Temperature-Dependent Development of the Predator, Scolothrıps Sexmaculatus (Pergande) (Thysanoptera:Thripidae)

Abstract

The temperature is an important factor that affects the efficacy of biological control agents. Effect of the temperature on life table, parameters of Scolothrips sexmaculatus (Pergande) (Thysanoptera: Thripidae), the predator of the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) was studied under laboratory conditions at three constant temperatures (20, 25 and 30°C). These experiments were conducted at the General Commission for Scientific Agricultural Research (GCSAR), Damascus countryside, Syria. The durations of development of egg, 1 st and2 nd larval instars, pupa, and adult at the three tested constant temperatures were measured. The total developmental period from egg to adult's emergence was estimated by 23.2, 13.3 and 10.8 days, respectively. The developmental period decreased significantly with increasing the temperature from 20 to 30°C. Survival rate was the highest at temperature (30°C) in comparison with the other temperatures (20 and 25°C). Egg stage of S. sexmaculatus showed highest mortality levels at all temperatures. Generation period, as well as the ovipositional period decreased significantly at the temperatures ranged from 25.1 to 11.54 days, 52.8 to 41.2 days between the two temperature extremes, respectively. The maximum total fecundity (229.3 eggs/ female) and the minimum (94.1 eggs/female) were recorded at 30 and 20°C, respectively. The mean number of fertile eggs, laid per female per day, was highest at 30•C (4.9 eggs) and lowest (2.7 eggs) at 20•C. Thermal requirements for developmental thresholds and thermal constant of S. sexmaculatus were estimated as 10.8°C and 200 degree-days (DD), using the common linear model. 30°C was the optimum temperature for development. The results showed that the population of S. sexmaculatus was able to develop at a broad range of temperatures; therefore it is well adapted to the temperatures of the Mediterranean region.