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J. Torkamani,
Volume 6, Issue 3 (10-2002)
Abstract
The main objective of the present study is to investigate the production and marketing of fresh figs in Garmsar Region. Semnan Province has the largest area under fresh figs in Iran. About 84 percent of this area is in Garmsar region, hence, it was selected as the study area. Data were collected by random sampling method through interviews with a sample of 70 fresh fig producers in Garmsar region in summer 1999. The production functions of fresh figs were estimated using translog form for the study region. Technical efficiencies for fresh fig producers were estimated using translog stochastic frontier production function.
Results of the current study revealed that farmers are not using some of the inputs optimally. Study of technical efficiency of fresh fig producers did not show the possibility of increasing production by increasing farmers’ technical efficiencies. The average of retail, wholesale and marketing margins of one kilogram of fresh figs were estimated to be 900, 550 and 1450 Rials, respectively. Also, marketing efficiency was calculated as 151%.
M. J. Moghbeli Hanzaii, E. Tafazoli,
Volume 6, Issue 3 (10-2002)
Abstract
Alternate bearing is a key factor in limiting citrus production. Chemical controls have proved to be the most effective solution to this problem. Two different experiments were conducted to study the effects of different growth regulators (GA3, NAA, Ethephon) and urea on alternate bearing control in Kinnow mandarin (Citrus reticulata). In the first experiment, GA3 at concentrations of 0, 25, 50, 75 and 100 mgl-1 were applied 3 times during late autumn and early winter 1993 on off trees. Flowers reduced as a result of GA3 application in the following spring but increased in the second spring. Best results obtained with 50 and 75 mgl-1. In the 2nd experiment thinning agents: NAA (0, 100, 200 and 300 mgl-1), ethephon (0, 100, 200, 300 mgl-1) and urea (0, 4, 8 and 12%) were sprayed to the trees on on-year, when the fruitlets were about 0.75-1 cm in diameter. The results indicated that urea had no effect however, both NAA and ethephon were effective on thinning of fruits and control of fruiting. Ethephon at 200 and 300 mgl-1, and NAA at 400 mgl-1 gave the best results.
S. Ayoubi, J. Givi, A. Jalalian, A. M. Amini,
Volume 6, Issue 3 (10-2002)
Abstract
In quantitative land suitability evaluation, economic aspects land evaluation such as impact of environmental physical factors on crop production and the amount of yield per surface unit are considered. The purpose of this research was to study quantitative land suitability of northern Baraan area located in eastern Isfahan. The study was a continuation of the previously accomplished qualitative land suitability evaluation of the area. The economic studies include economic data collection, matching inputs and outputs and gross margins analysis.
Radiation-thermal production potential of the crops was calculated based on plant physiology and temperature (FAO model), which was 10.45, 10.11, 13.64 and 11.93 ton/ha for wheat, barley, maize and rice, respectively. Radiation-thermal production potential, observed and marginal yields and the results of the qualitative land evaluation were used to perform quantitative land evalution and to determine the corresponding suitability classes. The predicted yield in different land units varies between 1.64 and 9.17 ton/ha for wheat, 1.81 and 9 ton/ha for barley, 2.06 and 9.42 ton/ha for maize and 2.35 and 7.14 ton/ha for rice. Presence of significant statistical correlation between the observed and the predicted yield values reveals the validity of the evaluation methods used. The results from quantitative land evaluation show that most of the land units are slightly to moderately suitable for wheat, barley, maize and rice, while a few are not. The best land utilization type in each land unit can be selected through a combined consideration of quantitative land evaluation results, benefitability of each land unit and impact of the land use on the soil. Rice cultivation is not recommended in the study area, because of its adverse effect on soil physical properties and soil drainage.
