Pymetrozine: Selectivity spectrum to beneficial arthropods and fitness for integrated pest management

Pymetrozine is the first and only substance from the group of azomethine pyridines, a novel class of insecticides. The spectrum of activity covers sucking pests such as aphids, whiteflies and planthoppers.Tests were carried out in the laboratory and under field conditions to evaluate its impact on beneficial arthropods.In laboratory tests it demonstrated full selectivity against predaceous Coleoptera, Heteroptera, Neuroptera and the predatory mite Typhlodromus pyri.Following a single application at 250/200g a.i./ha on cotton in Egypt and in the USA, the regular sampling of predators over a period of three weeks revealed a similar population development in the pymetrozine and the untreated control plots. On okra, a vegetable crop in Egypt, it suppressed populations of Aphis gossypii with two sprays at 100g a.i./ha for the whole observation period of 23 days. It also allowed the survival of predators.These positive features make pymetrozine an ideal component in situations where sucking pests have to be controlled and natural enemies can play a substantial role as complementary control tools.     

Identification and pathogenicity of Neophysopella species associated with Asian grapevine leaf rust in Brazil

Asian grapevine leaf rust (AGLR) causes severe crop losses in Brazilian viticulture, mainly in latitudes <25°S. The purpose of this study was to identify the pathogen(s) involved with AGLR in Brazil, based on phylogenetic and morphological analysis and pathogenicity tests. In total, 56 monouredinial isolates from six Brazilian states were identified using the internal transcribed spacer 2 and the large subunit rRNA gene D1/D2 regions. All 50 isolates from the south-central region were classified as Neophysopella tropicalis, and the other six isolates from the north-east region as Neophysopella meliosmae-myrianthae. This result provides evidence that two pathogen introductions from different sources may have occurred in the country. For both species, paraphyses were cylindrical, incurved, aseptate, and hyaline, while urediniospores were short-pedicellate, obovoid or obovoid-ellipsoid, with the wall colourless or pale yellowish, evenly echinulate. Representative isolates from both species caused typical AGLR symptoms on Vitis vinifera 'Merlot' and V. labrusca 'Niagara Rosada'. Overall, regardless of the Neophysopella species, isolates caused similar leaf disease severities. Higher disease severity was observed in Niagara Rosada (average of 40.3% of diseased leaf area) compared to Merlot (20.5%). This study reports, for the first time, the characterization of Neophysopella species associated with AGLR in Brazil.     

Winter annual grassy weeds increase over‐winter mortality in autumn‐sown wheat

Over‐winter mortality, that is, winterkill, reduces cereal crop competitive ability and yield. While management and environmental variables are known to affect winterkill, the extent to which weeds contribute to increased winterkill is largely unknown. Winter annual weeds may increase winterkill through resource competition and by increasing incidence of and damage from plant pathogens that cause winterkill. We evaluated the impact of summer annual (Avena fatua) and winter annual (Bromus tectorum) weeds on the over‐winter survival rate of winter wheat over three winters, during which plots were covered with snow. Pink snow mould (Microdochium nivale), a winterkill pathogen known to infect B. tectorum and winter wheat, was common in wheat stands. In weed‐free treatments, mortality rates were initially near zero, but increased by nearly 45% in each subsequent winter, presumably due to an increase in snow mould disease in continuously cropped winter wheat. Whereas A. fatua infestation had no impact on crop survival rates, winter wheat survival in B. tectorum‐infested plots was 50% less than the weed‐free control in the second and third years of this study. Among B. tectorum‐infested plots, winter wheat over‐winter survival declined with increasing weed seed produced in the previous summer. Overall, this study demonstrated that winter annual weed infestations can reduce crop stand densities below replanting thresholds by reducing fall‐sown cereal winter survival. The effects of winter annual weeds on winter wheat may be meditated by increased proliferation of snow mould disease.     

