Cultural and insecticidal control of Thrips tabaci on onions in the Sudan

Onion thrips (Thrips tabaci) is the major pest of onions in the Sudan. In the Gezira Scheme onions are normally transplanted between October and January when the thrips population is very low. Later, thrips commence to breed. Early transplanted onions were well established before infestations became severe and, without the need for insecticidal control, produced significantly higher yields. Onions transplanted later, when thrips began to multiply, produced lower yields. Depending on the duration and intensity of infestation three to five sprays applied at fortnightly intervals were required to control thrips on the late transplanted crop. The effect of spray frequency on the development and yield of onions was investigated and the response found to be solely due to the extent of thrips control achieved. The toxicant itself had no effect on growth. Although the leaves were unaffected by the various treatments, spraying when most thrips were present increased fresh and dry leaf weights, bulb weight and, in the Hudeiba cultivar, the proportion of flowering plants. With the late-transplanted crop, light infestations led to yield losses of at least 39% whilst severe thrips attacks reduced the crop by 57%.     

Life history parameters of <Emphasis Type="Italic">Thrips tabaci</Emphasis> (Thysanoptera: Thripidae) on six commercial cultivars of canola

The onion thrips, Thrips tabaci Lind. (Thysanoptera: Thripidae), is an important pest of the canola crop, Brassica napus L., in the Ardabil region. In this study, life history parameters of T. tabaci were investigated on six canola cultivars, namely: Talayh, Zarfam, RGS003, Opera, Option500, and Hayola401. Experiments were performed in a climate chamber set at 25 ± 1°C and 55 ± 5% RH under 16L:8D. The results indicated that the development time of immature stages was significantly longer on RGS003 than on Opera, Hyola401, Zarfam, Option500, and Talayh. The onion thrips reared on RGS003 had the lowest number of eggs laid per female (15.5) and the lowest survival rate (40%) among the tested cultivars. The lowest intrinsic rate of natural increase (r _m) and population growth rate (λ) were observed on RGS003, and were the highest on Zarfam. The generation time (T) was shortest on Zarfam (21.5 days) and longest on RGS003 (26.5 days). Similarly, the doubling time (DT) was shortest on Zarfam (4.5 days) and longest on RGS003 (8.1 days). Considering the significant effect of the host plant on the life history parameters of onion thrips, it was concluded that RGS003 is the least suitable cultivar among the other tested canola cultivars for integrated management of onion thrips in canola fields.     

Evaluation of sampling methodology for determining the population dynamics of onion thrips (Thysanoptera: Thripidae) in Ontario onion fields

Onion thrips, Thrips tabaci Lindeman, are an economic pest of alliums worldwide. In Ontario onion-growing regions, seasonal abundance and population trends of onion thrips are not well known. The objectives of this research were to investigate onion thrips population dynamics by using both white sticky traps and plant counts, to gain insight into flight height, and to determine the genus and sex of thrips fauna present in monitored fields. Adult thrips were captured on white sticky traps placed in two commercial onion fields in the Thedford-Grand Bend Marsh region as early as mid-May in 2001, 2002, and 2003. Thrips were not recorded on onion plants in these fields until late June and early July. A comparison of sticky trap captures to plant counts revealed a strong, positive correlation, indicating that sticky traps, which consistently detected thrips earlier than plant counts, could be used instead of plant counts early in the season to monitor onion thrips populations. Pole traps placed in onion and an adjacent soybean, Glycine max (L.) Merr., field revealed that regardless of crop type, most thrips were captured 0.7-0.95 m above the soil surface. During this study, 70% of 137,000 thrips captured on sticky traps and 89% of 1,482 thrips captured in pan traps were female onion thrips. No male onion thrips were identified in this study: most of the remaining thrips were Frankliniella spp.     

The influence of temperature on weight loss from stored onion bulbs due to desiccation, respiration and sprouting

When onion bulbs were stored for 9 months at 2, 7.5, 15 or 25 °C and 70% r.h., the losses due to desiccation increased with temperature but less than 20 % was due to respiration at any of the storage temperatures. Respiration rates of onion bulbs transferred from 2 to 25 °C were higher from February onwards than those of bulbs stored continuously at 25 °C. Conversely, bulbs transferred from 25 to 2 °C respired less from February onwards than those kept at 2 °C. Sprouting, at the final assessment in June, was highest at 15 and 7.5 °C and lowest at 2 °C. Total weight loss was above 45 % in all the storage treatments except at 2 °C (12%). Storage at 7.5 °C is suitable until March but long-term storage until June requires low temperatures.     

