Field evaluation of aqueous extract of Melia azedarach Linn. seeds against cabbage aphid,Brevicoryne brassicae Linn. (Homoptera: Aphididae), and its predator Coccinella septempunctata Linn. (Coleoptera: Coccinellidae)

Aqueous extract of Melia azedarach seeds were tested against cabbage aphid, Brevicoryne brassicae, and its predator Coccinella septempunctata in a cabbage field. The field experiment was conducted at Bridge to Israel children village farm, around the vicinity of Tewodros campus, University of Gondar, where the cabbage was grown fully organically. A field experiment was started in the middle of April 2011 and completed at the end of May 2011. The experiment was conducted in a randomised block design (RBD). For the field trial, a total of 12 plots were prepared with 1 m² area for data collection. The powdered M. azedarach seeds were used to prepare 5% concentration of aqueous solution and sprayed. Before spraying, percentage of aphid infestation was recorded from the control plot and the experimental plot. The average percentage of cabbage infestation in the control plot was 72% and in the experimental plot before treatment was 80.85%. The percentage reduction of aphid population was 19.06% after the first spraying. However, maximum percentage reduction of 86.5% was recorded after the completion of six-week treatment. The overall percentage reduction increased proportionately from the first to sixth week. The number of predator population was reduced and the reduction was not statistically significant (p > 0.05). The present study proved that Melia seed extracts were effective against cabbage aphids under field condition. Further, it is evident that the beneficial interaction between botanical extracts and biological control organism in the field showed safety to natural enemies. In conclusion, Melia seed extract can be useful for small-scale farmers to protect their cabbage crop against cabbage aphid, B. brassicae.     

The influence of genetic background on resistance to the cabbage aphid (Brevicoryne brassicae) in Kale (Brassica oleracea var. acephala)

Resistance to Brevicoryne brassicae has been identified in the progeny of two selected kale (B. oleracea var. acephala) plants, one from the F1 hybrid cultivar ‘Arsis RS’ and one from the landrace ‘Butzo’. These plants were crossed with susceptible B. oleracea morphotypes that have different periods to flowering. The type of susceptible plant line used had an effect on the resistance phenotypc of the progeny. Tested F2 populations derived from these crosses show that resistance is not under simple genetic control. This, in addition to variation in aphid numbers within accessions, suggests that separation of genetic components of control from environmental ‘noise’ for any accession may only be possible by the production of double haploid plant lines.     

结球甘蓝和青花菜小孢子胚植株再生

结球甘蓝（Brassica oleracea var.capitata）和青花菜（Brassica oleracea var.italica）小孢子胚再生植株频率低是目前影响游离小孢子培养技术有效应用的关键问题之一,研究其小孢子胚植株再生频率的影响因素,提高胚再生植株频率,对促进游离小孢子培养技术在甘蓝类蔬菜育种中更好地应用具有重要意义。该文以结球甘蓝中甘11和青花菜TI-111等基因型为试材,对影响游离小孢子胚再生成植株的固体培养基类型、琼脂浓度、胚的类型及胚在液体培养基中的滞留时间等因素进行了研究。结果表明：游离小孢子培养25天的子叶胚在琼脂浓度为1%–1.25%的B5培养基上植株再生频率最高。进一步通过8个不同基因型对上述实验结果进行了验证,结果显示,游离小孢子培养25天的子叶胚在1%琼脂浓度的B5培养基上植株再生频率达77.8%–97.2%。     

Efficacy of Beauveria bassiana (Blas.) Vuill. against cabbage aphid Brevicoryne brassicae L. (Hem.: Aphididae) in laboratory condition

