Applied Entomology and Phytopathology
Year:2012 | Volume:79 | Issue:2 (93)|Papers Count:12

It is unarguably important that insecticides suppress target pest populations, but the primary goal for successful management of vectors of plant diseases should be to minimize the feeding by all life stages on the crop. Thus, it is paramount that comprehensive testing of insecticides includes assessments of how they affect probing and feeding behavior and oviposition. In this laboratory study, we counted number of stylet sheaths (indication of probing and feeding), total oviposition, and mortality of adult potato psyllids, Bactericera cockerelli (Sulc) (Hemiptera: Psyllidae) when exposed to potato leaves treated with abamectin, flonicamid, novaluron, distilled water, and a surfactant. Treatments with abamectin, flonicamid and novaluron caused significant decreases in both oviposition and numbers of stylet sheaths. Choice test was included to simulate incomplete leaf coverage, and the results highlighted the importance of including the effect of canopy coverage (application method) in performance analysis of insecticides.

The effect of ten soybean cultivars, Glycine max (L.) (including, "Clark", "Sahar", "JK", "032", "033", "Williams", "L17", "Zane", "Gorgan3" and "DPX") on developmental parameters and reproduction of the lima bean pod borer, Etiella zinckenella Treitschke (Lepidoptera: Pyralidae), was studied at 25±1°C, 60±5% RH and a photoperiod of 16:8 h (L:D). The larval period ranged from 13.42±0.10 days on "Clark" to 16.28±0.14 days on "033". The female and male lifespans were longest on "032" (55.84±0.27 and 56.80±0.10 days) and shortest on "Clark" (51.18±0.11 and 52±0.13 days), respectively. The oviposition period was longest on "Clark" (15.46±0.19 days) and shortest on "Gorgan3" (9.52±0.13 days). The mean number of eggs laid per female was significantly different among the cultivars, ranging from 11.21±0.22 eggs (on "JK") to 16.16±0.56 eggs (on"Clark"). Based on development and reproduction parameters, it can be concluded that "Clark", "Zane", "Williams", "L17" and "033" might be the susceptible host plants and "DPX", "Sahar", "032", "JK" and "Gorgan3" might be the partially resistant host plants for E. zinckenella.

Bacillus thuringiensis transgenic plants substantially reduce the use of conventional insecticides for insect pests. Despite sufficient evidences of cross resistance between the Bt toxins, studies on crosses resistance between the Bt toxins and non-Bt insecticide are rare. In the present study, similar cross-resistance mechanism was investigated in a Plutella xylostella population possessing single-gene, recessive mode of inheritance but lacking toxin-binding mechanism. Bioassays on unselected (Unsel-Karak) and Cry1Ac-selected (Sel-Karak) populations of P. xylostella revealed that deltamethrin, chlorpyrifos and spinosad were significantly more toxic than Cry1Ac. The resistance ratio against Cry1Ac in Sel-Karak population was more than 660-fold compared with the susceptible population (Lab-UK). However, compared to Unsel-Karak the resistance ratio against Cry1Ac in Sel-Karak population was less than10-fold. In the present study, it was found that a population with mode 1 resistance (the most common type of lepidopteran resistance to Bt toxins) and single factor (i.e., Sel-Karak) is unlikely to show a common resistance mechanism to both the conventional insecticides and Bt toxin, this might be mainly due to highly different mode of action of the insecticides.

Ear rot of corn caused by Fusarium species could create an overall comprehensive problem. Fusarium species can produce mycotoxins such as trichothecenes which threat the human's health. Cultivation of maize in Moqhan region was about 10000 hectares. Forty (5-10 Kg) samples each including 10 subsamples of corn ears collected at harvest time, kernels separated from the ears, dried and divided into two parts: one part for mycological studies and another part for toxicology studies. The media Nash-Snyder, PDA and Czapek were used for isolation, and PDA and CLA for identification. Deoxynivalenol detection and measurement of the corn samples were carried out using IAC - HPLC (High Performance Liquid Chromatography and immunoaffinity Columns). To study the potential of deoxynivalenol production of the isolates, ten isolates (two of each species) were selected as the representative of each species, the potential of DON production for each isolate was measured after one week incubation at 25-27ºC and two weeks at 12ºC alternatively. To ensure the deoxynivalenol production of the two F. proliferatum isolates, these isolates inoculated artificially in corn ears and after 10 days the amount of DON was detected in the grains. Fusarium species and the frequency of isolation were F. verticillioides, 47.65%, F. proliferatum, 33.873%, 15.33%, F. nygamai, 4.86%, F. oxysporum ,3.06 . Deoxynivalenol was detected in 45% of the samples. The total mean of contamination was 45% and the range of contamination was 59.4 – 542.55ng/g with the mean of 95.30ng/g. Among the Fusarium species isolates two isolates of F. proliferatum could produce DON in artificial conditions.

Increasing of population and outbreak of the turnip sawfly Athalia rosae (Hym.: Tenthredinidae) caused severe damages in many fields of Marivan region in 2001. In this study, biological traits and population dynamics of this pest were investigated in Marivan region during 2004-2005. Results showed that this pest has 3 generations per year and main damage to canola caused by larvae of 3rd generation that its adults emerged in mid of September. The larvae of first and second generations feed on weeds and vegetables in Brassicaceae family. The adult of first generation emerge at early of April and they mate immediately then lay the eggs. Maximum number of laid eggs by one female sawfly in laboratory condition was 57 and mean was 28.2±14. The average developmental periods of egg and larvae were 5.1±0.59 and 17.65± 1.57 days, respectively and the means of pupa stage for females and males were 9.8±1.29 and 12±1.95 days, respectively and total life span was 32-38 days. Average longevity of adult female and male was 9.4±2.24 and 5.7±1.42 days respectively. Sexual ratio (male: female) in the natural condition were 1: 2.68 and 1: 3.03 in 2004 and 2005 respectively. This insect overwinters as final instar larva in a coccon in a few centimeters deep in the soil.

