The roles of olfaction and vision in host-plant finding by the diamondback moth, Plutella xylostella

The relative roles of olfaction and vision in the crepuscular host-finding process of a major lepidopteran pest of cruciferous crops, the diamondback moth Plutella xylostella are investigated in a series of laboratory and semi-field experiments. Flying female moths use volatile plant chemical cues to locate and to promote landing on their host, even in complex mixed-crop environments in large cages. Multiple regression analysis shows that both the plant position (front, middle or back rows) and the type of plant (host plant, nonhost plant) are needed to explain the distribution of insects in such a mixed-crop situation. This strong plant position effect indicates that, when host plants are present in a mixture, foraging P. xylostella are more likely to alight on the first row of the plants. The findings are discussed with regard to current theories of host-plant location by phytophagous insects and the possible implications for integrated pest management.

Managing outbreaks of invasive species: eradication vs. suppression

A framework is developed to evaluate eradication as one of three alternative management responses to an outbreak of an invasive species: eradication, suppression or no action. This framework can be used to establish under what conditions an eradication option could provide an expected net economic benefit, and whether this net benefit exceeds that of the other two options. The eradication option is more likely to be preferred in situations where there is an immediate export benefit that is derived from eradication of the outbreak, and also the uncertainty associated with the likely success of eradication is low.

Pathogenicity of the bacterium Pseudomonas putida from the entomopathogenic nematode Steinernema abbasi and its secretion against Galleria mellonella larvae

The Entomopathogenic bacterium Pseudomonas putida from Steinernema abbasi and its metabolic secretions were lethal to the Galleria mellonella larvae. Different laboratory experiments on time interval, substrate, moisture, temperature, dose, penetration of cells, stored and dried metabolites were conducted in sand and filter paper bioassays. It was concluded that death was probably due to the toxic metabolites. This bacterium and its metabolites were found very effective at 30 degree C. Penetration of bacterium was rapid after application on G. mellonella larvae. P. putida cells were recovered from the haemocoele when suspensions containing bacterial cells were applied to the G. mellonella indicating that bacterial symbionts do have a free-living existence and can enter the haemocoele in the absence of nematode vector. Stored metabolite and dried metabolites were found persistent for long time. This bacterium or its toxic secretions can be used for insect control that can be important component of integrated pest management against different insect pests. P. putida and its secretions are suggested as the most appropriate suspension to apply against insect pest control program in tropical ecological regions.

Pathogenicity of the bacterium Xenorhabdus nematophila isolated from the entomopathogenic nematode Steinernema carpocapsae and its secretions against Galleria mellonella larvae

The entomopathogenic bacterium, Xenorhabdus nematophila was isolated from the hemolymph of Galleria mellonella infected with Steinernema carpocapsae. The bacterial cells and its metabolic secretions have been found lethal to the Galleria larvae. Toxic secretion in broth caused 95% mortality within 4 d of application whereas the bacterial cells caused 93% mortality after 6 d. When filter and sand substrates were compared, the later one was observed as appropriate. Similarly, bacterial cells and secretion in broth were more effective at 14% moisture and 25 °C temperature treatments. Maximum insect mortality (100%) was observed when bacterial concentration of 4×106 cells/ml was used. Similarly, maximum bacterial cells in broth (95%) were penetrated into the insect body within 2 h of their application. However, when stored bacterial toxic secretion was applied to the insects its efficacy declined. On the other hand, when the same toxic secretion was dried and then dissolved either in broth or water was proved to be effective. The present study showed that the bacterium, X. nematophila or its toxic secretion can be used as an important component of integrated pest management against Galleria.

Managing arable weeds for biodiversity

As a result of the recent intensification of crop production, the abundance and diversity of UK arable weeds adapted to cultivated land have declined, with an associated reduction in farmland birds. A number of questions need to be addressed when considering how these declines can be reversed. Firstly, can the delivery of crop production and biodiversity be reconciled by spatially separating cropping from designated wildlife areas? A number of subsidised environmental schemes in the UK take this approach and are focused on establishing vegetation cover on uncropped land. However, because of the lack of regular disturbance in these habitats, they are dominated by perennials and they therefore have limited potential for promoting the recovery of annual weed populations. A number of farmland bird species also rely on the provision of resources in field centres, and it is therefore likely that the recovery of their populations will rely on weed management options targeted at the cropped areas of the field. This raises two further questions. Firstly, is it possible to identify beneficial weed species that are relatively poor competitors with the crop and also have biodiversity value? Secondly, are the tools available to manage these species at acceptable levels while controlling pernicious weeds? A number of approaches are being employed to answer these questions, including predicting yield loss from weed competition models and exploiting herbicide selectivity. The further development of these tools is crucial if farmer opposition to managing weeds in crops is to be overcome. (c) 2007 Society of Chemical Industry.