Effects of manipulating spray-application parameters on efficacy of the entomopathogenic fungus Beauveria bassiana against western flower thrips,Frankliniella occidentalis,infesting greenhouse impatiens crops

The effects of various spray application parameters on the efficacy of a clay-based wettable powder formulation of Beauveria bassiana strain GHA conidia against western flower thrips, Frankliniella occidentalis, were evaluated in a series of greenhouse tests. With the aim of optimizing spray application methods to maximize biopesticide efficacy, a series of independent experiments was conducted that varied four spray parameters: application interval, rate, volume, and spray-program timing. Impatiens crops infested with western flower thrips were treated with (1) multiple sprays at the rate of 5×10¹³ conidia in 935 L aqueous carrier ha^?1 applied at 3-, 5-, and 7-day intervals, (2) weekly sprays at rates of 5×10¹³, 1×10¹⁴, and 2.0×10¹⁴ conidia in 935 L carrier ha^?1, (3) weekly sprays at a rate of 2.0×10¹⁴ conidia in volumes of 935, 1870, and 3740 L water ha^?1, and (4) multiple sprays at the rate of 2.0×10¹⁴ conidia in 3740 L carrier ha^?1 applied at 5-day intervals in spray programs initiated before versus after the onset of flowering. Pollen-bearing impatiens flowers were sampled twice weekly to estimate thrips population density, and adult female and second-instar thrips were collected 24 h post application for determination of acquired dose (conidia/insect). Numbers of conidia inoculated onto thrips increased with increasing spray frequency and volume. Dose was unexpectedly not directly correlated with application rate when volume was held constant, suggesting that thrips avoided concentrated spray residues. Statistically significant thrips population reductions relative to controls were achieved only when three to four sprays were applied at the highest label rate in the highest volume at < 7-day intervals. Applications against thrips infesting young, preflowering impatiens crops were not consistently more effective than applications in older crops. The most effective treatment programs reduced pest populations by 30–40% compared to untreated controls; this slowed, but did not stop, the growth of pest populations. Results indicate that use of fungi for thrips management will require integration with other control agents.     

Cropping system influences Tomato spotted wilt virus disease development,thrips population and yield of tomato (Lycopersicon esculentum)

Yield of tomato is limited by many diseases including Tomato spotted wilt virus disease. This study was conducted in the field at Kenya Agriculture Research Institute Njoro, Kenya, in 2004 and 2006 to determine the effect of intercropping on disease development, thrips population and yield of tomato variety Cal J grown under four intercrop systems involving kale, onion, maize and sole tomato. The experimental design was a Randomised Complete Block Design (RCBD) replicated three times. Disease scores on tomato–maize differed significantly from tomato–kale and tomato–onion in both years of the study. Maize cropping system had a low significant thrips population from the other cropping systems. Tomato–maize intercrop produced the lowest fruit weights and marketable yield in 2004 and 2006, while yield of onion, kale and maize in intercrops were not significantly different from their monocrops. Land equivalent ratio was >1 in all the cropping systems.     

Use of mycorrhizal fungi and phosphorus fertilization to improve the yield of onion (Allium cepa L.) plant

Improving the economical yield of commonly cultivated crops is one of the most pressing social and scientific issues in modern agriculture. This paper was conducted to investigate the bio-efficacy of arbuscular mycorrhizal fungi (AMF) in improving phosphorous (P) utilization and increasing the yield of onion plant grown in sandy soil under a drip irrigation system. The obtained results showed that AMF inoculation of onion and application of 120 kg P fertilizer ha⁻¹ significantly increased the fresh and dry weights, chlorophyll content of onion as well as P concentration in the root, shoot, and bulb during two growing seasons. Moreover, AMF increased the bioavailability of P in the rhizosphere and significantly enhanced the N-utilization by the inoculated plant. The economic yield of the onion plant inoculated by AMF and fertilized by different doses of P fertilizer was much higher than that obtained by the control (without AMF). These findings indicated that inoculating the onion plant in the field with AMF could be very effective in increasing the yield of the onion plant. Additionally, this study suggests AMF as a low-cost and promising candidate for the sustainable production of the onion crop using reclaimed sandy soils and a drip irrigation system.Keyword: Onion, Mycorrhizal Fungi, Economic yield, P fertilization, N utilization, ¹⁵N     