H. R. Karimzadeh, A. Jalalian,
Volume 6, Issue 3 (10-2002)
Abstract
For the study of field wind erosion and the design and evaluation of wind erosion control techniques, detailed observations of soil particle transport and vertical destribution of eroded soil particles are needed. The objectives of this study were: 1) To describe one device for soil transport particle measurement, i. e. the BSNE sediment catcher and 2) To assess vertical distribution of wind–eroded sediment with height in eastern Isfahan. The BSNE sediment catcher is a wind erosion sampler that traps eroded material at seven heights of 0.24, 0.60, 1.08, 2.00, 3.00, and 4.00 m above the soil surface. Each trap consists of a steel container with an inlet and outlet, mounted on a wind vane that rotates about a central pole. Before using the sampler in the field, it was tested and calibrated in the wind tunnel. The results showed that the average trapping efficiency with speeds ranging from 5.2 to 7.2 m sec-1 for 4 different wind–eroded sediments was 0.44 to 0.68. However the trapping efficiency depended on wind speed, particle size distribution, particle density and type of sediment. The sampler had the lowest efficiency for particles < 44 μm. A BSNE sediment catcher was installed in Babaii Air Base. After a sampling period, the sediment in each trap was collected and weighed. The trapped materials were a mixture of saltation and suspension particles. Vertical distribution of wind–eroded sediment showed that the amount of soil collected decreased with increased height and the percentage of fine particles (<63μm) increased with height. The amount of trapped materials for each cm2 frontal intake with increased height were 12.00, 3.42, 1.44, 1.56, 0.75, 0.21, and 0.39 g cm-2, respectively, for the one sampling period.
A. A. Safari Sinejani, G. Emtiazi, H. Shariatmadari,
Volume 6, Issue 3 (10-2002)
Abstract
Soil organic matter and clay minerals adsorb and immobilize extracellular enzymes of microorganisms and increase soil enzymes stability. This study aims to clarify the relative importance of soil organic matter and clay minerals on the cellulolytic activities of soils. Fluca prepared cellulase was immobilized on some agricultural residues and clay minerals, avicel and a sample of soil. Immobilized exoglucanase and endoglucanase were assayed at different times. Activities of the immobilized enzymes were strikingly dependent on the kind of sorbent. After 20 days of storing in refrigerator at 4oC, the deactivation of immobilized enzymes on the organic substances (as avicel) was very low but deactivation of immobilized enzymes on the soil and clay minerals was relatively high. On the other hand, the activities of immobilized enzymes on the agricultural residues and avicel were significantly higher than the soil and clay minerals. So it may be concluded that a large part of cellulolytic activity of soil is related to immobilized enzymes on agricultural residues. Coating of the clay minerals, soil and avicel with 4 mmol of Al (OH) x per mg of them significantly increased their immobilization capacity and activities of immobilized enzymes. Activities of immobilized exoglucanase and endoglucanase on the Ca- homoionized soil and clay minerals were significantly higher than the K- homoionized soil and clay minerals. However, these effects may be related to the specific effects of cations on the method of enzyme assay or enzymes activities. These homoionizing-cations effects on the activity of immobilized enzymes on avicel were not significant.
G. Saeidi,
Volume 6, Issue 3 (10-2002)
Abstract
Edible-oil flax (Linum usitatissimum L.) can be an alternate oil-seed crop in Isfahan region. Seeding date is very important in obtaining higher grain yields and a successful flax production. The present study was conducted at the research farm, Isfahan University of Technology in the year 2000 to determine the effect of seeding date and genotype on yield, yield components and maturity of edible-oil flax. In this study, a RCBD with three replications, in which the treatments were organized as a split-plot experiment, was used. Seeding dates (Oct. 17, Nov. 16, March 15, April 13, May 14, June 13, July 15) and genotypes (four breeding lines of edible-oil flax) were considered as the main and the subfactor, respectively. The number of capsules per plant, seeds per capsule, 100-seed weight and seed yield were highest for all genotypes in the first seeding date. Average seed yield in the first seeding date was almost twice, triple and eight times as much as the second, third and the last three seeding dates, respectively. In the second seeding date there was no emergence because of low temperature. The genotype and seeding date interaction on seed yield and maturity was significant. In general, delayed seeding was accompanied by reduction of emergence, number of days to maturity, yield and yield components in all genotypes, with the exception that the last seeding date led to increased number of days to maturity and seeds per capsule. Based on regression analysis, seed weight, number of seeds per capsule and number of seedlings/m2 were the most important components that contributed in seed yield variation, respectively. But, most of the variations in seed yield per plant was affected by number of copsules per plant and number of seeds per capsule, and in that order.
