الفهرس 
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Abstract
Cabbage And Cauliflower Are The Most Important Cruciferous Crops Cultivated In Egypt And Many Countries In The World With The Aim Of Consuming Leaves Of The First And The Flower Buds Of The Second . In Egypt Both Crops Grow in Three Periods . Cabbage And Cauliflower Are Attacked With Numerous Insect Pests In The Field. The Small Cabbage White Butterfly Pierris Rapae L. Which Synonyms With Artogeia Rapae Is One Of The Most Serious Insect Pests Which Infests Cruciferous Vegetables and Causing considerable Damage Especially To Cabbage And Cauliflower As Determined By Jankowska . Feeding Injury caused By This Caterpillar May Reduce Production To Zero. During The Three Plantations Summer Late Of Autumn And Winter P. Rapae Showed Fluctuation In Its Population Especially In Autumn . The Number Of Generations Was Recorded Two Generations Or Three Generations Annually On Cabbage Related To Tropical And Subtropical Areas.
SUMMARY
The small cabbage white butterfly, Pieris rapae L., is one of the most serious insect pests which infest cruciferous vegetables that caused considerable damage especially to cabbage and cauliflower. P. rapae population could be limited by various natural enemies e. g. the egg parasitoid Trichogramma, the pupal parasitoids, Pteromalus puparum, Brachymeria femorata, Phryxe vulgaris, the larval parasitoid, Sinophorus xanthostomus and the larval pathogen, Bacillus thuringiensis.
1. Ecological studies:
During the three successive seasons 2007, 2008 and 2009; two selected fields of cabbage and cauliflower were chosen. Population fluctuations of pupal stage of P. rapae were studied. On the other hand, pupal parasitoids were recorded weekly on each crop as parasitism percentages in relation with the population of the host.
1. 1. Seasonal abundance of P. rapae pupae and pupal parasitoids on cabbage and cauliflower fields:
Three parasitoids were recorded as pupal parasitoids (i.e., Brachymeria femorata Panzer, 1801; Pteromalus puparum Linné, 1758 and Phryxe vulgaris Fallen, 1810(.
1. 1. 1. Survey on cabbage crop in season 2007:
During the period ranged between September 15th and December 29th, the average number of the host pupae recorded was 54.3/50 plants of which averages of 21.6, 35.7 and 0.4 % were parasitized by B. femorata, P. puparum and P. vulgaris, respectively. Average parasitism rate of the pupal parasitoids in this season was 57.6 % with a minimum of 17.6 % and a maximum of 85.8 %.
1. 1. 2. Survey on cauliflower crop in season 2007:
At the same period of survey mentioned before in cabbage, from the average of 50.4 pupae/50 plants in cauliflower, 12 % were parasitized by B. femorata, 38.6% by P. puparum, and 0.1 % were parasitized with P. vulgaris. The pupal parasitoids parasitized on 50.6 % with a minimum of 17.6 % and a maximum of 85.8 %.
1. 1. 3. Survey on cabbage crop in season 2008:
During 14 weeks began in September 12th finished in December 12th, and from the average of 65.8 pupae/50 plants, 32.5 % were parasitized by B. femorata, 23.2 % by P. puparum and only 0.6 % was parasitized by P. vulgaris. Total parasitism by the three pupal parasitoids can control the pest with an average parasitism rate of 56.3% with a minimum parasitism of 18.8% and a maximum parasitism 85.3%.
1. 1. 4. Survey on cauliflower crop in season 2008:
At the same period mentioned of survey in cabbage 2008, an average of 43.9 pupae/50 plants was collected from the field. The most abundant parasitoid was B. femorata followed by P. puparum, and P. vulgaris, with parasitism rates of 17.3, 11.0 and 0.8 %, respectively. In this season, primary parasitoids suppressed the host in pupal stage with an average parasitism rate of 29.0 % with a minimum parasitism of 11.3 % and a maximum parasitism 47.3 %.
1. 1. 5. Survey on cabbage crop in season 2009:
Along the season with the period between September 7th and December 28th, an average of 45.3 pupae/50 plants was collected from the field, of which 22.5, 35.1 and 0.8 % were parasitized by B. femorata, P. puparum and P. vulgaris, respectively. In this season, pupal parasitoids suppressed 58.4 % of P. rapae population with minimum and maximum of 17.4 and 100 %, respectively.
1. 1. 6. Survey on cauliflower crop in season 2009:
At the same period of survey mentioned in cabbage 2009, an average of 22.4 collected pupae, of which 25.9 % were parasitized by B. femorata, 20.0 % by P. puparum and only 0.9 % by P. vulgaris. Weekly parasitism with the three parasitoids showed an average parasitism ratio of 46.7 % with minimum and maximum of 8.3 and 100%, respectively.
