الفهرس 
Literature reviewOnly 14 pages are availabe for public view
 |  | from | 217 |  |  |
| | | from | 217 | | |
Abstract
VI- SUMMARY
The Indian meal moth, P. interpunctella and the Mediterranean flour moth, E. kuehniella are among the most common stored product pests. Owing to their habitat, eggs and larvae of stored grain and fruit pests are often the most difficult life stages to control. Parasitizatoin is the best alternative to insecticides as biocontrol agents. Hymenopterous parasitoids are natural components of the stored grain ecosystem and some species are of potential value as biocontrol agents. Bracon hebetor is a gregarious, idiobiont ectoparasitoid that is known to attack and develop successfully on the larvae of many lepidopterous pests of stored products.
This study was conducted to understand the interfering between B. hebetor parasitoid and its hosts. Therefore, the research focused on the effect of P. interpunctella and E. kuehniella on different biological aspects of the parasitoid and the impact of parasitization on the immune response of these hosts. So, the present study covers the following points:
1. Effect of the two hosts, on the biology of the parasitoid wasp, B. hebetor:
1.1. The developmental time and longevity of B. hebetor:
B. hebetor indicated insignificant difference in developmental time of immature stages on the two hosts. The present study assured that male and female longevity of the parasitoids was significantly longer when reared on E. kuehniella than P. interpunctella.
The bee honey meal solution played an obvious role in significant increasing the male and female longevity for parasitoid reared on E. kuehniella (18.58 ± 0.15 and 24.67 ± 0.14 d, respectively) and P. interpunctella (15.33 ± 0.14 and 21.92 ± 0.29 d, respectively). In general, male longevity was shorter than female longevity of the two hosts with and without feeding.
1.2. Susceptibility of the two hosts to the parasitization:
B. hebetor showed significantly increasing parasitization level on the 5th instar host larvae of P. interpunctella and E. kuehniella than other larval instars. B. hebetor preferred to paralyze P. interpunctella rather than E. kuehniella with significant difference at P ≤ 0.05.
2. Nutritional value and body mass of the two hosts, P. interpunctella and E. kuehniella 5th larval instar:
Results showed that the protein content was higher in 5th larval instar of P. interpunctella than E. kuehniella with significant change P ≤ 0.05. On the other hand, E. kuehniella had the higher carbohydrate and lipid content than P. interpunctella with significant change P ≤ 0.05. These results revealed that the ratio of protein: carbohydrate: lipid (P: C: L) in P. interpunctella was higher (6.3: 2.3: 1) than those of E. kuehniella (2.6: 1.7: 1). On the other hand, insignificant difference between the body mass of E. kuehniella and P. interpunctella was observed.
3. Effect of the B. hebetor parasitization on the heartbeat rates of the two hosts:
Host larvae were paralyzed and their mobility was inhibited completely when parasitized by B. hebetor. The results indicated that the heartbeat rate highly decreased significantly in the two hosts at 12, 24, 48 and 72 hrs post parasitization with respect to non-parasitized larvae. However, the cardiac muscle was still playing its function until 3 days after parasitization.
4. Immune response:
In order to screen the interactions between parasitoids and their hosts, immunological studies have been conducted through the characterization of haemocytes, some enzyme activities and gene expression of Hsp90 in 5th larval instars of the both hosts.
4.1. Effect of B. hebetor parasitization on cellular immune response of the two hosts:
4.1.1. Haemocytes description in normal P. interpunctella and E. kuehniella 5th larval instar:
Morphological characteristics of normal haemocytes were distinguished based on cytological parameters and staining properties using light microscope. Five types of haemocytes were found; PRs, PLs, GRs, SPs and OEs.
4.1.2. Haemocytes changes in P. interpunctella and E. kuehniella 5th larval instar:
After parasitization by B. hebetor certain changes were observed in the P. interpunctella and E. kuehniella haemocytes of 5th larval instar at 12, 24, 48 and 72 hrs. These changes characterized as: (1) haemocytes became irregular in shape, (2) distortion and degeneration of the plasma membrane, (3) vacuolization and degeneration of the cytoplasm and (4) nuclear appeared irregular.
4.1.3. Total haemocyte counts (THCS) in P. interpunctella and E. kuehniella 5th larval instar:
Results indicated that non-significance change in the THCs of the two lepidopteran hosts at 12 and 24 hrs post parasitization compared with nonparasitised larvae. On the other hand, at 48 and 72 hrs THCs showed a significance decrease in both hosts compared with nonparasitised larvae.