In order to replace the conventional chemical pesticides, extensive researches have been done on entomopathogenic fungi. Entomopathogenic fungus Beauveria bassiana is an important biocontrol agent against major economic pests and is being employed in Integrated pest management (IPM) along with synthetic pesticides. Cabbage aphid Brevicoryne brassicae L. is one of the important pests of Brassicaceae family. Therefore, in this research, the virulence isolate of B. brassicae (IRAN 429C) was investigated on adults of cabbage aphid under laboratory conditions. The experiments were conducted at 25 ± 2 °C, 60 ± 10 R. H. and a photoperiod of 16:8 (L: D). After preliminary experiments, the adult aphids were treated with fungal concentrations of 1 × 10³ to 1 × 10⁷ spores/ml. Probit analysis was conducted to calculate LC₅₀ and LC₉₅ values for the isolate. Positive correlation was observed between concentrations and pest mortality. LC₅₀ and LC₉₅ values calculated for IRAN 429C isolate are 2.04 × 10⁵ and 1.82 × 10⁸, respectively. The mortality was counted one day after the treatment and then continued for 14 days. Cumulative mortality for 14 days after treatment varied from 54% for IRAN 429C at low concentration (10³ conidia/ml) to 83% at high concentration (10⁷ conidia/ml). The lowest LT₅₀ was obtained at 7.67 days for IRAN 429C isolate at concentration 1 × 10⁷ spore/ml. According to the insecticidal activity of mentioned fungi on cabbage aphid, it can be used in biocontrol programmes of B. brassicae.     

Temperature and host plant effects on development and fecundity of Brevicoryne brassicae (L.) (Homoptera: Aphididae)

The development, survival and reproduction of the cabbage aphid, Brevicoryne brassicae (L.) were evaluated at three constant temperatures (20, 25 and 30°C) on cabbage, cauliflower, red cabbage, turnip and radish. The development periods of immature stages ranged from 10.7 d at 20°C to 7.60 d at 30°C for red cabbage. Total percentages of survivorship of immature stages varied from 39.40 and 82.50 within the temperature range of 25–30°C on radish. The average progeny per female was 31.15, 28.95 and 23.77 at 20, 25 and 30°C on cabbage.     

Rice-Straw Mulch Reduces the Green Peach Aphid,Myzus persicae (Hemiptera: Aphididae) Populations on Kale,Brassica oleracea var. acephala (Brassicaceae) Plants

Organic mulches, like peel and rice-straw, besides other materials affect the UV and temperature, which cause a reduction in the aphid arrival. The aim was to evaluate the effect of covering the soil with straw on the populations of the green peach aphid, Myzus persicae on the kale, Brassica oleracea var. acephala plants. The first experiment evaluated the direct effect of the rice-straw mulch and the second its indirect effect on aphid immigration, testing the plant characteristics that could lead to the landing preference of this insect. The third experiment evaluated the direct effect of the mulch on the aphid population. In the second and third experiments, four plants, each in a 14 L polyethylene pot with holes at the bottom, were used in areas with and without soil mulching. These pots were changed between areas, after seven days, to evaluate the effects of this change on the arrival of the winged aphids to the plants. Each plant was covered with anti-aphid gauze and inoculated with one winged M. persicae. Winged and apterous adults of this insect were counted per plant after 15 days. The temperature increased in the mulched plots to a maximum of 21–36°C and to 18–32°C in the plots with or without soil covering, respectively. Plant growth reduced the numbers of the winged aphids landing before and after they were moved to the bare soil plots. The nutrient content was similar in plants in both the mulched and no mulched plots. The population growth of M. persicae was higher in the control than in the mulched plots. This was partially due to temperatures close to 30°C in these plots and changes in the plant physiology. The soil mulching with rice-straw decreased the M. persicae landing, increased the plot temperatures and improved the vegetative growth of the kale plants.     

