الفهرس 
INTRODUCTION
Ecobiological studiesOnly 14 pages are availabe for public view
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Abstract
The present investigation was carried out to study the effect of some ecological factors such as temperature and photoperiod on the development of immature and adult stages of the granary weevil, Sitophilus granarius infesting wheat in Upper Egypt. Beside this, the susceptibility of certain wheat varieties to infestation with the weevil was also investigated. The study was also extended to test the toxicity and repellency effects of some pesticide alternatives, 2 plant essential oil, 2 plant extracts and 2 inorganic salts against the pest. The results could be summarized as follows:
1- Effect of temperature:
Effect of temperature regimes 15, 20 and 25°C on various developmental stages was studied.
1.1- Immature stages:
1.1.1- Egg stage:
The incubation period of the egg stage decreased significantly with the increase in temperature. The embryonic development averaged 15.3, 11 and 5.8 days at 15, 20 and 25°C, respectively. Also, the developmental threshold of the egg stage was calculated to be 9.79°C and the thermal units required for the development of the egg stage were 93 day degrees.
1.1.2- Larval stage:
At given temperature, the time needed for the development of larval stage decreased significantly with the increase in temperature. Larval duration varied from 46.6 days at 15°C to 21.2 days at 25°C. The developmental period of larval stage was approximately three times more than that of egg stage at any given temperature. The calculated developmental threshold of the larval stage is about 7.31°C and average of about 394 day degrees are needed for the larva to complete its development.
1.1.3- Pupal stage:
The temperature threshold of the development of pupal stage was 14.08°C. Thus, the accumulative effective temperature required for the development of this stage was about 45 day degrees. This result indicates that pupal stage needed about 89% less thermal units for its development than larval stage and about 51% than egg stage.
1.1.4- from egg to adult:
The total developmental period from egg to adult emergence including the remaining period of adult inside the wheat grains was found to be significantly affected by the variation in temperature. The longest duration required for insect to complete its life cycle was 106.4 days and that achieved at 15°C. Increasing temperature from 15 to 25°C reduced this period to 37.4 days. Developmental threshold for egg to adult was 9.97°C and the corresponding thermal constants needed for the development of one generation were about 562 day degrees. It could be concluded that increasing temperature by 10°C i.e. from 15 to 25°C decreased the total developmental period of the pest by about 65% comparing with that observed at 15°C.
1.2- Adult stage:
1.2.1- Adult remaining period:
The granary weevil, after emergence from pupa remains inside the grains for some days before existing out. This period is called remaining period. Thus, the results indicated that adult weevil remained for short periods (6, 5.6 and 5 days) inside the grains at 15, 20 and 25°C, respectively. Statistical analysis of the data showed insignificant effects of tested temperature on this period.
1.2.2- Ovi-position periods:
- Pre-oviposition period
The period between the adult moult and the onset of reproduction which is called pre-oviposition period was gradually decreased with the increase in temperature. This period ranged between 34.3 days at 15°C and 5.1 days at 25°C. At 15°C females began to lay eggs after 34.3 days from emergence, while at 20 and 25°C, they started laying eggs after 6.8 and 5.1 days, respectively. Thus, this period was negatively correlated with the temperature. Regardless of the temperature this period extended to the shortest time of the whole longevity of adult female stage (14.1%). Statistical analysis of the data revealed significant effect of temperature on pre-oviposition period.
- Ovi-position period
Temperature affects significantly the duration of ovi-position period of insect females, the higher the temperature, the shorter the oviposition period. At 15°C ovi-position period lasted for 92.2 days, but at 25°C this period decreased up to 63.1 days. Irrespective to temperature, the ovi-position period extended to the longest time of the whole longevity of adult female stage (71.0%).
- Post-oviposition period
The post-oviposition period followed nearly the same pattern of the pre-oviposition and ovi-position periods, where it was decreased with the increase in temperature. This period ranged between 21.4 days at 15°C and 6.8 days at 25°C which was approximately one third of that recorded at 15°C. Post-oviposition period as pre-oviposition period extended to the shortest time of the whole longevity of adult female stage (13.9%). The analysis of variance showed significant effect of temperature on this period.
1.2.3- Adult longevity:
Survival periods of adult decreased considerably with the increase of temperature from 15 to 25°C. Adults reared at 25°C survived only about half of those reared at 15°C. At all tested temperatures adult males lived longer than females.
1.3- Determination of annual generation numbers:
Based on threshold temperature of various developmental stage of the pest, about 9 generations could be developed annually under Assiut prevailing conditions.
2- Effect of photoperiod
Photoperiod is one of the most important environmental factors affecting development of several insect species. Therefore, the effect of this factor on different developmental stages of S. granarius could be summarized as follows:
2.1- Immature stages:
2.1.1- Egg stage:
The highest mean incubation period (3.9 days) was recorded at 24 hr photophase, while the lowest (3.1 days) was observed at 16 hr photophase. Statistical analysis of the data indicated that incubation period of eggs was considerably affected by the experimental photoperiod at 16 and 24 hr photophase.
