Beziehungen zwischen Befallsdichte und Schaden im System Gewächshausgurke/Weiße Fliege

Zusammenfassung Befall mit Weißer Fliege führte zu einer deutlichen Abnahme der Blattfläche und zu Ertragsdepressionen, die in ihrem Ausmaß von der Ausgangspopulationsdichte des Schaderregers (2, 10 bzw. 25 Weibchen pro Pflanze) abhing. Jüngere Gurkenpflanzen reagierten in ihrem Blattflächenwachstum und im Fruchtertrag wesentlich stärker auf den Befall als Pflanzen in einem fortgeschrittenerem Entwicklungsstadium. Die durchT. vaporariorum hervorgerufenen Blattflächenreduktionen korrelierten positiv mit den Ertragsverlusten, ebenso bestand zwischen der Populationsdichte des Schaderregers und der Ertragseinbuße eine enge Beziehung. Die Ertragsverluste beruhten auf einer geringeren Anzahl erntefähiger Früchte und verstärktem Abstoßen junger Früchte und Blüten. Der von den Tieren abgegebene Honigtau wurde von Schwärzepilzen besiedelt, die Stärke ihres Auftretens hing von der Befallssstärke und Befallsdauer der Pflanzen mit der Weißen Fliege ab.

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Relation between population density and damage in the system cucumber/whitefly

Infestation of cucumber-plants with greenhouse whitefly,T. vaporariorum, had an adverse effect on leaf area and cucumber yield. The extent of reduction was dependent from initial density of whiteflies (2, 10 and/or 25 females per plant) just as much as from age of the plants at start of the experiments. Yield loss was strictly correlated with leaf area reduction, as well as with density of whitefly populations. Yield loss based on a decreased number of fruits worth for harvest and on increased drop of flowers and young fruits. Honeydew excreted by whiteflies was settled with sooty mould which extent was dependent from intensity and duration of whitefly infestation. This resulted also in leaf area reduction.

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Mit 5 Abbildungen und 3 Tabellen     

Rapid emergence of baculovirus resistance in codling moth due to dominant, sex-linked inheritance

Insect-specific baculoviruses are increasingly used as biological control agents of lepidopteran pests in agriculture and forestry, and they have been previously regarded as robust to resistance development by the insects. However, in more than a dozen cases of field resistance of the codling moth Cydia pomonella to commercially applied C. pomonella granulovirus (CpGV) in German orchards, resistance ratios exceed 1000. The rapid emergence of resistance is facilitated by sex-linkage and concentration-dependent dominance of the major resistance gene and genetic uniformity of the virus. When the gene is fixed, resistance levels approach 100,000-fold. Our findings highlight the need for development of resistance management strategies for baculoviruses.     

Influence of pollen feeding on body weight and body size of the predatory mite Amblyseius swirskii (Acari,Phytoseiidae)

Journal of Plant Diseases and Protection - The nutritional quality of pollen was assessed measuring biomass and body size of freshly emerged, 1, 3, and 30 day old adult Amblyseius swirskii...     

Comparative biology and life tables of <Emphasis Type="BoldItalic">Trichogramma aurosum</Emphasis> on <Emphasis Type="BoldItalic">Cydia pomonella</Emphasis> at constant temperatures

The influence of constant temperatures on biological parameters of German strains of Trichogramma aurosum Sugonjaev & Sorokina (Hymenoptera: Trichogrammatidae) was evaluated in the laboratory on eggs of Cydia pomonella L. (Lepidoptera: Tortricidae). Development time and longevity of all strains were decreased as temperature increased. Development time of the strains differed significantly only when exposed to 15°, 20°, and 25°C. Cumulative fertility and longevity differed significantly at 15° and 20°C. Realized fertility differed significantly at all constant temperatures. Emergence rates of all strains were less than 65% and were decreased even further as temperature increased. Female-biased sex ratio ranged from 65% to 100% at all constant temperatures. The low temperature threshold for T. aurosum was 10°C and the mean number of degree-days at 15°, 20°, 25° and 30°C was 175, 183, 173 and 185, respectively. The Bavarian strain tolerated high temperatures and had the highest parasitization capability, while the Hessian strain had the lowest parasitization at all temperatures. Fertility life table analysis revealed a major effect of temperature on the population growth parameters. Net reproductive rate was highest at intermediate constant temperatures in all strains, with the highest rate recorded for the Bavarian strains at all constant temperatures. Mean cohort generation time, and population doubling time decreased as temperature increased. The daily intrinsic rate of increase and finite rate of increase were positively correlated with temperature. The relevance of our results is discussed in the context of climatic adaptation, intraspecific variability and biological control.     