Influence of water stress on the glucosinolate profile of Brassica oleracea var. italica and the performance of Brevicoryne brassicae and Myzus persicae

Drought stress alters the chemical composition of plants, which can influence their tolerance to insect herbivory. To evaluate plant chemical responses to drought stress, broccoli, Brassica oleracea L. var. italica Plenck (Brassicaceae), was grown under well‐watered, drought, and water‐logged conditions. The glucosinolate (GS) levels and the performance of two aphid species, the specialist Brevicoryne brassicae (L.) and the generalist Myzus persicae (Sulzer) (both Hemiptera: Aphididae), in relation to water stress conditions were studied. High Performance Liquid Chromatography analysis showed that water stress changed the levels of GS in broccoli plants. Plants grown for 2 weeks under drought stress were significantly smaller and showed decreased levels of total GS when compared with GS contents of well‐watered plants, whereas water‐logged conditions led to a slight increase in the GS contents. A substantial decrease in indolyl GS was detected in water‐deficient plants, whereas aliphatic GS decreased slightly. Analysis of sugar levels in phloem sap of broccoli plants revealed that plants under water‐logged conditions contained the highest amounts of sugars followed by drought‐stressed and well‐watered plants. The two aphid species responded differently to water stress‐induced changes in their host plants. Significantly larger populations of M. persicae were recorded on plants with a limited water supply than on plants grown under well‐watered or water‐logged conditions. Brevicoryne brassicae was less affected by water stress, and similar population sizes were found on plants that were subject to different treatments. Analysis of covariance showed a significant effect of the plants’ water condition but no significant effect of GS content on the performance of M. persicae. However, the specialist B. brassicae remained unaffected by changes induced under water stress conditions.     

结球甘蓝和青花菜小孢子胚植株再生

结球甘蓝(Brassica oleracea var. capitata)和青花菜(Brassica oleracea var. italica)小孢子胚再生植株频率低是目前影响游离小孢子培养技术有效应用的关键问题之一, 研究其小孢子胚植株再生频率的影响因素, 提高胚再生植株频率, 对促进游离小孢子培养技术在甘蓝类蔬菜育种中更好地应用具有重要意义。该文以结球甘蓝中甘11和青花菜TI-111等基因型为试材, 对影响游离小孢子胚再生成植株的固体培养基类型、琼脂浓度、胚的类型及胚在液体培养基中的滞留时间等因素进行了研究。结果表明: 游离小孢子培养25天的子叶胚在琼脂浓度为1%–1.25%的B5培养基上植株再生频率最高。进一步通过8个不同基因型对上述实验结果进行了验证, 结果显示, 游离小孢子培养25天的子叶胚在1%琼脂浓度的B5培养基上植株再生频率达77.8%–97.2%。     

Sampling a weighted pest complex: caterpillars in North Korean cabbage (Brassica oleracea var. capitata) crops

The lepidopteran pests Plutella xylostella L. (Plutellidae) and Pieris rapae L. (Pieridae: Pierini) are responsible for major yield losses of cabbage, Brassica oleracea L. (Brassicaceae), in North Korea. Preliminary integrated pest management (IPM) programmes using economic thresholds (ETs) to schedule insecticide applications have proved promising and have demonstrated marked increases in yield compared to standard farming practice, which relies heavily on synthetic insecticides. To use ETs effectively on a routine basis, farmers need efficient yet sufficiently precise methods of surveying crops for pests. Here we construct and validate binomial sequential sampling plans for the two-species pest complex and for P. rapae alone. The recommended plans would be practical to implement, demanding maximum sample sizes below 50 plants, and proved very slightly conservative with respect to classifying the population relative to the ET (i.e., they were slightly more likely to suggest control at the ET than not).     

Clonal mixing in the soldier-producing aphid Pemphigus spyrothecae (Hemiptera: Aphididae)