Fungicide resistance: the dose rate debate

It makes economic sense to use as little fungicide as possible on a crop. In many settings, it is common to apply less than the manufacturer's recommended dose. If sources of disease are scarce, or conditions are unsuitable for it to increase, the reduced control from a low dose may be adequate. In other cases, a big reduction in dose may cause little reduction in control, again permitting savings - especially for growers prepared to run a little risk. But the label recommendations for most fungicides state that to avoid resistance, a full dose must always be used. Are individual cost-savings therefore endangering everyone's access to an exceptionally useful tool? The emergence of fungicide resistance is evolution in action. In all cases, it involves the genetic replacement of the original susceptible population of the pathogen by a new population with genetically distinct biochemistry, which confers resistance. The resistant biochemistry originates in rare genetic mutations, so rare that initially the population is hardly altered. Replacement of susceptible forms by resistant ones happens because, with fungicide present, the resistant form multiplies more rapidly than the susceptible form. The key point to notice is that only the relative rates of multiplication of the resistant and susceptible types are involved in the evolution of resistance. The absolute rates are irrelevant.

Agronomic techniques to control Lobesia botrana

The grapevine moth Lobesia botrana (Denis & Schiffermuller) (Lepidoptera: Tortricidae) is a key pest of grapevines in Greece. As part of a broader study on integrated pest management, the effects were investigated of different cultural methods on the establishment and survival of L. botrana, specifically: application of different nitrogen levels (30 and 100 units of ammonium sulfate or 70 units of Agrobiosol); summer leaf and shoot pruning; application of growth regulators (Regalis, probexadione-calcium; or Falgro, gibberellic acid). There were significant differences among the three levels of N application. The lowest L. botrana infestation rates were found in plots treated with 30 units of (NH4)(2)SO4 and plots that received some summer pruning. Following the application of plant growth regulators, the lowest L. botrana infestation levels occurred in the plots treated with Regalis or Falgro at the manufacturers' recommended concentrations. On vines where growth regulators had been applied, the clusters had fewer berries than those not treated with growth regulators.

Suitability of Arabidopsis thaliana as a model for host plant-Plutella xylostella-Cotesia plutellae interactions

Successful pest management is often hindered by the inherent complexity of the interactions of a pest with its environment. The use of genetically characterized model plants can allow investigation of chosen aspects of these interactions by limiting the number of variables during experimentation. However, it is important to study the generic nature of these model systems if the data generated are to be assessed in a wider context, for instance, with those systems of commercial significance. This study assesses the suitability of Arabidopsis thaliana (L.) Heynh. (Brassicaceae) as a model host plant to investigate plant-herbivore-natural enemy interactions, with Plutella xylostella (L.) (Lepidoptera: Plutellidae), the diamondback moth, and Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae), a parasitoid of P. xylostella. The growth and development of P. xylostella and C. plutellae on an A. thaliana host plant (Columbia type) were compared to that on Brassica rapa var. pekinensis (L.) (Brassicaceae), a host crop that is widely cultivated and also commonly used as a laboratory host for P. xylostella rearing. The second part of the study investigated the potential effect of the different A. thaliana background lines, Columbia and Landsberg (used in wider scientific studies), on growth and development of P. xylostella and C. plutellae. Plutella xylostella life history parameters were found generally to be similar between the host plants investigated. However, C. plutellae were more affected by the differences in host plant. Fewer adult parasitoids resulted from development on A. thaliana compared to B. rapa, and those that did emerge were significantly smaller. Adult male C. plutellae developing on Columbia were also significantly smaller than those on Landsberg A. thaliana.

Relationship between resistance factors and treatment efficacy when bromadiolone was used against anticoagulant-resistant Norway rats (Rattus norvegicus Berk.) in Wales

We investigated the relationship between the severity and incidence of resistance among Norway rats (Rattus norvegicus) on a farm in Wales and the subsequent outcome of a practical rodent control operation. Bromadiolone resistance factors were estimated for rats trapped on the farm using the blood clotting response test, and were found to be 2 to 3 for male rats and approximately 6 for females. The incidence of resistance in the rat population was high. Infestation size was estimated by census baiting and tracking, and was found to be substantial, with a maximum of 6.5 kg of bait being eaten on a single night. A proprietary rodenticide (Deadline (TM)), containing 0.005% bromadiolone, was used to control the infestation. The duration of baiting was 35 days and, according to the two methods of assessment used, treatment success was in the region of 87 and 93%. No evidence was observed of a significant impact of resistance on the rat control operation, and the remaining rats of this very heavy infestation would probably have been controlled if baiting had continued for longer.

Greenhouse whitefly (Homoptera : Aleyrodidae) dispersal under different UV-light environments

The greenhouse whitefly, Dialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae), is known to respond to UV light (UV). Field studies were conducted to improve our understanding of the behavioral effects and practical implications of using UV-blocking plastic films for the control of whitefly. Adult whiteflies were released in outdoor-located choice-chamber experiments with compartments clad with a range of films that transmitted incident UV to different extents. In release-recapture experiments, a very small proportion of the whiteflies recovered had dispersed into compartments where the entire UV spectrum was blocked, whereas the major proportion preferred compartments with UV. Compartments clad with films that blocked LTV below 375 nm attracted significantly more whiteflies than films that blocked UV below 385 nm, whereas the absorption of LTV wavelengths above 385 nm did not show any further effect on whitefly numbers. A reduction in the side cladding of the compartments by > 20% significantly reduced the advantage of using LTV-blocking films. Adult whitefly did not discriminate between direct- and diffused-light environments, as long as the UV-absorbing properties of the films were equivalent. Whitefly dispersal was influenced by the time of the day when adult whitefly were released, with a higher proportion of whitelly avoiding compartments clad with LTV-blocking films, at times of the day when light intensities were higher. The future use of UV-blocking films as a potentially highly effective component of integrated pest management systems for the control of whitefly is discussed.

