Plant Protection
Year:2009 | Volume:32 | Issue:1|Papers Count:9

The relationship between diversity of plant and arthropod species was studied in sugarcane fields in Ahwaz, Southern Iran during 1998 to 2001. Strips of alfalfa were planted along the short side of each 250 x 1000 m block. Arthropod species were collected monthly for 24-48 hours using Malaise and pitfall traps which were located inside the sugarcane blocks. One Malaise trap at 3 meters and two pitfall traps at 2 and 4m from the margin were established in each sugarcane block. The diversity (species richness) and evenness (relative abundances) of arthropod species were measured by Shannon indices. The percentages of stems attacked by the two stem borers, Sesamia cretica and S. nonagroides (Lepidoptera: Noctuidae) were also recorded on each sampling day. Data was compared for sugarcane blocks with and without alfalfa strips. Results indicated that species richness was higher and the percentage of infection to stem borers was lower significantly in sugarcane blocks with strips of alfalfa than without.

Biological characteristics of Chrysoperla carnea (Stephen.) fed on Hyalopterus pruni (Goff), Brevicoryne brassicae (L.) and Aphis pomi (Degeer) were studied under laboratory conditions. Developmental time of C.carnea on the above mentioned aphids were 24.75, 25.77 and 30.75 days, respectively. Preimeainal mortality was 60.69, 43.75 and 63.1%, respectively. Female longevity of C.carnea was equal to 28, 27.5 and 19.7 days, and total eggs laid was 402, 428 and 375 eggs, respectively. It can be concluded that B. brassicae was the most suitable prey for development and reproduction of C.carnea in laboratory conditions.

The amount of nitrogen fertilizer is an effective factor on the growth, development, and reproduction of phytophagous insects. To investigate the effect of nitrogen fertilization on intrinsic rate of increase of cabbage aphid, Brevicoryne brassicae L., plants rape oilseed (RGS003cultivar) were treated with four nitrogen levels (zero (check) 50, 100, and 150% of recommended levels. The results showed that increase in nitrogen fertilization resulted in increase in the percentage of soluble nitrogen concentration in plants. All the experiments were carried out at environmental chamber (25±1oC, 70±10% RH, and 14:10 L:D photoperiod). The aphids feeding on plants receiving higher nitrogen fertilizer (150%) had shorter pre-reproduction period, longer reproductive, as well as greater fecundity, although nitrogen fertilization had no effect on adult longevity. The intrinsic rate of increase in four treatments was determined as 0.249, 0.215, 0.267, and 0.317 (female/female/day), respectively. The results revealed that cabbage aphid developed on treated plant with 150% nitrogen had the highest population growth. This means that higher nitrogen fertilization improves the susceptibility of rape oilseed for cabbage aphid.

Sunn Pest, Eurygaster integriceps Put., is the most important pest of wheat and barley in most producing regions of Iran, including Lorestan province. Spatial distribution and fixed precision sequential sampling plans of Sunn pest by the use of two quadrate sizes 0.25 and 0.5 m2 were investigated in rainfed wheat fields in Borujerd during 2004 and 2005. Based on R square of regression, Taylor's power law and Iwao's patchiness regression models provided a more adequate description of variance-mean relationships for 0.25 and 0.5 m2 quadrate sizes, respectively. Taylor's b and Iwao's b were significantly b>1, for two quadrate sizes, indicating that over-wintered Sunn pest population was aggregated in rainfed wheat fields. Fixed-precision sequential sampling plans (Green's and Kuno's model) were designed for estimating over-wintered adult stage of E.integriceps density at three fixed precision levels (0.1, 0.15 and 0.25). For each quadrate size, Green's and Kuno's fixed precision sequential sampling plans were validated using 12 independent data sets ranging in density from 0.09 to 2.65 (for smaller quadrate) and 0.1 to 5.24 (for larger quadrate) over-wintered adults per quadrate. To achieve a precision of 0.25 in Green's fixed-precision sequential sampling (by use of 0.25 m2 quadrate), which is generally accepted in IPM programs, it is necessary to take samples with an average sample number (ASN) of 26. As the precision level was increased to 0.10, average sample size (for smaller quadrate) increased to 157. For Kuno’s Fixed-precision sequential sampling plan (use of quadrate 0.5 m2), an average sample number of only 16 quadrates was necessary to achieve a precision level of 0.25. As the precision level was increased to 0.10, average sample size (for larger quadrate) increased to 90. Therefore, Green’s fixed precision sequential sampling plan (by use of quadrate 0.25 m2) that has the least cost and the highest ASN was the most preferred and suitable quadrate size to forecasting of over-wintered adults of E. integriceps in rainfed wheat fields.