Illuminating the genetic relationships within soldier-producing aphid colonies is an essential element of any attempt to explain the evolution of the altruistic soldier caste. Pemphigus spyrothecae is a soldier-producing aphid that induces galls on the leaf petioles of its host (trees of the genus Populus). At least a quarter of the aphids within the clonally produced gall population are morphologically and behaviourally distinct first-instar soldiers that defend the gall population from predation. Using field trapping and microsatellites, we investigated the degree of clonal mixing within natural gall populations. Field trapping in the UK showed that all the migrants of P. spyrothecae and of two other Pemphigus species were wingless first-instar soldiers. The average degree of mixing estimated from trapping P. spyrothecae migrants was 0.68% (range = 0-15%). Microsatellite genotyping of 277 aphids from 13 galls collected in Italy revealed an average mixing level of 10.4% (range = 0-59%). Six galls contained more than one clone (range = 2-5 clones). Non-kin aphids were not restricted to the soldier caste but were evenly distributed across instars. An additional gall, from which 527 occupants were genotyped, contained 12 non-kin aphids distributed among nine clones, showing that clonal diversity can be high even when mixing is very low. These observations suggest that although soldiers migrate regularly and can moult and reproduce within foreign galls, clonal mixing in this species is generally low and is unlikely to provide a barrier to the evolution of investment by the aphid clones in an altruistic soldier caste.     

Selection for resistance to clubroot (Plasmodiophora brassicae) in marrowstem kale (Brassica oleracea var. acephala L.)

Ninety-six cultivars of Brassica oleracea were screened for clubroot resistance in a seedling test using two populations of Plasmodiophora brassicae. The most resistant cultivars were kales. Sixteen resistant marrowstem kale cultivars of diverse geographical origin were used to start a selection programme for clubroot resistance. Four generations of selection, involving single plants, half-sib and full-sib families, reduced a disease index averaged over six clubroot populations from 41.2 to 12.5. This was lower than the most resistant cultivar in the original population, cv. Mixti 28.8, and as good as a German landrace of cabbage noted for its resistance, Bohmerwaldkohl 10.5. In comparison, the mean of five kale controls, cvs Bittern, Canson, Condor, Kestrel and Merlin, was 61.1 and the value for the most susceptible control, cabbage cv. Septa, was 89.3. In the final assessment, there were no clubroot population x B. oleracea genotype interactions and in the initial assessment of cultivars there were only small interactions which could be removed by an angular transformation of the data. It was concluded that a high level of non-differential resistance had been achieved and that it may prove durable. It was also concluded from a small field trial that this level of resistance would prevent serious yield losses in practice.     

Two mitochondrial haplotypes in Pterochloroides persicae (Hemiptera: Aphididae: Lachninae) associated with different feeding sites

Pterochloroides persicae (Cholodkovsky) is an aphid species belonging to the subfamily Lachninae that uses different members of Rosaceae (specially Prunus spp.) as hosts. Partial sequences from the mitochondrial cytochrome c oxidase 1 (COI) and the nuclear long‐wave opsin genes were obtained for approximately 100 P. persicae aphid individuals sampled from 34 colonies collected mainly in Tunisia and other Mediterranean locations. The variability found at the mitochondrial locus revealed the presence of two maternal haplotypes in the studied area that differed in a single nucleotide. The nuclear gene analyzed, however, failed to reveal any variability in this species. The variability found at the COI locus was related to the season of aphid sampling and with the site of feeding, with haplotype I mostly detected in samples collected in spring and summer on trunks and branches and haplotype II only detected in aphids collected in autumn on roots. The observed pattern of molecular variation suggests the presence of two clonal races of P. persicae coexisting in the studied area differentially adapted to conditions prevalent in the alternative seasons and/or to different feeding sites.     

Sub-lethal effects of tiametoxam on life table parameters of the cabbage aphid,Brevicoryne brassicae (L.) (Hemiptera: Aphididae) under laboratory conditions

