Increasing the survival and efficacy of entomopathogenic nematodes on exposed surfaces by Pickering emulsion formulations offers new venue for foliar pest management.

Formulation technology has been the primordial focus to improve the low viability and erratic infectivity of entomopathogenic nematodes (EPNs) for foliar application. Adaptability to the fluctuating environment is a key trait in ensuring the survival and efficacy of EPNs. Hence, tailoring formulations towards EPNs foliar applications would effectively deliver consistent and reliable results for above-ground applications. EPNs survival and activity were characterized in novel Pickering emulsion post-application in planta cotton foliage. Two different types of novel formulations, Titanium Pickering emulsion (TPE) and Silica Pickering emulsion Gel (SPEG), were tailored for EPNs foliar applications. We report an extension of survival and infectivity to 96 hrs under controlled conditions by SPEG formulations for survival of IJ's on cotton foliage. In addition, survival of IJs (LT50) was extended from 14hrs in water to > 80 hrs and > 40 hrs by SPEG and TPE respectively. SPEG accounted for the slowest decrease of live IJs per surface area in comparison to TPE and control samples over time, exhibiting a 6-fold increase at 48 hrs. Under extreme conditions, survival and efficacy were extended for 8hrs in SPEG compared to merely 2hrs in control. Potential implications and possible mechanisms of protection are discussed.

Individual Coating of Entomopathogenic Nematodes with Titania (TiO2) Nanoparticles Based on Oil-in-Water Pickering Emulsion: A New Formulation for Biopesticides.

This study presents a new eco-friendly formulation of entomopathogenic nematodes (EPNs) based on individual coating of EPNs with titanium dioxide (TiO2) nanoparticles (NPs) and mineral oil via oil-in-water Pickering emulsions. Mineral oil-in-water emulsions stabilized by amine-functionalized titanium dioxide (TiO2-NH2) particles were prepared. 40:60 and 50:50 oil-water volume ratios using 2 wt % TiO2-NH2 particles were found to be the most stable emulsions with a droplet size suitable for the formulation and were further studied for their toxicity against the incorporated EPNs. Carboxyfluorescein was covalently bonded to TiO2-NH2 NPs, and the resulting composite was observed via fluorescence confocal microscopy. The dry coating was evaluated using SEM and confocal microscopy, which showed significant nematode coverage by the particles and oil. The final formulation was biocompatible with the studied EPNs, where the viability of the EPNs in the formulation was equivalent to control aqueous suspension after 120 days. Finally, yields of nematodes from infected Galleria mellonella cadavers collected for 150 days showed no significant differences (P > 0.05) using the tested emulsions compared to the control containing nematodes in water.

Survival and efficacy of entomopathogenic nematodes on exposed surfaces.

Entomopathogenic nematodes (EPN) species differ in their capability to withstand rapid desiccation (RD). Infective juveniles of Steinernema carpocapsae are a better adaptable and tolerant than Steinernema feltiae or Heterorhabditis bacteriophora as, an optimal RH of > 90% is required by S. feltiae and H. bacteriophora while maintaining RH equivalent to 74% could sustain survival of S. carpocapsae under RD. Our findings from infectivity suggest that following application, shrunk IJs are acquired passively by the larvae, probably rehydrate and resume infection within the insect gut. Water loss rate is a key factor affecting survival of S. carpocapsae on exposed surfaces. The present study provides the foundation for characterizing mechanism of rapid rate of water loss in EPN. ATR-FTIR is a rapid and reliable method for analysis of water loss. Changes in peak intensity was observed at 3100-3600 cm-1 (OH bonds of water), 2854 cm-1 (CH stretching of symmetric CH2, acyl chains), 2924 cm-1 (CH stretching of anti-symmetric CH2, lipid packing heterogeneity), 1634 cm-1 (amide I bonds) indicate major regions for hydration dependent changes in all EPN species. FTIR data also indicates that, S. carpocapsae contains strong water interacting regions in their biochemical profile, which could be an influencing factor in their water holding capacity under RD. ATR-FTIR were correlated to water content determined gravimetrically by using Partial Least square -Regression and FTIR multivariate method, which could be used to screen a formulation's potential to maintain or delay the rate of water loss in a rapid and efficient manner.