Biological and ecological studies on the sugar-beet fly,Pegomyia mixta Vill. (Diptera: Anthomyiidae) on sugar-beet in Egypt

The sugar-beet fly, Pegomyia mixta Vill., is the most serious insect pest affecting sugar-beet plantations in Egypt. This study wase carried out in field in the El-Nubaria region ofEl-Behare Governorate. Peak numbers of flies were taken in sweep nets in December. Development of the fly appeared to be restricted to the months between November and May. In the hot months, adults were most active early in the morning and late in the afternoon, but in the cold months the peak of activity occurred at about midday. The flies were generally found on the upper surfaces of the leaves at temperatures below 16 °C and on the lower surfaces at temperatures above 24 °C. Females were generally more numerous than males. The eggs were observed from the first week of November to the end of April; the population was three blotches of eggs and 17 larvae/20 plants. The highest infestation of this insect in El-Nubaria was recorded at the end of March in both seasons (10 blotches of eggs, 20 larvae, and five pupae, and 12 blotches of eggs, 22 larvae, 13 pupae, respectively). The eggs are deposited in groups (3–8 eggs). The larvae bore its blotch in the leaf, about 3–7 larvae may be found in one blotch.     

Compatibility of entomopathogenic nematodes with fipronil

The survival and infectivity of infective juveniles (IJs) of three species of entomopathogenic nematodes, Steinernema carpocapsae Weiser, S. arenarium (Artyukhovsky) (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), were determined after exposure to different concentrations (250, 500, 1000 and 2000 ppm) of fipronil, an insecticide acting on the GABA receptors to block the chloride channel. Heterorhabditis bacteriophora was very tolerant to all concentrations of fipronil, with the highest mortality of 17% being observed at 2000 ppm of fipronil after 72 h exposure. Steinernema carpocapsae showed a similar response, with the highest mortality of 11.25% of IJs being observed after 72 h exposure to 2000 ppm of fipronil. Steinernema arenarium was, however, more sensitive to fipronil, and at 2000 ppm mortality rates of 94.6% and 100% were observed after 24 and 72 h, respectively. Fipronil had negligible effects on the infectivity of the three nematode species tested. The IJs which survive exposure to all concentrations of fipronil tested can infect and reproduce in Galleria larvae. The moderate effects on entomopathogenic nematodes of a lower fipronil concentration (250 ppm) and the field rates (12-60 ppm) of fipronil used as insecticide, suggest that direct mixing of entomopathogenic nematodes and fipronil at field rates is a viable integrated pest management option.     

Optimizing a pheromone lure for the sugar beet root maggot fly,Tetanops myopaeformis

We previously described a putative aggregation pheromone in adults of the sugar beet root maggot, Tetanops myopaeformis (von Röder) (Diptera: Ulidiidae), comprising nine compounds identified from males. Here, we conducted a series of experiments aimed at simplifying the blend of compounds necessary to achieve attraction as well as determining the dose that maximizes captures when formulated into an attractant lure. In all experiments, females showed stronger and more consistent evidence of attraction than males. White sticky traps baited with different blends of pheromone compounds that included the major component, (R)-(−)-2-nonanol, showed significantly higher female captures relative to those baited with blends that excluded the major component. (R)-(−)-2-nonanol alone was at least as effective as any blend that included this compound with other minor pheromone components. Lures using racemic 2-nonanol were as effective as the (R) enantiomer for both females and males, with some evidence of weak attraction to the (S) enantiomer (which is not produced by males) observed as well. Maximum capture rates using racemic 2-nonanol were estimated to occur with doses of ca. 795.5 and 621.6 mg for females and males, respectively. Addition of 2-nonanol lures to standard orange sticky stake traps currently used to monitor flies increased captures of both sexes. The pheromone lure developed here could improve trapping efficiency of current monitoring programs for T. myopaeformis and may also be used to develop other management tools for this important pest of sugar beet.     

Susceptibility of the Mediterranean fruit fly (Ceratitis capitata) and the Natal fruit fly (Ceratitis rosa) to entomopathogenic nematodes

The potential of entomopathogenic nematodes, Heterorhabditis bacteriophora, Heterorhabditis zealandica and Steinernema khoisanae, to infect pupariating larvae, pupae and adults of Ceratitis capitata and Ceratitis rosa was investigated in laboratory bioassays. Pupariating larvae and adult flies were susceptible to nematode infection, with no infection recorded for the pupae. Pupariating larvae of C. capitata were generally more susceptible to infection than those of C. rosa. Significantly more larvae of C. capitata were infected by H. bacteriophora. For C. rosa, highest infectivity of larvae was obtained with H. zealandica. In contrast, adults of both species were highly infected by S. khoisanae.     

