Compatibility of OMRIcertified surfactants with three entomopathogenic fungi

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Compatibility of OMRI-
certified surfactants with three
entomopathogenic fungi
Christopher A. Dunlap
a
, Robert W. Behle
a
& Mark A. Jackson
a
a
US Department of Agriculture, Crop Bioprotection Research Unit,
National Center for Agricultural Utilization Research, Agricultural
Research Service, Peoria, IL, USA
Accepted author version posted online: 23 Jan 2014.Published
online: 10 Mar 2014.
To cite this article: Christopher A. Dunlap, Robert W. Behle & Mark A. Jackson (2014) Compatibility
of OMRI-certified surfactants with three entomopathogenic fungi, Biocontrol Science and
Technology, 24:4, 436-447, DOI: 10.1080/09583157.2013.870532
To link to this article: http://dx.doi.org/10.1080/09583157.2013.870532
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RESEARCH ARTICLE
Compatibility of OMRI-certified surfactants with three
entomopathogenic fungi
Christopher A. Dunlap*, Robert W. Behle and Mark A. Jackson
US Department of Agriculture, Crop Bioprotection Research Unit, National Center for
Agricultural Utilization Research, Agricultural Research Service, Peoria, IL, USA
(Received 17 September 2013; returned 29 October 2013; accepted 26 November 2013)
The Organic Materials Review Institute (OMRI) is a non-profit organisation
providing an independent review of products intended for use in organic
production systems to certify compliance with US national organic standards.
Since all adjuvants to be used in organic agriculture production are required to
meet these standards, OMRI’s certified list of products is a convenient starting
point when developing organic pest control formulations. In the current study, six
OMRI-certified surfactants are tested for their compatibility with three common
entomopathogens: Beauveria bassiana, Metarhizium brunneum and Isaria fumo-
sorosea. The fungi were evaluated in two common propagule forms, solid-state
produced conidia and liquid-media produced blastospores. The results show that
most of the surfactants are compatible with the fungi at a high surfactant
concentration (2% w/v). In general, the conidia showed a higher susceptibility
(greater reduction in spore germination) to the surfactants than the blastospores
under these conditions. In addition, the surface tension and foaming properties of
the surfactants were determined.
Keywords: organic; surfactant; entomopathogen; foam; formulation; conidia;
blastospore
Introduction
Over the past 50 years, global movements concerned about pollution and the
environment have lobbied for more sustainable forms of agriculture. These activities
inspired the organic agriculture movement. In 1972, the International Federation of
Organic Agriculture Movements was founded during an international congress on
organic farming to disseminate the principles and practices of organic agriculture
(Courville, 2006). The success of the organic farming movement necessitated the
development of standards and uniform codes of practices.
In the USA, many local and regional groups developed their own standards for
organic production during this period of early adoption. This led to consumer
confusion on food labelled ‘organic’. The Organic Foods Production Act of 1990
established the National Organic Program to define standard organic farming
practices and acceptable production inputs on foods marketed as ‘organic’ (Heck-
man, 2006). The National Organic Standards (NOS) were published in 2000 and
define acceptable practices and inputs for organic production. The Organic
*Corresponding author. Email: christopher.dunlap@ars.usda.gov
Biocontrol Science and Technology, 2014
Vol. 24, No. 4, 436–447, http://dx.doi.org/10.1080/09583157.2013.870532
The work was authored as part of Christopher A. Dunlap, Robert W. Behle and Mark A. Jackson’s official duties as
employees of the United States Government and is therefore a work of the United States Government. In accordance with
17 U.S.C. 105 no copyright protection is available for such works under U.S. law.
Downloadedby[DigiTop-USDA'sDigitalDesktopLibrary]at08:1909April2014

Materials Review Institute (OMRI) is a non-profitorganisation providing farmers
and suppliers an independent review of products intended for use in organic
production systems to certify compliance with NOS guidelines. Products with an
OMRI certification have been certified to have met the NOS guidelines and are
acceptable for use in organic production systems.
Entomopathogenic fungi as biocontrol agents have been successful in controlling
insect pests in a variety of farming systems. These microbial biocontrol agents are
often marketed as a natural alternative to the synthetic chemical insecticides used in
conventional farming. However, being natural pathogen is not enough to qualify it
as an organic pest control option. The microbial agents must be produced using
organic-approved products and methods. In addition, any ingredients in the final
formulation must also be approved for use in organic systems. This requirement
makes the OMRI product list as a convenient starting point for formulation
adjuvants when developing a new pest control formulations for organic applications.