Overwintering locations and hosts for onion thrips (Thysanoptera: Thripidae) in the onion cropping ecosystem in New York

Identifying locations where onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), overwinter and subsequently disperse is important for designing control strategies. In upstate New York from 2003 through 2006, potential overwintering sites in the commercial onion, Allium cepa L., cropping system were investigated early in the spring before onion seedling emergence and again late in the season after onions were harvested. Onion thrips adults were sampled directly from the soil and indirectly from the soil by using emergence cages. Sampling locations included onion field interiors and edges and areas outside of these fields, including woods. Host material sampled included onion culls; volunteer onions, which sprout from cull onions left behind after harvest; and weeds. Onion thrips adults were found in all sections of onion fields and in locations outside of onion fields, with the fewest emerging from woods. Emergence began in early May and extended into June. Peak emergence occurred during the last half of May, at which time 50-75% of the population had emerged. Adults colonized volunteer onions as early as late March and as late as mid-November. No adults were found overwintering in onion cull piles. Adults also colonized several weed species, especially pigweed, Amaranthus hybridis L., and lambsquarters, Chenopodium album L., late in the fall. Our results indicate that onion thrips adults overwinter in the soil within and near onion fields and that they probably colonize volunteer onion plants before subsequent generations infest the onion crop in the spring. Volunteer onions and weeds also provide onion thrips with a host after onions are harvested. Consequently, onion thrips management strategies should include tactics that reduce volunteer onion and weed abundance.     

气象因素对芒果蓟马种群数量动态的影响

明确芒果园中蓟马复合种种群动态与气象因子之间的关系。用粘虫板定期定点监测芒果园中蓟马的种群消长情况;通过相关分析、主成分分析和灰色关联分析,分析其与气象因素的关系。芒果花期蓟马种群数量为全年发生高峰。相关分析结果表明,监测日蓟马种群数量与日平均气温(℃)、日最大风速(m/s)显著正相关,与日最低气温(℃)显著负相关。芒果花期蓟马种群数量与2月降水量(mm)、3月平均风速(m/s)、1-2月平均气温(℃)、2月月均最高、最低气温(℃)、2-3月平均相对湿度(%)及1-3月平均最小相对湿度(%)显著相关。主成分分析表明,月平均温度(℃)和月最低气温(℃)是影响蓟马种群动态的主要因素,对蓟马种群动态的影响达56.0%。灰色关联分析表明,月均最低气温(℃)对芒果蓟马种群数量影响最大。月最低气温(℃)和月平均温度(℃)是影响芒果园中蓟马复合种种群数量动态的主要气象因素。芒果蓟马复合种种群数量受食物、种群扩散、天敌、自身繁殖和气候因素的共同影响。     

Impact of straw mulch on populations of onion thrips (Thysanoptera: Thripidae) in onion

Development of insecticide resistance in onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), populations in onion (Allium spp.) fields and the incidence of the T. tabaci transmitted Iris yellow spot virus have stimulated interest in evaluating alternative management tactics. Effects of straw mulch applied in commercial onion fields in muck areas of western New York were assessed in 2006 and 2007 as a possible onion thrips management strategy. In trials in which no insecticides were applied for thrips control, straw mulch-treated plots supported significantly lower T. tabaci populations compared with control plots. In both years, the action thresholds of one or three larvae per leaf were reached in straw mulch treatments between 7 and 14 d later than in the control. Ground predatory fauna, as evaluated by pitfall trapping, was not increased by straw mulch in 2006; however, populations of the common predatory thrips Aeolothrips fasciatus (L.) (Thysanoptera: Aeolothripidae) were significantly lower in straw mulch plots in both years. Interference of straw mulch in the pupation and emergence of T. tabaci was investigated in the lab and their emergence was reduced by 54% compared with bare soil. In the field the overall yield of onions was not affected by the straw mulch treatment; however, the presence of jumbo grade onions (>77 mm) was increased in 2006, but not in 2007. These results indicate that populations of T. tabaci adults and larvae can be significantly reduced by the use of straw mulch without compromising overall onion yield. The use of this cultural practice in an onion integrated pest management program seems promising.     

