Applied Entomology and Phytopathology
Year:2007 | Volume:75 | Issue:1 (83)|Papers Count:10

Empoasca decipiens (Hom.: Cicadellidae) is one of the important pests of different crops in Iran. The field studies were conducted for determining the seasonal parasitism caused by Anagrus atomus (Hym.: Mymaridae) on the leafhopper eggs and relationship between parasitism rate and population density of the leafhopper on four bean species including Phaseolus vulgaris L. var. Talash, P. lunatus L. var. Sadaf, P. calcaratus Roxb var. Goli and Vigna sinensis L. var. Parastoo in Tehran area, during 2004-2005. The samples (bean leaves) were kept in laboratory conditions (26 ± 1oC, RH: 70 ± 5% and a photoperiod 16:8 L:D h.) until the parasitoids emerged, and the number of leafhopper nymphs and emerged wasps were counted. The maximum parasitism rate was occurred on Parastoo variety during two years that was in 2004 (24.34%) and in 2005 (33.33%). The parasitism was not observed on the other varieties except Goli in two sampling dates. The parasitism rate of A. atomus was determined as density independent to its host density, partly because of its wide host range among other cicadellids.

Usefulness and validity of different empirical yield loss models to predict the effect of common lambsquarters competition in corn were evaluated in a two year experiment in Karaj, Iran during 2001 and 2002 growing seasons. Experimental factors were 2, 5, 10 and 15 plants m-2 in the first experiment and 6.6, 13.3 and 20 plants m-2 in the second experiment and relative time of common lambsquarters emergence of simultaneous to, at 2-3 and 4-5 leaf stages of corn in the first experiment and simultaneous to, at 2-3 and 5-6 leaf stages of corn in the second experiment. Results indicated that the highest corn yield and LAI losses were observed at simultaneous emergence of weed and corn resulted in 85 and 92% yield loss, and 73 and 53% LAI loss in the first and second years of experiments, respectively. Also, delaying common lambsquarters emergence reduced its competitive ability against corn. Comparison of different empirical models revealed that the empirical yield loss models based on density and the relative time of weed emergence, and the weed relative leaf area, also the rectangular hyperbolic yield loss model based on weed density were more reliable at predicting corn yield and LAI losses according to their high coefficient of determination (R2). Also, results indicated that the negative effect of the relative time of common lambsquarters emergence on corn yield loss was more than weed density, so that the rectangular hyperbolic yield loss model based on weed density was more capable to predict yield loss at each of weed emergence times.

Seasonal activity of citrus aphids was monitored by direct sampling and yellow water–pan traps during 2003 and 2004, in citrus groves in Sari area of Mazandaran. Citrus tristeza virus transmission ability of the predominant aphid species was also studied. The proportions of the different aphid species from direct sampling were: Aphis gossypii (78%), Toxoptera aurantii (8%), Macrosiphum euphorbiae (8%) and Aulacarthum solani (6%) in 2003, and A. gossypii (51%), Aphis spiraecola (21%), T. aurantii (12%), Aphis fabae (9%), Aphis craccivora (3.5%), Aphis nasturtii (2%), Myzus persicae (0.5%), M. euphorbiae (0.5%) and Aphis rumicis (0.5%) in 2004. The results provided additional evidence for A.gossypii as the most common aphid species in citrus groves in this area. Transmission tests were conducted using Mexican lime seedlings as donor and receptor plants for the virus, 20 and 10 aphids of the four aphid species (A. gossypii, T. aurantii, A. spiraecola and A. fabae) were used per to infest receptor plant. Rates of the infected plants by the 20 and 10 individuals of A. gossypii were equal to 3.33 and 1.66 percents respectively and probability of the individual aphid transmission was calculated 0.17% in the two cases.The other aphid species were not able to transmit the CTV in the East of Mazandaran. The yellow water-pan trap method had not adequate efficiency in comparison to the direct sampling of aphids. A. rumicis, A. nasturtii and A. solani were the first record of aphids fauna on citrus in the North of Iran.

Using Sunn pest as target insect the LC50 and LT50 of eight different Iranian and imported isolates of Beauveria bassiana have evaluated under laboratory condition. The lowest LC50 and LT50 values were observed in isolate DEBI002 being 3.78×10 3 spores/ml. and 8.55 days respectively showing among tested isolates the latter is the most virulent one. Five different plant oils were used to evaluate the viability of the spores of selected isolate during storage. Among the oils tested the palm oil showed to be the most and Sesame oil the least suitable carriers for B. bassiana aerial conidia.

