Impact of different types of fertilizers to reduce the population density of the sap sucking pests to bean plants

The experiment was laid out in a randomized complete block design with three replicates. The aim of the work is to investigate the effect of different fertilizers on the rates of beans infestation by different piercing sucking pests Tetranychus urticae, T. cucurbitacearum, Bemisia tabaci and Thrips tabaci and on the resulting crop yield. The fertilizer treatments are Ammonium sulfate, Calcium super phosphate, Potassium sulfate, a mixture of NPK and Micro-elements (Zn, Mn, Fe, Cu, Bo & Mo). Results showed that means of green pods yielded by NPK fertilizer was significantly higher than other fertilizers in the two seasons.


INTRODUCTION
Bean plant, Phaseolus vulgaris L. is a member of family Leguminosae, rich in nutrients containing relatively high percentage of protein where consumed freshly as green pods or as dry seeds.Also its leaves encourage pest development, increased their fecundity and longevity (Braikel and Post, 1959) which threatens both quality and quantity of the resultant yield and cause serious damage either directly by sucking plants juice or indirectly as vectors of virus diseases.
Fertilizers are sources of mineral elements which plants required for growth and development.Essential mineral elements are ammonium sulfate, potassium sulfate, super phosphate, mixture of NPK and Microelements which have great effects in plant growth and development; their deficiencies or excesses result in marked effects on growth and yield crops.
The effect of NPK and Microelements were studied on parameters such as insect pests' numbers.The fertilizer NPK is one that contain three keys constituent chemical elements that are Nitrogen which promotes vegetative growth and green coloration of foliage; Phosphorus plays a major role in root growth, photosynthesis, respiration, energy storage, cell division and maturation; Potassium is important in flower and fruit growth, a plant metabolism, protein synthesis and chlorophyll development Yagoub et al. (2011).Researchers have demonstrated that high Nitrogen levels in plant tissue can decrease resistance and increase susceptibility to pest attack.Most studies assessing the response of mites to nitrogen fertilizers have documented dramatic expansion in post numbers with increases in fertilizer rates Altieri and Nicholls (2003).Alternatively, reduced susceptibility to pests may be reflection of differences in plants health as mediated by fertility management, Phelan et al. (1995).
Some microelements have toxic effect for pests (Tomlin, 1994) by losing a part of body water content of these pests as result of osmotic force and indirect mechanism due to that foliar fertilizer increase, also, the natural plant immunity through improving the plant nutritional status (Nowosielski et al., 1988).Zinc is required for normal plant growth.It is necessary in synthesis of indol of acetic acid, an important growth hormone in plant (Meyer and Anderson, 1961) and it accelerates protein synthesis and encourages phospholization and green plastids enzymes (Tsui,1948).Iron is an indispensable element for the synthesis of chlorophyll in green plants (Ferry and Ward, 1969).Manganese acts as an activator of many enzymes and essential for formation of chlorophyll (Pandy and Sinha, 1978).Cupper concentration of 9 mg.caused toxic effects in the insect species, i.e. egg sterility, decreased fecundity and morphological abnormalities when these insect larvae fed on contaminated with cupper (Habuštová and Weismann, 2001).Buzuk (1986) stated that microelements especially Mn, Zn, Fe and Cu increased alkaloids in plant tissues.Alkaloids contain toxic substances which protect plants from insect attack (Paech and Tracey, 1955).
The objective of this study was to investigate the effectiveness of different fertilizer treatments on the rate of pests' infestation to bean plants and their effects on the resultant yield.

MATERIALS AND METHODS
Field study: A field experiment was conducted for two successive seasons 2012-2013 in the Horticultural Research Station at Kanater El-Khairiya, Qualiobeya Governorate to focus on the effect of the different fertilizer treatments on the rates of beans infestation by different pests Tetranychus urticae Koch, T. cucurbitacearum (Sayed), Bemisia tabaci (Gennadieu) and Thrips tabaci Lindquist and on the resulting crop yield.
Seeds of "Paulista" variety of beans were sown in March 1 st in two successive years.The experimental area was about 84 m 2 divided into 18 equal plots of about 3.6 m 2 each for the five different fertilizers and the control.Each plot with two rows of 1.8 m 2 length and 60 cm apart.Plots were distributed in a randomized complete block design with three replicates for each treatment.The tested fertilizer used as follow: 1-Ammonium sulfate, 20% N 2 used by the rate of 200 kg/feddan.2-Calcium super phosphate, 15% P 2 O 5 used by the rate of 200 kg/feddan.3-Potassium sulfate, 48% K 2 O used by the rate of 100 kg/feddan.4-A mixture of the 3 previous fertilizers N, P & K at the rate of 200, 200 and 100 kg/feddan respectively.5-Micro-elements solved in water as Folifert (Zn 7.06 %; Mn 4.20 %; Fe 2.80 %; Cu 2.0 %; Bo 0.60 % & Mo (Molibidium) 0.05 % 6-The control plots (without any fertilizer).
Spraying the Micro-elements fertilizer was applied by using plastic atomizer and were sprayed two times, the first after complete germination and the second spray on leaves at the time of flowering.The Ammonium sulphate and the other different fertilizers applied by adding them around the plant in the bottom of the straight and they sprayed also two times.The control plots were treated with water in the same days of spraying fertilizers.Precautions had been done to prevent contamination among fertilization treatments.
All plots received the normally recommended agricultural practices and kept free from any insecticidal treatments throughout the two seasons.At the end of each season, the green pods of each treatment were picked and weighted to estimate the final yield.