In addition to the regulatory considerations, microbial pest control formulation
adjuvants must also provide performance enhancements to the final product. In
developing formulations of entomopathogenic fungi, surfactant selection is an
important consideration. Depending on the type of formulation (e.g. wettable
powder, emulsifiable concentrate, aqueous suspension), surfactants can play many
important roles in the formulation, such as dispersant, emulsifier and wetting agent
(Bernhard, Holloway, & Burges, 1998). Recent studies have identified surfactant
properties and assays useful in selecting surfactants for entomopathogenic fungal
formulations (de Santos, da Silva, Monteiro, & Gava, 2012; Jin, Streett, Dunlap, &
Lyn, 2008). While surfactants can provide useful chemical properties, they also have
the potential to be cytotoxic to entomopathogens (Jaronski, 1997). This combination
of potentially desirable and detrimental properties of surfactants dictates they must
be evaluated for each entomopathogen.
The goal of the current study was to evaluate the compatibility of a group of
OMRI-certified surfactants with three common entomopathogenic fungi. The fungi
were evaluated on their ability to germinate in the presence of the surfactants. Tests
were conducted using two common propagule forms of the fungi, solid-state
produced conidia and liquid-media produced blastospores. In addition, surfactants
were evaluated on their chemical properties to ensure they perform the function they
are supposed to address; e.g. a wetting agent or a foaming agent.
Materials and methods
Fungal strains
Three entomopathogenic fungi were examined in this study: Metarhizium brunneum,
Isaria fumosorosea and Beauveria bassiana. The M. brunneum strain used in this
study was a commercial strain, F52 (ATCC 90448), the I. fumosorosea strain
ARSEF 3581 used in this study was isolated from an infected silverleaf whitefly
(Bemisia argentifolii) in Mission, Texas, and the B. bassiana strain ARSEF 6444
(GHA) is a commercially available strain. Stock cultures of all fungal strains were
grown from single-spore isolates on potato dextrose agar (PDA) plates and were
stored in 10% glycerol at –80°C.
Biocontrol Science and Technology 437

Culture conditions
Stock cultures of each fungal strain were plated weekly on PDA plates and incubated
for 2–3 weeks at room temperature (~22°C) to produce aerial conidia for surfactant
compatibility studies. Conidia from sporulated agar plates were also used as
inoculants for the liquid culture production of blastospores, yeast like vegetative
propagules of these dimorphic fungi.
Conidial suspensions of each fungal strain were obtained by rinsing sporulated
agar plates with 10 mL of sterile, deionised water. A final concentration of 5 ×
105
conidia mL–1
blastospore production medium was used in these experiments.
The blastospore production medium and culture conditions have been previously
described in Jackson (2012). Briefly, 100-mL culture volumes were grown for four
days in 250-mL baffled flasks in a rotary shaker incubator at 350 rpm and 28 °C.
The blastospore production medium was composed of basal salts, trace metals
and vitamins with 80 g L–1
glucose and 25 g L–1
acid hydrolysed casein.
Blastospores were separated from hyphae by filtering cultures through two layers
of cheesecloth. These blastospore suspensions were used to evaluate surfactant
compatibility.
Conidia/blastospore germination assay
Conidia or blastospore suspensions were prepared containing approximately 1 × 106
propagules mL–1
in potato dextrose broth media supplemented with surfactant at the
final concentration, 2.0% (w/w) for all assays. The assays were conducted in 50 mL of
media in a 125-mL Bella fluted flask. The suspensions were then incubated at 28°C
and 300 rpm. The numbers of germinated blastospores for the three fungi were
counted after 6 hours of incubation. The number of germinated conidia of B. bassiana
and M. brunneum were counted after 24 hours. The number of germinated conidia of
I. fumosorosea was counted after 14 hours, since the germinated conidia would start
to aggregate before 24 hours for some surfactant solutions. The assay consisted of the
three replicates of each treatment and the experiment was performed twice with
unique biological replicates.
Surfactants
The tested surfactants were chosen from the OMRI product list and obtained from
the listed manufacturer. Table 1 provides the details of the specific compounds
tested. Surfactants were used as delivered with no additional sterilisation procedures.
Surface tension measurements
The equilibrium surface tension of 2% (w/w) surfactant solutions was determined
using the pendant drop method (Thiessen, Chione, McCreary, & Krantz, 1996).
