Plant Protection
Year:2010 | Volume:33 | Issue:1|Papers Count:11

Functional response of Stethorus gilvifrons Mulsant to varying densities of different developmental stages of Eutetranychus oriental is Klein was examined in a simplified castor bean leaf disc arena under the laboratory condition. One S.gilvifrons female was isolated individually for 24h with different prey densities (4, 8, 12, 24, 48, 96, 120) at 300C and photoperiod of 14:10 (L:D) h. The number of prey consumed by the predator was checked after 24 h. S. gilvifrons showed a type II functional response to all different developmental stages of E. oriental is. Based on the random predator equation, estimated attack rates of S. gilvifrons after 24h were 0.0464,0.0442 0.0450, 0.0484 and 0.0480, and estimated handling times to eggs, larvae, nymphs, adult females and adult males were 0.082, 0.060, 0.066, 0.045 and 0.076, respectively.

Orius albidipennis Reuter is an important predator of economic pests in greenhouse. In this studu, investigations were performed on toxicity values of abamectin, spinosad and chlorpyrifos in laboratory (Petri dish) and greenhouse (clip cage) conditions. LC50 and LC90 values were determined to both sexes, male and female, by using SAS software, and comparisons were made according to ratio of LC50 values and 95% confidence limits. For males, toxicity of the insecticides was more than females in laboratory and greenhouse conditions. Toxicity rates were significantly different between the insecticides. Chlorpyrifos had the most toxicity in laboratory (LC50=0.06 ppm for males and LC50= 0.05 ppm for females) and greenhouse conditions (LC50=83 ppm for males and LC50= 99.3 ppm for females) and spinosad had the least one. Laboratory and greenhouse trials showed that toxicities of these insecticides were lower in greenhouse bioassay than in laboratory bioassay but this difference was notable for spinosad. It is concluded that multiple testing methods should be used in evaluating the effects of pesticides on beneficial arthropods.

Beauvoir bassiana (Balsamo) Vuillemin (Deut., Moniliaceae) is one of the fungus biocontrol agents of saw toothed beetle Oryzaephilus surinamensis L. (Col., Silvanidae). Fungi pathogenesis was investigated on larval and adult stages of pest on three date cultivars-Sayer, Zahedi and Deiri-under laboratory conditions (temperature 25±2oC, relative humidity 60% and Photoperiod 12D:12L). In adult, the minimum lethal concentaration for 50% (LC50) 2.46x104 conidia/ml was obtained on Zahedi and maximum 3.69x104 Conidia/ml on Deiri. In larvae, the minimum LC50 3.31x103 conidia/ml was obtained on Sayer and the maximum 6.29x103 conidia/ml on Deiri. The minimum time for 50 present mortality (LT50) was 4.68 and 6.68 days for larval and adult of Sayer, respectively. The maximum LT50 was 6.62 and 7.07 days for larval and adult stages of Deiri, respectively. It is concluded that the recommendation of the effective dose of Beauveria bassiana depends on the insect-host stage and the media that host reared on it.

Reactions of 20 cucumber cultivars, tested to Fusarium stem and root rot disease, have ranged from susceptible to tolerant. The most susceptible cultivars were 8-Ayat, 32-PV, CB- 61688222, Janette, Nasco, Negeen, Nicoo 100, PSR36-47112, Rubah-l, Rubah-s and Sultan and tolerant cultivars were 120118, Ayat, Jakie, FD-C101, Festival, Khassib, PSR 36-45007, SR36-45664 and Storm. Between these cultivars, Negeen as susceptible cultivar and Festival as tolerant cultivar were selected for biochemical studies of soluble peroxidase (SPOX) and the roots phenolic compounds. The seedlings with 1-2 trueleaves of each cultivar were transplanted into inoculated soil by two pathogen isolates. Plants treated similarly and transplanted in sterile soil containing sterile mixture of sand and corn meal were used as control. One, three, five, seven and 10 days after inoculation, samples were prepared from crown and roots of infected plants and used for enzyme extraction, and the activities of soluble peroxidase (SPOX) and the roots phenolic contents were determined based on spectrophotometric analysis. Results of experiments on quantitative changes phenolic compounds in tolerant and susceptible cultivars (Festival and Negeen respectively) indicated that there had been no significsnt differences of total phenol content in the infected tissue (mg per gr of fresh weight of root) of tolerant cultivar compared to the susceptible one. Based on results of peroxidase activity, there had been significant differences of activities of soluble peroxidase in the infected tissue of tolerant cultivar compared to the susceptible one, and the content of enzyme in infected tissue of tolerant cultivar was more than the susceptible one.