4.1.4. DHCs in P. interpunctella 5th larval instars:
The results showed that the predominant type of the haemocytes is the, GRs (35.33 ± 5.84 %) followed by the PLs (26.67 ± 6.06 %) then SPs (26.00 ± 0.58 %) with insignificant difference then OEs, (7.33 ± 0.33 %) and finally. PRs (4.67 ± 3.71%) with significant difference.
After parasitization, PRs decreased significantly at 12, 24 and 48 hrs post-parasitization, respectively compared to non-parasitized larvae. At 72 hrs post-parasitization the increase was insignificant. Concerning to PLs, they showed slight change at all interval time post parasitization. Related to GRs, they increased significantly P ≤ 0.05 at all interval time post parasitization. The maximum increase of GRs at 24 hrs and decreased at 72 hrs post parasitization. OEs decreased significantly at 12 and 24 hrs post parasitization and increased insignificantly at 48 and 72 hrs post parasitization compared to non-parasitized larvae. Finally, SPs decreased significantly at all-time intervals.
4.1.5. DHCs in E. kuehniella 5th larval instars:
The haemocyte types were investigated and the results indicated that GRs, PLs and OEs are the predominant types of the haemocytes (30.67 ± 1.68, 30.00 ± 3.75 and 26.33 ± 1.25, respectively) in normal non-parasitized larvae. They are followed by SPs, (9.33 ± 1.15) then PRs, (3.67 ± 0.77).
Owing to parasitization, PRs disappeared at 12 hrs post parasitization. They decreased significantly (P ≤ 0.05) at 24 and 48 hrs post parasitization compared to non-parasitized larvae. While, at 72 hrs post parasitization PRs increased significantly (P ≤ 0.05). Moreover, the results showed a significant increase of PLs at all-time intervals in comparison with non-parasitized larvae. On the other hand, GRs were recorded insignificant decrease at all-time intervals compared to non-parasitized larvae. Concerning to OEs, they increased insignificantly at 12 and 24 hrs post parasitization compared to non-parasitized larvae. They reached its maximum increase at 48 hrs post parasitization with significant change relative to non-parasitized larvae. While, they decreased insignificantly at 72 hrs post parasitization compared to non-parasitized larvae. Finally, SPs decreased significantly at 24 and 48 hrs (P ≤ 0.05) and in significantly at 12 and 72 hrs post parasitization.
4.2. Effect of parasitization by B. hebetor parasitization on humoral immune response of the two hosts:
The effect of parasitization on some enzymatic activities which might play an important role in the immune response of both hosts was conducted.
4.2.1. PO activity:
Results of parasitization by B. hebetor on PO activity of P. interpunctella indicated that highly significance decrease at 12, 24 and 72 hrs post parasitization compared with control. Additionally, nonsignificant decrease in PO activity was recorded at 48 hrs. In concerning with E. kuehniella, there was a significant increase in PO activity compared to control at all-time interval but decraesed at 72 hrs after parasitization.
4.2.2. SOD, peroxidase and esterases activity:
The obtained results by measuring SOD, peroxidase and esterases outlined a significant increase at all hours post parasitization in comparison with non-parasitized larvae in both hosts.
5. Gene expression of heat shock protein 90 (Hsp90) in the two hosts:
The current study cleared the role of hsp90 during the parasitization of B.hebetor on 5th larval instar of P. interpunctella. The results showed a significant downregulation of Hsp90 at 12, 24 and 72 hrs after parasitization compared with control. On contrary, there was highly significant upregulation at 48 hrs after parasitization.
Moreover, after parasitization of E. kuehniella 5th larval instars there was obvious positive relationship between hsp90 gene expression level and the time. Although the rate gene expression decreased significantly all time intervals post parasitization comparing with the control. This rate continued to rise and even remained significantly below the normal rate comparing with control insect and reached the peak after the 72hrs after parasitization.
In conclusion, ectoparasitic wasp, B. hebetor is an important parasitoid of a vast array of pests in agricultural systems. In this study, P. interpunctella 5th larval instars are more suitable hosts than E. kuehniella for the parasitoid B. hebetor. The obtained experimental data showed the suppression of the main immune reactions in both hosts parasitized by female of B. hebetor. Such influence on the host organism can be beneficial for a parasitoid because the products takes part in the coagulation of haemolymph and in haemocyte aggregation would lead to difficulties in the feeding of parasitoids. In general, each parasitoid-host system is unique. It is our hope that these data would be helpful in understanding the host immune response to parasitization.