Solution was prepared with deionised distilled water and analysed with FTA 4000
surface tension instrument (First Ten Angstroms inc. Portsmouth, VA). Measure-
ments were made with a 22-gauge blunt needle with a 7 μl drop. The values reported
represent an equilibrium surface tension determined 60 seconds after drop formation.
The reported values are the average of a minimum of six separate solutions.
438 C.A. Dunlap et al.

Foam characterisation
Foam characterisation was performed using a modified method, based on
standard techniques (Phillips et al., 1990). Foam was produced using a commer-
cial foam generator (pestifoamer pf-2, Richway Industries Ltd., Janesville, IA)
charged with various foam-producing solutions. Foam was discarded until
uniform foam was produced. The foam was then collected in a 250-mL graduated
cylinder and its weight and volume determined. The expansion index of the foam
is the volume of foam generated divided by its mass. The longevity of the foam
was determined by measuring the volume of foam remaining after 1 hour. Three
or more replicates were performed for two or more separate surfactant
preparations.
Data analysis
Statistical analysis was performed on the data using excel 2010 software. A single
factor analysis of variance (ANOVA) was performed on the germination percentage
means for each fungi (p < 0.05). Tukey’s honestly significant difference (HSD) test
was used to compare all possible pairs of means for within each fungi group (α=
0.05). Surface tension data analysis was limited to standard deviation.
Results
Compatibility of surfactants with blastospores
Blastospores of the three entomopathogenic fungi (B. bassiana, M. brunneum and
I. fumosorosea) were evaluated for compatibility with selected OMRI surfactants
(Table 1). Compatibility was evaluated based on a germination assay in the presence
of 2% (w/w) surfactant. The surfactant concentration was chosen to meet or exceed
concentrations typically used in pesticide formulations. The results of the assay are
reported in Figure 1. The results show that most of the surfactants had minimal
effect under these conditions. A notable exception is Silwet Eco when combined with
B. bassiana, which shows a significant decrease in germination percentage (p < 0.05).
Data are not available for M. brunneum and I. fumosorosea combined with Yucca
Ag-Aide, since these formulations formed aggregates under these conditions and
could not be counted accurately.
Table 1. Surfactants evaluated in this study.
Product name Chemical class Manufacturer
Yucca Ag-Aide Saponin, Y. schidigera extract Desert King International, LLC
Armak 2042 Polyoxyalkylene Glycol Butyl Ether Akzo Nobel inc
Armak 2079 Ethoxylated castor oil – HLB 11.6 Akzo Nobel inc
Armak 2081 Ethoxylated castor oil – HLB 14.4 Akzo Nobel inc
Armak 2087 Polyoxyethylene sorbitan monooleate Akzo Nobel inc
Silwet Eco Spreader Organomodifed
polydimethylsiloxane
Momentive inc

Compatibility of surfactants with conidia
Conidial propagules of the same three entomopathogenic fungi were evaluated for
compatibility with the selected OMRI surfactants. The results of the germination
assay are reported in Figure 2. The results for the conidia are much more variable
than the blastospore results. For B. bassiana conidia, all of the surfactants were
suitable except for Yucca Ag-Aide, which dropped the germination percentage from
93 ± 3% (control) to 34 ± 6%. For M. brunneum conidia, two of the surfactants
Armak 2079 and Armak 2081 formed aggregates under these conditions and were
not able to be accurately assayed. The remaining surfactants were compatible with
M. brunneum, except for Yucca Ag-Aide which completely inhibited germination.
For I. fumosorosea conidia, Armak 2042, Armak 2081 and Armak 2087 were all
compatible, while Armak 2079, Silwet Eco and Yucca Ag-Aide all reduced the
germination percentage under these conditions.
Surface tension measurements
The ability to reduce the surface tension of an aqueous solution is an important
property of surfactants. The equilibrium surface tension for 2% (w/v) solutions
was determined for the selected surfactants. The results show five of the
surfactants had similar surface tension parameters with values ranging from 36
to 43 dyn/cm (Table 2). The Silwet Eco solution had a considerably lower surface
tension of 21.5 dyn/cm.
Figure 1. (Colour online) Germination assay of blastospores of entomopathogenic fungi in
the presence of 2% (w/w) surfactant.
*Data for M. brunneum and I. fumosorosea are not available for Yucca Ag-Aide since they
formed aggregates under assay conditions. Means followed by a different letter are
signiﬁcantly different (p < 0.05); error bars represent SD.

