الفهرس 
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Abstract
Onion (Allium cepa L.) is one of the most important vegetable crops grown in Egypt. It is grown for consumption as green leaf and mature bulbs. Both mature and immature bulbs of onion are used as vegetable and also as a condiment The present studies were conducted on onion thrips infesting onion crop in Assiut with the following objectives: 1- Studying the seasonal population fluctuation of onion thrips infesting onion plants. 2- Make a model applied to describe thrips population on onion. 3- Elucidate the dominance of the common predators associated with onion thrips on onion plants. 4- Survey of entomopathogenic fungi as endophyte from onion leaves as well as from infecting thrips under field conditions. 5- Bioassay of isolated fungi species against thrips (In Vitro). 6- Effect of certain agricultural practices on thrips infestation: a. The susceptibility degree of different onion cultivars towards thrips infestation. b. Effectiveness of planting dates of onion on thrips population. c. Infestation of onion plants by thrips in relation to Nitrogen fertilizer. d. Determine losses of onion yield in relation to previously agricultural practices. The results could be summarized as follow: 1- Brief description of onion thrips, Thrips tabaci L Owing to survey studies during the period of 2015-2017 onion growing seasons. Onion thrips, Thrips tabaci L. was found infesting onion plants. Nymphs and adults of this pest were commonly intermixed together at the same location on the onion plants. 2- Some natural enemies (predators and entomopathogenic fungi) recorded associated with onion thrips on onion plants at Assiut 2.1- Predators Results indicated that the presence of 6 species belonged to 6 families and 5 orders collected, as well as unidentified species of true spiders. These orders are Coleoptera, Diptera, Neuroptera, Heteroptera and Thysanoptera. The recorded families were Coccinellidae, Staphylinidae, Syrphidae, chrysopidae, Anthocoridae and Thirpidae. The green lacewing, chrysoperla carnea (Steph.), the hover fly, Syrphus corolla F. and the lady beetles, Coccinella undecimpunctata L., and some unidentified species of true spiders were the most abundant predators which recorded and identified. Species such as Paederus alferii Koch, Orius sp. and Scolothrips sexmaculatus (Pergande) were collected
occasionally in low numbers 2.2- Entomopathogenic fungi The results showed three species of mycopathogens, belonging to order Hyphomycetes. The identified fungi were Beauvera bassiana as endophyte isolated from onion leaves as well as Cladisporium and Paceilomyses were recovered on infected onion thrips as cadaver. 3- Dominance degrees of the predators associated onion thrips inhabiting onion plants: Generally, regardless of the growing seasons, data showed that C. undecimpunctata seems to be the most important economic predator on onion plantations. 4- Population of onion thrips on onion plants 4.1- First sowing date (01 November): 4.1.1- 2015-2016 Season T. tabaci began to appear in the field of onion in relatively high numbers (6.67 individuals / bulb) after transplanting when the plants were in the Cotyledon senescence stage. This period coincided with a maximum temperature of 28.00 C, a minimum temperature of 11.71 C, a maximum RH of 69.42% and a minimum RH of 9.57%. Thereafter, the population density of the pest fluctuated in scarcely numbers to attain the peak (122.42 individuals / bulb) during the third week of February when the plants were during the end of bulbing stage. The recorded weather factors in this period were 26.28 C and 10.42 C for max. and min. temperature and 72.28% and 13.57% for max. and min. RH, respectively. Then the number of T. tabaci decreased gradually till the end of March, when the onion plants were in the Fall down stages. The recorded weather factors were 27.42 C and 15.77 C for max. and min. temperature and 61.22% and 14.57% for max. and min. RH, respectively. 4.1.2- 2016-2017 season The population trend was nearly similar as in 2016 season. T. tabaci were first appeared in relatively high numbers during the first week of December after transplanting when the plants were in the cotyledon senescence stage. Then, the number increased gradually forming the peak of 162.35 individuals / bulb during the first week of March (the beginning of the bulb swelling stage). The recorded max., min. temperatures were 26.17 C; 11.17 C and the max., min. RH were 74.17%, 12.33%, respectively. The population then decreased to its lowest level (3.37 individuals / bulb). The recorded max., min. temperature were 30.00 C, 17.00 C and the max., min. RH were 73.61%, 16.33%, respectively. 4.2- Multi-correlation analysis of some factors affecting the infestation of onion by T. tabaci The relationship between incidence of the onion thrips infesting onion plants and selected abiotic and biotic factors was statistically analyzed using multiple regression analysis. The selected abiotic factors were air and soil (5cm) temperatures; and two biotic factors i.e. plant age (in days), and number of predators during the first sowing date of (01 November) 2015-2016 and 2016-2017 growing seasons. 4.2.1- Biotic factors