Onion thrips (Thysanoptera: Thripidae): a global pest of increasing concern in onion

During the past two decades, onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), has become a global pest of increasing concern in commercial onion (Allium cepa L.), because of its development of resistance to insecticides, ability to transmit plant pathogens, and frequency of producing more generations at high temperatures. T. tabaci feeds directly on leaves, causing blotches and premature senescence as well as distorted and undersized bulbs. T. tabaci can cause yield loss > 50% but can be even more problematic when it transmits Iris yellow spot virus (family Bunyaviridae, genus Tospovirus, IYSV). IYSV was identified in 1981 in Brazil and has spread to many important onion-producing regions of the world, including several U.S. states. IYSV symptoms include straw-colored, dry, tan, spindle- or diamond-shaped lesions on the leaves and scapes of onion plants and can cause yield loss up to 100%. Here, we review the biology and ecology of T. tabaci and discuss current management strategies based on chemical, biological, and cultural control as well as host resistance. Future directions for research in integrated pest management are examined and discussed.     

Bulb Development in Onion (Allium cepa L.) IV. Influence on Yield of Radiation Interception, its Efficiency of Conversion, the Duration of Growth and Dry-matter Partitioning

Increases in total dry-matter yield during bulb growth in well-irrigatedonion crops were correlated with the total solar radiation interceptedby the leaf canopy. The mean efficiency of conversion of interceptedradiation to dry-matter was 1.58 g MJ^–1. However, efficiencieswere significantly different between seasons and in two yearsout of three they were lower for spring-sown crops than forautumn-sown crops. The lower efficiencies coincided with periodsof high mean temperature and irradiance. The percentage of thetotal irradiance intercepted by the canopy during bulbing (1%)was increased by higher plant densities, earlier sowing andin later-maturing cultivars. It was higher in spring-sown thanin autumn-sown crops especially at low plant densities. Theduration of bulb growth was negatively correlated with 1% andwith the mean air temperature during bulb growth. Consequentlyautumn-sown crops had a longer duration of bulb growth thanspring-sown crops and produced exceptionally high bulb yieldsat high plant densities. Non-irrigated crops had a lower 1%and a shorter duration of bulb growth than irrigated crops,and a lower conversion efficiency in a season of high mean temperatureand irradiance. Onion, Allium cepa L., bulb, irradiance, efficiency, partitioning, plant population, temperature, irrigation, growth-analysis, water-stress, leaf-area-index     

广州地区红火蚁工蚁的巢外活动及有翅蚁的婚飞规律

为了阐明红火蚁Solenopsis invicta Buren的发生危害规律,为制定红火蚁的监测与防治措施提供科学依据,本研究调查了广州地区（113°45′E,22°43′N）红火蚁工蚁巢外活动日节律和季节性变化,以及有翅蚁的婚飞活动。结果表明,工蚁巢外活动日节律随季节或月份的不同而存在着明显差异：其中12-2月份的日活动节律为单峰型,即在中午温度较高时数量较大,而在5-10月份的日活动节律为双峰型,即在上午或下午工蚁数量较大,其余月份的活动为不明显的双峰型。工蚁巢外活动数量和时间随季节的不同而有显著差异。其中以6月和10月份的日活动数量最多,而在1月和2月份的活动数量最少,时间最短,其余月份活动数量居中。工蚁在阵雨前后的活动数量明显多于晴天,但处于降雨时刻的巢外工蚁数量极少。蚁巢受侵扰后出巢工蚁数量在30 s内最大,之后便随时间的延长而逐渐减少,该种现象可以用房室函数进行描述。另外,工蚁的巢外数量会随侵扰强度的加大而增加。在试验区内全年都可见到红火蚁婚飞,但婚飞活动主要集中在3-5月份,每日婚飞活动主要发生在下午,并主要发生在雨前或雨后。上述结果对于了解我国红火蚁的发生危害规律和提升其监控技术水平有较大参考价值。     

