Suppression of the Root-knot Nematode Meloidogyne javanica by Alginate Pellets Containing the Nematophagous Fungi Hirsutella rhossiliensis , Monacrosporium cionopagum and M. ellipsosporum

The endoparasitic fungus Hirsutella rhossiliensis and the nematode-trapping fungi Monacrosporium cionopagum and M. ellipsosporum were formulated as hyphae in alginate pellets. In a soil microcosm experiment, dried pellets of all three fungi decreased the invasion of cabbage seedlings by the root-knot nematode Meloidogyne javanica when juvenile nematodes were placed 2 cm from roots; M. cionopagum was more effective than the other two fungi, reducing nematode invasion by 40-95% with 0.24-0.94 pellets cm - 3 of soil. In a field microplot experiment, in which neither H. rhossiliensis nor M. ellipsosporum suppressed nematodes, 0.5 pellets of M. cionopagum cm - 3 of soil suppressed M. javanica invasion of tomato seedlings by 73%. In a second microplot experiment with only M. cionopagum , again at 0.5 pellets cm - 3 of soil, the fungus suppressed the invasion of tomato seedlings whether the pellets were added 0, 5 or 14 days before planting; the population density of M. cionopagum increased to nearly 3000 propagules g - 1 of soil by day 8 and then declined to less than 300 by day 22. Enchytraeid worms were observed in and around damaged and apparently destroyed pellets in both microplot experiments. Whether enchytraeids consumed the fungi or otherwise affected biological control requires additional research.     

The Importance of the Host Plant on the Interaction Between Root-knot Nematodes Meloidogyne spp. and the Nematophagous Fungus, Verticillium chlamydosporium Goddard

The effect of the host plant on the efficacy of Verticillium chlamydosporium as a biological control agent for root-knot nematodes was investigated in four experiments. The growth of the fungus in the rhizosphere differed significantly with different plant species, the brassicas kale and cabbage supporting the most extensive colonization. The presence of nematodes in roots increased the growth of the fungus on most plants, and this effect was associated with the emergence of egg masses on the root surface; the presence of Meloidogyne incognita did not stimulate growth of the fungus in the rhizosphere until 5 weeks after the addition of infective juveniles to soil. The susceptibility of the plant host to M. incognita attack influenced the numbers of nematode eggs parasitized by the fungus. The control of the nematode was less effective on tomato roots, which produced large galls as a result of nematode infection compared with control on potato roots where galls were smaller, despite the greater abundance of the fungus in the rhizosphere of tomato plants. In large galls, a significant proportion of the egg masses remained embedded in the roots and was isolated from the fungus which was confined to the rhizosphere. Hence, the plant species has a marked effect on the efficacy of V. chlamydosporium as a biological control agent.     

酸黄瓜南方根结线虫病抗性与葫芦素B含量的关系

采用高效液相色谱分析法,通过测定3种不同抗性甜瓜属作物根系中葫芦素B含量的差异,探讨酸黄瓜南方根结线虫病抗性与葫芦素B含量的关系.结果表明:(1)接种根结线虫前,供试材料根系中的葫芦素B含量以酸黄瓜的最高(1.31μg/g),非洲角次之(0.85μg/g),北京截头最低(0.35μg/g),表明酸黄瓜中葫芦素B的本体含量较高;接种根结线虫后,酸黄瓜、非洲角、北京截头根系中的葫芦素B含量升高至3.88、2.67和0.49μg/g,较相应未接种对照分别升高了2.57、1.82和0.14μg/g,表明酸黄瓜经线虫诱导后葫芦素B含量上升较大.(2)酸黄瓜受线虫危害低于非洲角并显著低于北京截头,说明酸黄瓜的抗线虫能力较强;供试材料受害程度与葫芦素B含量相关性分析表明,作物的抗线虫能力与根系中的葫芦素B含量呈正相关关系,其含量越高,抗性越强.研究认为,酸黄瓜的高葫芦素B含量是其南方根结线虫病抗性的化学证据.     

