الفهرس 
INTRODUCTION
On canola plantsOnly 14 pages are availabe for public view
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Abstract
Studies of certain factors affecting the abundance of some Aphids and thrips in Assiut Governorate
The obtained results clear that aphid species infesting were the cabbage aphid Brevicoryne brassicae L., the green peach aphid Myzus persicae (Sultz.), and the turnip aphid Lipaphis erysimi (Kalrenbach), as well as, thrips Thrips tabaci Lind. On the other hand onion (Allium cepa L.) which considered as the most important vegetable crop in Egypt for export and local consumption was infested mainly by thrips.
Therefore, the present investigation has been conducted to study the following points:
1- Studying the population of aphid and thrips inhabiting canola and onion plants and their natural enemies.
2- Studying factors affecting the population of aphid species and thrips infesting canola and thrips infesting onion plants.
3- Determination the suitability of two canola cultivars to aphid and thrips and susceptibility of three onion cultivars to thrips infestation.
4- Studying the effect of certain chemical and alternative compounds in reducing aphids and thrips infesting canola and onion plants.
I - Studies on Canola
1- Faunistic composition of arthropod pests and associated natural enemies inhabiting canola plantations:
By using sweeping net and direct count methods 16 arthropod species, belonging to 12 families and 6 orders, other than the predatory true spiders were collected from canola plantations in Assiut, Upper Egypt. The most frequent arthropod species inhabiting canola were: onion thrips T. tabaci, the cabbage aphid B. brassicae and the peach aphid M. persicae, as well as, the aphid hymenopterous parasitoids Diaeretiella rapa (McIntoch) and Praon necans Mackau. The other collected phytophagous or predatory arthropod species was observed as rare as low presence.
2- Dominance and abundance percentages of canola arthropod pests and their associated natural enemies:
Sweeping net, leaves and whole plant direct count methods were used to determine the dominance and abundance percentages of canola arthropods. Data indicated that T. tabaci¸ and both of B. brassicae and M. persicae aphid species were found to be the highest dominant and abundant species inhabiting canola. In respect to the natural enemies, parasitoids ranked the first with the highest dominance and abundance percentage when compared with the predatory group.
3- Population fluctuations of the major arthropods inhabiting canola plantations:
3.1- Population of canola aphids:
Population trend of both B. brassicae and M. persicae showed clear difference on their incidence. Semi equal numbers of the two pests were captured by using sweeping net method. However, B. brassicae showed 3.18 fold of M. persicae by using whole plant direct count with an average of 29.65 > 9.31 individuals/1canola plant. Conversely, the later showed higher numbers than the first when collected by using leaves direct count method (1.52 fold). Although, B. brassicae was found to be active on flowers and/or pods, M. persicae was found to be active on plant leaves. This behavior could be due to the preference of each species to special nutritional substances concentrated in each plant part. On the other hand, the turnip aphid L. erysimi showed the lowest incidence by using the three sampling methods.
3.2- Population fluctuations of canola aphid parasitoids:
The first appearance of aphid mummies (immature parasitoid stage) was recorded in February 27 at plant age 87 days old by using whole plant direct count. Mummy’s numbers were rapidly increased till harvesting. The effect of canola cultivars on the incidence of this parasitoid was very clear. Mean numbers of mummies in Serw cultivar, recorded 1.27 fold of that recorded on Bactol cultivar by using sweeping net method. The same trend was obtained by using whole plant direct count with 2.30 fold. Conversely, they showed 0.62 fold when the canola leaves direct count was used. The obtained result could be attributed to the aphid distribution on the plant parts, whereas, the visual observations insure that aphid species especially B. brassicae preferred the development tip and/or immature pods.
3.3- Population fluctuations of Thrips tabaci inhabiting canola plantations:
The first appearance of T. tabaci on canola plantations was detected in February 6, and plant age 66 days old. Regardless the sampling method, one peak only was seasonally detected. Sampling method could be had a distinct role to clear the presence of this insect pest. Sweeping net method can be considered as the most favorable method to express about the true presence of T. tabaci. The obtained results indicated that 60.06% of thrips inhabiting canola was collected by the sweeping net method. However, 25.94% and 14% of thrips were collected by using leaves and whole plant direct counts, respectively.
4- The impact of some abiotic and biotic factors on the population fluctuations of aphids and some abiotic factors on thrips:
4.1- Impact of some abiotic factors on the incidence of aphids and onion thrips infesting canola.
4.1.1- Aphid species
The lowest populations of aphid species were coincided with the end of canola seedling stage at plant age of 59 days and consequently with low average of temperature and relative humidity. On the other hand, aphid species recorded their seasonal peak during canola flowering stage with the optimum levels of temperature and relative humidity.
4.1.2. Onion thrips T. tabaci:
Onion thrips, T.tabaci exhibited its highest numbers during canola flowering stage at 101 plant days old. So, its peak was coincided with high levels of both (T oC) and (RH%), as well as, high levels of soil temperature at 5 and 10 cm under the soil surface.
4.2- Impact of biotic factors (parasitoid mummies) on the incidence of canola aphid species:
The obtained data showed that the first appearance of the parasitized mummies was detected at late February after 3 weeks of the aphid appearance. However, the greatest parasitism percentages were recorded in plant age between 108 to 129 days old (March, 19 – April, 9). It is of importance to note that parasitism percentages on Serw cultivar were higher than that those recorded on Bactol cultivar. Reasons responsible about this behavior could be due to plant chairomnes and/or antexinosis (preference and non-preference) of aphid species and their parasitoids to the tested canola cultivars.
