JOURNAL OF CROP PROTECTION
Year:2017 | Volume:6 | Issue:4 |Papers Count:7

To examine the differences between spinetoram and spinosad in their insecticidal activity and stability on the stored wheat, bioassay tests were carried out for six consecutive months at 20 and 30 ± 1 ° C by adults of Rhyzopertha dominica (F. ) (Coleoptera: Bostrichidae). Samples were taken after zero, 2, 3, 5, 7, 15, 30, 60, 90 and 180 days of insecticides application. Results of median lethal concentrations (LC50s) determined after three days of treatment indicated that spinosad was significantly more toxic than spinetoram against the adults. Results also revealed that mortality decline of R. dominica was correlated with temperature and the gradual degradation of the two insecticides over time during storage period. The half-life of spinosad and spinetoram on stored wheat were 99. 02 and 69. 32 days at 20 ± 1 ° C, respectively. These were shortened at 30 ± 1 ° C to 49. 51 and 46. 21 days, respectively. However spinosad displayed more bioactivity and stability than spinetoram. It can be concluded that spinosad and spinetoram do not remain persistent and even a slow degradation of these insecticides is likely to occur during wheat storage. Residues of spinosad and spinetoram persist on the wheat grains at levels well below the established tolerance levels.

Witches' broom disease of lime (WBDL) is a lime disease that has destroyed several citrus orchards in Oman, United Arab Emirates and Iran. WBDL is caused by a bacterium ''Candidatus Phytoplasma aurantifolia'' which is spread through the citrus orchards by a leafhopper, Hishimonus phycitis (Distant) (Hemiptera: Cicadellidae). Leafhoppers are associated with symbiotic microorganisms which provide them with essential amino acids lacking in their diets. Yeast-like relationships with insects are known as common and obligate symbiotic relationship. A prerequisite for the development of future strategies for the symbiotic control of insect pests and insect-vector competence is the identification of insect-associated yeast-like symbionts. In the present study, yeast-like symbionts housed in H. phycitis were investigated in insects collected from 13 districts of citrus orchards distributed in southern Iran (Hormozgan, Kerman, Sistan-Balushestan and Fars provinces). Insects were collected from infected lime trees by a D-Vac and stored at-20 º C up to the DNA extraction. Total DNA was extracted and PCR was conducted with specific primer sets targeting 18S rRNA and 26S rRNA genes of the symbionts. Results revealed that the vector harboured two yeast symbionts, namely Yeast like symbiont of H. phycitis (Hp-YLS) and Candida pimensis, with a similarity of (98-99%) to those reported from the other Cicadellids. These results substantiate the association of these two endosymbiotic microbiota with H. phycitis which may suggest their ecological interactions. To establish any endosymbiotic relationship and probable interfering in pathogen transmission, further studies are needed.

Oak trees form the major elements of the Zagros forests at western part of Iran. The activity of cynipid gall wasps (Hymenoptera: Cynipidae) greatly affects survival and fertility of these trees, by inducing formation of various galls on a certain part of the oak trees (Quercus spp. ). In this study, population fluctuation and spatial distribution of four common species, Andricus asetivalis (Giraud), Aphelonyx persica (Melika), Neuroterus lanuginosus (Giraud) and Neuroterus saliens (Kollar) were studied in Kermanshah province from the early February to the late December of 2011. The galls that formed on the 100 cm end of branches from the four cardinal directions were sampled in two different heights of 1. 5 and 2. 5 m on each tree every 7-10 days throughout the season. To estimate the spatial distribution patterns, data were analysed through regression models. According to the Taylor's power model, in the height of 1. 5 m, the slope of regression line was not significantly different from 1, indicating a random pattern for all gall wasp species. Also the spatial distribution pattern of N. lanuginosus and N. saliens was determined as random in the height of 2. 5 m. Using Iwao's patchiness regression, similar patterns were distinguished for all species in two different heights except for A. aestivalis and N. lanuginosus in the height of 1. 5 m which regression between Lloyd’ s mean crowding and mean density was not significant. At early season, just sexual galls of A. aestivalis and A. persica were observed and the first asexual galls of N. lanuginosus and N. saliens were formed on the branches starting in early August. Combining data of both heights of 1. 5 and 2. 5, the peaks of gall density of A. aestivalis, A. persica, N. lanuginosus and N. saliens were observed on 23 May, 27 June, 4 September and 15 September as 2. 85 ± 1. 60, 34. 40 ± 22. 17, 159. 27 ± 40. 01 and 4. 50 ± 1. 38, respectively. Overall, the most observed galls belonged to N. lanuginosus. The activity period of N. saliens was clearly shorter than other species and lasted only less than two months.