Biological Studies on Agamermis unka (Nematoda: Mermithidae), a Parasite of the Brown Planthopper Nilaparvata lugens

The mermithid parasite, Agamermis unka, is the most important natural enemy of the brown planthopper (BPH), Nilaparvata lugens, in Korean rice fields. Very little is known about many aspects of the mermithid's life cycle and behavior, and a study was undertaken to close the data gap. The sex ratio of A. unka isolated from field-collected BPH showed a strong female bias. Even when several A. unka occurred within a BPH, the majority were females. Similarly, the sex ratio of field-collected A. unka adults that were in the soil was strongly biased towards females and, in many instances, the females were found in the absence of males. Females collected from the field from January to May and maintained in water at 25 C had a mean pre-oviposition period of 17-28 days and a mean oviposition period of 17-37 days, and averaged 543-1851 eggs/female. The eggs averaged 20, 17 and 36 days to hatch at 30, 25 and 20 C respectively, but none hatched at 15 C. Most of the eggs (96%) hatched at 25 and 20 C, but only 64% hatched at 30 C. Agamermis pre-parasites could be found on rice stems in the field and laboratory. In the field, BPH-susceptible and BPH-resistant rice cultivars showed no significant difference in the numbers of pre-parasites on the stem. In the laboratory, the number of pre-parasites recovered/rice stem was significantly higher in two out of three trials when BPH nymphs and adults were present. When BPH nymphs were exposed to the pre-parasites in the laboratory, 39% of the brachypterous females and 4.5% of the brachypterous males were parasitized, whereas 0.3% of the macropterous females and 0% of the macropterous males were parasitized. The parasitism data obtained under field conditions showed similar trends. The reason(s) for these differences in parasitism between the BPH sex and wing types that have been observed both in the laboratory and field is unknown. Because brachypterous males and macropterous females and males occur in lesser numbers than the brachypterous females, this may, in part, account for the differences in parasitism observed. However, BPH behavior cannot be discounted as a factor in the differential parasitism.     

Entomopathogenic Nematodes and Bacteria Applications for Control of the Pecan Root-Knot Nematode, Meloidogyne partityla, in the Greenhouse

Meloidogyne partityla is a parasite of pecan and walnut. Our objective was to determine interactions between the entomopathogenic nematode-bacterium complex and M. partityla. Specifically, we investigated suppressive effects of Steinernema feltiae (strain SN) and S. riobrave (strain 7–12) applied as infective juveniles and in infected host insects, as well as application of S. feltiae''s bacterial symbiont Xenorhabdus bovienii on M. partityla. In two separate greenhouse trials, the treatments were applied to pecan seedlings that were simultaneously infested with M. partityla eggs; controls received only water and M. partityla eggs. Additionally, all treatment applications were re-applied (without M. partityla eggs) two months later. Four months after initial treatment, plants were assessed for number of galls per root system, number of egg masses per root system, number of eggs per root system, number of eggs per egg mass, number of eggs per gram dry root weight, dry shoot weight, and final population density of M. partityla second-stage juveniles (J2). In the first trial, the number of egg masses per plant was lower in the S. riobrave-infected host treatment than in the control (by approximately 18%). In the second trial, dry root weight was higher in the S. feltiae-infected host treatment than in the control (approximately 80% increase). No other treatment effects were detected. The marginal and inconsistent effects observed in our experiments indicate that the treatments we applied are not sufficient for controlling M. partityla.     

Overall Versus Band Application of the Nematode Phasmarhabditis hermaphrodita With and Without Incorporation into Soil, for Biological Control of Slugs in Winter Wheat

In two concurrent field experiments, the effects of three types of soil cultivation and two patterns of nematode application were studied in order to investigate their effects on damage to winter wheat by slugs (assessed at Zadoks Growth Stage 12). In experiment 1, infective juveniles (IJs) of the nematode Phasmarhabditis hermaphrodita were applied to soil as an overall spray or as a band spray (8-cm wide), centred on the drill rows (16.7-cm apart). Nematodes were either left undisturbed on the soil surface or harrowed into the soil immediately after application. The control provided by nematodes was compared with that provided by metaldehyde and methiocarb pellets broadcast at the recommended rate immediately after drilling. In this experiment, winter wheat on plots treated with IJs showed significantly less slug damage than on wheat plots treated with metaldehyde or methiocarb pellets or untreated plots. There was no significant difference in plant damage between plots treated with band and overall spray applications of IJs, nor was there any significant difference between plots with and without harrowing. There was also no significant difference between untreated plots and plots treated with metaldehyde or methiocarb pellets, probably because rainfall shortly after treatment rendered the pellets ineffective. In experiment 2, nematodes were applied as an overall spray or plots were not treated with nematodes before soil was cultivated with tines, Roterra or Dutzi cultivators. Nematode application before soil cultivation using tines or Roterra reduced the number of plants damaged significantly. However, nematodes applied before Dutzi cultivation appeared to be rendered ineffective. Damage to winter wheat was lowest in plots that had been sprayed with nematodes and subsequently cultivated with tines or Roterra.     

