JWSS - Journal of Water and Soil Science

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The difficulties of control of greenhouse whitefly on crops and greenhouse plants make extensive studies and investigations necessary in different areas of Iran. Morphological and biological studies were carried out on a prevailing species of greenhouse whitefly, Trialeurodes vaporariorum Westwood, in Isfahan.

In this study, six species of whiteflies T. vaporariorum on Althaea sp. and Lantana camara, Bemisia tabaci Gennadius, B. argentifolii Bellows & Perring and B. hancoki Corbett, on Lantana camara, Aleyrodes proletella L. on Brassica sp. and Aleyrodes rosae on Rosa sp. were collected. These species were described using different identification keys. Morphological characteristics and different growth stages of greenhouse whitefly including egg, 1st to 4th nymphal instars and adult were defined and figures drawn. Biological studies were conducted in 24±1°C, 65±5% RH and 16:8 (L:D) on eggplant, solanum melongena. The developmental time for egg, 1st, 2nd, 3rd and 4th nymphal instars was 7.33±0.48, 3.37±0.52, 3.25±0.45, 2.51±0.26 and 7.66±0.83 days, respectively. The total period from egg to adult lasted 24.12±0.51 days. The number of eggs laid in 24 hours varied between 1 to 10 with an average of 5.93±1.67. Life-span of the male ranged between 19 to 23 with an average of 20.88±1.54 and that of the female varied between 20 to 28 with an average of 26.44±1.17 days. Four nymphal instars were identified and three substages for the 4th nymphal instars were determined. There was a positive correlation between nymphal instars and average body length and width. Since only male offsprings were produced through parthenogenesis, the strain of greenhouse whitefly in Isfahan was found to be European.

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Regarding the importance and high potential of Encarsia formosa Gahan (Hymenoptera: Aphelinidae) for control of the greenhouse whitefly, Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae), the effect of different diets and storage of the parasitoid at low temperatures on its longevity and efficiency was studied. The average longevity of the parasitoid on different diets including honey-syrup 15%, honey-syrup 10%, sucrose syrup 15%, honeydew of whitefly were significantly different at 1% from distilled water and control (without water and food) treatments.

Change in honey-syrup concentration at a range of 5% did not affect the longevity of the parasitoid. The honeydew and sucrose-syrup treatments were not significantly different. This was probably due to the relative similarity of food quality of these two diets. Storage of host parasitized nymphs containing pupae of 1-2 days-old of E. formosa at 8±1°C affected the emergence rate and efficiency of adult parasitoids.

Four treatments including the pupae of parasitoids in 4th nymphal instars of the greenhouse whitefly were stored at 8±1°C for 5, 15, 25 and 35 days. Control treatment included pupae of parasitoid that were held at room temperature, 24±4°C. Host nymphs were parasitized by the parasitoids emerging from all treatments. The average parasitized nymphs by parasitoids emerging from 5, 15 days and control treatments were not significantly different at 1 %.