الفهرس 
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Abstract
Vegetables are considered as an important crops as a source of fibers, carbohydrates, proteins, vitamins and other nutrient elements needed for human food. Several pests attacking these crops and affected the yield quantity and quality. The present study was conducted in the Farm of the Faculty of Agriculture, Minia University during two successive years of 2005 and 2006.
Three vegetable crops belonging to three different families i.e. snap-beans (Phaseolus vulgaris: Leguminosae), cucumber (Cucumis sativus: Cucurbitaceae) and tomato (Lycopersicon esculentum: Solanaceae) were chosen to survey and investigate the population density and fluctuations of common sucking insects and their natural enemies, as well as, the leafminers. The study also, extended to examine the effect of plant cultivar, host plants, hand-hoeing, biocides on the leafminer infestation and yield. Moreover, the effects of weather factors on the population density of sucking insects and leafminers were also included and discussed.
1.General survey of insect fauna:
Survey studies of the insect fauna on the three vegetable crops revealed the presence of 26 insect species belonging to 17 families and 8 orders on all crops by using visual direct count method. The harmful insect species represented by 13 species on tomato, cucumber and snap-beans associated with 6 predaceous species on all crops and one parasitoid species on tomato and cucumber. Only one insect species of pollinator (Apis mellifera) was generally recorded.
In general, the common sucking insect pests were Thrips tabaci, Bemisia tabaci, Empoasca spp., Aphis gossypii, Aphis craccivora, Myzus persicae and the predators i.e. Coccinella undecimpunctata, Orius spp., Chrysoperla carnea and Metasyrphus corollae. However, low numbers of Spodoptera littoralis, Spodoptera exigua, Agrotis ipsilon, Nezara viridula, Oxycarenus hyalinipennis and other natural enemies were observed on all studied crops. Moreover, Cosmolyce baeticus on snap-beans, Heliothis armigera on tomato, Dacus ciliatus and Epilachna chrysomelina on cucumber were observed.
2. Population density of sucking insects:
The population density and fluctuation were investigated on snap-beans, cucumber and tomato as follows:
a. On snap-beans
The most abundant sucking insect pests as average numbers/10 leaflets was Thrips tabaci followed by whitefly, B. tabaci then jassid, Empoasca spp. during the two successive seasons of 2005 and 2006. Thrips numbers gradually increased from the beginning of both seasons and showed remarkable two peaks during the 4th week of April (115.5 individuals) and the 4th week of May (90 individuals) during 2005 season, while one peak only was recorded during the 4th week of May 2006 (82.2 individuals). Whitefly B. tabaci appeared with low numbers and reached its maximum density during the 3rd week of May for both seasons (37-41.2 individuals). The leafhopper, Empoasca spp. population was fluctuated during both seasons and reached its maximum number during the 2nd week of May (26.2-33.5 individuals). The cowpea aphid A. craccivora was slightly abundant for 12 weeks during 2005 season and the maximum numbers were 40 individuals/10 leaflets, however, it was appeared 5 weeks only during 2006 season and not exceeded 11 individuals/10 leaflets.
b. On cucumber:
The onion thrips T. tabaci was the most abundant pest. Three peaks were detected during April and May 2005 and two peaks in the same months during 2006. The peak occurred during the 4th week of May for both seasons was the greatest (520.3-762.3 individuals/10 leaves). Whitefly, B. tabaci population was abundant during April-May and declined during June of both seasons. The maximum numbers were recorded in the 2nd week of May 2005 and one week later during 2006 season (160.5 and 263.2 individuals/10 leaves, respectively). Leafhoppers number was relatively high during 2005 season and showed 2-3 peaks for each season ranged between 18-23.3 individuals/10 leaves. The melon aphid was slightly occurred throughout 6-8 weeks and the maximum density was observed during the 2nd week of May for both 2005 and 2006 seasons (28.3 and 18 individuals/10 leaves, respectively).