Foaming properties
The ability of surfactants to produce foams can be a useful property. The ability of
the surfactants to produce foam was evaluated using a common foamer used in pest
control applications. The results show Yucca Ag-Aide and Armak 2042 are
moderate foam producers with expansion ratios in the 4–6 range (Table 3). The
others were poor foaming agents. Armak 2079 and Armak 2087 gave expansion
ratios in the 2–3 range, while Armak 2081 and Silwet Eco did not produce foams.
Since Yucca Ag-Aide and Armak 2042 were moderate successful foam producers, we
evaluated the longevity of the produced foam. For Yucca Ag-Aide, 85% of the initial
foam remained as foam 1 hour later, while Armak 2042 had 20% of the initial foam
after 1 hour.
Table 2. Equilibrium surface tension of tested surfactants at 20°C.
Product name Surface tension
Yucca Ag-Aide 37.5 ± 0.6
Armak 2042 36.2 ± 0.3
Armak 2079 42.3 ± 0.5
Armak 2081 39.2 ± 0.4
Armak 2087 43.0 ± 0.4
Silwet Eco Spreader 21.5 ± 0.3
Figure 2. (Colour online) Germination assay of conidia of entomopathogenic fungi in the
presence of 2% (w/w) surfactant.
*Data for M. brunneum are not available for Armak 2079 and Armak 2081 since it formed
aggregates under assay conditions. Means followed by a different letter are signiﬁcantly
different (p < 0.05); error bars represent SD.

Discussion
In the current study, we tested surfactants certified to conform with US NOS for
compatibility with entomopathogenic fungi. We tested the surfactants at a rate (2%
w/v), which would be the maximum anticipated rate of use. This high rate would only
be needed in formulations that require high surfactant concentrations, such as
foaming. For standard spray applications, a much lower rate surfactant would be
sufficient. Typically surfactants in these applications are used at a concentration that
is a few times higher than the critical micelle concentration (CMC) of the surfactant
(Crooks, Cooper-White, & Boger, 2001). The CMC is the concentration of surfactant
that saturates the surface of the solution at equilibrium; at this concentration the
surface tension of the solution is at the minimum. The CMC for Armak 2087
(Polyoxyethylene sorbitan monooleate) was reported to be 0.0015% (w/v) (Chou,
Krishnamurthy, Randolph, Carpenter, & Manning, 2005) and a saponin mixture
similar to Yucca Ag-Aide was determined to be 0.025% (w/v) (Stanimirova et al.,
2011). The surfactants that tested poorly at 2% may be an option at a much lower
concentration. There were several considerations in choosing a higher concentration
than typically found in entomopathogen formulations. We are not aware of any of
the commonly used biopesticide surfactants or the surfactants tested in the current
study significantly altering their physicochemical properties in this concentration
range (> CMC to 2% w/w). In this range, toxicity and dose response are generally
positively correlated with concentration for common adjuvants (lower concentrations
are less toxic) (Nobels, Spanoghe, Haesaert, Robbens, & Blust, 2011). It is difficult to
estimate the ‘effective’ concentration of adjuvants after application. For example, if
you spray a solution of 0.1% surfactant solution with some entomopathogenic
propagules, what is the effective or bioavailable concentration of the surfactant after
the droplet has partially dried or dried and before the propagule has germinated? The
answer is difficult to predict since it depends on the equilibrium constants between
the surfactant and all the surfaces present. Under these circumstances, the authors
thought it was prudent to test the surfactants under more demanding conditions
(higher concentrations) and be confident that the results would be transferable to
most applications. It is also important to note that many surfactants are phytotoxic
(Sun, Policello, & Paccione, 2003) at these higher concentrations, so this is another
variable to be considered when developing potential formulations.
The compatibility of surfactants with microorganisms is often correlated with
lipophilicity of the surfactant (Leal et al., 2009), with the length of the alkyl chain
being an important determinant (De Jonghe, Hermans, & Höfte, 2007; Oros,
Table 3. Foaming properties of tested surfactants.
Product name Expansion ratio*
Yucca Ag-Aide 6.0 ± 1.3 A
Armak 2042 4.7 ± 0.5 B
Armak 2079 2.7 ± 0.2 C
Armak 2081 ≤ 2 D
Armak 2087 2.8 ± 0.2 C
Silwet Eco Spreader ≤ 2 D
*Means followed by a different letter are significantly different (p < 0.05); error bars represent SD.