Evaluation of Steinernema carpocapsae Weiser for Control of Carrot Weevil Adults, Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae), in Organically Grown Carrots

Under controlled conditions, application of Steinernema carpocapsae using a baiting method consistently reduced the oviposition of Listronotus oregonensis adults at all moisture regimens. At 80 and 95% relative humidity, soil applications at 10 4 infective juveniles (IJs) cm-2 and 10 5 infective stages (400 IJs cm-2) per pot reduced the survival and oviposition of L. oregonensis adults; soil applications were ineffective at relative humidity lower than 80%. When timed correctly, soil application at the rate of 2 105 IJs/linear meter of row (4.4 109 IJs ha-1) reduced damage by up to 59%.     

Evaluation of Entomopathogenic Nematodes for the Control of Mediterranean Fruit Fly (Diptera: Tephritidae)

The virulence of various entomopathogenic nematode (EPN) strains was evaluated against the Mediterranean fruit fly, C. capitata . The selected nematodes were assessed for their infectivity for the final larval stage of the insect host and under varying environmental conditions. Among 12 EPN strains tested, Steinernema riobrave Texas ( Sr TX) and Heterorhabditis sp. IS-5 (H IS-5), showed high activity and induced >80% mortality. Six EPN strains showed limited activity (>30% mortality), and four strains had no effect (<20% mortality). Sr TX was more effective than H IS-5. Mature C. capitata larvae were most susceptible to nematode infection during the first 4h after they began to emerge from their diet to pupate. Activity of the two nematode strains at a constant inoculation rate was dependent on insect larval density. The highest activity was recorded at 1.88 larvae cm -2 and decreased at higher larval densities. EPN activity was also directly related to nematode density. Maximal activity was shown at a density of 150 infective juveniles cm -2 . A similar activity pattern was also recorded with Sr TX in four different soil types. The persistence of this EPN in the soil extended over 5 days but there was no activity after 14 days. Except for a lower activity under cool conditions (17°C), temperatures ranging between 22 and 41°C, or moisture levels in the treated soil ranging between 3 and 20%, had no significant effect on nematode activity. Our results suggest that application of Sr TX against C. capitata may have potential for controlling C. capitata .     

Field Evaluation of Fungal Competitors of Fusarium culmorum and F. graminearum, Causal Agents of Ear Blight of Winter Wheat, for the Control of Mycotoxin Production in Grain

Thirty-seven antagonists, from a collection of 113 pre-screened microorganisms, were tested in field experiments on winter wheat for their ability to control ear blight and production of mycotoxins, particularly deoxynivalenol (DON), in grain by Fusarium culmorum and F. graminearum. Ears were spray-inoculated during anthesis with spore suspensions, first of test fungi and then of the pathogen. Isolates of F. equiseti were the most effective treatments. A strain of F. equiseti (G9) decreased DON consistently on wheat inoculated with F. culmorum, compared with the control, often by more than 70%. It performed well under severe disease pressure (F. culmorum at 10⁵ conidia mL^-1) and similarly to a standard fungicide, tebuconazole. Percentages of diseased grains and amounts of DON corresponded well. Small quantities of nivalenol (NIV) occurred in grain samples after treatment with some F. equiseti strains. On wheat inoculated with F. graminearum, F. equisti G2 decreased the percentage diseased grains by 92% and DON by 94%. One strain of F. equiseti (G2) was found to produce small amounts of NIV in pure culture.     