5- Suitability of canola cultivars to the selected species under field conditions:
Preference of especial plant part may be express about suitability and/or susceptibility of the host plant to the pest. So, according to the obtained data, canola inflorescence, flowers and pods were appeared as the most suitable parts for B. brassicae feeding. However, canola leaves were appeared as the most suitable parts for M. persicae feeding.
6- The role of certain chemical and alternative compounds in reducing the selected species inhabiting canola plantations:
6.1- Cabbage aphid B. brassicae and beach aphid M. persicae:
The general reduction percentages on B. brassicae numbers can be arranged in descending order as follows: Radiant 12% SC by 84.74 > Tracer 24% SC by 83.67 > Mospilan 20 SP by 81.14 > Achook 0.15 by 69.68 and > Nat 1 oil by 61.45%. It is of importance to conclude that Radiant 12% SC exhibited the greatest reduction percentage on B. brassicae numbers than the remaining compounds. Similar trend was recorded on M. persicae.
6.2- Aphid parasitoids:
The impact of the tested compounds on the parasitoid mummies showed highly acceptable and satisfied reduction percentages. It is clear that the general reduction percentages ranged between 12.87 % for Mospilan 20% SP and 28.85 % for the natural oil compound Nat 1. So, the high reduction percentages on the pest numbers and the low reduction percentages on the parasitoid mummies numbers could be encourage the use of these compounds against aphids in canola plantations.
6.3- Onion thripds T. tabaci
Tracer 24% SC and Radiant 12% SC showed semi equal reduction percentages with Mospilan 20% sp with an average of 82.32, 84.53 and 82.21%, respectively. Azadarichtin compound (Achook 0.15%) and the natural oil compound Nat 1 oil showed 71.86 and 47.55% reduction percentages, respectively. So, the use of Tracer 24% SC compound was the most successful and safe applicable method for controlling thrips infesting canola plantations.
II- Studies on onion (Allium cepa L.)
1- Population fluctuations and damage caused by (Thrips tabaci Lind.) feeding on onion plants:
1.1- Population trends of T. tabaci.
The pest appeared on the tested onion cultivars in relatively high numbers at the beginnings of January 2013 and then by low numbers increased gradually till late January. The pest recorded three peaks throughout the onion growing season. Variations between the tested cultivars recorded highly significant differences. On the other hand, variations between inspection dates or plant age were also highly significant. The obtained results during 2014 onion season showed similar trend of those obtained during 2013 season. This finding is considered as a proof that onion thrips has had three generations throughout onion growing season. Appearance of the pest in relatively high numbers at the beginnings of January at few days after transplanting could be refer to the presence of the first low peak before transplanting onion.
1.2- Damage caused by T. tabaci feeding habits:
It is of importance to calculate the amount of silver patches caused by thrips feeding on onion leaves. Mean numbers of silver patches exhibited gradually increase from the beginning until the end of 2013 season, with highly significant variations between the inspection dates. Also, variations between the tested cultivars showed significant difference. Data clarified the relation between the populations of T. tabaci and numbers of silver patches caused by its feeding habits on onion leaves. The correlation between thrips and patches mean numbers was estimated. So, it can be note that each thrips individual can cause less than 2 patches/leaf at its first peak. However, each thrips individual can cause 3-3.5 and round up of 19 patches/leaf during its 2nd and 3rd peaks, respectively as accumulative damage.
2- The impact of some abiotic factors on the incidence of thrips inhabiting onion plants:
2.1- Prevalent temperature and relative humidity:
The obtained results showed that the insect pest three peaks were coincided with the moderately high (T oC) and (RH%).
2.2- Soil temperature:
Relation between thrips population trends and soil temperature at depth of 5 and 10 cm under the soil surface was determined during 2013 and 2014 season. The first peak of the pest was coincided with the relatively high maximum and minimum soil (T oC) recorded during January. degrees with 15 and 15.5°C under 5 and 10 cm of the soil surface, respectively. The same result was obtained during the second and the third peaks. Correlation coefficient (r) between thrips population development and plant age in addition to both of 5 and 10 depth under soil temperature during the entire period of study was estimated. Average temperature of the two studied depth showed positive (r) with the insect pest development. This finding proves that, T. tabaci development showed its highest levels during the low temperature and the less humidity days.
3- Identify the susceptibility degree of the tested onion cultivars to T. tabaci:
During 2013 season Giza 6 cultivar appeared as a susceptible (S) cultivar. On the other hand, Giza 20 and Shandaweel 3 cultivars appeared as low resistant (LR) cultivars. During 2014 season and the entire period of study the tested cultivars showed the same trend. Differences between the tested cultivars could be due to some factors i.e., plant color, angel measurement between onion neck and leaves and suitability of plant constituents to the insect pest.
4- The role of certain chemical and safe alternative compounds in reducing thrips inhabiting onion plants:
The chemical insecticides (Bleo 50% EC and Dolf 2.5% EC) in addition to (Radiant 12 % SC) were applied with three concentrations of the later. The highest concentration of Radiant 12 % SC exhibited the greatest reduction in thrips numbers, while the rest of concentrations exhibited quietly similar reduction percentages.
In a comparison between the tested compounds the chemical compound “Dolf 2.5% EC ” showed the highest reduction percentage of the pest numbers, with an average of 84.48%. However, the chemical compound “Belo 50% EC ” exhibited the lowest percentage by 74.26%.
So, it can be concluded that the use of Radiant 12% SC by low concentration could be consider to be the favorable method to control T. tabaci in the field than other high concentrations and/or certain chemical compounds.