Nine wild olive accessions collected from the Golestan province, the North of Iran, were screened under greenhouse conditions for their resistance to Verticillium wilt. Plants of the highly susceptible cv. ‘ Zard’ , frequently used as a local cultivar, were also included in this test. Nine-month-old nursery olive plants were inoculated by root-dip method with defoliating (VCG1, D) and non-defoliating (VCG4B, ND) isolates of Verticillium dahliae, both obtained from diseased olives in Golestan province. Resistance was evaluated by assessing symptom severity using 0-4 rating scale and estimating the area under disease progress curves. The percentage of plants killed, final mean severity of symptoms, frequency of V. dahliae reisolation from olive xylem, dry weight of new green leaves and shoots and total phenol content in root tissues were used as additional parameters. The results showed that seven of the nine wild olive accessions were highly resistant to D and ND isolates of V. dahliae. A second group of wild olive accessions (P4 and P7) were classified as moderately resistant and resistant to D and ND isolates of V. dahliae, respectively. Phenol content was significantly higher in highly resistant plants and correlation coefficient analyses revealed a negative relation between disease severity and root total phenol contents. Dendrogram of wild olive accessions and ‘ Zard’ cultivar based on all parameters represented two main clusters, major and minor. Minor cluster comprised only two wild olive accessions and ‘ Zard’ cultivar. Major cluster could be divided into two groups, I and II, showed a highly resistance reaction to pathotypes of V. dahliae.

The thermophilic fungus Mycothermus thermophilus is one of the most important thermophilic fungi in mushroom composting process. Thirty nine isolates of M. thermophilus were collected from nine provinces of Iran and were identified as M. thermophilus based on morphological features and ITS regions. The studied isolates significantly increased the growth of Agaricus bisporus hyphae compared to control when used in vitro situation. Also the colony morphology of the mushroom changed when it grew on the colony of M. thermophilus. While the studied thermophilic isolates were morphologically different, no diversity was observed in terms of Random Amplified Polymorphic DNA (RAPD) finger-printing. The genetically clonal population of M. thermophilus collected from Iranian mushroom composting farms was attributed to lack of sexual reproduction, similar raw materials used in compost formulations, compost temperature, and concentration of ammonia during pasteurization as selection pressures.

Antifeedant activity of the aqueous and hydroalcoholic extracts of leaves of Descurainia sophia L. and Thuja orientalis L. were tested against adults of Tribolium castaneum (Herbst). The experiment was designed to measure the nutritional indices such as relative growth rate (RGR), relative consumption rate (RCR), efficiency of conversion of ingested food (ECI) and feeding deterrence index (FDI). Treatments were evaluated by the method of flour disc bioassay under dark condition, at 27 ± 1 ° C and 60 ± 5% RH. Ten microliter portions of each extract at concentrations (0. 25-2. 0%) was spread evenly on the flour discs. Results indicated that nutritional indices were significantly affected as extract concentrations increased. In this study extracts from T. orientalis decreased RGR, RCR and ECI significantly more than that of D. sophia. In addition, hydroalcoholic extracts decreased RGR, RCR and ECI significantly more than those by aqueous extracts. Both of plant extracts increased FDI as the extract concentrations were increased, showing high feeding deterrence activity against T. castaneum. Generally, antifeedant activity of T. orientalis was greater than D. sophia and hydroalcoholic extracts were more effective than aqueous extracts.

By conducting three different methods, we report on the isolation of five novel strains of non-symbiotic bacteria from crushed infective juveniles (IJs) of four species of entomopathogenic nematodes (EPN) including Heterorhabditis bacteriophora, Steinernema carpocapsae, Steinernema feltiae, and Steinernema glaseri and five bacterial species from hemolymph of insect larvae infected with EPNs. Samples of hemolymph of infected Galleria mellonella L. larvae by EPNs and crushed surface sterilized IJs were bulk streaked onto both MacConkey and NBTA agar. To further ensure diagnoses, extracted DNA from IJs bulk was subjected to PCR by 16S-rRNA bacterial universal primers. Bacteria were identified using biochemical and phylogenetic analysis. Based on 16S-rRNA gene sequence, maximum parsimony, maximum likelihood and neighbour joining phylogenetic analyses were conducted, as well as comparisons of predicted RNA secondary structures. Four species of bacteria were identified including: Stenotrophomonas maltophilia strain IR11 from S. feltiae; S. pavanii strain IR20 from S. glaseri; Acinetobacter junii strain IR8 from S. carpocapsae; and Alcaligenes faecalis strains IR1 & IR15 from S. feltiae and H. bacteriophora respectively as non-symbiotic bacteria from IJs and five species probably originated from G. mellonella intestine including Citrobacter gillenii isolate S3, Enterobacter asburiae isolate S4, Klebsiella oxytoca isolate S5, Morganella morganii isolate S6 and Serratia marcescens isolate S6.