Environmental Effects on the Development and Survival of the Scale Insect Abgrallaspis cyanophylli (Signoret) (Homoptera: Diaspididae) with Reference to its Suitability for Use as a Host for Rearing Biological Control Agents

Developmental and survival rates of the locally important diaspidid pest, Abgrallaspis cyanophylli (Signoret) reared on Solanum tuberosum L . tubers were examined under light and dark conditions; humidities of 33, 53, 62 and 75% relative humidity (RH); varying population densities; constant temperatures in the range of 20 to 30oC and at cycling temperatures of 12 h at 14°C and 12 h at 30°C. Developmental rate was slightly lower under constant light conditions but mortality was higher in the dark, particularly amongst the males. At 26°C, there were no differences in developmental rate in relation to the various humidity levels. However, survival was significantly lower at 33% RH, with females suffering higher mortality than males. Population density was found to have no effect on developmental rate or size of the females. Overall mortality increased in line with population density although the result was poorly correlated. Within the range 20-28°C developmental rate increased with rising temperature but decreased at 30°C. Thermal summation and polynomial regression data show a theoretical lower thermal threshold for development of 12.47°C. The thermal constant was 541.7 degree days. Survival was lowest at 20°C and 30°C and highest at temperatures in the median range and under cycling conditions. Male survival was significantly higher than that of the females at 30°C and under the cycling regime of 14/30°C. The results suggest that the optimum conditions for rearing A. cyanophylli on potatoes would be at temperatures in the range 24-26°C and humidities of 55-65% RH.     

Evaluation of the Predatory Wasp, Ancistrocerus gazella, for Biological Control of Leafrollers in Otago Fruit Crops: 1. Prey Composition, Nest Structure and Wasp Productivity from Artificial Nests

Groups of artificial nest tubes were deployed in the field for colonization by the accidentallyimported wasp, Ancistrocerus gazella (Panzer), a reported important predator of lepidopterous larvae, especially pest tortricids. There were 3-4 nest sites in each of seven study areas, and four tube lengths (75, 100, 125, 150 mm) were compared. Nests were dissected at various stages after occupancy to determine the prey composition and nest structure, and the numbers and sex of adults produced. The wasps collected larvae of nine lepidopterous families, including many tortricids, but pest leafrollers comprised only 4.1% and 1.5% of all larvae collected respectively in 1995-96 and 1996-97. Prey included beneficial species feeding on weeds and the larvae of some non-pest native insects. Prey species composition was highly site-dependent and was a major determinant of the numbers of larvae per cell. Cells for male wasps were smaller and contained fewer larvae than those for females. Tube length did not affect colonization rates but more cells and adult wasps were produced in longer tubes. The results cast serious doubt on the proposed management of A. gazella for biological control of leafrollers, but suggest that this approach could be useful for other pests, such as Coleophora spp., which were collected in large numbers.     

Field Evaluation of a Commercial Formulation of the Spodoptera exigua (Lepidoptera: Noctuidae) Nuclear Polyhedrosis Virus for Control of Beet Armyworm on Vegetable Crops in Thailand

Small - scale field trials were conducted in the Kanchanaburi and Ratchaburi provinces of Thailand between December 1994 and March 1996 to gather efficacy data to support a registration dossier for a commercial formulation of a nuclear polyhedrois virus of beet armyworm , Spodoptera exigua, under the tradename Spod - X . A liquid concentrate formula tion of Spod - X was compared with two commercial standards , Bacillus thuringiensis subsp . aizawai (CenTuri 3 . 5 WDG) and the insect growth regulator tebufenozide (Mimic 20F , a benzoylhydrazine ecdysone agonist) , for control of beet armyworm on garden pea , Chinese kale , shallot and table grape . Spod - X applied at 4 - day intervals at 3 . 1 - 12 . 5 1011 occlusion bodies (OBs) ha 1 in a spray volume of 625 - 1000 l ha 1 provided excellent control of beet armyworm on garden pea and grape (75 - 100 % reductions) after the second application . On Chinese kale and shallot , rates of Spod - X in the rate 5 - 60 1011 OBs ha 1 sprayed every 4 days in a spray volume of 1000 l ha 1 provided significant protection from infestation of beet armyworm over the growing season; however , efficacy was poor to moderate . Tank - mixing Spod - X with the pyrethroid , deltamethrin (Decis3EC) , did not improveefficacy on shallot;however , combinations of virus and B. thuringiensis or tebufenozide achieved commercially acceptable levels of crop protection on Chinese kale compared with virus alone . Lower levels of control and crop pro tection observed with all materials on Chinese kale and shallot reflect , in part , the tendency of S. exigua larvae to feed within sheltered sites and directly damage marketable plant parts . In general , all rates of Spod - X performed as well as , or better than , the B. thuringiensis standard (56 . 3 - 105 g ha 1 a.i.) on all crops tested . In general , reductions of beet armyworm larval populations and plant damage provided by all labeled rates of the chemical standard , tebufenozide (125 - 250 g ha 1 a . i .), were marginally greater than all rates of Spod - X tested . On crops such as pea and grape , where beet armyworm predominately feed on exposed leaf surfaces , our data unequivocally support the use of Spod - X for cost - effective , season - long pest management . Strategies to improve the efficacy of virus on shallot and kale are discussed .     