The damage of sugarcane whitefly, Neomaskellia andropogonic Corbett, has recently increased dramatically in sugarcane fields in Khuzestan province. In this study, biology of N. andropgonis on four sugarcane commercial cultivars was evaluated under laboratory conditions. In this experiment, the preimaginal development, adult longevity and fecundity were studied in a growth chamber that was set at 27± 1oC, 60-70%R.H. and 12:12 light dark. The leaf cages were used for the experiment and the cultivars included CP69-1062, CP57-1062, CP48-103 and NCO-310. Mean preimaginal development time was 24.09, 28.06, 27.27 and 26.64 days on the above mentioned cultivars, respectively, producing only female whiteflies. Mean longevity of females was 6, 8.49, 4.15 and 4.60 days on four cultivars, respectively. Females laid 61.80, 58.80, 41.10 and 39.38 eggs on CP69-1062, CP57-1062, CP48-103 and NCO-310 cultivars, respectively. According to the results of this study, the biotic parameters of the pest were lower in CP48-103 and NCO-310 than the other two cultivars.

In this study, 99 isolates of Rhizoctonia were recovered from root and crown samples of pistachio seedlings, and soil samples were collected from major pistachio orchards in Kerman province. Results revealed that 96 isolates were multinucleate and 3 binucleate. MNR belonged to ¬AG-4. Results of the pathogenicity tests carried out in the greenhouse, using pistachio isolates, revealed that all MNR isolates were pathogenic to pistachio. For evaluation of the stock resistance to the disease, 3 stocks including Badamy reez (the most common stock in the province), Sarakhs and Baneh (wild stocks) were used in greenhouse study. For seedling inoculations, 3 isolates of the pathogen with the highest levels of pathogenicity were used. Barley grains inoculated with the pathogens were used as inoculum in pathogenicity tests. Two weeks after inoculation, disease severity was assessed and the results indicated that Baneh and Badamy reez were the most and the least resistant stocks respectively.

Toxicity of spinosad was primarily evaluated with three bioassay methods: feeding, spraying (Residual exposure) and combination with larval medium against one susceptible and one field population. Feeding method was selected as efficient method for survey of susceptibility or resistance of seven field populations. In feeding bioassay method, spinosad LD50 of susceptible strain at 24h and 72h were 3.78 and 1.54 mg (AI) per gram bait and for LD95 were 5.59 and 3.35 mg (AI) /g, respectively. LD50 of field populations at 24h ranged  from 3.974- 4.303 and for LD95 from 7.33- 8.30 mg (AI)/gr. LD50 at 72h ranged from 1.54-1.72 mg/gr and LC95 were 3.31- 3.93 mg /g, respectively. Determination of lethal dose ratios with lower and upper limits indicated no significant difference between spinosad LD50 of susceptible and field population at 24h and 72h. In Residual method, spinosad LD50 of susceptible and field population (AHDS) at 24h were 0.015 and 0.016 and for LD95 were 0.03, 0.033 g (AI) per m2, respectively. At 72h, LD50 were 0.0065, 0.007 and LD95 were 0.014, 0.015 g (AI)/ m2 for the above populations. In combination of spinosad with larval medium, LD50 and LD95 of susceptible population were 9.79 and 29.5 mg (AI) per kg medium. For field population (AHDS), LD50 and LD95 were 9.95 and 56.6 mg (AI)/kg. There was no significant difference at LD50 of susceptible and field population with these two methods. Totally, the result of this study indicated that LD50 values decrease approximately 2-3-fold between 24 and 72 h and all field populations were susceptible to spinosad.