الفهرس 
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Abstract
The lesser grain borer, R. dominica (F.) is a primary and common insect pest of stored grain worldwide.
The present investigation was carried out in the laboratories of the Faculty of Agriculture, Assiut University during 2018-2020. The main objectives of this work are to study the following points:
1- Biology of R. dominica under different constant temperatures.
2- Preference of certain gramineous species.
3- Susceptibility of some wheat varieties to the infestation with R. dominica.
4- Effect of temperature and microwave radiation on R. dominica as an alternative procedure to protect stored grains against R. dominica attack.
5- Description of a new mite species associated with R. dominica.
6- Preliminary evaluation of the new mite species for being an effective biological control agent.
The obtained results could be summarized as follows:
1 - Biological studies:
Effect of constant temperature of 25°, 30° and 35°C on the development of R. dominica
1.1. Immature stages:
1.1.1. Egg stage:
The incubation period varied from 10.14 to 6.04 daysin average at 25° and 35°C, respectively. There is a significant difference between of incubation periods at 25°, 30° and 35°C, which was 10.14, 8.2 and 6.04 days, respectively. The highest percentage of hatchability was (68%) at 25°C, whereas the lowest (40%) was noticed at 35°C. Developmental threshold of the egg stage was calculated to be 10.77°C and the thermal units required for development of this stage were about 150.85 (DD).
1.1.2. Larval and pupal stage:
Duration of larval and pupal stage was 52.2, 35.8 to 27.02 days in average at 25°, 30° and 35°C, respectively. The highest percentage of larval and pupal survival (58.48%) was recorded at 25°C, whereas the lowest (19.2%) was at 35°C. Developmental threshold was 14.25°C, and the thermal units required for development of this stage were about 561.9 (DD).
Duration of pupal stage varied from 13.84 days at 30°C to 25.14 days at 20°C. The highest pupal survival was (94.52%) at 30°C, whereas the survival percentages were 87.80 and 35.11% at 20° and 25°C. Developmental threshold of the pupal stage was 16°C, and the thermal units required for development of this stage were 150 (DD).
1.1.4. from egg to adult emergence:
The lesser grain borer R. dominica can complete its life cycle at the three constant temperatures. The longest period needed for the pest to complete its life cycle (62.34 days) was achieved at 25°, whereas it was 33.06 days at 35°C. The highest percentage of survival (58.48%) was recorded at 25°C, whereas the survival percentages were 19.2 and 39.48% at 35°C and 30°C. Developmental threshold for development of R. dominica from egg to adult emergence was 13.86°C, and the thermal units required form egg to adult development was 701.2 DD Developmental threshold for development of R. dominica of one generation were about 14.45°C, and the thermal units required for one generation was (840.35DD). under Assiut conditions, the pest could develop about 5.2 generations in a year.
1.2. Adult longevity and fecundity:
At constant temperature of 25°, 30°, 35°C mean pre-oviposition period of the pest was 16.5, 10.9 and 7.6 days, mean oviposition period was 70.75, 42.95 and 28.7 days and the post-oviposition period was 40.8, 31.2 and 22.7 days at 25°, 30° and 35°C, respectively. The mean numbers of eggs laid per female were 420.07, 322.9 and 151.7 at 25°, 30° and 35°C, respectively.
1.3. Some life table parameters:
At 25°, 30° and 35°C, the life table statistics of R. dominica, which taken into consideration are respectively, as follows:
• Generation time lasted for 110.7, 78.7 and 55.5 days.
• The population of the pest had the capacity to double (population doubling time, DT) every 16.9, 14.2 and 15.5 days.
• Net reproductive rate (Ro) was 92.07, 46.20 to 11.90 ♀/♀/generation.
• The values of the intrinsic rate of increase (rm) was 0.04085, 0.04886 and 0.04461.
• The population of the lesser grain borer could multiply about 1.0417, 1.0500 and 1.0456 ♀/♀/day.
Examination of the foregoing results clearly indicate that temperature of 30 °C was the most favorable condition for the development and reproduction of the lesser grain borer.
2. Susceptibility of certain gramineous species to infestation with R. dominica:
2.1. Susceptibility of different gramineous species:
2.1.1. Choice-infestation test:
All gramineous species except the polished rice and paddy rice had some degree of infestation by the pest. On the base of percentage of damaged grains and loss in weight, the least susceptible gramineous species was rice, where the percentage of infestation was 0 %, whereas the most susceptible species was yellow maize where the percentage infestation was 83.30% other crops were inbetween.