Cserhàti, & Vrbanovà, 1999). The longer the alkyl chain of the surfactant, the more
toxic the surfactant is to microorganisms. Alternatives with reduced fungicidal
activity are available to replace the traditional alkyl chain-based surfactants,
including surfactants based on branched alkyl chains (Ayala-Zermeno, Navarro-
Barranco, Mier, & Toriello, 1999), block co-polymers (Baur, Kaya, Gaugler, &
Tabashnik, 1997) and protein hydrolysates (Dunlap, Jackson, & Wright, 2007).
These surfactants all limit the length of alkyl chains that can enter the membrane
which reduces their toxicity to the fungus. Of the tested surfactants, only Armak
2079, Armak 2081 and Armak 2087 have a linear alkyl chain for the lipophile. The
lipophile for Armak 2087 is monooleate, a monounsaturated C18 chain. Both Armak
2079 and Armak 2081 are based on castor oil fatty acids, which are 90% ricinoleate
(Ayorinde, Garvin, & Saeed, 2000), a monounsaturated C18 chain with an unusual
hydroxyl function group on the 12th carbon atom. There is some evidence that
suggests unsaturated lipophiles are less toxic than saturated counterparts in
antimicrobial assays (Jossifova, Manolov, & Golovinsky, 1989). Nevertheless, the
effect of wetting agents needs to be empirically determined as compatibility will
differ among fungal species (Jaronski, 1997).
The most toxic of the tested surfactants was Yucca Ag-Aide. Yucca Ag-Aide is
an extract from Mohave yucca plant (Yucca schidigera). The surface active
components of the extract are a group of steroidal saponins. The primary saponins
from Y. schidigera were reported as glycosides of three C-25 epimeric pairs of
sapogenins: sarsasapogenin and smilagenin, markogenin and samogenin, gitogenin
and neogitogenin (Kaneda, Nakanishi, & Staba, 1987). More recently, analysis
indicates that there are at least 19 saponins in the extract of Y. schidigera
(Kowalczyk, Pecio, Stochmal, & Oleszek, 2011). Saponins from Quillaja saponaria
were shown to inhibit Botrytis cinerea and various yeasts, while nematicidal against
Xiphinema index (Fischer et al., 2011). The only report of saponin toxicity on
entomopathogens was a report using blastospores of I. fumosorosea (formerly
Paecilomyces fumosoroseus) (Vega, Dowd, McGuire, Jackson, & Nelsen, 1997).
Under much lower concentrations (0.01–0.1%), the saponin did not inhibit
germination on agar plates. The lack of cytotoxicity may be due to the lower
concentration of saponin tested, a different structural isomer of saponin with
different biological activity or the use of agar plates that may have altered
the bioavailability of the compound (Hood, Wilkinson, & Cavanagh, 2003). The
cytotoxic effects of saponins appear to arise from their ability to disrupt the
biological membrane of cells (Böttger, Hofmann, & Melzig, 2012). The broad
spectrum activity of Yucca Ag-Aide against these entomopathogens suggests that the
same mode of action is responsible for this activity that we observed.
Surfactants play a few important roles in pest control formulations of
entomopathogenic fungi. They are commonly used to improve dispersion, enhance
wetting and spray droplet adhesion. Surfactants accomplish these tasks by reducing
the interfacial surface energy between materials and lowering the overall energy of
the system. In order for a spray droplet to adhere to a surface, the droplet must first
be able to wet the surface. In general terms, for a liquid to wet a solid, the surface
tension of the liquid must be lower than the surface energy of the solid (Zisman,
1964). Most of the targets of these insect pest spray applications are hydrophobic or
low surface energy targets (insect cuticles, plant surfaces, etc.), which repel water and
have energetically unfavourable interactions with water. Aqueous spray applications

require a surfactant that lowers the surface tension of the solution enough to wet the
surface, since the surface tension of the solution must be reduced below that of the
solid for wetting to occur. Surfactants enhance wetting of powder formulations
through a similar mechanism. As a dispersant, surfactants reduce the interfacial
surface energy between particles and the solution; this allows the suspension to be
more energetically favourable.
All of the surfactants tested were able to significantly reduce the surface tension
of water. The Silwet Eco provided the greatest decrease in surface tension with a
surface tension of 21.5 dyn/cm, which is significantly lower than the other
surfactants. Silwet Eco is a trisiloxane (organosilicone surfactant), which is a class
of surfactants known as superspreaders. Superspreaders are surfactants that promote
the rapid spreading of an aqueous droplet on a hydrophobic surface to a final
contact angle close to zero (Hill, 1998). The mechanism behind this phenomenon is
still being debated (Ivanova & Starov, 2011).