Pathogenic and molecular variability of 30 isolates of Ascochyta rabiei the causal agent of Ascochyta blight of chickpea collected from five provinces of Iran including Ilam, Kermanshah, Kohkiloyeh-Boyerahmad, East Azarbaijan and Lorestan was studied. Based on pathogenicity test, which was conducted using 7 differential chickpea cultivars, the isolates were categorized into 16 groups. All isolates collected from East Azarbaijan (Ar17, Ar18, Ar19), two isolates from Kohkiloyeh- Boyerahmad (Ar16, Ar34), one isolates from Kermanshah (Ar27), and one isolate from Lorestan (Ar2) had the highest pathogenicity. These isolates have potential to be used in breeding for resistance to ascochyta blight disease.Molecular variability of the isolates was studied using nine random RAPD primers and the data was analyzed using UPGMA clustering method and Jaccard similarity coefficient. The isolates were categorized into nine clusters. The average genetic similarity of isolates was 75% which indicates there was a high level of genetic variability in the population.

The beet armyworm, Spodoptera exigua (Hubner), is one of the most important pests of sugar beet that overwinter as mature larvae or pupae in the soil. In this research, the influence of cold acclimation in full-grown larvae and tolerance at temperatures below their body supercooling point (SCP) was studied. Moreover, the influence of soil humidity was investigated on temperature that pest may expose. After six different temperature treatments on lab-reared mature larvae, cold tolerance of the larvae was measured under two different programs executed on them. In the first program, larvae were acclimated by cooling rate of 1°C/min and reached to -5°C or -15 °C, for 24h then it was raised to +25°C. During second program the temperature was decreased with much lower cooling rate (0.01°C /min) to -15°C and kept for 2h then it was increased again to +25°C. These two temperature programs were also performed on different soil humidity (dry, humid and humid covered with an ice layer). The results showed that these pest larvae will only be able to tolerate -15°C when they were acclimated with slow cooling rate to reach below their SCP. These findings indicated that cold acclimation at sub-zero may induce expression of freezing tolerance in these larvae. It was shown that humid soils especially those covered with an ice layer, are more resistant against temperature decreasing rather than dry soils and could play an important role in the cold-hardiness strategy and mortality of this pest under low temperatures.

In order to identify plant parasitic nematodes fauna in farmlands and orchards of Ardebil province (Nir, Namin and Ardebil), Iran, twenty-six species were identified which 22 species belonged to suborder Tylenchina and four species to suborder Dorylaimina. Among them, Pratylenchoides magnicauda from apple orchard, Trophurus minnesotensis from potato, rapeseed and alfalfa fields and Xiphinema basilgoodeyi from apple and walnut orchards are new records for Iran. Their morphological characters and morphometric features are dissuccced.

Chemical pesticides used in the agriculture including cotton cultivation may have different harmful impacts on the agricultural environment. Since, one of the most suitable strategies for controlling cotton diseases is biological control, we therefore studied the possibility of biological control of cotton Verticillium wilt and seedling damping-off diseases in the field condition. The effectiveness of antagonistic fungi (Trichoderma harzianum and Talaromyces flavus) on above-mentioned diseases and several growth characteristics was investigated in Neishaboor and Moqan cotton fields. Each experiment was conducted as a randomized complete block with ten treatments and four replications. Overall results obtained from Neishaboor experiment showed that antagonistic fungi did not affect growth characteristics, but soil treatment with T. flavus or T. harzianum mediated maximum decrease in disease incidence. On the other hand, in Moqan experiment, application of both antagonistic fungi as soil and seed treatment, significantly increased growth characteristic and caused a significant decrease in the incidence of both diseases.

So far seventeen species of parasitic wasps have been reported on rose gall wasp Diplolepis fructuum (Rübsaamen) (Hym.: Cynipidae) in Iran. During study of this association in the northern part of West-Azarbaijan (northwest of Iran) two brachypterous eupelmid species were found. These species were identified as Eupelmus impennis (Nikol'skaya) and Eupelmus vesicularis (Retzius) that was confirmed by Dr. G. Gibson. These two species have not been reported from Iran and only two species Eupelmus fulvipes Forster, 1860 and Eupelmus urozonus Dalman, 1820 were reared on D. fructuum.

There are several mirid bug species associated with cultivated- and wild- pistachio trees in Kerman province, southern of Iran. Among them, four species were found dominant. The very young and immature pistachio nuts may be attacked by either adult or nymph of some hemipteran bugs particularly those belonging family “Miridae” in spring. Campylomma diversicorne Reuter, 1878 and Campylomma verbasci (Meyer-Dür, 1843) both attack the newly formed and very young pistachio nuts at early spring causing epicarp lesion. This injury leads to desiccation and dropping of the damaged nuts from the trees. Epicarp lesion is considered as one of the important problems in pistachio orchards in Iran (1), which mainly causes by the mirid bugs. Campylomma verbasci may be considered as phytozoophagous insect (4). As a phytophagous, young nymphs feed on plant sap, pollen and nectar, injury being important on apples. As a predator, nymphs and adults feed on aphids, mites, thrips and pear psylla (3, 6). Campylomma verbasci was also reported as the pest of apple trees in west Azerbaijan, Iran (5).