1. 1. 7. Population fluctuation of P. rapae on cabbage and cauliflower:
Population fluctuation of P. rapae in season 2007, 2008 and 2009 showed that there were many peaks of P. rapae pupae population occurred either on cabbage or on cauliflower plants.
1. 1. 8. Activity of pupal parasitoids in relation to crops and seasons:
Comparing the results among the three seasons, P. rapae recorded high density in season 2008 with an average of 230.25 pupae/ month on cabbage, meanwhile on cauliflower the highest average number of 153.50 pupae/month was recorded in season 2008. P. rapae preferred cabbage crop more than cauliflower, since it was recorded with high population in the first rather than in the second crop with a ratio of 1.42:1 (213.25 pupae in cabbage: 150 pupae in cauliflower). Concerning parasitism, the pupal parasitoid, P. puparum was the main pupal parasitoid in each crop. It was recorded with an average parasitism of 31.15 % on cabbage and 23.00% on cauliflower during the three tested seasons. B. femorata recorded the highest activity in cabbage with an average of 25.89 % parasitized pupae, meanwhile in cauliflower the parasitism ratio was less recording 18.18% parasitized pupae. The third parasitoid was P. vulgaris which did not increase its parasitism over 0.6 % parasitized pupae at all tested seasons.
1. 2. Activity of larval parasitoids of P. rapae in cauliflower during seasons 2007, 2008 and 2009:
In comparison between the three seasons, the larval parasitoid Sinophorus xanthostomus showed its activity in the second week of November with parasitism rate ranged between 10 and 15 %. S. xanthostomus increased its activity in November and December reaching the highest activity in third week of December 2007, 2009, and at the last week of November 2008 with parasitism rate of 65, 75 and 95%, respectively. The average parasitism recorded 23.53% in season 2009, and 18.75% in season 2008, while in season 2007 the lowest parasitism ratio of 12.67% was recorded.
1. 3. Activity of larval parasitoids of P. rapae in cabbage during seasons 2007, 2008 and 2009:
Weekly investigations of twenty larvae of P. rapae collected from cabbage crop were carried out through the three successive seasons 2007, 2008 and 2009. All obtained larvae were free from parasitism by the larval parasitoid Sinophorus xanthostomus or any other larval parasitoids in the field.
1. 4. Activity of the egg parasitoids of P. rapae:
The weekly data during the three successive seasons on the two tested crucifer crops (20 larvae of P. rapae were collected/ week) showed that Trichogramma evanescens or any other egg parasitoids were not recorded on P. rapae eggs.
1. 5. The percentage of primary parasitism on P. rapae immatures:
P. puparum was observed as the main parasitoid in controlling the pest with percentage of 26.87 % parasitism. The following parasitism was B. femorata (23.82%) followed by S. xanthostomus (10.34%), and P. vulgaris (0.60%). Parasitization of P. rapae recorded the levels of 60.21 and 63.06 % in cabbage and cauliflower, respectively, with an average of 61.63 % in the two tested crops.
1. 6. The hyperparasitoid limiting the activity of P. rapae primary parasitoid:
During the three successive seasons 2007, 2008 and 2009 there was only one hyperparasitoid; Tetrastichus galactopus (Ratzeburg) (Hymenoptera: Eulophidae) attacking the primary larval parasitoid, S. xanthostomus, in the area of survey. T. galactopus was observed at one time during the period of study. It is observed that less than 5 % of S. xanthostomus was parasitized with T. galactopus. The hyperparasitoid, T. galactopus, makes a whole less in length and width than those made by the primary parasitoid, S. xanthostomus. Numbers of 10-20 of T. galactopus adults were emerged from each host.
2. Biological studies:
2. 1. The pupal prasitoid Pteromalus puparum:
2. 1. 1. Discrimination of host stage and developmental period of P. puparum immatures
The results indicated that the prepupal stage of P. rapae was the most suitable stage for parasitism with high parasitism rate of 55.57 %, associated with the shortest period in the parasitoid immature stage either in egg-larval stages (12.67 days) or in pupal stage (10 days). Sex ratio was found to slope more to the female with a ratio of 1 male: 2.08 female.
2. 1. 2. Effect of P. puparum female numbers on parasitism rate in prepupal stage of P. rapae:
In each treatment the parasitism ratio was 100%. Immature durations decreased related with the increment of parasitoid female numbers. The parasitoid recorded prolonged period in treatment with three females since egg-larval and pupal stages spent averages of 16.33 and 11.0 days, respectively, associated with a sex ratio of 1 male: 1.41 female. Meanwhile, the numbers of dead parasitoids inside each host increased related with density of female by product to parasitism pressure.