2.1.2- Larval stage:
The duration of larva was gradually increased with the increase in photophase hours. The shortest larval duration was observed at complete darkness, whereas the longest one (25.3 days) was shown at 24 hr photophase. Statistical analysis of the data proved significant effect of photoperiods on the larval developmental period of S. granarius. These results show that continuous light increases larval developmental period indicating that granary weevil larvae in their response to light are photonegative.
2.1.3- Pupal sage:
Pupae exposed to continuous light (24 hr L: 0 hr D) showed the lowest mean pupal period (4.7 days) as compared with 5.4 days for pupae exposed to 16 hr L : 8 hr D and 6.2 days for those reared at 0 hr L : 24 hr D. These results showed that pupae of S. granarius in contrast to larvae are photopositive.
2.1.4- from egg to adult:
The period from egg to adult was markedly influenced by the tested photoperiods. The longest developmental period (40.9 days) was observed at 24 hr photophase and the shortest one (33.7 days) was recorded at 0 hr photophase (complete darkness).
2.2- Adult stage:
2.2.1- Adult remaining period:
Adult that remained inside wheat grains after its emergence from pupal stage was influenced by the three experimental light systems. The adults of both sexes reared under complete darkness remained shorter period (4.4 days) inside the grains than those reared under continuous light (5 days).
2.2.2- Ovi-position periods:
- Pre-oviposition period:
The longest pre-oviposition period (6 days) was observed for females kept at continuous light whereas, the shortest one was recorded for females kept under complete darkenss. Pre-oviposition period for adult females exposed to 16 hr photophase lasted for 5.2 days. Statistical analysis of the data showed significant effect of photoperiod on pre-oviposition period.
- Ovi-position period
Adult females kept in complete darkness recorded the longest ovipositioin period (89.4 days). Meanwhile, the shortest period (84.6 days) was observed for females lived under continuous illumination.
- Post-oviposition period
The post-oviposition period of adult females decreased by increasing the photophase period. Adult females reared under continuous illumination had the shortest ovi-position period 11.7 days while those exposed to complete darkness had the longest one (17.3 days).
2.2.3- Adult longevity:
Adults exposed to complete darkness lived longer (109.2 days) than those lived under continuous illumination (102.9 days) or those exposed to darkness even for a short time (105.5 days). Generally, both sexes lived nearly equal periods at any tested photoperiodic regimes. Significant effects of photoperiod on adult longevity were also observed.
3- Susceptibility of wheat varieties to the infestation with S. granarius:
Relative susceptibility of ten Egyptian wheat varieties to the infestation with the granary weevil, S. granarius, was evaluated. The loss in grain weight and the percentage of infested grains after three generations of the pest were determined in choice and no-choice (force) infestation tests. Results obtained from both tests indicated that non of the tested varieties were completely resistant against the attack by the insect, but their susceptibility to the infestation varied considerably.
3.1- Choice infestation test:
On the base of percentage of damaged grains and weight loss of the tested wheat varieties after three generations of the pest, the results indicated generally that Beny-Sewif 4, followed by Sakha 94 and Sakha 95 varieties were the least susceptible, whereas Gemmiza 9 and Gemmiza 7 were the highly susceptible ones. However, the results showed also that after the third generation percent of infestation and weight loss seemed to be greater than those recorded after first and second generations.
3.2- No-choice (force) infestation test:
Generally, infestation levels and weight loss values in case of no-choice infestation test were lower than those observed in choice infestation test. According to the weight loss, the adult after the first generation had not caused loss greater than 2.19 g/100 g grains. Beny-Sewif 4 appeared to be the least damaged variety with an average weight loss of 0.54 g/100 g grains while Gemmiza 7 was the most damaged one with an average weight loss of 2.19 g/100 g grains. After the second generation, granary weevil was damaging some varieties more severely than others. Here also, Gemmiza 9 and Gemmiza 7 were the highly susceptible varieties. After the third generation the situation did not differ than that observed after the first and second generations where Beny-Sewif 4 followed by Sakha 94 and Sakha 95 were the least susceptible varieties, while Gemmiza 7 followed by Gemmiza 9 and Shandwil 1 were the most susceptible ones. Statistical analysis of the data proved clear significant differences between some varieties concerning their susceptibility to infestation.
from choice and no-choice infestation test results, it may be suggested that wheat varieties could be classified into three groups on the base of infestation percent and weight loss values. Highly susceptible varieties Gemmiza 7, Gemmiza 9 and Shandwil 1. Moderating susceptible varieties Giza 168, Sids 1, Sohg 2 and Sohag 3. Slightly susceptible varieties Beny-Sweif 4, Sakha 94 and Sakha 95.
