الفهرس 
Introduction
Ecological studiesOnly 14 pages are availabe for public view
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Abstract
The cucumber, Cucumus sativus L. (Fam. Cucurbitacae) is one of the most important vegetable cash crops in Egypt and has significant economic values. The present studies were conducted at the Experimental Farm of Plant Protection Department, Faculty of Agriculture, Assiut University during the period from summer 2014 to spring 2016. Field and laboratory studies were oriented.
The main objectives of the present work are:
(1) Survey of pests and the natural enemies inhabiting cucumber plants in Assiut.
(2) Determine the relative abundance and dominance of the arthropods inhabiting cucumber plants.
(3) Determine seasonal population trends of the major pests and their predators inhabiting cucumber plants.
(4) Study the influence of the major weather factors such as, temperature and relative humidity (max. and min.) as well as biotic factors on the population activity of the major pests on cucumber plants.
(5) Study the effect of different constant temperature regimes on some biological aspects of the two-spotted spider mite infesting cucumber.
A) Ecological studies
1- Survey of pests and the associated natural enemies recorded on cucumber plants in Assiut
1.1. Results of survey indicated the presence of 39rthropods species a belonged to 28 families and 13 orders as well as some species of true spider (unidentified). The collected species can be classified as piercing-sucking pests. Five species of the key pests were recorded on cucumber plants: two-spotted spider mite, Tetranychus urticae;whitefly, Bemisia tabaci (Gen.); onion thrips, Thrips tabaci L. and cotton aphid, Aphis gossypii L.
1.2. Results also indicated that fifteen species were identified as entomophagous as well as true spiders (unidentified species).These species belonging to 11 families and 7 orders (Dermaptera, Thaysanoptera, Hemiptera, Neuroptera, Coleoptera, Diptera and Acari).The common predators were eleven spotted lady beetle, C. undecimpunctata (Coleoptera), C. impicta (Hemiptera: Heteroptera) and S. sexmaculatus. As well as a single species of fungal pathogen, attacking thrips on cucmber field.
2- Dominance and abundance degrees of the pests and the associated predators inhabiting cucumber
The field studies through the period extended from summer 2014 to spring 2016 seasons; showed the presence of four species of serious pests on cucumber plants: the two-spotted spider mite, T. urticae.;whitefly, B. tabaci;onion thrips, T. tabaci and cotton aphid, A.gossypii.
2.1. During spring plantations regardless of the growing seasons, T. urticae is the most important economic pests as indicated by the highest value of dominance and abundance degree (77.02 and 100%). However, the highest abundance degrees (100.00%) of B. tabaci and T. tabaci which had relatively high dominance degrees (12.40 and 9.96%) indicated that these species could be of economic importance. Meanwhile, A. gossypii which had low values of dominance and abundance degree (0.06 and 60.00%) is expected to be of little economic importance during the spring plantations
2.2. During summer plantations regardless of the growing seasons, B. tabaci seemed to be the most important economic pests as indicated by the highest value of dominance (57.04%) and abundance (100%). However, the relatively high abundance degrees of T. urticae and T. tabaci which had relatively low dominance degrees (19.68 and 8.49%) indicated that these species could be of economic importance during summer plantations. Meanwhile, A. gossypii which had low values of dominance and abundance degrees (1.16 and 75.00%) is expected to be of little economic importance.
2.3. The present results indicated generally that the numbers of pests of cucumber plants were higher during spring plantations than that during summer plantations. The mean number of the pests during spring plantation was 437.55 individuals leaf as compared with 129.15 individuals leaf during summer plantations.
2.4. The low dominance degrees of the recovered natural enemies showed that these predators may play an insignificant role in regulation the pest populations in cucumber during spring and summer plantations.
3. Relative abundance of arthropod pests inhabiting cucumber plants
Seasonal abundance of the pests infesting cucumber plants was studied by taking weekly samples during three seasons of 2014, 2015 and 2016 in Assiut Governorate.
3.1. During spring plantations of 2015 and 2016 it is cleared that, the two spotted spider mite, T. urtica was the most common pest followed by whitefly, B. tabaci, onion thrips, T. tabaci.thenthe cotton aphid, A. gossypium. However, the number of natural enemies was relatively low in the studied area during this season.
3.2. The obtained results showed that the spider mite, T. urtica population during spring plantation of 2016 fluctuated in relatively high densities during whole season with a peak during the middle of May when the plant age was 43 days old and the presence of an average level of temperature and relative humidity.
3.3. The data of the spring plantation of 2015-2016 revealed that the young cucumber plants harbored higher B. tabaci population than the older ones.
3.4. The population level of the pests infesting cucumber during the spring seasons was nearly in at the same level during 2015 and 2016 seasons. In addition, the data indicated that the number of predators was not significantly correlated with pest populations during the spring plantations of 2015 and 2016 seasons, probably because of the lowestnumbers of predators recored in the studied area.
3.5. The population of the pests was relatively higher during summer plantations of 2014 than that of 2015 season. The cucumber plants were severely infested by B. tabaci during summer plantations than other pests and the number of cotton aphid, A. gossypii was extremely low in the studied area during this season.
3.6. The cucumber plants cultivated in the spring plantation harboured relatively high numbers of pests, Meanwhile, the plants in summer plantations harboured relatively low numbers of the pests. The present study showed that the cucumber plants severely affected by the two spotted spider mite, T. urticae and the whitefly, B. tabaci. In addition to the scarce numbers of predators recored during spring and/or summer plantations.
B. Biological studies:
Biological events of the arthropods in relation to key environmental factors are necessary to determine the extent of their influence on the population dynamic of the pests. Temperature has long been recognized as a primary environmental factor influencing the rate of development of arthropods. Although much information are available regarding the two- spotted spider mite T. urticae, little attempt has been made to utilize the theories of the thermal constants to characterize the population growth of this pest. The present investigations were carried out to study the effect of constant temperature regimes of 20º, 25º and 30ºC on the development of T.urtica in order to estimate the temperature developmental threshold (t0ºC) and thermal units (day-degrees) required for the development of the immature stages as well as the reproductive potential of adult of the two- spotted spider mite, T. urticae.
1. The calculated developmental threshold (t0) of T. urticae was 10.41ºC. By using this value as a base temperature, an average of about 173.39 day-degrees is needed for the two spotted spider mite to complete one generation.
2. The values of reproduction rate (Ro),intrinsic rate of increase (rm) and finite rate of increase(ʎ) increased with an increase of temperature.While mean generation time (Gt) and generation doubling time (DT) value decreased when temperature increased,thus T.urtica favored hightemperature in the range of the tested temperature.
3. The foregoing results concerning, the duration, survival and index of efficiency in relation to temperature clearly indicated that temperature degrees of 25º and 30ºC were the most preferable temperature for development and multiplication of the two-spotted spider.
4. The results of the present work may add some knowledge to be used in the integrated pest management programs for control cucumber pests.