Thieves,bats and fruit flies: local ecological knowledge on the weaver ant Oecophylla longinoda in relation to three ‘invisible’ intruders in orchards in Guinea

We held interviews with 100 mango and cashew growers in Guinea, West Africa. Fewer than 20 questions dealing with the tree-inhabiting weaver ant Oecophylla longinoda were developed, based on local context and related research conducted on farmers' knowledge in other countries. More than half of the growers reported that ants protect their orchard from thieves. Apart from deterring snakes, about 46% of the growers mentioned that weaver ants reduce damage by fruit-eating bats; some reported that bats do dislike the smell of weaver ants. Whereas the relationship between ants and humans or conspicuous fruit bats is well understood, a quantitative appreciation of the effect of Oecophylla on small insect pests, such as fruit flies, is more complex. Despite the fact that 57% of the growers reported that Oecophylla had a positive effect on mango fruit quality, many classified Oecophylla as a pest due to its nuisance during harvest, and they requested the plant protection staff to help them with pesticides. Strategies to strengthen local ecological knowledge are discussed.     

Sexual Recombination in Gibberella zeae

ABSTRACT We developed a method for inducing sexual outcrosses in the homothallic Ascomycete fungus Gibberella zeae (anamorph: Fusarium graminearum). Strains were marked with different nitrate nonutilizing (nit) mutations, and vegetative compatibility groups served as additional markers in some crosses. Strains with complementary nit mutations were cocultured on carrot agar plates. Ascospores from individual perithecia were plated on a minimal medium (MM) containing nitrate as the sole nitrogen source. Crosses between different nit mutants segregated in expected ratios (3:1 nit(-):nit(+)) from heterozygous perithecia. Analysis of vegetative compatibility groups of progeny of two crosses indicated two and three vegetative incompatibility (vic) genes segregating, respectively. For rapid testing of sexual recombination between nit mutants, perithecia were inverted over MM to deposit actively discharged ascospores. Development of proto-trophic wild-type colonies was taken as evidence of sexual recombination. Strains of G. zeae group 2 from Japan, Nepal, and South Africa, and from Indiana, Kansas, and Ohio in the United States were sexually interfertile. Four group 1 strains were not interfertile among themselves or with seven group 2 strains. Attempts to cross G. zeae with representatives of F. acuminatum, F. avenaceum, F. culmorum, F. crookwellense, F. oxysporum, and three mating populations of G. fujikuroi were not successful.     

Seasonal changes in germination response of buried seeds of Orobanche crenata Forsk.