Sampling technique
Sampling started four weeks after sowing beans and continued weekly until harvest.Sampling continued for 10 weeks throughout the two years 2012 & 2013.Adults of B. tabaci were counted on 10 plants /replicate in the morning before sunrise when they are more stable on the undersides of leaves.Samples of 10 leaflets from each replicate were randomly picked up every week from three levels of plants, then kept in tightly closed paper bags and transferred to the laboratory where the observed pests were counted by the aid of stereomicroscope.The total individuals of T. urticae and T. cucurbitacearum (eggs and moving stages), B. tabacci (eggs, nymphs & pupae) and T. tabaci (nymphs and adults) were estimated by counting the total numbers on the upper and lower surfaces of the leaflet.

Estimation of beans leaves components:
The phytochemical components of leaves for beans (Paulista) variety were estimated to determine the relation between the plant components and the high infestation by white fly Bemisia tabaci in different fertilization treatments under field condition in 2012 and 2013seasons.
Leaves of each sample were cleaned and washed with distilled water, then quickly dried by placing them gently between filter papers to remove the excess of water.The fresh weight of leaves was recorded.The leaves were placed in dry oven at 60°C for one day.The dry powder of leaves was stored in glass bottle to determine the percentages of total protein, reduced sugar, non reduced sugar and total sugar according to A.O.A.C. (1995).

Statistical analysis
Statistical analysis for ANOVA was carried out by using SAS 9.3.1 Portable.Whereas the means were compared through LSD tests, least significant differences at P= 0.05 level.

Spider mite, Tetranychus urticae Koch
Among the different treatments in the two seasons 2012 &2013, the lowest effects on the motile stages of spider mites were noticed in plots treated with N 2 with mean seasonal numbers 4.96 and 2.21 individuals / leaflet for motile stages in the two seasons, respectively, which were insignificant compared to the untreated plants (Control) and the other treatments in the first season, and significantly with plants treated with K 2 O and mixture (4.22 & 4.30 individuals / leaflet), respectively in the second seasons.
Baidoo and Mochiah (2011) indicated these results, in which increasing nutrient application enhances plant growth; however growth can make the plant more attractive to pests attack due to the better growth of plants which supported their survival and reproduction.

Tetranychus cucurbitacearum (Sayed)
Plots treated with Mixture (NPK) and Micro-elements showed the greatest mean numbers of eggs and motile stages recorded (15.13&15.13eggs/ leaflet) and (7.14&7.14individuals/ leaflet) in the first season, and (3.25&3.01eggs/leaflet) and (0.84 & 0.65 / leaflet individuals) in the second season, respectively, with highly significant differences compared to control.Plots treated with N 2 showed the lowest mean numbers of eggs and motile stages recorded (10.21 & 1.55 eggs/ leaflet) and (3.91 & 0.28 individuals/ leaflet) in the two seasons, respectively.Our results are agreement with Habashi et al. (2007), they proved that chelated micro-elements (12% Zinc, 12% Cupper, 12% Manganese and12% Iron) had a high incidence of spider mite, T. urticae compared to the effective microorganisms (EM) and a mixture of microorganisms and micro-elements together.
According to L.S.D values, there were significant differences between plots treated with N 2 and plots fertilized by Mix.(NPK) and Micro-elements, while insignificant differences between the other treatments.