Efficiency of tiametoxam was determined on population growth parameters of cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae) using demographic toxicology by leaf spray method. At first, bioassay was performed. The LC₅₀ values and confidence limits for thiamethoxam were 169.05?ppm (92.61–342.51). To evaluate, the sub-lethal effect of this insecticide on population growth parameters of cabbage aphid, LC₂₅ and LC₁₀ concentrations of tiametoxam were used at 58.8 and 22.05?ppm, respectively. Also, the LC₅₀ value of insecticide on the life table estimates was measured. Experiments were carried out in the laboratory at 23?±?1?°C, 60?±?5% RH and 16:8 (L:D) photoperiod on cabbage seedlings, Brassica oleracea, var. capitata L. Net fecundity rate decreased in insecticide-treated populations. Intrinsic rates of increase (r_m) were lower in tiametoxam treatment than in controls. There was a relative increase in intrinsic death rates of treated populations. The mean generation time and doubling time were also lower in population treated with insecticide than the control. There was a considerable reduction in the average numbers of nymphs reproduced per female as compared with the control. The average longevity of female adults in the control was significantly different (p?<?0.05) from those treated with thiamethoxam.     

Spatial and temporal dynamics of blue agave (Agave tequilana Weber var. azul) wilt in Jalisco Mexico

Tequila is a Mexican alcoholic beverage made from the fermentation and distillation of the blue agave (Agave tequilana Weber var. azul) stem. This crop is affected by a wilt associated mainly with Fusarium oxysporum. This disease can produce considerable yield losses. Little is known about the spatial and temporal behaviour of blue agave wilt. In this work, the spatial and temporal dynamics of the disease in commercial blue agave plantations in the state of Jalisco, Mexico, were analysed. Four fields of approximately 1 ha were selected in the municipalities of Arandas and Magdalena, in which disease assessments were carried out over a year of evaluation. Each plant was categorized based on a scale with four severity classes (healthy plant, severity class 1, severity class 2 and severity class 3). Maps of disease distribution were made. The spatial pattern was analysed by means of four indicators of spatial variation for binomial data; the spatial and temporal variation was analysed by means of transition matrices. An aggregate spatial pattern was observed in all fields. The transitions in severity classes were not completely unidirectional; some plants showed symptom remission between the date of first and second disease assessment, while others remained at their original severity. Severity class 1 occurred most frequently in Arandas fields (from 12.9% to 40.3%). There was a notable increase in wilt severity to class 2 in the Magdalena fields (from 4% to 50.6%). The rates of disease development towards severity class 3 are low and do not suppose a significant loss for the crop; nevertheless, the rates of disease development towards the wilt severity class 2 do put in risk the health of the crop and the availability of the raw material for the making of tequila.     

Forecasting migration of cereal aphids (Hemiptera: Aphididae) in autumn and spring

The migration of cereal aphids and the time of their arrival on winter cereal crops in autumn and spring are of particular importance for plant disease (e.g. barley yellow dwarf virus infection) and related yield losses. In order to identify days with migration potentials in autumn and spring, suction trap data from 29 and 45 case studies (locations and years), respectively, were set‐off against meteorological parameters, focusing on the early immigration periods in autumn (22 September to 1 November) and spring (1 May to 9 June). The number of cereal aphids caught in a suction trap increased with increasing temperature, global radiation and duration of sunshine and decreased with increasing precipitation, relative humidity and wind speed. According to linear regression analyses, the temperature, global radiation and wind speed were most frequently and significantly associated with migration, suggesting that they have a major impact on flight activity. For subsequent model development, suction trap catches from different case studies were pooled and binarily classified as days with or without migration as defined by a certain number of migrating cereal aphids. Linear discriminant analyses of several predictor variables (assessed during light hours of a given day) were then performed based on the binary response variables. Three models were used to predict days with suction trap catches ≥1, ≥4 or ≥10 migrating cereal aphids in autumn. Due to the predominance of Rhopalosiphum padi individuals (99.3% of total cereal aphid catch), no distinction between species (R. padi and Sitobion avenae) was made in autumn. As the suction trap catches were lower and species dominance changed in spring, three further models were developed for analysis of all cereal aphid species, R. padi only, and Metopolophium dirhodum and S. avenae combined in spring. The empirical, cross‐classification and receiver operating characteristic analyses performed for model validation showed different levels of prediction accuracy. Additional datasets selected at random before model construction and parameterization showed that predictions by the six migration models were 33–81% correct. The models are useful for determining when to start field evaluations. Furthermore, they provide information on the size of the migrating aphid population and, thus, on the importance of immigration for early aphid population development in cereal crops in a given season.     