Acaricide toxicity and resistance in larvae of different strains of Tetranychus urticae and Panonychus ulmi (Acari: Tetranychidae)

The toxicities of eight structurally different acaricidal compounds to six‐legged larvae (first motile stage) of three laboratory strains of the two‐spotted spider mite, Tetranychus urticae, and the European red mite, Panonychus ulmi, were evaluated following spray application. The larvae of five field‐derived strains of T urticae originating from France, Italy, Brazil, California and Florida were also tested for their susceptibilities to discriminating concentrations of several acaricides resulting in 95% mortality when applied to the organophosphate‐resistant laboratory reference strain WI. The spray bioassay used was robust and gave repeatable results with a wide range of acaricidal compounds, irrespective of their mode of action (ovo‐larvicides or primarily acting on motile life stages). Compounds tested were abamectin, azocyclotin, chlorpyrifos, clofentezine, deltamethrin, fenpyroximate, hexythiazox and pyridaben. Larvae of one of the laboratory strains of T urticae, AK, originally collected in Japan in 1996 and maintained without further selection pressure, exhibited 2000‐ and >4000‐fold resistance to the mitochondrial electron transport inhibitors pyridaben and fenpyroximate, respectively. Another strain of T urticae, AU, obtained from Australia and maintained in the laboratory under selection with hexythiazox and clofentezine since 1987 showed >770‐ and >1000‐fold resistance to clofentezine and hexythiazox, respectively. The same resistance pattern was observed against larvae of a laboratory strain of P ulmi, CE, also selected with hexythiazox. Larvae of one of the field‐derived strains of T urticae, BR, showed a lower susceptibility to a number of compounds, whilst the others were susceptible to all compounds except the organophosphates. © 2001 Society of Chemical Industry     

Performance ofAphis Fabae on Chocolate Spot Disease-Infected Faba Bean Plants

The effect of chocolate spot disease (incited byBotrytis fabae) on the host plant quality of two cultivars of faba beans (Vicia faba) for the black bean aphid (Aphis fabae), was investigated under greenhouse conditions. Faba bean cultivar Bolero is resistant to the aphid, whereas cv. Diana is susceptible. On healthy leaves of cv. Bolero, aphids completed their development one day later than the aphids reared on infected leaves of this cultivar and those which matured on healthy or infected leaves of cv. Diana. Mean weight of apterous virginoparae, mean relative growth rate, and intrinsic rate of natural increase were enhanced if the aphids were reared on infected leaves of either cultivar. Mean total progeny per female increased only on infected leaves of cv. Bolero, but not on cv. Diana.     

Target-site resistance to pyrethroids in European populations of pollen beetle, Meligethes aeneus F.

Pollen beetle, Meligethes aeneus F. (Coleoptera: Nitidulidae) is a major univoltine pest of oilseed rape in many European countries. Winter oilseed rape is cultivated on several million hectares in Europe and the continuous use of pyrethroid insecticides to control pollen beetle populations has resulted in high selection pressure and subsequent development of resistance. Resistance to pyrethroid insecticides in this pest is now widespread and the levels of resistance are often sufficient to result in field control failures at recommended application rates. Recently, metabolic resistance mediated by cytochrome P450 monooxygenases was implicated in the resistance of several pollen beetle populations from different European regions. Here, we have also investigated the possible occurrence of a target-site mechanism caused by modification of the pollen beetle para-type voltage-gated sodium channel gene. We detected a single nucleotide change that results in an amino acid substitution (L1014F) within the domain IIS6 region of the channel protein. The L1014F mutation, often termed kdr, has been found in several other insect pests and is known to confer moderate levels of resistance to pyrethroids. We developed a pyrosequencing-based diagnostic assay that can detect the L1014F mutation in individual beetles and tested more than 350 populations collected between 2006 and 2010 in 13 European countries. In the majority of populations tested the mutation was absent, and only samples from two countries, Denmark and Sweden, contained pollen beetles heterozygous or homozygous for the L1014F mutation. The mutation was first detected in a sample from Denmark collected in 2007 after reports of field failure using tau-fluvalinate, and has since been detected in 7 out of 11 samples from Denmark and 25 of 33 samples from Sweden. No super-kdr mutations (e.g. M918T) known to cause resistance to pyrethroids were detected. The implications of these results for resistance management strategies of pollen beetle populations in oilseed rape crops are discussed.