Imperial College of Science, Technology and Medicine
Department of Biological Sciences
PhD Project: Andrew Brown
From October 2003
Entomopathogenic nematodes (EPN) and nematodes pathogenic to molluscs (MPN) are, after Bacillus thuringiensis, the most widely used biopesticides in agriculture. With a spectrum well beyond that of any microbial biological control agent, their extraordinary host range is one of the main reasons for the considerable interest in development of nematodes for biological control (Kaya and Gaugler, 1993). They can be excellent biological control agents for soil-dwelling stages of many insect pests and have the additional advantage compared with most microbial agents of being fast acting, killing target species in 48-72 h.
More than 90 % of insects, including many pest species, have at least one stage of their lifecycle in the soil (Akhurst, 1986), along with the rapid mortality of hosts it permits the EPN to exploit a range of hosts that spans nearly all insect orders (Poinar, 1979). Especially in cases when this stage is larval or pupal, it offers an opportunity for an effective management programme to be developed, targeting specific pest species when the ability of the target species to relocate is much reduced.
Commonly used pest control methods include cultural methods such as crop rotation along with chemical pesticide applications. Combinations of target pest chemical insecticide resistance, demand for more environmentally friendly farming, and agricultural intensification means alternatives to these practices are being sort. EPN formulations applied directly to the soil offer a more environmentally friendly, chemical-free, possibility.
As is the case with many biological control organisms, nematodes are only used as niche products. Their more widespread application depends on a variety of factors, including improved application and a better understanding of their behaviour in the environment. One area of research that has received little attention is application technology (Mason et al., 1999). Integration into already established irrigation systems is a potential area for advances in this field. Minimal labour costs, high moisture provision, and flexibility in application timing are some of the benefits offered by application of these nematodes through already established irrigation systems.
Current limitations of nematodes as agricultural pest control agents are their cost (Ehlers, 1996) and their uneven distribution following application. Cost of application remains high as the current application technique most widely used are spray equipment (Miklasiewicz et al., 2002), where each individual plant has to be sprayed. This labour intensive method of application has high manpower costs. Uneven distribution of application, from backpack sprayers to irrigation systems, which have been investigated, have a universal problem of nematode settling in the storage tank prior to application. The resulting uneven distribution of nematodes in the applied water gives poor pest treatment. This is the biggest problem to be overcome in order to widen the possibilities for crop pest treatment using applications of both EPN and MPN, especially in the case of slow release methods such as drip-line tape.
Costs of application can be reduced by applying a commercially available packet of highly concentrated nematodes at the start of the irrigation system, therefore removing the need for labour intensive administration to individual plants, this combined with over-coming nematode settling will improve the attractiveness of the use of nematodes in pest control.
Aims and objectives of research
The primary aim of this project is to assess the ability of drip line irrigation systems to administer EPN’s. We also hope to improve the application procedure to overcome some of the current problems associated with this method of application, such as irregularities in both temporal and spatial distribution of EPN and MPN release from the line. This work will be carried out on both field and laboratory systems. An irrigation rig has been built in IPARC (International Pesticide Application Research Centre) at Imperial College London, Silwood Park campus specifically designed to allow sampling of water emitted from points along the line.
This project also aims to assess the placement and transfer of nematodes once in the soil matrix in relation to abiotic and biotic factors. An improvement in understanding these factors will advance field efficiency and reduce application costs so making these more economically viable and thus is an important step to the more widespread use of nematodes as biological control agents.
With demand from both producers and consumers for cost effective, environmentally friendly, pest treatment, integration of EPN and MPN into already present irrigation systems will offer efficient insect and mollusc pest management. With minimal alteration to equipment and therefore cost to farmers, there are great developmental prospects.
An 18 m long irrigation system has been built specifically designed to allow easy, and accurate, sampling. The T-tape line has emitters every 30 cm and the system is designed so that emitted water can be automatically sampled every 90 cm. Water is stored in a 200 l reservoir tank, and pumped into the irrigation line by a variable pressure, electric pump. Nematodes are held in a smaller container, connected to the system via a Dosatron® DI 16, which is responsible for administering the nematode dose to the irrigation water. The Dosatron® can vary the dose of EPN applied between 0.2-1.6 % dilutions.
Field trials are being carried out on both lettuce and strawberry crops. For the lettuce crops, Nemaslug® (Phasmohabditis hermaphrodita ) is applied to control slug pests: primarily Deroceras reticulatum. On strawberry crops Nemasys®L (Steinernema kraussei ) is applied as a bio-control agent for Black Vine Weevil larvae (Otiorhynchus sulcatus ). The nematodes are applied to a field via a drip line irrigation system. This field trial offers the ability to study EPN release across an entire field to supplement the more detailed work being carried out on the single line setup in IPARC.
the irrigation system (right hand rows)
Nematodes are added to irrigating water at one point per field using a modified Venturi mechanism (right). Because of the design of the irrigation system, the irrigating water then carries the nematodes to all parts of the field where crops are present.
International Pesticide Application Research Centre,
Department of Biological Sciences,
Imperial College London, Silwood Park campus,
Buckhurst Road, Ascot,
Berkshire SL5 7PY, U.K.
I wish to thank Prof Denis Wright, Dr Simon Piggott and Dr Roy Bateman for advice and guidance, and Mr Paul Beasley for constructing the Irrigation system.
Funding for my PhD research is from BBSRC and BeckerUnderwood.
I would like to thank BeckerUnderwood (Littlehampton, UK) for supplying the nematodes and irrigation equipment.
Akhurst, R.J. [ed.] 1986. Controlling insects in soil with entomopathogenic nematodes. Wageningen: Int. Colloquium of Invertebrate Pathology.
Ehlers, R.U. 1996. Current and future use of nematodes in biocontrol: Practice and commercial aspects with regard to regulatory policy issues. Biocontrol Science Technology 6: 303-316.
Kaya, H.K. and Gaugler, R. 1993. Entomopathogenic Nematodes. Annual Review of Entomology 38: 181-206.
Mason, J.M., Matthews, G.A. and Wright, D.J. 1999. Evaluation of Spinning Disc Technology for the Application of Entomopathogenic Nematodes against a Foliar Pest. Journal of Invertebrate Pathology 73: 282-288.
Miklasiewicz, T.J, Grewal, P.S, Hoy, C.W. and Malik, V.S. 2002. Evaluation of entomopathogenic nematodes for suppression of carrot weevil. Biocontrol 47: 545-561.
Poinar, GO. 1979. Nematodes for Biological Control of Insects. Boca Raton, FL: CRC.