Applied Entomology and Phytopathology
Year:2005 | Volume:73 | Issue:1|Papers Count:11

In order to study yield loss percentage and weed threshold density in grain corn, an experiment was conducted in 2002 at the Agricultural College, Ferdowsi University of Mashhad using a factorial arrangement of treatment, using additive series in a randomized complete block design. Two factors were involved in the experiment, redroot pigweed density in five levels (0, 2, 4, 6 and 12 plantm-2) and corn density in three levels (7, 9 and 11 plantm-2). Two parameters hyperbolic model was fitted to seed yield loss of corn. Minimum seed yield loss percentages were 6.54, 4.35 and 4.1 at 7, 9 and 11 plantm-2 corn density, respectively. Minimum seed yield loss decreased by 37% when corn density increased from 7 to 11 plantm-2. Maximum seed yield loss was 50.43, 34.16 and 24.6% at 7, 9 and 11plant m-2 corn densities, respectively. When corn density increased from 7 to 11 plantm-2 maximum seed yield loss decreased by 51%. Increasing corn density caused the increment at weed threshold density, so that it increased by 35% and reached from 0.13 to 0.2 plantm-2. Also increasing corn density caused the increment at weed economic threshold density from 1.5 to 2.8 plantm-2. Generally, density had a significant effect on competition between redroot pigweed and corn and threshold density, and increment of corn density increased corn competitive ability and reduced damage of redroot pigweed.

Cotton aphid, Aphis gossypii, and large cotton aphid, Acyrthosiphon gossypii (Hom.: Aphididae) are the most important aphids of cotton fields in Iran. The large cotton aphid is more important in Khorasan, therefore this research was conducted in Kashmar region for determination of Economic Injury Level of this aphid during 1999-2000. The complete randomized block design with 3 replication was used and treatments included 0, 5, 10 and 15 aphid per leaf under cages measuring 2x2x1 m. For control of the aphids in check treatment, plants were sprayed with Confidor (250CC/h) S.ampling has been done from three upper leaves of 5 plants in each plot with 10 days interval. At the end of this study, datas concerning boll weight, %boll opening, yield and fiber length was analyzed with SAS and JMP. Economic injury level of this aphid was calculated using regression equations and Norton formula. Results indicated that EIL for large cotton aphid, Acyrthosiphon gossypii in Kashmar was 6.3-6.9 aphid per 3 upper leaf of stem.

The rate of incidence of Potato virus Y (PVY), Potato virus X (PVX), Potato virus S (PVS), Potato virus M (PVM), Potato leafroll virus (PLRV) and Alfalfa mosaic virus (AMV) in potato fields of Khuzestan province was studied by ELISA, using 582 leaf samples collected in growing seasons of 1999 and 2000.The results showed that one or more viruses infected 87 percent of samples. Among the viruses infecting potato, PVY with the incidence of 74% was the most common, followed by PVS, PVX, PLRV, PVM and AMV with the prevalence of 68, 44, 25, 22 and 11.5 percent, respectively.Isolates of PVY, PVX and AMV were biologically purified and propagated in a suitable host. Based on the reaction of potato and indicator plants to 25 isolates of PVY and transmission tests with aphids (Myzus persicae), three strains of the PVY, namely PVYo, PVyN and PVyC, were identified.All seven PVX isolates were similar. Likewise, all AMV isolates were similar and belonged to Calico strain.

In recent years damage of green bud borer, Eucnaemidophorus rhododaetylus Den. & Schiff. (Lep.: Pterophoridae), has increased in the rose gardens of Kashan area. The adults are generally brown to gray, with length of 6-8 mm and wingspan of 20-24 mm. fore and hindwings are divided into 2 and 3 lobes, respectively. The larvae are yellow to green, fusiform with maximum length of 12-13 mm. The pest spines silk treads to make its feeding nest in which it feeds on buds and flowers. Therefore, it reduces the flower number and amount of perfume and essence. Biology and growth characters of the pest were studied through regular inspections of different rose gardens. Longevity of adults and egg-laying capacity of females was studied using net sleeves. To study hibernation of the pest, samples from soil, debris, and bush foliage were inspected in laboratory. The study showed that in the region the pest feeds only on danlask rose bushes. The highest damage rate was observed in rose fields of Barzok amounting 33.75%.The pcst showed to be univoltine and hibernates as diapausing first instar larvae under cockles. Diapauses takes from mid July to early April and larvae renewed their activity when rose bushes restart their growth. Average duration of different growth stages under field conditions were recorded as follows: egg 12.5 days, larva 60 days, pupa 10 days, and adult 15 days.

In order to determine the amount of Deoxynivalenol (DON) in flours, five flour factories were selected among Tehran provinces' flour factories. One kilogram samples of five kinds of flour (whole, debranned, Setareh, Nool and Semolina flour) were taken from each factory randomly. The samples were transferred to laboratory and divided into 100 and subsequently into 10 gram of sub samples. Then the samples were extracted by Immunoaffinity column and analyzed with HPLC instrument which was equipped with DV detector and C18 column. Mobile phase was Acetonitrile - Water in the ratio of 10-90 (VIV).DON was detected in all fourty flour samples. The Maximum amount of DON was in whole flour with an average level of 130.05 µg/g. The minimum amount of DON was obtained in debranned flour with average level of 39.93 µg/g. Statistical analysis of data showed that there is a significant difference between whole flour and debranned and Setareh flours (P value= 0.0171).