4.2.1.1- Plant age Plant age has a coefficient of determination of about 35.38% out of 70.53% and 32.86% out of the total efficiency 62.17%. This evidence indicated that about 34.12% of the variability of the infestation was due to plant age under the studied variables (8 variables). The rating sort of the plant age cames in number one. 4.2.1.2- Predators Predators seemed to be responsible for about 7.94% and 6.74% during 2016 and 2017 seasons of the total changes in the population of T. tabaci. Predators and came in the rating sort in number two. 4.2.2- Abiotic factors 4.2.2.1- Air, soil temperature and humidity Maximum and minimum temperatures have a coefficient of determination of about 4.37% and 5.19% out of 70.53% during 2015- 2016 season and 4.05 and 2.33% out of 62.17% during 2016-2017 season. The rating sort of the maximum and minimum temperature came in number six and five (2016) and five and seven (2017). The maximum and minimum relative humidity was found to be responsible for 4.05% and 0.76% during 2016 and 2.25 and 4.36 during 2017 seasons of the variability of number of thrips infesting onion, respectively. The maximum and minimum soil temperatures (5cm) were found to be responsible for about 7.18 and 5.66% during 2016 and 5.92 and 3.66% during 2017 of the onion infestation with T.tabaci. Soil temperature came in the rating sort in number three and four (2016) and three and seven (2017) of the variability of number of thrips infesting onion, respectively. >4.3- Population age structure of onion thrips: 4.3.1- First sowing date (01 November): from the foregoing results the population development of onion thrips at Assiut area, in southern Egypt can be described by dividing this populations into five phases and calculated from the beginning of transplanting (1 st of November) as starting date (tables 10 and 11) as follows. P1: The initial population density of thrips occurred after 31 days when first of November (transplanting) was used as starting date during both sesaons. P2: Population of the pest increased to reach 10% of the maximum level after 40 and 36days with an average of 38.00 days during 2016 and 2017 sesasons. P3: Thrips population increased to the maximum level after 117 and 124 days with an average of 120.50 days, 2016 and 2017 seasons. P4: When the population decline to reach 10% of the maximum number after 157 and 151 days with an average of 154.00 days, during the last week of March. P5: Disappearance of thrips from the onion plants was occurred after 166 and 159 days with an average of 162.50 days, during 2016 and 2017 seasons. Its clear that the onion thrips needed about 131.50 days (18 – 19 weeks) from the first appear on the onion plant to their disappearance (P1-P5). 4.3.2- Second sowing date (01 December): 4.3.2.1- 2015 - 2016 Season Data showed that the T. tabaci began to appear in the field of onion in relatively high numbers (9.30 individuals / bulb) after transplanting during the first week of January when the plants were in the transplanting (Cotyledon senescence stage). This period coincided with a maximum temperature of 21.71 C, a minimum temperature of 7.14 C, a maximum RH of 73.85% and a minimum RH of 18.00%. Thereafter, the population density of the pest fluctuated in scarcely numbers to attain the peak (77.33 individuals / bulb) during the third week of February when the plants were in the end of leek stage and beginning of the fall of the first leaf stage. The recorded weather factors in this period were 26.85 o C and 7.42 o C for max. and min., temperatures and 73.57 and 9.57% for max. and min. RH. Then the number of T. tabaci decreased during the next two weeks. A second peak of 95.63 individuals / bulb was recorded during the fourth week of March when the plants were in the begning of bulbing stage. The recorded weather factors were 26.71 C and 10.28 C for max. and min. temperature and 72.42 and 5.71% for max. and min. RH,. 4.3.2.2- 2016 - 2017 season T. tabaci were first appeared in high numbers during the first week of January when the plants were in the Cotyledon senescence stage. Then, the number increased gradually forming the first small peak of 57.38 individuals / bulb during the end of January (the beginning of the leek stage). The recorded max. and min. temperatures were 22.00 C; 7.57 C and the max. and min. RH were 67.57% and 9.14%, respectively. This peak was followed by another peak of population (142.25 individuals / bulb) occurred during the first week of March (fall of the first leaf stage). The recorded max., min. temperatures were 26.33 C; 11.83 C and the >max., min. RH were 74.00%, 10.67%. A lowest level was recorded during the first week of April. The recorded max., min. temperature were 29.43 C, 8.51 C and the max., min. RH were 76.26% and 18.21%,
respectively. 4.4- Multi-correlation analysis of some factors affecting the infestation of onion by T. tabaci Simple correlation analysis revealed a significant positive effect of maximum and minimum temperature and the minimum relative humidity (R. H.). On the other hand, maximum R.H. had insignificant effect on the< incidence of T. tabaci. However, coefficient of determination (R 2 ) was (65.45 and 66.76 during 2016 and 2017, respectively The studied variables can be arranged in descending order during 2016 and 2017 seasons as follows: Plant age, Predators, Max. soil temp., minimum R.H., Max. air temperature, minimum air temperature, Max. R.H. and minimum soil temperature. 4.4.1- Population age structure of onion thrips during 2 nd sowing date (01 December): Regardless of the growing seasons it could be concluded that: (P1): Onion thrips was detected after 32 days after transplanting. (P2): In this phase the population of thrips increased slowly to reach 10% of the maximum level with about one month. (P3): Thrips populations increased to a maximum level within an average of 17-18 weeks. (P4): The fourth phase includes the population decline, the present data show that the population declined to reach 10% of the maximum level with an average of 129.50 days. (P5): disappearance of thrips from onion fields that has been observed within an average of 136.50 days form transplanting, from the beginning of December.