Effects of accumulate dead and alive insects in trap on the capture ofTribolium castaneum (herbst)

In the trapping ofTribolium castaneum (Herbst), the activity of traps baited or not baited with aggregation pheromone 4,8-dimethyldecanal is influenced by the presence in the traps of accumulate specimens trapped. This fact has been observed both in trap containing alive or dead specimens. Interactions in the different substances produced by adults of Red Flour Beetle during their communication relationship are involved in this behaviour.The results obtained in the trials suggests that the presence of alive insects in traps is attractive for other free specimens, but under conditions of overcrowding quinone produced by them regulate population density by counteracting the effect of the aggregation pheromone, causing the insects to disperse or suppressing aggregation behaviour.     

Specificity of polycllonal and monoclonal antibodies for the identification of Xanthomonas campestris pv. campestris

Polyclonal and monoclonal antibodies (PCAs and MCAs), produced to whole cells and flagellar extracts ofXanthomonas campestris pv.campestris (Xcc), respectively, were tested for specificity. In immunofluorescence microscopy (IF) the three PCAs tested, reacted at low dilutions with all Xcc strains, some other xanthomonads and non-xanthomonads. At higher dilutions most cross-reactivity with non-xanthomonad strains disappeared. However, the cross-reactivity with strains ofX. c. pv.vesicatoria (Xcv),X. c. pv.amoraciae (Xca) andX. c. pv.phaseoli var. fuscans (Xcpf) remained.Six MCA-producing cell clones viz. 20H6, 2F4, 18G12, 10C5, 17C12 and 16B5 were selected for specificity tests with an enzyme immunoassay (EIA), IF and a dot-blot immunoassay (DBI). None of the MCAs reacted with all Xcc strains in IF and EIA. In DBI, only MCAs 17C12 and 16B5 reacted with all Xcc strains. All six MCAs tested, cross-reacted in one of either tests with other pathovars ofX. campestris, such as Xcv or Xca. The MCAs were also tested in immunoblotting experiments using total bacterial extracts, cell envelope and flagellar extracts. MCAs 20H6, 2F4, 18G12 and 10C5 reacted with the lipopolysaccharide (LPS) of Xcc. MCAs 16B5 and 17C12 reacted with a 39 kilodalton and a 29 kilodalton protein, respectively.It is concluded that the PCAs and MCAs discussed in this study may be used for routine identification and differentiation of (a group of) Xcc strains. The significance of the cross-reactions with other pathovars ofX. campestris needs to be determined by testing seed lots.     

Parry's disease of pears is similar to pear decline and is associated with mycoplasma-like organisms transmitted by Cacopsylla pyricola

Mycoplasma-like organisms (MLOs) were detected by fluorescence microscopy in a number of pear cultivars and pear seedlings growing under a range of different conditions. In the cultivar Conference, MLOs were consistently associated with symptoms of Parry's disease, a decline-like disease of young trees with quince rootstocks. MLO-free pear seedlings rapidly became infected when they were planted outside. Experimental transmission of MLOs to pear seedlings and Conference trees was achieved using pear psyllids, caught outside or raised on infected plants under controlled conditions. Conference trees in an orchard trial remained free from the severe spring symptoms of Parry's disease when they were protected from feeding insects during spring of the previous year. MLOs were graft transmissible, but were not perpetuated by the standard propagation practices of budding or grafting when quince rootstocks were used. Parry's disease appears to be similar to pear decline, an MLO-induced disease well established in several other parts of the world. It is suggested that Parry's disease should be referred to as pear decline.     

Development of a monoclonal antibody-based immunodetection assay for Botrytis cinerea

Three hybridoma cell lines secreting antibodies that specifically recognize Botrytis cinerea and B.fabae , but not B. allii, have been raised from splenocytes of mice immunized with a low molecular-weight fraction (30 kDa) from surface washings of B. cinerea. Antibodies from these cell lines have been used to develop an antigen-based elisa test that will detect B. cinerea in strawberries. This monoclonal antibody immunoassay detection assay should prove useful to both the cut-flower and wine industries. Supernatants from the three specific cell lines recognize mycelial fragments, saline extracts of mycelia and germinating conidia by both ELISA and immunofluorescence. Recognition of non-germinating spores is poor. Supernatants from the specific cell lines did not recognize other fungi normally involved in post-harvest spoilage of fruits and vegetables. Supernatants from KH4 gave the lowest background values with healthy tissue. Indirect evidence from heat, protease and periodate treatment of the antigens indicates that antibodies from all three specific cell lines are recognizing carbohydrate epitopes on a glycoprotein.     

Molecular breeding for virus resistant potato plants

To engineer resistance against potato virus X (PVX), the viral coat protein (CP) gene has been introduced into two potato cultivars. Stable expression of the gene in transgenic clones throughout the growing season has been obtained and resulted in considerably increased virus resistance. With varying frequencies depending on the original cultivar used, true-to-type PVX resistant transgenic clones have been obtained. Since deviant light sprout characteristics were invariably associated with aberrations in plant phenotype, they can be used in procedures to early screen for deviations. Furthermore, it has been possible to unequivocally discriminate between the original untransformed and independent transgenic cultivars. Although no relation has been found between the presence, if any, of the CP of potato virus Y (PVY) or potato leafroll virus (PLRV) in CP gene transgenic potato, appreciable levels of resistance to these viruses has been obtained. This suggests that the mechanism by which a viral CP gene in the potato genome evokes resistance, differs amongst various viruses.     