In this study 7 bean lines, which showed relative resistance to two-spotted spider mite in field condition, were selected from local variety "Lordegan" and tested in greenhouse and field condition. Study was conducted in a randomized complete block design with 3 replications. In greenhouse, studies were carried out in 2 stages. Preliminary stage consisted of 9 treatments including Lines 1-7, Talash and Lordegan varieties and advanced stage consisted of 6 treatments including Lines 1-4, Talash and Lordegan varieties. Artificial infestation was done with introducing 5 adult females (3-5 days) on each plant. To determine the mite population density (including eggs and active stages), sampling was carried out 2 and 4 weeks after infestation. Damage score was from 0 (no damage) to 9 (death of plant). Under the field condition, in order to determine the mite population density, sampling was done from onset of infestation up to the end of growing season. Results indicated that, line 1, which was selected from local variety "Lordegan", was resistant to two-spotted spider mite, because in this line, oviposition, population density and mite damage were significantly lower compared to the others. Therefore, it is introduced for mass production or using in plant breeding programs.

In order to evaluate interference of common bean and weeds an experiment was conducted during 2001-2002 growing season in Lorestan Province. The experimental design was a randomized complete block, with 4 replications. Treatments included crop density with 3 levels (20, 30, and 40 plants/m2) in presence, and absence of weeds. In presence of weed competition, crop biomass production was increased by 20%, as crop density increased from 20 to 40 plants/m2. Increasing crop density from 20 to 30, and 40 plants/m2, caused significant increase in crop grain yield (15.4, and 24.7 % respectively). Increasing crop density from 20 to 40 plants/m2, reduced total weed biomass by 30 %. In addition to weed biomass, crop plant density significantly influenced weed species richness. Weed species richness decreased as crop density increased. Weed biomass showed an asymptotic response to species richness. By increasing weed species richness, weed biomass in the beginning increased, and later by initiation of negative response, reached a relatively constant level. Common bean biomass production decreased as weed species richness increased. In fact, by increase in species richness, total biomass production per unit area increased, but the share of each species, among them bean, decreased.

This study was carried out to detect biological variations of Iranian isolates of B. thuringiensis collected by standard methods from different regions of Iran. Experiments were fulfilled using twelve Iranian isolates and DipelÒ as a standard B.t. product on Helicoverpa amligera reared on artificial diet. The evaluation was conducted on 4 days old larvae under laboratory controlled conditions in a randomized complet design consisting 14 treatments each replicated 3 times. Larval mortality was evaluated after 3, 7 and 13 days. The results indicated significant difference among pathogenicity of the isolates. Some of them were in same group with Dipel. LC50 of isolate 6R (as more effective isolate) and Dipel were estimated 6x106 and 8x106 CFU per milliliter, respectively. LT50 of larvae was 3.37, 3.81, 4.05, 4.41, 4.85 and 27.2 days for isolates Dh11, Dipel, 6R, 3R, 4T and Krm23, respectively.

A study carried out on cherry weevil in Bastam and Zirstagh regions of Shahroud district during 1999-2000. Stone fruits production playing an important role in economy of region. Currently the cherry weevil is the most important insect pest of cherry, sour cherry and other allied species in Shahrood. Adult insects are metalic green or red in colour, having scattered hairs on elytra. Max., Min. and mean length of adult females was 10.4, 12 and 10.7 and those of males 10, 10.6 and 10.1mm respectively. Length of first instar larva was 1-1.5mm and the last instar measured 7.3-11mm with mean of 9.3 mm. The insect showed to hibernate as last instar larvae in mud chambers at the depth of 5-10 mm in the siol. Adults appeared in mid April and their appearance coincided cherry tree bloosoming. They mated several times after feeding on fruit pulp and young leaves. Oviposition period lasted 28-39 days with mean of 32.3 days. The onset of oviposition coincided the completion of petals fall.Females layed only one egg on each fruits. No. of eggs were 29-193 per female with mean of 99.3. Eggs hatched after 3-5 days with mean of 4.2 days. Min., Max. and mean pupal period were 25, 35 and 29.4 days respectively. Longevity of adults males and females were between 35-60 days with mean of 44.3 days under lab. conditions (25±1°C, 40-50% RH). Under field condition eggs hatched after nearly 10 days and 1st instar larvae penetrated into fruits' stones after 24hrs. larval period lasted 18-20 months, thus each generation of this insect completed in two years. The main hosts of cherry weevil showed to be cherry and sour cherry and subcidiary hosts that tolerate only minor injuries are apricots, peaches, almonds and pulms.

The experiments were conducted in two phases under laboratory and field conditions.Laboratory tests were performed in 5 treatments under Choice and No-choice feeding conditions.In the single-dose experiments N. indica consumed on an average 17.17±1.9 gmlanimal Baraki-wax block, 16.2±3.9 gm/animal Baraki-pellet and 16.7±2 gm/animal Lanirat. Food preference results in N. indica were determined as 33.04% (carrot), 25.65% (Baraki-Wax block), 24.92% (Lanirat) and 16.33% (Baraki-Pellet).Toxicity symptoms like nose and anal bleeding was observed from the 4th day and 100% mortality was observed from the 6th day until the 10th day after initiation of the experiment.In the second phase, the experiments in the field were performed using completely randomized block design in four replicates with three experimental and one control blocks. 20 gm/complex burrow of Baraki (Pellet), wax block and Lanirat were used in the three experimental blocks respectively and the fourth block was kept as control without application of any rodenticide. The percentage of success was determined using Henderson and Tilton (1955) formula. Percent success observed in N. indica by Baraki wax block and pellet was 97.75% and 97.25% respectively and about 94.75% when Lanirat was used. The LD50 value of Difethialone for N. indica was estimated as 0.82 mg/kg BW.