The family of Anthocoridae, which is known as flower bugs, are small predators and feed on many different species of injurious arthropods. The present study made use of white tray, sweeping net and lamp trap for faunistic study of Anthocoridae. Random sampling was carried out in Mashhad weekly during 2006-2007. Six species and 1 subspecies belonging to Anthocorinae (Oriini and Anthocorini) were identified as follows: Orius vicinus (Ribaut, 1923), O. niger (Wolff, 1811), O. horvathi (Reuter, 1884), Anthocoris nemoralis (Fabricius, 1794), A. pilosus (Jakovlev, 1877), A. guentheri Pericart, 2007 and Temnostethus redovinus parilis (Horvath, 1891). In order to assess biodiversity of these species, the dominance index and diversity index (Shannon-Wiener Index and Simpson's Index) were calculated by using the specimens collected by white tray. Among these species, Orius vicinus was determined as predominant species of Anthocoridae in Mashhad.

In this research, efficacy of Thymus persicus (Roniger ex Reach F.) and Prangos acaulis (Dc.) Bornm essential oil was investigated against egg hatching larvae and adults of Callosobruchus maculatus (F). This experiment was performed at 27±1 oC and 60±5% R.H. under dark condition. Concentrations tested included six concentrations (of 0.36 - 3.57ml/l air) for 1 and 4-day old eggs hatching, six concentrations (1.78-8.92 ml/l air) for 1, 7 and 14 days larvae and four concentrations (51.9-340.7 mL/L air) for adults at five replications. Increasing the essential oil concentrations resulted in increase of insecticidal activity on eggs, larvae and adults. Based on LC50 values calculated for eggs and larvae, ovicidal and larvicidal activity of T. persicus was not significantly different with that of P. acaulis essential oil. Moreover, this activity did not differ between 1 and 4-day-old eggs. Toxic effect of the oil was reduced as larval stage increased, showing that older larvae could be more resistant than younger larvae. At the highest concentration (370.4 ml/l air) essential oil of T. persicus and P. acaulis caused 100% of mortality in adults after 6 and 4.5 hours, respectively. LC50 values of T. persicus (2.39 ml/l air) were siginificantly higher that P. acaulis (1.31 ml/l air). Results showed that these essential oils were effective and can be used as a potential control practice against cowpea beetles.

Twenty four isolates of Cercospora beticola were collected from Khuzestan, Ardebil, Golestan and Mazandaran provinces and purified, and one isolate was used to represent each province. After optimization of spore production on different media, pathogenic variability of selected isolates on five sugar beet varieties with different levels of resistance was studied under green house condition. Four month-old plants were inoculated by the pathogen on each plant, four mature leaves were tagged and each leaf was inoculated with one isolate. Spore concentration was adjusted to 3x104 conidia/ml. The experiment was carried out on the basis of factorial random design with four replications (eight plants per replication). Disease severity and incubation period were measured as investigated characters. The results showed that there was a significant difference among cultivars for both characteristics. Puma and 191 were the most resistant and susceptible cultivars respectively. Cercospora isolates had significant differences for disease severity and were categorized in two groups, while there was no difference for incubation period among the isolates. Isolate×cultivar interaction led to no significant differences for both characters. It seems that reaction of cultivars to isolates is not different and in spite of variability among isolates of C. beticola, resistance in sugar beet to the fungus was effective against all Iranian isolates.