Orobanche crenata seeds, collected in Syria, Egypt and Spain, were buried in the field in Syria (all three seed lots) and Spain (only Spanish seeds) and at regular intervals exhumed and tested for germination, to investigate whether the seeds exhibit an annual dormancy/non-dor- mancy cycle. When exposed directly to the synthetic germination stimulant GR24 for 7 days at 20°C, seeds only germinated in autumn after the first rains and to a limited extent in winter. When the seeds were conditioned for 11 days at 20°C prior to exposure to GR24, germination occurred during summer and autumn, but seeds were dormant in winter and early spring. The observed seasonal pattern in germinability, in relation to rainfall and soil temperature, was largely consistent with the results of an in vitro experiment by Van Hezewijk et al. (1993), investigating the effect of conditioning temperature and conditioning period on germination capacity and the development of secondary dormancy. Moisture and temperature can therefore be considered the major factors regulating induction and alleviation of dormancy in buried O. crenata seeds. There were no basic differences in response owing to site of collection of O. crenata seeds, nor to the location where they were buried. Variations saisonnières des exigences de germination de graines enfouies d'Orobanche crenata Forsk. Des graines d'Orobanche crenata récoltées en Syrie, en Égypte et en Espagne ont été enfouies au champ en Syrie (les 3 lots) et en Espagne (seules les graines d'Espagne) puis ont été exhumées a intervalles régulier pour que leur aptitude à la germination soil évaluée. Le but était de déterminer si les graines possédaient un cycle annuel dormance/non dormance. Quand elles étaient directement exposées au stimulant de germination synthétique GR24 pendant 7 jours à 20°C, les graines ne germaient qu'à l'automne après les premières pluies et peu en hiver. Quand les graines restaient pendant 11 jours à 20°C avant leur exposition au GR24, la germination seproduisait en été et à l'automne mais les graines restaient dormantes en hiver et au début du prin-temps. Les variations saisonnières d'aptitude à la germination, liées aux précipitations et à la temperature du sol, étaient en accord avec les résultats d'une expérience in vitro de Van Hezewijk et al. (1993) concernant l'effet de la température et de la durée pendant laquelle elle est appliquée, sur l'aptitude à la germination et le développement de la dormance secondaire. L'humidité du sol et sa température peuvent ainsi être considérées comme les principaux facteurs qui induisent et lèvent la dormance de graines de O. crenata enfouies. On n'observait pas de différences importantes dues au lieu de récolte ou à l'endroit oü elles étaient enfouies. Jahreszeitliche Änderungen der Keimung von vergrabenen Samen von Orobanche crenata Forsk. Proben von in Syrien, Ägypten und Spanien gesammelten Orobanche-crenata-Samen wurden in Syrien und Proben nur spanischer Herkunft in Spanien im Freiland im Boden ausgelegt und in regelmäßigen Zeitabständen ausgegraben und auf ihre Keimfähigkeit getestet, um zu untersuchen, ob die Samen einen jährlichen Dormanz-Zyklus haben. Beim direktem Auslegen in dem synthetischen Keimungsmittel GR24 öber 7 d bei 20°C keimten die Samen nur im Herbst nach den ersten Regenfällen und in beschränktem Umfang im Winter. Wenn die Samen för 11 d bei 20°C vor dem Auslegen in GR24 vorbehandelt worden waren, keimten sie im Sommer und Herbst, aber im Winter und fröhen Fröhjahr waren sie dormant. Das jahreszeitliche Verhalten der Keimfähigkeit in Abhängigkeit von Niederschlag und Bodentemperatur stimmte weitgehend mit den Ergebnissen eines In-vitro-Versuches von Van Hezewijk et al. (1993) öber die Wirkung einer Wärmevorbehandlung und Vorbehandlungszeit auf die Keimfähigkeit und die Ausprägung sekundärer Dormanz öberein. Bodenfeuchte und -temperatur können deshalb als die wichtigsten Faktoren för die Induktion und Aufhebung der Dormanz von Orobanche-crenata-Samen im Boden angesehen werden. Herkunft und Versuchsort hatten keinen erheblichen Einfluß auf die Ergebnisse.     

Temperature-dependent development rates of <Emphasis Type="Italic">Bracon vulgaris,</Emphasis> a parasitoid of boll weevil

The duration of development of Bracon vulgaris Ashmead, parasitoid of the boll weevil Anthonomus grandis Boheman, was determined at nine constant temperatures between 18°C and 38°C. Nonlinear regression analysis was used to test the fit of temperature-dependent development rates to the Sharpe and DeMichele and Lactin et al. models. At the highest tested temperature (38°C) all the parasitoid eggs died before hatching and no evidence of development was observed. The high values of R ² for the models of Sharpe and DeMichele (0.8432 to 0.9834), and Lactin et al. (0.9071 to 0.9795) indicated that these models are suitable to estimate the development rate of B. vulgaris as a function of temperature. B. vulgaris showed tolerance to high temperature which is represented by the high value of H _H (change in enthalpy associated with high-temperature inactivation of the enzyme) for the prepupa stage of this insect obtained with the Sharpe and DeMichele model. According to that model, B. vulgaris exhibits thermal stress at 35.7°C, which indicates that maximum thermal stress estimated by this model was close to the real one.