Under our assay conditions, some of the fungal propagules aggregated. In the
case of conidia of I. fumosorosea (Figure 2), aggregation could be overcome by
shortening the incubation period from 24 hours to 14 hours. Aggregation was only a
problem once hyphal growth started, since propagules are well dispersed and the
aggregates did not form until germ tube extension progressed. This phenomenon
should not impact bioefficacy for most applications, since this would occur long after
the spores would have been applied to the target.
In the case of conidia of M. brunneum (Figure 2), the propagules were very
hydrophobic and the three surfactants that formed aggregates (Armak 2079, Armak
2081 and Yucca Ag-Aide) never fully dispersed the propagules. The control (water
only) also did not disperse the conidia, but after germination, enough individual cells
and small aggregates could be counted effectively to estimate germination rates.
Because the three surfactants could not disperse the conidia, one of the primary
reasons for adding a surfactant, an estimate of germination was not made. It is
noteworthy that the aggregates of Armak 2079 and Armak 2081 appeared to be
mainly made up of germinated conidia, while Yucca Ag-Aide aggregates appeared
to be made up of ungerminated conidia. In addition, reducing surfactant concentra-
tions (data not shown) did not alter the dispersion or aggregation.
In the case of blastospores of I. fumosorosea and M. brunneum, in combination
with Yucca Ag-Aide (Figure 1), the surfactant caused already dispersed cells to
aggregate. Blastospores are generally known to be hydrophilic and have a negative
free energy of aggregation (cell-to-cell aggregates are energetically unfavourable)
(Dunlap, Biresaw, & Jackson, 2005). While surfactants are not needed to disperse
blastospores, surfactants are often used in their formulations to aid in rehydration of
wettable powders (Bernhard et al., 1998), in spray applications to improve droplet
size and adhesion (Forster, Kimberley, & Zabkiewicz, 2005) or as a foaming agent
(Dunlap et al., 2007). Because Yucca Ag-Aide negatively altered the dispersion of
these blastospores, no effort was made to estimate germination, since they would not
be recommended as formulation adjuvants for these propagules.
Only two of the surfactants tested showed moderate activity as foaming agents,
Yucca Ag-Aide and Armak 2042. Foam formulations have been used to deliver
entomopathogenic fungi to difficult-to-reach insect habitats, such as termite galleries
(Dunlap et al., 2007). While poor foaming characteristics of most of the surfactants limit

their ability to be useful in foam formulations, low foaming surfactants are a benefit for
typical spray application, since foaming in the tank is an undesirable property.
In addition to modifying the physical properties of a formulation, surfactants
also have the ability to become a biologically active component of the formulation.
Surfactants themselves have been shown to be insecticidal to a variety of pest species
(Liu & Stansly, 2000; Srinivasan, Hoy, Singh, & Rogers, 2008; Xia, Johnson, &
Chortyk, 1998). Silwet L-77, a closely related trisiloxane surfactant of Silwet Eco,
has been reportedto kill a variety of insect species (Chandler, 1994; Cowles, Cowles,
McDermott, & Ramoutar, 2000; Dentener & Peetz, 1992; Imai, Tsuchiya, &
Fujimori, 1995; Imai, Tsuchiya, Morita, & Fujimori, 1994; Shapiro, Schroeder, &
Stansly, 1998; Wood, Tedders, & Taylor, 1997). It has also been reported to kill
Asian citrus psyllid, Diaphorina citri nymphs, while exhibiting no activity against its
parasitoid Tamarixia radiata (Cocco & Hoy, 2008). No data can be found on the
insecticidal activity of any of the surfactants in the current study.
In conclusion, the current study evaluated the compatibility and physical
properties of a group of surfactants that have been certified by the OMRI for use
in organic production systems. This list provides a convenient starting point for
selecting surfactants to be used in formulations of entomopathogenic fungi intended
to meet US NOS.
Acknowledgements
The authors would like to thank Anthony Smith, Angela Payne and Erica Geott for expert
technical assistance. Any opinions, findings, conclusions or recommendations expressed in this
publication are those of the author(s) and do not necessarily reflect the view of the US
Department of Agriculture (USDA). The mention of firm names or trade products does not
imply that they are endorsed or recommended by the USDA over other firms or similar
products not mentioned. USDA is an equal opportunity provider and employer.
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