H. Seyedoleslami, A. R. Hadian, A. Rezai,
Volume 6, Issue 3 (10-2002)
Abstract
Color sticky board traps are used in pest management for capture of adult insect, to estimate and predict population densities in later stages. Yellow sticky board traps showed high attraction for pistachio psylla. It is important to study these relationships for the right placement of traps. For each of three repetition in one year, four pistachio trees were selected randomly in one orchard. Eight traps were located on two heights and four cardinal directions of each tree (32 traps in each repetition). After one week the adult psylla captured were counted. One and two weeks 1ater, eggs and nymph densities were counted on five leaves in one of the eight positions of each tree on four other randomly selected trees (total 160 leaves each time). Data were subjected to analysis of variance. Coefficient of variation was determined between adults captured in each position and eggs and nymph density counts.
There were significant differences for adult capture and egg density among directions, and in most cases significant correlations were observed between adults captured on each position and total egg and nymph density count on trees. It was concluded that for egg and nymphal density estimation, we can place traps on either of two heights and four directions except on lower east part, but preferably on either height in south direction of the trees . Also suggestions for egg and nymph sampling are given in the text.
A. A. Pourmirza, M. Tajbakhsh,
Volume 6, Issue 3 (10-2002)
Abstract
Due to the need for new fumigants to control insects that attack food commodities, the toxicity of acetone was determined on some species of stored pest insects in Urmia University in the year 2000. In empty space tests, the LC50 values of acetone for Oryzaephilus surinamensis (L.), Callosobruchus maculatus (F.), Tribolium confusum (Duv.) and Sitophilus granarius (L.) were 15.40, 15.51, 17.55 and 18.26 μl/liter, respectively. The experiments of acetone penetration to wheat mass revealed that the application of acetone in headspace led to the penetration of acetone vapours into the wheat mass and killing the S. granarius and T. confusum had been concealed in interkernel space. The comparison of LC50 values of empty space tests with LC50 values of penetration experiments revealed that the increase in penetration toxicity was 8.63 fold for S. granarius. A similar trend was observed for T. confusum adults. In hidden infestation tests, the application of acetone to the headspace resulted in destroying the developmental stages of S. granarius concealed in wheat and achieved 75% mortality at a dose of 160 μl/liter during seven weeks. Acetone showed no deleterious effects on the germination and vigor of wheat seeds.
M. R. Bahremand, M. Afyuni, M. A. Hajabbassi, Y. Rezaeinejad,
Volume 6, Issue 4 (1-2003)
Abstract
A field experiment was conducted to investigate the effects of sewage sludge and of time lapse after sludge application on soil physical properties. Four sewage sludge treatments (0, 25, 50, and 100 ton/ha) in a complete randomized block design with three replications were applied and mixed to a depth of 20 cm. Wheat was planted and soil physical properties were measured 23, 85, 148, and 221 days after sewage sludge application.
Sewage sludge application significantly increased MWD, hydraulic conductivity, final infiltration rate, moisture percentage at 1/3 and 15 bars, and plant available soil moisture, while it significantly decreased soil bulk density. In general, the best results obtained with the 100 ton/ha sewage sludge treatment. Time lapse after sewage sludge application caused soil physical properties to approach the values of the control. However, even 221 days after sludge application, the 50 and 100 ton/ha treatments had significantly different values compared with the control treatment. The results in this research show that sewage sludge can help to improve soil physical conditions and this effect persists over long periods. This effect is specially important with plant available soil moisture and infiltration.
M. J. Monem, M. R. Alirezaee, E. Salehi,
Volume 6, Issue 4 (1-2003)
Abstract
Recent studies have shown poor performance of irrigation systems, which indicates the requirement for special attention to performance improvement. The first step for improving the performance of irrigation systems is evaluation of the present situation. Performance evaluation methodologies presented so far are either qualitative such as DA (Diagnostic Analysis), RA (Rapid Appraisal) and FA (Framework Appraisal), or they are similar to classical methods even if they produce quantitative indicators. They fail to introduce performance standards. In this study, using Data Envelopment Analysis (DEA), which is a quantitative method and produces realistic standards, 8 irrigation systems were evaluated and their performances were determined. With respect to the number of decision-making units, inputs, outputs, and corresponding returns to scale for irrigation systems, a suitable DEA model was selected. Capabilities of DEA allow for separate treatment of performance evaluation of overall irrigation network and its operating company. This feature is implemented using different technical and operational indicators.