c. On tomato:
The whitefly, B. tabaci was the most abundant pest. Its numbers were sharply fluctuated during the all periods of both seasons. The highest numbers were appeared during the 4th week of April 2005 and the 3rd week of May 2006 (55 and 52.1 individuals/10 leaflets, respectively) and the population decreased from July of both years. Thrips showed three distinct peaks during 2005 season and only one peak during 2006 (ranged between 20-30.5 individuals/10 leaflets) and the pest disappeared from the 1st week of July 2005 and one week later during 2006 season. Leafhoppers population showed its maximum numbers during May and June and peaked two times of each season ranged between 16.5-22.7 individuals/10 leaflets. The green peach aphid, M. persicae existed for 11 weeks during 2005 and showed maximum numbers during the 3rd week of April (22 individuals/10leaflets). However, during 2006 season it is appeared only 4 weeks and not exceeded 2.5 individuals/10 leaflets.
In general, the overall of Thrips tabaci in both seasons was represented by 76 and 48.2% of the total mean numbers of sucking insects on cucumber and snap-beans, respectively, however, the whitefly represented by 47.5% on tomato plants.
3. Population density of the predators and its relationship with their preys:
The most common predators were Coccinella undecimpunctata and Orius spp that occurred on the all studied crops and approximately showed similar densities except that the lady bird beetle was permanently existed during both seasons, while the predaceous anthocorid bug appeared during May and June. Chrysoperla carnea and Metasyrphus corollae were observed during May till mid-June with very low numbers on all studied vegetable crops.
Significant positive correlation between the population density of predators and their preys (sucking insect) were recorded on all crops during both seasons of 2005 and 2006 (“r” ranged between 0.561-0.886).
4. Effect of weather factors on the population abundance of sucking insects on vegetable crops:
Simple correlation coefficient values between the population density of sucking insects and weekly means of maximum and minimum temperatures were positive and significant (r= ranged between 0.709-0.876) for cucumber during 2005-2006 seasons, while it was positive and significant for snap-beans during 2006 season (“r” ranged between 0.666-0.748). However, temperatures showed insignificantly negative correlations on tomato. Relative humidity showed significant negative correlation on cucumber during 2005 season only (r= 0.759). However, relative humidity showed insignificant positive correlation with sucking insects density on tomato during both seasons.
Explained variance (E.V. %) for the combined effect of the three weather factors on the total population of sucking insects infesting snap-beans and tomato during 2006 season were highly significant (E.V. % = 96.31 and 88.77%, respectively). Also these factors significantly affected the sucking insects infesting snap-beans and cucumber during 2005 season (E.V.% =70.36 and 85.52, respectively). However, weather factors were insignificantly affected the sucking insects abundance on tomato during 2005 and cucumber during 2006. This indicated that the weather factors were within the optimum zone of sucking insects development and lost its complete efficacy.
5. Population density of leafminer on snap-beans, cucumber and tomato:
The leafminer density was determined as an average number of mines and larval content on snap-beans and tomato/10 leaflets and on cucumber/10 leaves during summer cultivations of 2005 and 2006 growing seasons.
a. On snap-beans:
The leafminer infestation appeared from the beginning of both seasons and until harvest. The maximum numbers of mines and larvae detected during the 4th week of April 2005 were (22 mines and 5.1 larvae), while it was one month later during 2006 season (12.5 mines and 6.4 larvae). The larval population peaked 2-3 times/season indicated the same number of generations of this pest on snap-beans (2-3 generations/season).
b. On cucumber:
Low number of mines and larval content was appeared in the beginning of both seasons. The pest was abundant during April 2005 and May 2006. The maximum number of larvae was recorded in the 4th week of April (29.5 larvae) during 2005 season, while it was recorded during the 1st week of May 2006 (24.5 larvae). In general, the pest had 1-2 generations/season on cucumber plants.
c. On tomato:
Results indicated that the greatest number of mines and larval content were observed during May and June of both seasons. The maximum larval number occurred in the 3rd week of June 2005 and the 1st week of July 2006 (8 and 7.1 larvae, respectively). Leafminer complete four generations on tomato/season according to the peaks of larvae and mines on tomato leaflets.