Serological Detection of Beet Western Yellows Luteovirus in the Non-vector,Brevicoryne brassicae (Homoptera: Aphididae)

The interaction between beet western yellows luteovirus (BWYV) and the aphid species Brevicoryne brassicae was investigated using virus transmission and serological detection experiments. This species failed to transmit a BWYV isolate from infected to healthy oilseed rape plants, although virus was readily detected by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) in single B. brassicae adults. When virus-carrying adults were tested by ELISA after different inoculation access periods, the number of virus-positive individuals decreased after 5 days, whereas with the efficient vector Myzus persicae, virus-positive individuals were found even after 10 days. This confirms the inability of B. brassicae to transmit BWYV, even though it may acquire the virus. It is suggested that B. brassicae, as compared with the efficient vector M. persicae, may serve as an experimental model for studying the mechanisms of the luteovirus-vector specificity     

Population growth parameters of the cabbage aphid,Brevicoryne brassicae (L.) (Hemiptera: Aphididae), exposed to sublethal doses of thiacloprid

The cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae) is a major pest of cabbage in the world. In this study, the influence of thiacloprid on population growth parameters of B. brassicae using demographic toxicology by leaf spray method was determined. The LC₅₀ values and confidence limits for thiacloprid were 274.89?ppm (185.22–479.22), respectively. To evaluate the sublethal effect of this insecticide on population growth parameters of cabbage aphid, LC₂₅ and LC₁₀ concentrations of thiacloprid were used at 76.44 and 23.52?ppm, respectively. Also The LC₅₀ value of this insecticide on the life table estimates was measured. Experiments were carried out in the laboratory at 23?±?1?°C, 60?±?5% RH and 16:8 (L:D) photoperiod on cabbage seedlings, Brassica oleracea, var. capitata L. Intrinsic rates of increase (r_m) were lower in thiacloprid treatment than in controls. The mean generation time and doubling time were also lower in populations treated with insecticide than in controls. There was a considerable reduction in the average numbers of nymphs reproduced per female as compared with the control. The average longevity of female adults in the control was significantly different (p?<?0.05) from those treated with thiacloprid. According obtained results, thiacloprid is a good choice for control of the B. brassicae.     

结球甘蓝游离小孢子胚胎发生

以结球甘蓝品种“强夏”为材料进行游离小孢子培养,对与胚胎发生关系密切的因子进行探讨。研究结果表明,在盛花前期取材最适宜;单核晚期至双核期的小孢子才能发育成胚状体;含17%蔗糖的培养液在培养初期有利于小孢子存活;培养3d后胚胎诱导则以14％蔗糖浓度为最好;高浓度（17％）蔗糖培养3d后添加低浓度（11％）蔗糖培养液能大大提高胚胎发生能力,比一直在14％蔗糖培养液培养的提高282．4％,比更新培养液培养的提高126．1％。     

Control of Aphis gossypii and Myzus persicae (Hemiptera: Aphididae) by a flightless strain of Harmonia axyridis (Coleoptera: Coccinellidae) on green pepper plants in open fields

The cotton aphid Aphis gossypii Glover and the green peach aphid Myzus persicae (Sulzer) are economically important pests with a worldwide distribution. We evaluated the efficacy of releasing a flightless adult strain of the multicolored Asian lady beetle Harmonia axyridis (Pallas) as a control measure against these aphids on green pepper plants in open fields. Flightless H. axyridis adults were observed on the green pepper plants in the releasing plots throughout the experimental period and were found to be effective biocontrol agents, markedly decreasing the numbers of aphids. These results suggest that adults of this flightless strain of H. axyridis are effective in controlling aphids on green pepper plants in open fields.