White fly, Bemisia tabaci (Gennadieu)
More whiteflies were found on fertilized plants than on non-fertilized plants.Higher deposit eggs of whiteflies were found in plots treated with N 2 , with means of 0.77 &1.02eggs/ leaflet compared to control (0.39& 0.19 eggs/ leaflet) in the two seasons, respectively, with significant differences between them.While plots treated with Microelements revealed the minimize infestation by eggs of whiteflies (0.40 & 0.78 eggs/ leaflet) in the two seasons, respectively, with a significant differences comparing to N 2 treatment in the first season only while insignificant differences compared to control and between treatments.This finding agrees with Jo-Ann et al. (1995) who reported that acceptability of a plant by whitefly is in response to plant tissues; these tissues reflect changes in N 2 or K 2 O content and are perceived during probing of the leaf surface by female whiteflies.Moreover, Reddy and Rao Appo (1982) proved that plants received more N 2 fertilizers become more vulnerable to whiteflies attack.
More crawlers hatched from eggs, laid on plants treated with N 2 fertilizer, were more than those treated with other fertilizers without significant differences between means in the first season.In the second season, the application of Micro-elements considerably reduced the mean population of whitefly nymphs (1.27 nymphs/ leaflet) with a significant differences between Mix, N 2 fertilizers (1.99 & 2.23 nymphs/ leaflet), respectively.The quiescent stage of whiteflies (pupae) were affected by the different fertilizers; the lowest means of pupae occurred in plots received the Micro-elements fertilizer (0.04& 0.05 pupae/ leaflet) without significant difference compared to control and between treatments.
More adults were produced from fertilized plants than from non fertilized plants; in the first season, plants treated with N 2 showed the highest infestation (6.23individuals/ leaflet) with highly significant difference compared to control , while the Micro-elements treatment showed the lowest incidence of whitefly population with means 2.53individuals/ leaflet with insignificant difference compared to control (2.40 individuals/ leaflet) and highly significant difference compared to N 2 and P 2 O 5 fertilizers of means 6.23, 4.60 individuals/ leaflet, respectively.The previously mentioned results agrees with Habashi et al. 2007 andEl-Lakwah et al. (2010); they indicated that the population density of B. tabaci has a positive response to the applied rate of nitrogenous fertilizer and the plant, so plant treated with high level of N 2 harbored the highest numbers of whiteflies in different crops.

Thrips tabaci Lindquist
The highest infestation level by T. tabaci on bean leaves was observed on plants received Mixture (NPK) fertilizer in the two seasons recorded 8.33& 0.43 individuals/ leaflet, respectively, with highly significant difference compared to untreated plants (3.43& 0.25 individuals/ leaflet).While the N 2 treatments recorded the lowest infestation (3.99 & 0.30 individuals/ leaflet) in the two seasons, respectively.
Statistical analysis showed that the infestation by T. tabaci was significantly with plants fertilized by N 2 compared to other fertilizers.These results are in agreement with Ukey et al. (2001), they indicated that the lowest means population of thrips was observed at the lower dose of N 2 .Also, Ebaid and Mansour (2006) mentioned that Microelements (Zn, Mn, Fe and Cu) had significant differences in the reduction of thrips population on cotton plants.

Total fruit yield
From data in Table (1&2), the highest total green pod yields were obtained by applying the mix of NPK recorded (366.67&473.33 Kg / fed.) in the two seasons, respectively, while K 2 O fertilizer and untreated plants gave the lowest green pods (165.00 & 191.67 Kg / fed.) and (228.33 & 261.37 Kg / fed.), in the two seasons, respectively.Statistical analysis demonstrated that means of green pods yielded by NPK fertilizer was significantly higher than other fertilizers.Despite the fact that pest infestation on NPK treated plots were high, it did not significantly affect on the yields, this was due to the phenomena of tolerance; this result indicated by Huber 1989.

Estimation of beans leaves components
Data in Table (3) indicated that the percentages of total protein contents in bean plant leaves were high in the plant treated with N in the two seasons recorded 25.93 and 31.13%, respectively, showed significant differences among other treatments and control in the two seasons.This finding are in accordance with the results obtained by Marschner (1995) who proved that an excess of N or a deficiency of K can lead to a higher accumulation of amino acids which, in turn, can increase attack rates of sucking insects such as Aleurothrixus aepim Goeldi (Homoptera : Aleyrodidae ) in cassava plants.The lowest percentage of total sugar contents were found in plants treated with phosphorus fertilizers in the two seasons recorded 1.6 and 2.1%, respectively being high significant differences compared to control and between other treatments in the two seasons.The reduced sugar contents were higher in the Microelement treatments (2.65 & 3.25 %) being insignificantly with other treatments and significantly with plants treated with phosphorus.Meanwhile, the non reduced sugar contents were higher in the Microelement treatments in the two seasons (0.59 & 2.46 %).
Population abundance of B. tabaci, adults on bean plants during high infestation showed significantly relation with total protein and total sugar.While, negative correlation value was calculated in case of phosphorus fertilizers.

CONCLUSION
Fertilizer management has several effects on plant quality which effects on insect abundance and on subsequently herbivore damage.Although more research is needed, preliminary evidence suggests that fertilizer can influence the relative resistance of agricultural crops to insect pests.In this research, sucking pests attracted to plants treated by NPK and Microelements fertilizers more than N 2 , P 2 O 3 , and K 2 O which used alone.That may be due to the better growth of treated plants which supported their survival and reproduction.Similar report by Baidoo and Mochiah (2011) which state that, NPK contains nitrogen which promotes better growth of plants on the other hand, attacking by sucking pests were increased.

Table 1 :
Effect of fertilizers on population of four sap sucking pests infesting bean plants during 2012 season

Table 2 :
Effect of fertilizers on population of four sap sucking pests infesting bean plants during 2013

Table 3 :
Chemical analysis of bean leaves at high infestation by whiteflies in 2012 & 2013