Suppression of the blossom-blight phase of fire blight is a key point in the management of this destructive and increasingly important disease of apple and pear. For blossom infection to occur, the causal bacterium, Erwinia amylovora, needs to increase its population size through an epiphytic phase that occurs on stigmatic surfaces. Knowledge of the ecology of the pathogen on stigmas has been key to the development of predictive models for infection and optimal timing of antibiotic sprays. Other bacterial epiphytes also colonize stigmas where they can interact with and suppress epiphytic growth of the pathogen. A commercially available bacterial antagonist of E. amylovora (BlightBan, Pseudomonas fluorescens A506) can be included in antibiotic spray programs. Integration of bacterial antagonists with chemical methods suppresses populations of the pathogen and concomitantly, fills the ecological niche provided by the stigma with a nonpathogenic, competing microorganism. Further integration of biologically based methods with conventional management of blossom blight may be achievable by increasing the diversity of applied antagonists, by refining predictive models to incorporate antagonist use, and by gaining an improved understanding of the interactions that occur among indigenous and applied bacterial epiphytes, antibiotics, and the physical environment.

MANAGEMENT OF FIRE BLIGHT: A Case Study in Microbial Ecology

Insecticides with growth regulating properties (IGR) may adversely affect insects by regulating or inhibiting specific biochemical pathways or processes essential for insect growth and development. Some insects exposed to such compounds may die due to abnormal regulation of hormone-mediated cell or organ development. Other insects may die either from a prolonged exposure at the developmental stage to other mortality factors (susceptibility to natural enemies, environmental conditions etc) or from an abnormal termination of a developmental stage itself. Insect growth regulators may come from a blend of synthetic chemicals or from other natural sources, such as plants. The chemical composition of hormones indigenous to insects is now being studied and used as a basis for developing analogs or mimics against insects. The similarities, however, in certain aspects of biochemistry among vertebrates and invertebrates may result in the limited development of IGRs. Environmental contamination also creates a hurdle as well as a challenge for industries to develop compounds that provide a more environmentally or ecologically sound insect pest control.

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Insect Growth Regulators for Insect Pest Control

This paper reviews a wide variety of behavioural effects that have been reported in bees following exposure to pesticides, primarily insecticides. These range from effects on odour discrimination in the individual to the loss of foraging bees due to disruption of their homing behaviour. Some of these effects have the potential to have a significant impact on the development and survival of colonies. However, there is currently little guidance available on the types of behavioural data which should be collected during laboratory, semi-field or field regulatory studies or how they should be included and interpreted in risk assessment. Further work is required to allow risk assessment to include significant behavioural effects and their longer term consequences on colony survival and development. Such an approach will require a larger base set of data to predict the longer-term consequences on colonies of short-term effects on individuals, e.g. through population modelling.

Behavioural effects of pesticides in bees--their potential for use in risk assessment.

Inhibition of vitellogenin synthesis in Apis mellifera workers by a juvenile hormone analogue, pyriproxyfen

A novel method, which involves a nested PCR in a single closed tube, was developed for the sensitive detection of Erwinia amylovora in plant material. The external and internal primer pairs used had different annealing temperatures and directed the amplification of a specific DNA fragment from plasmid pEA29. The procedure involved two consecutive PCRs, the first of which was performed at a higher annealing temperature that allowed amplification only by the external primer pair. Using pure cultures of E. amylovora, the sensitivity of the nested PCR in one tube was similar to that of a standard nested PCR in two tubes. The specificity and sensitivity were greater than those of standard PCR procedures that used a single primer pair. The presence of inhibitors in plant material, very common in E. amylovora hosts, is overcome with this system in combination with a simple DNA extraction protocol because it eliminates many of the inhibitory compounds. In addition, it needs a very small sample volume (1 μl of DNA extracted). With 83 samples of naturally infected material, this method achieved better results than any other PCR technique: standard PCR detected 55% of positive samples, two-tube nested PCR detected 71% of positive samples, and nested PCR in a single closed tube detected 78% of positive samples. When analyzing asymptomatic plant material, the number of positive samples detected by the developed nested PCR was also the highest, compared with the PCR protocols indicated previously (17, 20, and 25% of 251 samples analyzed, respectively). This method is proposed for the detection of endophytic and epiphytic populations of E. amylovora in epidemiological studies and for routine use in quarantine surveys, due to its high sensitivity, specificity, speed, and simplicity.

Development of a Highly Sensitive Nested-PCR Procedure Using a Single Closed Tube for Detection of Erwinia amylovora in Asymptomatic Plant Material

SUMMARYThese insect growth regulators were administered in 1:1 sucrose solution to young bumble bee (Bombus terrestris) colonies kept in the dark in a controlled climate chamber and fed with 50% sucrose solution and bee-collected pollen. Three colonies received Admiral (pyriproxifen at either 20 ppm a.i., or 2 ppm a.i., or 0.2 ppm a.i.) and one received Insegar (fenoxycarb 100 ppm a.i.). One colony was fed with Nomolt (teflubenzuron 150 ppm a.i.), which was known to be toxic to bumble bee brood. A sixth colony, fed with pure sucrose solution, acted as a negative control. After the 24-h feeding period the amounts of ingested sucrose solutions were determined and the colonies, which had been photographed daily for one week before treatment, were photographed daily for the next five weeks. There was no significant difference between colonies in the amount of food consumed on the day of treatment. The only colony to show larval mortality and arrested egg development was the one fed on teflubenzuron-sucrose so...

M. de Greef

Papers

Toxicity of pyriproxifen and fenoxycarb to bumble bee brood using a new method for testing insect growth regulators

Biology and Control of Melittobia Acasta

The honeybee as a possible vector of Erwinia amylovora (Burr.) Winslow et al.

Influence of the honeybee on fireblight transmission

De honingbij als mogelijke vector van Erwinia amylovora (Burrill) Winslow et al.