Nowadays new and safety pesticides have a significant importance on the integrated pest management in the world, so in this study we report the sublethal effects of imidacloprid on cotton aphid (Aphis gossypii) reproduction by demographic toxicology. These experiments were carried out at 25±1oC, 70 ± 5% RH and photoperiod of 16: 8(L:D). Leaf discs of cucumber immersed in the recommended concentration of the above mentioned insecticide and then located in the 5.5 cm diameter Petri dishes. A newly emerged adult female was released on the lower surface of each leaf discs. There after various parameters such as longevity, daily fecundity rate and the intrinsic rate of increase were recorded. Imidacloprid reduced adult longevity (4 days) compared to the control (16 days). Life expectation in control and imidacloprid treatment were 4.30 and 2.25 days respectively. Gross fecundity rate in imidacloprid treatment and control were 3.97 and 49.13 respectively. R0 were 13.52 and 1.45 in control and imidacloprid treatment respectively. The intrinsic rate of increase (rm) was 0.05 in imidacloprid and 0.26 in control that is reduced by 81% in imidacloprid treatment. These results show the significant effects of imidacloprid on the life table parameters of A. gossypii.

The prevalent aphid pests of almond are Brachycaudus amygdalinus Schout. (Hom.: Aphididae) and B. helichrysi Kalt. In Chahar-Mahal va Bakhtiari province. Seasonal variability of B. amygdalinus and B. helichrysi was studied in Shahre-Kord during 2003 and 2004. Aphid stages were counted in 100 sample unites, (twigs with 5 centimeter lengths), in 10 trees. The results showed that gynoparous of the two species were observed on almond trees in mid October in Shahr-e kord. Overwintering eggs were produced by viviparous females and laid on twigs near the developmental and flowering buds. The eggs of these two species were in diapause stage in winter. The fundatrices, which were produced from overwintered eggs, were apeterous with robust appearance. Many numbers of fertilized overwintered eggs died during winter so that 4.1% and 0.4% of two species remained to establish colonies on almond trees in 2003 and 2004, respectively. The viviparous forms produced from fundatrices and developed rapidly in April and May and reached to a high density of 116 B. helichrysi on 5 centimeter twigs. B. helichrysi developed at lower temperature and produced higher population density in Shahr-e kord. B. amygdalinus migrated to Polygonum persicaria L., P. aviculare L., P. patulum M. B. and P. aridum but B. helichrysi had many foliage hosts in summer.

In order to study the competitiveness of potato varieties against weeds, a field experiment was conducted in 2002 at agricultural research center of Hamedan. The experimental design was split plot in complete randomized blocks with four replications. In main plot, there were seven potato varieties (with variance in reaching), and subplots were divided into two treatments, one, with weeding, another without weeding. In this experiment, weed had natural growth. The results showed that medium-late varieties such as Cosmos and Diamante with the highest Competitive Index (CI) were competitor, Agria and Moren medium-late and lateseason varieties with the same CI were semicompetitor and Novita with the lowest CI was the weakest variety. The analysis of Ability of Withstand Competition (AWC) showed the medium-late and lateseason varieties such as Agria, Cosmos, Diamante and Moren (lateseason) were more tolerant varieties and on the other hand medium-early varieties such as Novita, Draga and Marfona had the lowest AWC so were recognized as sensitive varieties against weeds.

Grapevines in north-eastern provinces of Iran (North Khorasan, Razavi Khorasan, Semnan and Golestan) were randomly surveyed for presence of Grapevine fanleaf virus (GFLV), Grapevine leafroll associated virus 3 (GLRaV-3) and Grapevine virus A (GVA). Symptoms of mosaic, abnormal double nodes, Z shaped, abnormal shoot development and reduced growth were observed in few of the plants. 588 samples of grapevine were tested for presence of three viruses in dormant canes, young leaves, shoot tips and petioles by double antibody sandwich-enzyme linked immunosorbent assay (DAS- ELISA). All three viruses were found to be present in vineyards of north-eastern provinces of Iran. From the 588 samples tested, 78 vines were found to be infected with at least one virus. ELISA tests showed presence of GFLV, GLRaV-3 and GVA in 7%, 6.6% and 3% of samples respectively. In addition, reverse transcription-polymerase chain reaction (RT-PCR) was used to verify ELISA tests for GFLV in vine tissues. RT-PCR using specific primers directed to the GFLV coat protein gene region at the 3′ end of RNA2 amplified DNA of the expected size (321bp). Also the results showed presence of an unexpected 150 bp band in some samples.These results indicated that RT-PCR as a rapid and sensitive detection method is necessary to confirm healthy plant material.