3.3- Effect of wheat varieties on fecundity of S. granarius:
In choice infestation test, the maximum mean number of eggs/female (159.33) was observed on Gemmiza 7 followed by Gemmiza 9 (134.66) whereas, the minimum mean number (16.66) was recorded on Beny-Sewif 4 followed by Sakha 94 (24.66) and Sakha 95 (32.00). The rest of the tested wheat varieties was moderately preferred for egg laying. The same trend was shown in case of no-choice infestation test. These findings support the previously mentioned suggestion where wheat varieties could be classified into three classes, highly, moderately and slightly susceptible varieties.
3.4- Effect of proteins, carbohydrates and moisture contents of wheat grains on infestation levels:
Proteins, carbohydrates and moisture contents of ten wheat varieties were assessed. Statistical analysis proved significant differences between all tested varieties in the triple checked characters. Beny-Sewif 4 had the lowest content of proteins (12.66%), moisture (10.03%) and highest content of carbohydrates (73.43%) whereas, Gemmiza 7 had the highest content of proteins (16.54%), moisture (11.82%) and lowest content of carbohydrates (69.29%). These results came as it was expected that Beny-Sewif 4 was the most resistant while Gemmiza 7 was the most susceptible one.
4- Control studies:
4.1- Toxic effect of certain plant essential oil, plant extracts and inorganic salts against S. granarius:
Toxicity of 6 materials, 2 plant essential oil (clove and flax seed oil), 2 plant extracts (neem and harmal seed extract) and 2 inorganic salts (silica dust and tri-calcium phosphate) mixed with wheat grains at different concentrations was studied. Based on LC50, LC90, LT50 and LT90 values and both lower and upper values of confidence limits as well as slope value of LCP lines for the sixth materials, the obtained results indicated in general that, these compounds can be arranged according to their effectiveness at all tested concentrations as follows: clove oil > flax seed oil > silica dust > tri-calcium phosphate > neem seed extract > harmal seed extract.
4.2- Repellency effect of certain plant essential oil, plant extracts and inorganic salts against S. granarius:
4.2.1- Plant essential oil:
The obtained data showed that clove and flax seed oil play a significant role on the target species by forcing it to move from treated grains to untreated ones. The maximum percent (100%) of repealed alive insects due to clove oil was recorded after 2, 4 and 6 hours of treatment at concentrations of 20, 10 and 5 ml/kg grains. Similar results were obtained in case of flax seed oil where, the maximum repellency effect (100%) was observed after 2, 4, 6 hours of treatment at concentrations of 20, 15 and 10 ml/kg grains, but this maximum effect was prolonged to 8 hours after treatment at concentration of 5 ml/kg grains. Also, repellency activity of both oils was gradually decreased with the passage of time to reach its lowest levels after 12 hours of treatment. Considering the total mean effect of the two oil during the whole experimental period, it may be stated that both plant essential oil showed excellent results exhibiting potent repellent activity against granary weevil adults with non-significant differences among them and in all cases their repellency class tended to IV class or stronger during the whole exposure period.
4.2.2- Plant extracts:
The results on the repellency effects of neem and harmel seed extracts against granary weevil showed that both extracts had maximum repellency 89.69 and 86.52%, respectively at the highest concentration 1000 ppm, while the lowest concentration (250 ppm) had minimum repellency effects (62.92 and 71.56%, respectively). Repellency effects of these extracts were as in case of plant oil increased proportionally to the concentration, but in contrast to plant oil were gradually increased with the progress of exposure period up to 8 hours, then reduced till the end of experiment. Both extracts exhibited potent repellent activity against the pest and repellency values ranged between IV class and V class during the whole exposure period.
4.2.3- Inorganic salts:
The repellency action of silica dust and tri-calcium phosphate on the granary weevil followed nearly the same trend as that shown in case of plant essential oil and plant extracts. Highest repellent effect of silica dust (87.26%) during the whole exposure period was observed at concentration of 5 g/kg, while it was 79.39% for tri-calcium phosphate. Lowest mean repellency (56.39% and 41.04%) of silica dust and tri-calcium phosphate, respectively was recorded at concentration of 1.25 g/kg. Thus, these results show that both salts exhibited high repellency activity against S. granarius and repellency values ranged between III class and IV class.
Results on the toxicity and repellency effects of some pesticide alternatives lead us to believe that some plant extracts, plant essential oil and inorganic salts may prove to be a distinct class of insecticides only under some conditions against the granary weevil attack and to prevent post-harvest losses as well as to avoid problem results from traditional insecticides currently used against stored product insects.
Finally, it may be stated that the information given in the present study are of great value and can be used as a base for developing an integrated pest management program for controlling S. granarius in Upper Egypt.