Adenylate patterns of autumn-sown sugar beet differ from spring-sown sugar beet. Implications for root quality

Sugar beet ( Beta vulgaris L) is generally cultivated using two different planting and harvest patterns. In northern zones, spring sugar beet is sown in spring and harvested in autumn, whereas in subtropical latitudes, autumn sugar beet is sown in autumn and harvested in summer. The industrial quality of the root is frequently higher in spring-sown sugar beet crops. In order to explore physiological changes associated with this fact, this study has been focused on the seasonal changes of adenosine 5'-triphosphate and adenosine 5'-diphosphate levels in the storage roots of sugar beet plants, as an index of its metabolic status. The results obtained correspond to a different metabolic status of spring and autumn sugar beet at the moment of harvest. The adenylate patterns of autumn beets suggested a functional and active respiratory system. On the contrary, the patterns shown by spring beets corresponded to those we would expect to see in plants becoming dormant. The proline and glucose contents, which decrease the industrial quality of the root, and the respiratory rate measured in autumn-sown sugar beets, were nearly twice those of spring-sown sugar beets. The combination of an active respiratory system, which allows the carbohydrate catabolism and the synthesis of stress molecules, with the environmental factors at the time of the harvest, could be the underlying physiological mechanism causing some of the differences between spring- and autumn-sown sugar beet crops.     

Development of the one-on-one quality assessment assay for entomopathogenic nematodes.

The one-on-one bioassay was developed using Steinernema carpocapsae (All) nematodes against the wax moth larva, Galleria mellonella. The assay was used to develop and compare virulence profiles of both in vitro- and in vivo-produced nematodes and to provide a quality assessment 'standard' for in vitro-produced nematodes. The bioassay was subsequently used to develop virulence profiles for Steinernema carpocapsae (UK), S. feltiae (UK), S. feltiae (R1.5), S. feltiae (SN), S. glaseri (NJ-43), and S. riobrave (RGV). These profiles are unique for each species and isolate and are used as a standard of virulence in routine quality assessment of nematodes produced in liquid fermentation.     

病原线虫对桔小实蝇种群的控制作用

通过室内和田间实验研究了昆虫病原线虫对桔小实蝇Bactrocera (Bactrocera) dorsalis (Hendel)的控制作用。室内实验结果表明,供试的3种线虫的4个品系（小卷蛾斯氏线虫Steinernema carpocapsae All品系与A24品系,夜蛾斯氏线虫Steinernema feltiae SN品系和嗜菌异小杆线虫Heterorhabditis bacteriophora H06品系）,以小卷蛾斯氏线虫All品系对桔小实蝇的侵染力最强,其3天的LD₅₀和LD₉₅分别为35.0和257.1条/cm²土壤。按300条/cm²土壤的量施用,小卷蛾斯氏线虫All品系对当代桔小实蝇的控制效果为86.3%。用以虫期作用因子组建的生命表方法评价了小卷蛾斯氏线虫All品系对田间桔小实蝇下代种群的控制作用,结果表明,按300条/cm²土壤的量施用线虫,对照杨桃园的桔小实蝇种群趋势指数为105.9,而处理杨桃园的桔小实蝇种群趋势指数下降为15.5;小卷蛾斯氏线虫All品系对桔小实蝇的干扰控制指数为0.146,即线虫处理果园的下代种群密度仅为对照果园的14.6%。     

The effects of soil fumigation and nitrogen fertilizers on nematodes and sugar beet in sandy soils

In fifteen experiments on light land infested with plant-parasitic nematodes, fumigating the soil during the previous winter with D-D increased the average yield of sugar-beet roots from 25 to 36 t/ha; this was more than that obtained with various forms of nitrogenous fertilizers used in amounts up to 250 kg N/ha. Application of 85 kg N/ha increased yields on fumigated plots by 7 t/ha, and there was little benefit from giving more. Fumigation killed 65 % of the Pratylenchus spp., 80% of the Trichodorus spp. and 90% of the Tylenchorhynchus spp. in the top 5 cm of the soil and, at 15–20 cm deep, 90, 93 and 95% of these three genera. The increased yield from fumigant at different sites was not correlated with the initial populations of nematodes. The average increase in yield from fumigation was only poorly correlated with rainfall during May. The increases in nematode populations between April and August depended on rainfall, and were 0positively correlated both with the accumulated rainfall for the 10 weeks before sampling the soil in August and with the rainfall during the week previous to sampling. Fumigation not only improved the health of roots, and so enabled them to use nitrogen more efficiently, but also increased the amount of available nitrogen in the soil and decreased the amount lost by leaching. Injected anhydrous ammonia did not affect the populations of nematodes.     