2.1.2. No choice (force) infestation test:
In respect to the percentage of infestation, there were significant differences between the tested gramineous. The tested gramineous species could be divided according to their susceptibility to the pest as following: the highly susceptible species was yellow maize where the percentage of infestation was about 54%, whereas the least susceptible species was polished rice, where the percentage of infestation was 0 % other crops were inbetween.
2.2. Susceptibility of some wheat varieties to R. dominica:
2.2.1. Choice infestation test:
There were significant differences between the tested wheat varieties in relation to their percentages of infested grains and/or their weight losses. According to both parameters, Gmiza 9, Misr 1, Sakha 69 and Sids 1 were the least susceptible varieties, whereas Misr 2, Misr 3 and Gmiza 11 were the most susceptible ones. There is a significant positive correlation (0.81**) existed between the number of damaged grains and weight loss.
2.2.2. No choice (force) infestation test:
Wheat varieties Misr 1 and Sids 1 were the least susceptible, whereas Misr 2, Misr 3, Sakha 93, Sids 4 and Shandawil 1 were the most susceptible to the lesser grain borer. A significant positive correlation (0.94**) was also found between the number of grains damaged and weight loss.
The two tests showed that Misr 1 and Sids 1 were the least susceptible, whereas Misr 2 and Misr3 were the most susceptible to the lesser grain borer.
3. Control:
3.1. Physical control:
3.1.1. Effect of high and low temperatures on R. dominica adults:
The effect of high and low temperatures on the adult of the lesser grain borer, R. dominica , were assayed as a physical control method.
3.1.1.1. High temperature (55°C):
A twenty nine percent of death occurred after 30 minutes of exposure, and a complete kill was recorded after 60 minutes of exposure. The LT50 and LT90 values were 36.96 and 63.4 minutes.
3.1.1.2. Cold temperature (-7°C):
A twelve percent of mortality was estimated after 20 minutes post treatment, and a complete succumb was obtained after 75 minutes post treatment. The LT50 and LT90 values were 38.6 and 71.3 minutes.
3.1.2. Microwave radiation at power of 2450 MHZ:
Microwave radiation was tested as a heat disinfestation method against the lesser grain borer. About third (33%) of the treated population was killed after 10-second exposure time whereas, a 100% mortality was recorded after 35-second exposure. The LT50 and LT90 values were 12.8 and 26.3 seconds.
3.1.3. Effect of high and low temperatures and microwave radiation on the germination of wheat grains:
The effect of high and low temperature, and microwave radiation on germination of the tested grains was also checked. Germination rates of the tested grains, which were exposed to low temperature (-7 °C) for three months and high temperature (55°C) for 60 minutes were 70% and 77.50%, respectively. Meanwhile, germination rate of wheat grains, which were exposed to microwave (2450 MHZ) radiation for 30 seconds was 5%. Hence, microwave radiation caused adverse effects on the germination of wheat grains and should not be used for planting.
3.2. Biological control:
Five mites were surveyed during the present study; one of them, Acarophenax dominicai, was first described as new species, and was recognized as an egg parasitoid.
3.2.1. Description of the new species and some biological aspects on Its life:
The new species of mite, Acarophenax dominicai (n. sp.) is described and illustrated based on males and phoretic females. The new species was parasitizing on the eggs of lesser grain borer, Rhyzopertha dominica (F.). Female progeny produced per single mother ranged from 18 to 22 young females (mean = 19.70, SEM = 0.30, n =18). Males always produced in scarce numbers, or not be found within the mother, with an average of 0 - 1 male (mean = 0.77, SEM= 0.23, n=18). Mite sex ratios were highly skewed in favor of females with an average of 19.70 ± 0.30 female and 0.77 ± 0.23 male.
3.2.2. Efficacy of Acarophenax dominicai on the insect population:
The number of R. dominica eggs consumed per progeny of A. dominicai female progeny ranged between 10 – 15 eggs (mean = 11.80 ± 0.60, n = 18).
Mean number of R. dominica adults resulting from eggs laid by a single mother after 43 days was 20.90 ± 0.99 (mites absent); 4.50 ± 0.50 host adults (mites present). This indicates the ability of A. dominicai to regulate population of this stored wheat pest. The number of adults decreased by about 75% because of mite presence.