6. Effect of weather factors on leafminer abundance:
Concerning the relationship among each of weekly means of maximum and minimum temperatures and relative humidity (R.H.%) and the weekly mean numbers of mines and larvae of leafminer, the results showed that, the maximum and minimum temperatures were positively insignificantly affected the density of leafminer mines and larvae (“r” ranged between 0.087 to 0.511) on snap-beans, cucumber and tomato during 2005 and 2006 seasons. However, it was insignificant negative on leafminer infesting cucumber during 2006 season. Only the relative humidity showed significant negative correlation with larval number on snap-beans during 2005 season. However, R.H.% was insignificant negative or positive correlated with mines and larvae on all crops during both seasons.
Partial regression analysis revealed that the combined effect of the three weather factors was insignificantly affected the leafminer abundance on all crops during both seasons. (E.V. ranged between 9.02-37.4%. This indicated that the studied weather factors occurred within the optimum zone for leafminer development.
7. Susceptibility of different cultivars of snap-beans and cucumber to leafminer infestation:
Based on the grand mean of mines and larval content of leafminer and yield overall nili and summer cultivations of snap-beans and cucumber, it could be concluded that snap-beans, Giza 6 cv. and cucumber, Madena cv. were the most tolerate cultivars for leafminer infestation, however, snap-beans, Pollesta cv. and cucumber, Beit-alpha cv. were susceptible cultivars. The cultivars i.e. Giza 3 (snap-beans), El-Zaem, El-Nemis, Amira-II (cucumber) were moderately tolerate for leafminer infestation.
8. Effect of cultivation season on the leafminer infestation:
Regarding the effect of cultivation season on the leafminer infestation, it was obvious that early cultivations (summer season) of snap-beans and cucumber were less infested by leafminer and this resulted in yield increase. Meanwhile, late cultivations (nili season) of both crops showed significant increase of leafminer infestation and yield reduction.
9. Preliminary evaluation of squash cultivation as plant trap for leafminer infestation in tomato field:
Based on grand mean number of mines and larval content and the percentages of intensity rate of infestation, the results revealed that squash was the most favourable host plant attracted leafminer. This resulted in decreasing its infestation on tomato surrounded by squash border in comparison to tomato without squash border. This has been assured by the statistical analysis of the results.
10. Effect of host plants on seasonal abundance of leafminer pupae and adult emergence;
Results showed that the pupae were existed for 11 weeks on snap-beans and 8-9 weeks on squash and cucumber plants. Pupal density showed two peaks on both snap-beans and cucumber, meanwhile, only one peak was occurred on squash.
However, and based on the total number of pupae/10 inch² of leaves and the adult emergence percentages results showed that high larval population was developed in squash leaves, resulting in remarkable increase in the pupal density and high successful adult emergence (68.9%). However, cucumbers followed by snap-beans was produced moderate number of pupae and showed 41.2 and 49.2% adult emergence, respectively. This obviously indicated that squash plants were the most favourable host for leafminer development and showed significant differences with cucumber and snap-beans plants.
11. Effect of hand-hoeing and use of some insecticides on leafminer infesting snap-beans plants:
The application of certain insecticides (two sprays) and hand-hoeing (three times) against leafminer infestation on snap-beans (Giza 6) indicated that Romectin and Vapcomic as bioinsecticides and Evisect, respectively were the most effective followed by Metazon. Hand-hoeing reduced the leafminer density by 18.4% and increase the seed yield by 11.8%. Regression coefficient value indicated that the increase of mean larvae/25 leaflets by one individual decreased the seed yield by 0.02 kg/10.5m². Significant negative correlation between mean larval numbers and the yield was recorded (r= -0.902). The average reduction of leafminer larvae/25 leaflets post treatments was positively and significantly correlated with the seed yield (r= 0.996). It could be concluded that Romectin 1.8% E.C (30ml/100 L. water) was the most promising treatment for reducing the leafminer infestation and increasing the seed yield of snap-beans.