The results indicated that Zayandeh Rood irrigation system, among the 8 irrigation systems, has the highest technical efficiency. Minab and Varamin systems have the lowest technical efficiencies. Golestan and Behbahan Networks perform well, although their operating companies are inefficient. Garmsar, Ghazvin, and Moghan systems, although not inefficient, have some improvement potentials. In general, with respect to the capabilities of DEA in performance evaluation of irrigation systems and indicating appropriate standard, it can be concluded that this technique is quite efficient and successful for performance evaluation and improvement of irrigation systems.
M. Shafaei Bajestan, M. Salimi Golshaikhi,
Volume 6, Issue 4 (1-2003)
Abstract
Downslope soil movement along riverbanks is a significant erosion process. Plant roots, particularly of woody vegetation, apparently stabilize soil on slopes because in most areas where the vegetation is removed, frequent bank failure occurs. Plant roots increase soil-shearing resistance both directly by mechanical reinforcement and indirectly through removal of pore water by transpiration. In this study, the effects of two plant species on the stability of the Karoon River has been investigated. To determine the In-situ shear strength of soil, a special device was designed and manufactured. This device is capable of measuring the shear strength of soil blocks as large as two cubic meters. In this study, twelve soil blocks, four blocks with roots of each tree and four blocks of root permitted were measured.
Comparison of the soil shear strength with roots and root permitted soil shows that tree roots can significantly increase the shear strength of the soil. The amount of increase depends on the type of plant, the age of plant, the diameter of the roots and the percentage of roots in the block. In this study, the amount of increase varied between 20-66%. From the analysis of the data, two equations were developed to determine the increased shear strength.
A. Rezvanfar, H. Vaisy,
Volume 6, Issue 4 (1-2003)
Abstract
To improve livestock production and to modernize dairy husbandry in Iran, it is essential to disseminate the most recent information on dairy husbandry technologies and management practices through various means among farmers. An understanding of farmers’ communication behaviour is essential in formulating effective communication strategies for livestock development. For the purposes of this study, East Azarbaijan Province was selected. The study will examine how farmers obtain information on dairy husbandry technologies and management practices and how they communicate with agents of technology transfer (extensionists). The major channels and sources used in obtaining information and inter-system communication by farmers are discussed. To study the farmers’ communication behaviour, a sample of 154 farmers from a total of eight villages (four villages from high level plain areas and four villages from low level plain areas) were selected using “Stratified two-stage random sampling” method. Data were gathered by filling out questionnaires that had been tested before. The criteria like frequencies in terms of number and percentage, mean and product moment correlation were calculated. In addition, multiple regression analysis was used for the analysis of the data.
According to the findings of this study, most farmers in the two groups (98%) had low information input score. The independent variables such as information output, farmer inter-system communication, farmer-researcher communication, farmer-extensionist communication, education, family education status and availability of input facilities had positive and highly significant relationships (P<0.01) with information input.
G.pezeshki-Raad, M. Masaeli,
Volume 6, Issue 4 (1-2003)
Abstract
This study utilized a descriptive-correlational surveying approach to examine some economic factors involved in the adoption of an integrated campaign to control rice stem borer (Chilo suppressalis) in Isfahan Province. The population consisted of farmers living in the vilages where Biological Control Plan was conducted (N=6000). The population frame was obtained from Isfahan Agricultural Organization. The sample was obtained using the cluster random sampling method (n=361). Questionnaire and interview were used for data collection in this study. Face and content validity of the instrument was established using a panel of experts consisting of senior faculty members in agricultural extension and education at Tarbiat Modaress University. Further, the agricultural officer of Isfahan Province validated the questionnaire. A reliability analysis was conducted and Cronbach alpha value was reported to be 83 percent. The results showed that the rate of adoption of Integrated Campaign to Control Rice Stem Borer among the farmers was moderate. Among the economic characteristics, there was a significant relationship between adoption of integrated campaign and area of land, amount of area under cultivation, degree of family cooperation in the agricultural activities, access to agricultural inputs, access to financial resources, and yield of rice per hectare.