Effects of UV-blocking films on the dispersal behavior of Encarsia formosa (Hymenoptera : Aphelinidae)

The parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae) has been used successfully for the control of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae). The development of UV-blocking plastic films has added a new component to future integrated pest management systems by disrupting insect pest infestation when UV light is excluded. Because both T. vaporariorum and E. formosa are reported to have similar spectral efficiency, there was a need to identify the impact of UV-blocking films on the dispersal behavior of both the pest and the natural enemy. In field studies, using choice-chamber experiments, E. formosa showed some preference to disperse into compartments where less UV light was blocked. However, further studies indicated that the effect was primarily attributable to the different light diffusion properties of the films tested. Thus, unlike its whitefly host, when the UV-absorbing properties of the films were similar, but the light diffusion properties differed, E.formosa adults preferred to disperse into compartments clad with films that had high light diffusion properties. When the plastic films differed most in their UV-absorbing capacity and had no light-diffusion capability, the initial dispersal of E. formosa between treatments was similar, although a small preference toward the environment with UV light was observed over time. When parasitoid dispersal was measured 3 h after release, more parasitoids were found on plants, suggesting that the parasitoids would search plants for whitefly hosts, even in a UV-blocked light environment. The potential for the integration of UV-blocking films with E. formosa in an advanced whitefly management system is discussed.

Susceptibility to the anticoagulants bromadiolone and coumatetralyl in wild Norway rats (Rattus norvegicus) from the UK and Germany

A new blood clotting response test was used to determine the susceptibility, to coumatetralyl and bromadiolone, of laboratory strains of Norway rat from Germany and the UK (Hampshire), and wild rats trapped on farms in Wales (UK) and Westphalia (Germany). Resistance factors were calculated in relation to the CD strain of Norway rat. An outbred strain of wild rats, raised from rats trapped in Germany, was found to be more susceptible to coumatetralyl by a factor of 0.5-0.6 compared to the CD strain. Homozygous and heterozygous animals of a strain of resistant rats from Westphalia were cross-resistant to coumatetralyl and bromadiolone, with a higher resistance factor for bromadiolone than that found in both UK strains. Our results show that the degree of altered susceptibility and resistance varies between strains of wild rat and between resistance foci. Some wild rat strains may be more susceptible than laboratory rat strains. Even in a well-established resistance area, it may be difficult to find infestations with resistance high enough to suspect control problems with bromadiolone, even after decades of use of this compound.

An evaluation of the costs of making specific secondary metabolites: does the yield penalty incurred by host plant resistance to insects due to competition for resources?

The presumption that the synthesis of 'defence' compounds in plants must incur some 'trade-off' or penalty in terms of annual crop yields has been used to explain observed inverse correlations between resistance to herbivores and rates of growth or photosynthesis. An analysis of the cost of making secondary compounds suggests that this accounts for only a small part of the overall carbon budget of annual crop plants. Even the highest reported amounts of secondary metabolites found in different crop species (flavonoids, allylisothiocyanates, hydroxamic acids, 2-tridecanone) represent a carbon demand that can be satisfied by less than an hour's photosynthesis. Similar considerations apply to secondary compounds containing nitrogen or sulphur, which are unlikely to represent a major investment compared to the cost of making proteins, the major demand for these elements. Decreases in growth and photosynthesis in response to stress are more likely the result of programmed down-regulation. Observed correlations between yield and low contents of unpalatable or toxic compounds may be the result of parallel selection during the refinement of crop species by humans.

A standardised BCR resistance test for all anticoagulant rodenticides

This paper presents a reappraisal of the blood clotting response (BCR) tests for anticoagulant rodenticides, and proposes a standardised methodology for identifying and quantifying physiological resistance in populations of rodent species. The standardisation is based on the International Normalised Ratio, which is standardised against a WHO international reference preparation of thromboplastin, and allows comparison of data obtained using different thromboplastin reagents. ne methodology is statistically sound, being based on the 50% response, and has been validated against the Norway rat (Rattus norvegicus) and the house mouse (Mus domesticus). Susceptibility baseline data are presented for warfarin, diphacinone, chlorophacinone and coumatetralyl against the Norway rat, and for bromadiolone, difenacoum, difethialone, flocoumafen and brodifacoum against the Norway rat and the house mouse. A 'test dose' of twice the ED50 can be used for initial identification of resistance, and will provide a similar level of information to previously published methods. Higher multiples of the ED50 can be used to assess the resistance factor, and to predict the likely impact on field control.