2. 2. Biology of Sinophorus xanthostomus and preferable host of different larval instars:
Host larvae were divided into two groups (1st and 2nd larval instars and 3rd and 4th larval instars) and exposed to fertilizing parasitoid females. Among the first group (1st and 2nd larval instars), data showed from 15 hosts, only one nonparasitized larva was recorded and the other 14 were parasitized with average of parasitism rate 80.0 %. Average longevity period from egg to larva was 18.0 days, while the period of pupal stage was 10.67 days. The sex ratio was 1 male: 1.16 female. Also, S. xanthostomus spend mating duration with period ranged between 5 and 15 minutes. In the 2nd group (3rd and 4th larval instars), no parasitism was recorded for all exposed larvae.
2. 3. The effect of age of P. rapae eggs on the parasitism rate of Trichogramma evanescens:
Numbers of P. rapae eggs in different ages (12, 24 and 48 hour) were exposed to females of the parasitoid, T. evanescens, to determine the effect of age of P. rapae eggs on the parasitism rate of T. evanescens. The results indicate that 12 hr old eggs of P. rapae were the most suitable age to obtain high parasitism rate (81.25 %), and average of 1.62 parasitoids was emerged from 1 host egg. The developmental period of parasitoid immatures inside P. rapae eggs were three days for egg-larval stage and 7.33 days for pupa stage. Older host eggs of P. rapae decreased both parasitism rate and the emergency of parasitoid, while the developmental period of immatures increased.
2. 4. Susceptibility of P. rapae to Bacillus thuringiensis in Dipel-2X formulation:
The results indicated that the mortality value in the tested larvae fed on cabbage leaves was higher (50.85%) than those fed on cauliflower leaves (45.00%). Meanwhile, data showed also that the latent effect of the bioinsecticide in pupal stage was more pronounced in larvae fed on in cauliflower leaves with an average mortality rate of 21.66 %. After 72 hours post treatment with Dipel-2X on cabbage or cauliflower leaves, higher mortality was recorded in the last instar larvae fed on cabbage leaves than those of cauliflower ones. Such LC50 values were 1.41 and 1.98 gm/L in cabbage and cauliflower, respectively.
3. Cabbage field application with some biological control agents:
The experiment carried out in El- Mahmoudia district, El-Beheira Governorate to determine the efficacy of three biological control agents [i.e. the pupal parasitoid, P. puparum, the egg parasitoid, T. evanescens, and the larval pathogen, B. thuringienses (Dipel2-X 3200 Iu/mg) against white butterfly, P. rapae, in cabbage field. The data collected weekly from the field, at period ranged between September 2nd 2009 and January 19th 2010.
3. 1. Biological control with pupal parasitoid P. puparum:
Mixed numbers of P. puparum male and female adults were released at the center of plot area (the area= 20x20m) as inoculative release in cabbage field after the emergency from its host pupae. The data collected in distances of 0.2, 2, 5 and 10 m from the release point. The temperature affected host population and its parasitoid during the three tested months; the general average of host density was 9.9 pupae and the parasitism rate recorded average of 6.1 parasitized pupae (61.6 %) when the temperature averaged of 19.8 Cº.
3. 2. Biological control with egg parasitoid, T. evanescens:
The egg parasitoid, T. evanescens, was applied in cabbage field at two times in November 2nd and December 7th, data collected from four points of release (0.2, 2, 5 and 10 m) from the release point to estimated parasitoid dispersal and activity under the field conditions. Average of 22.2 eggs was collected from the area of study from which 2.4 were parasitized by T. evanescens. Accordingly, the percentage of parasitism was 13.8 %, as the temperature and RH recorded 21.4 Cº and 57.8 %, respectively. When the temperature was under 20.7 and RH ranged between 57.3 and 58.6 %, no any parasitoid was recorded.
The parasitism rate of the pupal parasitoid, P. puparum, and the egg parasitoid, T. evanescens, in P. rapae pupae and eggs was recorded. As inoculate release, P. puparum dispersed after the release and parasitized 82.9 % of the host pupae and increased its percentage till it recorded 94.6 %. Thereafter, it decreased till the end week (31.6 %) related to the decreasing in temperature and host density. Concerning the parasitism by T. evanescens, the actual parasitism was more pronounced to the temperature and the host density.
3. 3. Biological control with B. thuringiensis as Dipel-2X formulation:
To evaluate toxicity of B. thuringiensis against P. rapae larvae, four concentrations of the bioinsecticide were applied in cabbage field. Data collected from each area (200m2) sprayed with each tested concentrations of 2.5, 5, 10 and 15gm /L and compared in the same time with those obtained in control area. Percentages of mortality were calculated weekly for each concentration. Application with 15gm/L caused 100% mortality with an average mortality of 96.5 %, followed by 10gm/L with an average mortality of 91.6 %, and 5gm/L with an average mortality of 87.5%. Meanwhile, mortality of 48.2% was obtained with a concentration of 2.5gm/L of the tested bioinsecticide.
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