Relationships between insect predator populations and their prey,Thrips tabaci,in onion fields grown in large-scale and small-scale cropping systems

Onion thrips, Thrips tabaci Lindeman, is the primary pest of onion, which is grown in either large-scale, monoculture systems surrounded by other onion fields, or in small-scale systems surrounded by multiple vegetable crops. In 2011 and 2012, populations of insect predators and their prey, T. tabaci, were assessed weekly in onion fields in both cropping systems. Insect predator taxa (eight species representing five families) were similar in onions grown in both systems and the most commonly occurring predators were from the family Aeolothripidae. Seasonal population dynamics of predators and T. tabaci followed similar trends within both cropping systems and tended to peak in late July and early August. Predator abundance was low in both systems, but predator abundance was nearly 2.5 to 13 times greater in onion fields in the small-scale system. T. tabaci abundance often positively predicted predator abundance in both cropping systems.     

A new record of the tobacco thrips <Emphasis Type="Italic">Frankliniella fusca</Emphasis> (Hinds) (Thysanoptera: Thripidae) from Japan

The tobacco thrips, Frankliniella fusca, which is known as a vector of TSWV and Pantoea ananatis causing center rot of onion, and a serious pest of tobacco, cotton and groundnuts in North America, is newly recorded from the bulbs of Narcissus pseudonarcissus in Honshu, mainland Japan. Two strains were found in Shimane Prefecture. One strain was collected from a bulb produced in Niigata Prefecture in the winter of 2002, and the other was collected from bulbs produced in Fukushima Prefecture in the autumn of 2002. F. fusca can be easily distinguished from other members of this genus in Japan.     

DECISION TOOLS FOR MULBERRY THRIPS PSEUDODENDROTHRIPS MORI （NIWA, 1908） MANAGEMENT IN SERICULTURAL REGIONS; AN OVERVIEW

Mulberry thrips Pseudodendrothrips mori (Niwa, 1908) is a major pest of mulberry trees recorded from different sericultural regions of the world. The thrips infestation affects the qualitative and quantitative characters of mulberry leaf, by direct feeding damage to leaves and the ingestion of sap, which in turn affects the silkworm cocoon crop. This is most harmful in dry climates and seasons when heavily attacked plants lose moisture heavily. Under these conditions infestation can seriously deplete yields. The seasonal population fluctuation and the degree of damage caused to the host plant are influenced by various environmental factors including climate, host-plant variety, topography, soil type, and management regimes.This article attempts to review all available documents on mulberry thrips and to discuss the practical approaches for best control of this pest.     

DECISION TOOLS FOR MULBERRY THRIPS PSEUDODENDROTHRIPS MORI (NIWA, 1908) MANAGEMENT IN SERICULTURAL REGIONS; AN OVERVIEW

Abstract Mulberry thrips Pseudodendrothrips mori (Niwa, 1908) is a major pest of mulberry trees recorded from different sericultural regions of the world. The thrips infestation affects the qualitative and quantitative characters of mulberry leaf, by direct feeding damage to leaves and the ingestion of sap, which in turn affects the silkworm cocoon crop. This is most harmful in dry climates and seasons when heavily attacked plants lose moisture heavily. Under these conditions infestation can seriously deplete yields. The seasonal population fluctuation and the degree of damage caused to the host plant are influenced by various environmental factors including climate, host-plant variety, topography, soil type, and management regimes. This article attempts to review all available documents on mulberry thrips and to discuss the practical approaches for best control of this pest.     

