Scaleable downstream recovery of nematodes used as biopesticides

Abstract

This study assesses the suitability of sieving as a scaleable technique for the separation of adult nematodes from infective juveniles, the latter is an effective bioinsecticide whereas the former is waste material resulting from the fermentation process. Batch and semibatch experiments using conventional flow-assisted wet sieving and a novel cross-flow sieving technique were used to study the separation of juveniles from adult nematodes. The experiments were carried out using small-scale devices and the data were analyzed in terms of the screen effectiveness factor. The results were used to identify the sieve size and operating conditions for optimum juvenile recovery. It was found that, for a given species of nematode, optimum recovery was achieved when sieving was carried out in the cross-flow mode, the maximum recovery being a function of the size of the screen. Industrial-scale self-cleaning equipment capable of large-scale continuous screening was used to confirm the capacity of the small-scale operation for scale-up. Experimental results with this unit showed that in continuous operation sieving time is an additional parameter that influences separation performance.

Biological control of terrestrial molluscs usingPhasmarhabditis hermaphrodita—progress and prospects

“…With P. hermaphrodita there may be problems with flocculation of insoluble spent media, but this can be remedied by introduction of an air supply 53. Sieving at a flowrate of 200 mL min −1 and an aperture size of 75–106 µm can be used for the separation of adult nematodes from infective juveniles of P. hermaphrodita 54. Vibrating membrane filtration (VMF) equipment also provides a flexible operation for separation, cleaning and concentration of viable nematodes from fermentation broths 55…”

Vibrating membrane filtration for recovery and concentration of insect killing nematodes

“…Because adult nematodes are a waste component, it is possible to reduce their impact on the recovery and concentration of IJs by treating the culture medium with sodium dodecylsulfate (SDS) prior to filtration. Previous work (Wilson et al, 2001) has shown that SDS at 4% (w/v) concentration dissolves the cuticle of adult nematodes, causing their disintegration, but has no effect on IJs. SDS also dissolves some of the large debris in the fermentation medium, which improves their release through the membrane filter.…”

“…We recently reported improved recovery of IJs in a modified cross-flow sieving operation in which the deposited material on the surface of the filtering sieves was continuously removed by the action of a rotating helical blade (Wilson et al, 2001). In the present study we describe the operation of a new dynamic filtration method that utilizes a vibrating membrane filter.…”

Evaluation of a contraction flow field on hydrodynamic damage to entomopathogenic nematodes—A biological pest control agent

“…The maximum tensile force that an EPN would have experienced during flow along the center streamline was computed by multiplying the maximum center streamline tensile stress (j zz ) by the cross-sectional area of the EPN cuticle, the load-bearing membrane of the nematode body. The EPN cuticle thickness was assumed to be 0.07 times the nematode diameter (Wilson et al, 2001). The tensile loading was computed for each of the EPN species for the experimental conditions where appreciable damage (i.e., >15%) started to occur.…”

“…Recent advances in micromanipulation techniques have made it possible to measure the ultimate tensile strength of biological materials, however, this technology is still at early stages of development (Thomas and Zhang, 1998). Wilson et al (2001) used calibrated weights hung from a micro-wire attached to one end of an adult nematode to measure the average tensile force required to break the nematode, which was found to be approximately 5E-2 N. No specific nematode was mentioned for this test, but H. megidis and Phasmarhabditis hermaphrodita were used in other parts of their study. The tensile force values associated with nematode damage that were computed in the current study (Table III), for the infective juvenile (IJ) stage (J3), were considerably smaller than observed by Wilson et al (2001) for an adult nematode.…”