Progress in aphid forecasting systems

Potato virus Y and many other viruses of potatoes cause major economic losses to seed potato production in many countries. Potato virus Y, which is transmitted in a non-persistent manner, is one of the most important virus diseases of potatoes in many countries in Europe and especially in the northern regions.During the last decade there has been an increasing interest in developing methods for potato virus forecasting. The abundance of virus vectors is often estimated by yellow water traps (YWT), suction traps or field surveys. In Sweden the relationship between occurrence of alate aphids and the proportion of PVY infected progeny tubers has been studied since 1975. A dynamic simulation model for PVY has been designed for predicting the incidence of PVY. The simulation model describes a system which includes e.g., healthy and PVY diseased potato plants, different aphid species as virus vectors an their efficiency as virus vectors, the susceptibility of the potato crop according to mature plant resistance and date of haulm destruction. There was a good correlation between model output and samples of progeny tubers tested for PVY.     

Alarm pheromones and allelochemics as a means of aphid control

The relevance of studies on aphid-plant relationships for plant virus epidemiology is highlighted. Many behavior-modulating chemicals (semiochemicals) play a major role in intraspecific (pheromones) or interspecific (allelochemics) interrelations and therefore offer opportunities to interfere with virus transmission. Present knowledge on the role of semiochemicals in different behavioral events is emphasized using examples (alarm and sex pheromones, allelochemics involved in host selection, antifeedants) and their potential for controlling virus transmission and spread is discussed.     

Exploitation of predators in UK fruit and hop culture

A wide range of species of predators has been exploited, or has the potential to be exploited, as biological control agents against pests of fruit and hop. They include members of the families Miridae, Anthocoridae and Chrysopidae, and of the mite family Phytoseiidae. Some species can colonise fruit plantations naturally, whereas others are mass-cultured and introduced artificially. The characteristics of the various predator species are considered in relation to the requirements for biological control agents in specific crop situations.     

Non-chemical approaches to weed control in horticulture

Concern about herbicide safety has renewed interest in non-chemical systems of weed control. Alternative approaches for dealing with weeds can be broadly grouped into cultural and biological methods. Some of the options available for controlling weeds without the use of herbicides are discussed.     

The activity and mobility of triasulfuron in soil as influenced by organic matter,duration, amount and frequency of rain

The influence of different levels of organic matter and of the duration, amount and frequency of rainfall on the biological activity and mobility of triasulfuron were investigated. Biological activity was inversely related to the organic matter content of the soil. Movement of the herbicide down the soil profile, assessed by bioassay, was inversely related to the organic matter content of the soil, and the amount and frequency of rain directly influenced the extent of leaching of the herbicide. Triasulfuron was moved to a depth of at least 22.5 cm when soil columns were exposed to a total of 528 mm of natural rainfall over a period of 6 months. The presence of phytotoxic levels of the herbicide in the surface layers of soil columns 6 months after exposure to outdoor temperatures and natural rainfall suggested that triasulfuron may persist in soils for relatively long periods. Influence de la matiére organique, et de la durée, niveau et fréquence des précipitations sur l'activité et la mobilité du triasulfuron dans le sol L'influence de différentes teneurs en matière organique et de la durée, quantité et fréquence des pluies sur l'activité biologique et la mobilité du triasulfuron a étéétudiée. L'activité biologique est inversement liée avec la teneur enmatière organique du sol. Le mouvement descendant de l'herbicide dans le profil du sol, estimé par bio essai, est inversement lié avec la teneur en matière organique du sol, et la quantité et la fréquence des pluies influencent directement l'importance de la lixiviation de l'herbicide. Le triasulfuron s'est déplacé jusqu'à une profondeur d'au moins 22,5 cm quand les colonnes de sols ont été exposées à un total de 52,8 cm de pluies naturelles sur une période de 6 mois. La présence de taux phytotoxiques d'herbicide dans les couches superficielles des colonnes de sol 6 mois après l'exposition aux températures extérieures et aux précipitations naturelles montre que le triasulfuron peut persister dans 1s sols pendant des périodes relativement longues. Einfluβ der organischen Substanz des Bodens sowie der Niederschlagsdauer, -menge und -frequenz auf Persistenz und Mobilität von Triasulfuron im Boden Die biologische Aktivität sowie die Verlagerung von Triasulfuron im Boden, mit Biotests bestimmt, waren umgekehrt proportional zum Gehalt an organischer Substanz. Die Regenmenge sowie -frequenz beeinflußten die Einwaschung des Herbizids direkt. Bei insgesamt 528 mm natürlichem Niederschlag innerhalb 6 Monaten wurde Triasulfuron in Bodensäulen mindestens 22,5 cm tief eingewaschen. Aus dem Vorhandensein phytotoxischer Mengen des Wirkstoffs in den oberen Schichten der Bodensäulen nach 6 Monaten unter Freilandbedingungen wurde auf relativ hohe Persistenz im Boden geschlossen.