M. Sayyari, M. Rahemi,
Volume 6, Issue 4 (1-2003)
Abstract
‘Golden Delicious’ apples were vacuum infiltrated (250 mm Hg) with 0, 4, and 6% solutions of CaCl2 followed by heat treatment for 0, 48 and 72 hours at 38oC. Treated fruits were stored at 0oC with RH of 85-90% for 2.5 and 5 months, followed by one week of storage at 20C. The results showed that fruits treated with 4 and 6% of CaCl2 significantly increased calcium content of fruits after 2.5 and 5 months of storage at 0oC. With increasing calcium content, fruit firmness also increased. There was a positive relationship between fruit firmness and calcium content and regression coefficients after 2.5 and 5 months of storage at 0oC were 0.77 and 0.83, respectively. Heat treatment for 48 and 72 hours at 38oC significantly increased fruit firmness. Calcium chloride at 4 and 6%, plus heat treatment, significantly increased fruit firmness of those fruits held for one week at 20oC after removal from cold storage. In the second experiment, vacuum infiltrated fruits with 4 and 6% solutions of CaCl2 plus potassium permanganate (0, 10, and 20 g/bag) had no significant effect on fruit firmness, but potassium permanganate alone significantly increased fruit firmness.
M. R. Chakerolhosseini, A. Ronaghi, M. Maftoun, N. Karimian,
Volume 6, Issue 4 (1-2003)
Abstract
Iron (Fe) availability is low in calcareous soils of Iran due to high pH levels and presence of excessive amounts of CaCO3. Overfertilization by phosphorus (P) fertilizers may also decrease Fe availability. The objective of this study was to evaluate the effects of P, Fe and their interactions on the growth and chemical composition of soybean [Glycine max (L.) Merrill] under greenhouse conditions. Treatments consisted of a factorial arrangement of P rates (0, 40, 80, 120 and 160 mg kg-1 as KH2PO4) and Fe rates (0, 2.5, 5 and 10 mg kg-1 as FeEDDHA) in a completely randomized design with four replications. Plants were grown for 8 weeks in a loamy soil, classified as Chitgar series (fine-loamy, carbonatic, thermic, Typic Calcixerepts). Results showed that P application up to 80 and Fe at 2.5 mg kg-1 increased shoot dry matter. Phosphorus concentration, total uptake and P:Fe ratio in soybean increased by P application but decreased by Fe application. Application of Fe up to 2.5 mg kg-1 increased dry matter but decreased it at higher rates. Concentration and total uptake of Fe increased by Fe application but decreased by P application. Interaction of P and Fe had no effect on shoot dry matter. Zinc (Zn) and copper (Cu) concentrations decreased significantly when P was added and manganese (Mn) concentration increased up to 40 mg P kg-1 but decreased at higher rates. Iron application had no effect on soybean Zn and Cu concentrations but decreased Mn concentration at all rates. Prior to any fertilizer recommendations, it is necessary to study the effects of P, Fe and their interactions on soybean under field conditions.
A. Ahmadi Iikhchi, M. A. Hajabbassi, A. Jalalian,
Volume 6, Issue 4 (1-2003)
Abstract
Cultivating rangeland to be shifted to crop land farms commonly causes soil degradation and runoff generation. This study was conducted to evaluate the cultivation effects on runoff generation and soil quality. The experiment was performed in a rangeland and a 40-year cultivated land located at two slope positions (back slope and shoulder) of a hillside in Dorahan, Chaharmahal & Bakhtiari Province. A 60±5 mm.hr-1 rainfall intensity was simulated by a rainulator. Organic matter, mean weighted diameter, saturated hydraulic conductivity, collected runoff and sediments were measured. The differences between the means were tested using T-test. Results showed 35, 53 and 8% increases in the organic matter, mean weighted diameter, and saturated hydraulic conductivity in back slope, respectively. The increases in these parameters in shoulder position were 39, 60 and 33%. The values for runoff and sediments in back slope were 3 and 8 times greater than in other similar positions while the values in the shoulder position were 11 and 55 times greater than the same values in other positions.
K. Yussefi Kelaricolaii, A. Kamyab, M. Rezaei,
Volume 6, Issue 4 (1-2003)
Abstract
In a completely randomized design (CRD) experiment with 6 treatments and 4 replicates per treatment, the effect of energy and protein dilution during 6-12 days of age was tested in broilers. Rice hull was used for dilution of energy and protein at levels of 0.05 (control), 10, 15, 20, 25 and 30 percent. The metabolizable energy and crude protein content of the experimental diets were 3089, 2780, 2626, 2472, 2317 and 2163 KCal/kg and 21.45, 19.29, 18.23, 17.16, 16.10 and 15.02 percent, respectively.