Mutualistic association of Photorhabdus asymbiotica with Japanese heterorhabditid entomopathogenic nematodes

Gram-negative bacteria, Photorhabdus luminescens and P. temperata, form a mutualistic association with entomopathogenic heterorhabditid nematodes while P. asymbiotica is known as an opportunistic human pathogen that causes disseminated bacteremic spread on two continents, the United States and Australia. In the course of our phylogenetic study of Photorhabdus bacteria associated with Japanese Heterorhabditis nematodes, we found two Photorhabdus isolates (Photorhabdus sp. Cbkj163 and OnIr40) whose partial 16S rRNA gene sequence showed high similarities to clinical isolates of this pathogen from Heterorhabditis indica. The phylogenetic study, based upon the gyrase subunit B gene sequences of the two isolates, revealed clustering with these clinical isolates of P. asymbiotica from both the United States and Australia but not with other Photorhabdus bacteria associated with nematodes. The two bacterial isolates were also found to share microbiological and biochemical characteristics with clinical and entomopathogenic Photorhabdus strains. Moreover, not only the two novel Photorhabdus isolates but also an Australian clinical isolate of P. asymbiotica formed mutualistic association with H. indica isolates. These data suggest that the bacteria isolated from H. indica CbKj163 and OnIr40 are a novel subspecies of P. asymbiotica, and that some clinical isolates of P. asymbiotica could have originated from bacteria associated with entomopathogenic nematodes.     

Evaluation of entomopathogenic nematodes against the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae)

Infectivity of six entomopathogenic nematode (EPNs) species against Bactrocera oleae was compared. Similar infection levels were observed when third-instar larvae were exposed to infective juveniles (IJs) on a sand-potting soil substrate. When IJs were sprayed over naturally infested fallen olives, many larvae died within treated olives as well as in the soil; Steinernema feltiae caused the highest overall mortality of 67.9%. In addition, three laboratory experiments were conducted to optimize a time period for S. feltiae field application. (1) Abundance of fly larvae inside fallen olives was estimated over the 2006–2007 season with the highest number of susceptible larvae (3 mm and larger) per 100 olives being observed during December, 2006. (2) S. feltiae efficacy against fly larvae dropped to the soil post-IJ-application was determined. B. oleae added to the substrate before and after nematode application were infected at similar levels. (3) Effect of three temperature regimes (min–max: 10–27, 6–18, and 3–12 °C) corresponding to October through December in Davis, California on S. feltiae survival and infectivity was determined. After 8 weeks, the IJs at the 3–12 °C treatment showed the highest survival rate. However, the cold temperature significantly limited S. feltiae infectivity. Our results demonstrate that B. oleae mature larvae are susceptible to EPN infection both in the soil and within infested olives. Being the most effective species, S. feltiae may have the potential to suppress overwintering populations of B. oleae. We suggest that November is the optimal time for S. feltiae field application in Northern California.     

Soil mediates the interaction of coexisting entomopathogenic nematodes with an insect host

We tested for soil substrate effects on the movement and infectivity of naturally co-occurring entomopathogenic nematodes Steinernema feltiae and Heterorhabditis marelatus, alone and in combination. We manipulated the presence and bulk density of soil and added Galleria mellonella baits within capped and perforated 15mL centrifuge tubes. Sampling tubes were then deployed in situ into field and laboratory settings as experimental traps for infective juveniles. In comparisons with standard soil collections from Lupinus arboreus rhizospheres, sampling tubes were equally sensitive to the presence of H. marelatus and more sensitive to S. feltiae. In laboratory microcosms, both EPN species infected Galleria at high frequencies in tubes lacking soil and in the absence of heterospecifics. Infection frequency of S. feltiae was unaffected by the presence of H. marelatus, but it declined with higher soil bulk density inside tubes. In contrast, detectable infection frequency by H. marelatus was reduced only marginally by the presence of soil but severely by the presence of S. feltiae. Thus, the presence of soil in tubes reversed the identity of dominant species infecting Galleria in tubes, an effect magnified when soils were compacted. Moreover, S. feltiae rarely moved into tubes lacking Galleria baits, whereas H. marelatus colonized unbaited tubes 4- to 5-fold more frequently than S. feltiae. In situ, sampling tubes acted as filters to reduce interference and contamination by fungal pathogens common in field soils. The method allows precision sampling with minimal soil disturbance while protecting bait insects from scavengers. Manipulation of tube design may allow selective sampling of EPN species, depending on the abiotic characteristics of soils, and the biology, behavior, and interspecific interactions of coexisting species.     