Simple agrometeorological models for estimating Guineagrass yield in Southeast Brazil

The objective of this work was to develop and evaluate agrometeorological models to simulate the production of Guineagrass. For this purpose, we used forage yield from 54 growing periods between December 2004–January 2007 and April 2010–March 2012 in irrigated and non-irrigated pastures in São Carlos, São Paulo state, Brazil (latitude 21°57′42″ S, longitude 47°50′28″ W and altitude 860 m). Initially we performed linear regressions between the agrometeorological variables and the average dry matter accumulation rate for irrigated conditions. Then we determined the effect of soil water availability on the relative forage yield considering irrigated and non-irrigated pastures, by means of segmented linear regression among water balance and relative production variables (dry matter accumulation rates with and without irrigation). The models generated were evaluated with independent data related to 21 growing periods without irrigation in the same location, from eight growing periods in 2000 and 13 growing periods between December 2004–January 2007 and April 2010–March 2012. The results obtained show the satisfactory predictive capacity of the agrometeorological models under irrigated conditions based on univariate regression (mean temperature, minimum temperature and potential evapotranspiration or degreedays) or multivariate regression. The response of irrigation on production was well correlated with the climatological water balance variables (ratio between actual and potential evapotranspiration or between actual and maximum soil water storage). The models that performed best for estimating Guineagrass yield without irrigation were based on minimum temperature corrected by relative soil water storage, determined by the ratio between the actual soil water storage and the soil water holding capacity.irrigation in the same location, in 2000, 2010 and 2011. The results obtained show the satisfactory predictive capacity of the agrometeorological models under irrigated conditions based on univariate regression (mean temperature, potential evapotranspiration or degree-days) or multivariate regression. The response of irrigation on production was well correlated with the climatological water balance variables (ratio between actual and potential evapotranspiration or between actual and maximum soil water storage). The models that performed best for estimating Guineagrass yield without irrigation were based on degree-days corrected by the water deficit factor.     

Relationship between onion thrips (Thrips tabaci) and Stemphylium vesicarium in the development of Stemphylium leaf blight in onion

Stemphylium leaf blight caused by Stemphylium vesicarium and onion thrips (Thrips tabaci) are two common causes of leaf damage in onion production. Onion thrips is known to interact synergistically with pathogens to exacerbate plant disease. However, the potential relationship between onion thrips and Stemphylium leaf blight is unknown. In a series of controlled laboratory and field trials, the relationship between thrips feeding and movement on the development and severity of Stemphylium leaf blight were examined. In laboratory assays, onions (“Avalon” and “Ailsa Craig”) with varying levels of thrips feeding damage were inoculated with S. vesicarium. Pathogen colonisation and leaf dieback were measured after 2 weeks. In pathogen transfer assays, thrips were exposed to S. vesicarium conidia, transferred to onion and leaf disease development was monitored. In field trials, insecticide use was examined as a potential indirect means to reduce Stemphylium leaf blight disease and pathogen colonisation by reducing thrips damage. Results from laboratory trials revealed that a reduction in thrips feeding decreased S. vesicarium colonisation of onion leaves by 2.3–2.9 times, and decreased leaf dieback by 40–50%. Additionally, onion thrips were capable of transferring S. vesicarium conidia to onion plants (albeit at a low frequency of 2–14% of plants inoculated). In field trials, the symptoms and colonisation of Stemphylium leaf blight were reduced by 27 and 17%, respectively with the use of insecticide to control thrips. These results suggest that onion thrips may play a significant role in the development of Stemphylium leaf blight, and thrips control may reduce disease in commercial onion fields.     

Methyl benzoate fumigation for control of post-harvest pests and its effects on apple quality

Methyl benzoate is a newly discovered natural insecticide. In this study, we evaluated methyl benzoate as a potential fumigant for controlling four pests including western flower thrips (WFT), Frankliniella occidentalis, lettuce aphid, Nasonovia ribisnigri, rice weevil, Sitophilus oryzae, and bulb mites, Rhizoglyphus spp., at different temperatures and effects on post-harvest quality of apples. Methyl benzoate fumigations were effective against all four pests. Complete control of WFT and lettuce aphid was both achieved in 8, 16 and 24 hr at 25, 13 and 2°C, respectively. For rice weevil, complete control was achieved in 16 and 72 hr with and without rice at 25°C, respectively. Complete control of bulb mites was achieved in 64 hr at 25°C on peanut. In addition, a 24 hr methyl benzoate fumigation at 2°C had complete control of WFT but had no negative impact on visual quality of apples of three varieties 4 weeks after fumigation. These results suggest that methyl benzoate fumigation has potential to be an alternative treatment to methyl bromide fumigation, which has been phased out, for post-harvest pest control for stored products and may also have potential to control other pests on fresh products.