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

Abstract

Mechanized production and delivery of biological pesticides presents challenges because the biological agents must remain viable during these processes. This study evaluates the effect of flow through an abrupt contraction, where flow characteristics similar to that found within bioprocesses and spray equipment are developed, on damage to a benchmark biological pest control agent, entomopathogenic nematodes (EPNs). An opposed-pistons, contraction flow device generated volumetric flow rates ranging between 8.26 cm(3)/s and 41.3 cm(3)/s. Four EPN species were evaluated: Heterorhabditis bacteriophora, Heterorhabditis megidis, Steinernema carpocapsae, and Steinernema glaseri. Damage was quantified by counting living and dead EPNs. Optical and cold field emission scanning electron microscope (CFE-SEM) images provided qualitative information to describe how the damage occurred. The experimental flow field was completely described using FLUENT, a computational fluid dynamics program. Local flow parameters computed in FLUENT were compared to EPN damage. The type and extent of damage varied between EPN species. Damaged Heterorhabditis spp. generally remained whole with an internal rupture located near the center of the body, while Steinernema spp. most often broke into several pieces. The fast-transient stress field generated at the entrance to the contraction caused a momentary tensile loading and then relaxation that damaged the EPNs. At high flow rates, the tensile stresses became large enough to cause failure of the EPN structural membrane. The relative elasticity of the EPN structural membrane may explain the differences in damage observed between the species. It is speculated that the internal rupture of the Heterorhabditis spp. occurred during the processes of stretching and relaxing at the contraction entrance. Appreciable damage was observed at lower average energy dissipation rates for H. bacteriophora (1.23E + 8 W/m(3)), H. megidis (1.72E + 8 W/m(3)), and S. glaseri (2.89E + 8 W/m(3)) compared to S. carpocapsae (3.70E + 8 W/m(3)). Energy dissipation rates within an equipment component should be kept below 1E + 8 W/m(3) to avoid hydrodynamic damage to EPNs. The relationship between average energy dissipation and EPN damage provides important information for future simulation efforts of actual spray equipment components.

Spray Nozzles, Pressures, Additives and Stirring Time on Viability and Pathogenicity of Entomopathogenic Nematodes (Nematoda: Rhabditida) for Greenhouses

“…However, friction with the inner parts of the hydraulic circuit can cause physical damage to entomopathogens [8]. According to Fife et al [9] the cuticle structure of the infective juvenile (IJ), which can change in different species, can respond differently to hydrodynamic stress. Additionally, there might be an increase in tank mixture temperature throughout this process, which may reduce viability of the nematodes.…”

Computer simulations of the energy dissipation rate in a fluorescence‐activated cell sorter: Implications to cells

“…Bird et al (2001) defined the EDR as the irreversible rate of internal energy increase per unit volume. The EDR appears to be a good candidate to correlate cell damage for a number of reasons: it is a single, scalar parameter that can be obtained from the fundamental equations of fluid dynamics, it only depends on the intrinsic characteristics of the flow (i.e., it can be calculated for both laminar and turbulent flow), it is geometry-independent, it accounts for both shear and extensional components of the flow and it has been used successfully as a parameter to characterize and predict damage in a number of published studies (Aloi and Cherry, 1996;Fife et al, 2004;Gregoriades et al, 2000;Hu et al, 2007;Ma et al, 2002;Mollet et al, 2004Mollet et al, , 2007.…”

Evaluation of hydraulic, pneumatic and mechanical agitation for the spray application ofSteinernema carpocapsae(Rhabditida: Steinernematidae)

“…Fife et al (2007) concluded that a single passage of H. bacteriophora through various pumps did not damage the nematodes. Previous studies evaluating the effects of pressure differentials (Fife et al 2003) and hydrodynamic conditions (Fife, Derksen, Ozkan, Grewal, and Chalmers 2004;Fife, Ozkan, Derksen, Grewal, and Krause 2005) on nematode damage have demonstrated that EPN are relatively robust organisms with respect to mechanical stress. Therefore, Fife et al (2007) suggested that reductions in nematode viability during pump recirculation were likely the result of temperature influences and not mechanical stress.…”