Optimizing the application of entomopathogenic nematodes: experimental set-up

The complex issue concerning the spray application of Entomopathogenic Nematodes (EPNs) with a hydraulic sprayer is still not solved. This research project focuses on the effect of spray application technique on the viability and deposition of EPNs. In this paper the experimental set-up used for this evaluation is described. A modular spray application system has been developed and is currently used to evaluate the effect of different parts of a sprayer on the viability of the EPNs. Based on the results of experiments using this modular spray application system, recommendations regarding pump type, mixing system, nozzle type and filter size will be formulated. Because of the large number of experiments in this research project, an image analysis system for the determination of the viability of the nematodes is developed. This paper describes two experiments comparing the new developed image processing technique with the standard microscopic counting technique.     

Needle nematodes (Longidorus spp.) and stubby-root nematodes (Trichodorus spp.) harmful to sugar beet and other field crops in England

Longidorus attenuatus produces galls at the tips of roots of field crops, including sugar beet, growing in alkaline, sandy soils in eastern England. L. elongatus produces similar, but often larger, galls on the roots of sugar beet and other crops in sandy soils in the W. Midlands and in Fen peats. Trichodorus spp. cause ‘stubby root’ of sugar beet and can feed on many field crops. Seven species of Trichodorus were found in sandy soils in eastern England. L. attenuatus, L. elongatus and Trichodorus spp. aggregate around roots and stunt sugar beet and other crop plants. L. attenuatus is commoner below plough depth than in the topsoil, whereas T. cylindricus, T. pachy-dermus and T. anemones are more abundant in the topsoil. These nematodes cause some forms of ‘Docking disorder’.     

昆虫病原线虫液体培养研究概况

综述昆虫病原线虫液体培养的研究概况。包括液体培养的研究历史,不同培养基组分对昆虫病原线虫产量的影响,营养源的选择,培养参数在昆虫病原线虫液体培养过程中的作用,感染期昆虫病原线虫脂肪酸含量,以及昆虫病原线虫应用前景等。     

Electron microscopical proof of the presence of sugar beet yellows virus particles in the roots of sugar beet

The presence of beet yellows virus (BYV) particles was electron microscopically proved in the roots of sugar beet. Specimens for the electron microscopical examination of root sap were prepared by differential centrifugation. It was proved that, contrary to expectations, examinations in spring showed most virus particles in the basal part of the root. At the same time it was found by experiment that the diagnostical BYV antiserum, for which the antigen was prepared from sugar beet leaves, did not react with a purificate of BYV containing virus particles.     

An analysis of leaf growth in sugar beet.

The increase of leaf area index (L) was examined in a series of sugar-beet crops grown on different sites (Broom's Barn, Suffolk and Trefloyne, Dyfed) or with different husbandry treatments (sowing dates and nitrogen rates) between 1978 and 1982. The development of L could be described as a function of thermal time using three parameters; D_E, which was essentially an estimate of the thermal time required for crop establishment, and rH_L and D_L, the thermal rate and duration, respectively, of the increase of L. Variations in D_E between seasons and with sowing date were small, but significant; they were attributed to factors affecting the condition of the seedbed. There were much larger variations in rH_L, especially between seasons, sites and crops given different rates of nitrogen fertiliser, and there was a strong negative relationship between rH_L and D_L. Much of the variation in rH_L was associated with differences in the concentrations of nitrogen in the lamina dry matter. Faster rates for rH_L at Trefloyne than at Broom's Barn, and in the crop grown in 1982 as compared with other years, were also partly attributable to particularly warm conditions during the early development of some of the larger, faster-growing leaves within the canopy. The wider application of the relationships established from these experiments was tested with data from a series of crops grown on other sites between 1960 and 1962. The relationships held particularly well for beet grown on soils with high water-holding capacity but not for those on soils of low water-holding capacity.     

An analysis of leaf growth in sugar beet.

The responses of leaf appearance and expansion to temperature in sugar beet were measured under controlled conditions, using ruler and auxanometers, to establish a basis for a subsequent analysis of leaf growth in field crops. The studies showed that leaf appearance rate responded linearly to temperature above 1°C, that leaf expansion rate responded likewise above 3°C and that both rates were zero below these base temperatures. Auxanometer measurements of leaf extension showed that daily rates of expansion of leaf area increased linearly with the daily integral of temperature. However, hourly rates of extension in length alternated with those in width during each 24 h cycle in patterns that were not clearly related to hourly changes of temperature or to the day/night sequence.