 days for T. urticae female, and 22 and 21 days for female of Phytoseiulus persimilis on Phaseolus vulgaris leaf disk, and 29 and 36 days for female Stethorus gilvifrons on two hosts (Ricinus communis, eggplant) leaf disks at the two different temperatures respectively.
The total time of development of Stethorus gilvifrons immature stages varied significantly according to temperature. Total immature development period on eggplant leaf disk was longest (28.9±0.38 days) at 20 ±2 °C, and shortest (11.84 ±0.19days) at 30±2 °C. The development and survival of the predator affected by host plant of prey . All predator larvae died in the first or second instar when reared on Phaseolus vulgaris leaf disk, while eggplant and cucumber were suitable host plants for the development and survival of immature stages of S. gilvifrons. The longest development total time (egg, larva, pupa) was on cucumber(31±0.35 days) at 20 ±2 °C, and (28.9±0.38 days) on eggplant at the same temperature with significant differences.
The functional response of S. gilvifrons on different density of adult prey was studied in laboratory. The predator consumption increased with increasing prey density, until 57.96 adult/day when prey density was 100 adult/ leaf disk. So according Holling (1959) model of functional response , we put S. gilvifrons predator under third types (type III).
The T. urticae gross reproductive rates (GRR) were 143.6 and 120.5 eggs, and the net reproduction rates (R0) was 108.96 and 98.46 eggs and (T,DT) was 10.96 and 1.65day and 8 and 1.2 day at the two different temperatures, respectively. The (GRR) for Phytoseiulus persimilis was 48.35 and 42.91 eggs, and (R0) was 44.88 and 39.09 eggs, while (T,DT) was 9.79 and 1.82 day and 10 and 1.87day at the two temperatures, respectively.
The (GRR) for Stethorus gilvifrons was 127.46 and 212.5 eggs, and the (R0) was 122.23 and 195.207 eggs, while (T,DT) was 13.03 and 1.88day on Ricinus communis and 14.75 and 1.94day on eggplant.
The ability of the predator Stethorus gilvifrons Mulsant to control the spider mite Tetranychus urticae on eggplant was carried out in a greenhouse during 2007-2008. The best results were obtained in the releases rates 1:5, 1:10, the predator controlled T. urticae populations in the sixth week.