The results indicated that diet dilution at early age (6-12 days) increased feed consumption but energy and protein intake and weight gain were reduced. No significant differences in body weight were observed due to compensatory growth among treatments. After feed restriction, feed intake was lower for the birds receiving diluted diets as compared to control. Meanwhile feed efficiency somewhat improved among the birds fed with diluted diets, but the differences were not significant. Diet dilution had no significant effect on carcass and abdominal fat percentage at the slaughter age (45 days). Diet dilution with rice hull at 20 and 25 percent decreased feed consumption and improved feed efficiency and, therefore, its use can reduce feed cost.
M. Motallebi, M. R. Zamani, A. Hosseinzadeh-Kalagar,
Volume 6, Issue 4 (1-2003)
Abstract
A total of forty-three isolates of Ascochyta rabiei obtained from infected seeds and plants of chickpea from different areas of Kermanshah, Lorestan, Hamadan, Kordestan, and East and West Azarbaijan provinces were studied during the period 1996-1999. A rapid and simple method was developed for pathogenicity test in CDA (chickpea seed meal dextrose agar) medium. CDA medium was inoculated with different isolates and incubated at 21±1 oC for 9 days. The disease severity was scored as 0-100% at 24-hour intervals up to five days. Virulence forms were designated according to spectrum of disease reactions of each isolate. Thirteen isolates (IK04, IK08, IK10, IK13, IK14, IK17, IK19, IK21, IL01, IL10, IO00, IE04, IE06) were distinguished as highly virulent (HV) and 7 isolates (IK03, IK06, IK15, IE01, IE08, IL04, IL06) as weakly virulent (WV). Polygalacturonase activity of these isolates from 6 days old inoculated PZ (pectin zymogram) medium were assayed. Comparison of the results of pathogenicity test and PG activity of 43 isolates demonstrated that HV isolates show predominant enzyme activity while the WV isolates show enzyme activity.
S. M. Taghavi, K. Keshavarz,
Volume 6, Issue 4 (1-2003)
Abstract
During the period from 1997 to 1998, samples of wheat leaves were collected from different wheat farms in Fars and Kohgiluyeh & Boyrahmad provinces to identify the causal agent of wheat leaf blight. On the basis of LOPAT tests and production of fluorescent pigment on KB medium, 181 bacterial isolates were recovered from the samples. Based on biochemical, physiological and pathogenicity tests, the isolates were categorized in five groups. One group was found to be Pseudomonas fluorescens (Pf) and the remaining groups were identified as P. syringae pv. syringae (Pss). The pathogenicity test indicated that Pss strains were the causal agent of bacterial wheat leaf blight in Fars and Kohgiluyeh & Boyrahmad provinces. Whole protein electrophoretic patterns were similar in Pss isolates but only a few showed small variation in some subordinated bands. Pathogenic strains of Pss were also isolated from annual and perennial weeds such as foxtail, hairy vetch, oat grass, barley grass and Cynodon dactylon in some areas including Saadat Shahr and Marvdasht. Among the wheat cultivars tested, Tajan was susceptible to the pathogen but others were immune, resistant, moderately resistant, or moderately susceptible. The results showed that Pss is a seed-born pathogen in wheat kernel perhaps as endophyte in the seeds.
S. Ghadiri Rad, B. Hatami, G. Asadi,
Volume 6, Issue 4 (1-2003)
Abstract
The biology of predatory fly, Leucopis glyphinivora Tanas. was studied under greenhouse conditions. Adult longevity was 8 days and the average fecundity was 35.7 eggs. Incubation period, the 1st, 2nd, 3rd larval instars and puparium duration averaged 2.7, 2.16, 3.48, 5.7 and 8.45 days, respectively. Each generation lasted about one month. The predator efficiency was studied by applying the egg together with the adults of A. fabae at ratios of 1:1, 1:2, 1:4, 1:8 and 1:16 on broad bean. First larval instar was exclusively feeding on small nymphs (1st and 2nd nymphal instars) of aphid. Predator:prey ratios of 1:4, 1:8 and 1:16 decreased the number of prey to 97.9%, 98.8% and 61%, respectively, but ratios of 1:1 and 1:2 were unsuccessful in decreasing the number of preys due to predatory larvae leaving the host plant for searching small nymphs of aphid. As a result, the predatory larvae were efficient merely in a particular range of aphid density and age structure.