Response to carbon-starvation in Pseudomonas aeruginosa strain IE-6S+: analysis of general cross protection,production of some nematocidal compounds in vitro,and the biological control of Meloidogyne javanica in tomato

Adaptation to nutrient-limited conditions by repeated culture on soil agar media was found to induce resistance to osmotic, oxidation, thermal and pH stress as well as carbon-limited culture conditions in Pseudomonas aeruginosa strain IE-6S⁺. Culture filtrate of the resistant strains obtained from 10% strength King's medium B (KMB) caused greater (32–54%) mortality of Meloidogyne javanica juveniles compared with their parental strain. When 10% strength KMB was amended with 1% (w/v) glucose, the ability to cause nematode mortality was substantially enhanced by adapted strains, while activity of the parental strain was repressed. Two of the four starved bacteria IE-6S⁺PBK1 and IE-6S⁺KUC2 grown in KMB liquid medium amended with glucose synthesized salicylic acid (5.1 and 5.8 g ml^–1, respectively) and hydrogen cyanide (picrate paper turned yellow to brownish red for both strains) in greater quantities compared to wild type strain (SA = 4.4 g ml^–1, picrate paper turned orange-yellow). Neither wild type strain IE-6S⁺ nor its adapted strains were capable of utilizing tomato root exudates as a sole carbon source. Strains adapted to carbon-limiting conditions exhibited enhanced colonization in the rhizosphere and inner root tissues of tomato compared to their exponentially growing counterpart. Pre-adapted bacterial inoculants applied in the soil also caused greater (15%) reduction in nematode penetration compared to the parental strain or controls.     

The Use of Control Quantities in Computer Simulation Experiments: Application to the Exp-6 Potential Fluid

Abstract

Important quantities, which should be computed in the course of computer experiments in order to maintain the control over the development of the studied system, are summarized and their properties are discussed. The usefulness of these quantities is demonstrated by reference to published data for the exp-6 potential model. The ease with which it is possible to confuse solid and liquid states is illustrated.     

Field Evaluation of Brazilian Isolates of Neozygites floridana (Entomophthorales: Neozygitaceae) for the Microbial Control of Cassava Green Mite in Benin,West Africa

Two Brazilian isolates and one Benin (indigenous) isolate of Neozygites floridana were released against the cassava green mite, Mononychellus tanajoa , in January 1999 in the Adjohoun district, Ouémé administrative region, Republic of Benin. Post-release monitoring conducted 8, 14, 22 and 36 weeks later showed very low mean infection rates on M. tanajoa by isolate (0.03-0.4%). However, 48 weeks after releases, mean infection rates increased noticeably to between 2.3 and 18.7%, and higher infection rates were observed for the Brazilian isolates compared with the indigenous one. The highest infection rate for the indigenous isolate was 4.5% while it reached over 30% for the Brazilian isolates (36.5 and 34.0%). Observations made to study dispersal from inoculated plants showed the absence of infected mites at 4 m from the inoculated plants in all fields 8 weeks after the releases, while they were already present on those at 2 m away. From the next monitoring, 14 weeks after the releases, infection was found at all three sampling positions (inoculated plants and plants at 2 and 4 m away). Only four mites with resting spores were found in over 460 000 mites examined. The highest infection levels were observed in December during 'harmattan' a period characterized by hot days and cool nights with high relative humidity.