The Efficacy of Entomopathogenic Nematodes Plus an Adjuvant against Helicoverpa zea and Chrysodeixis includens in Aboveground Applications.

In the southern United States, corn earworm, Helicoverpa zea (Boddie), and soybean looper, Chrysodeixis includens (Walker) are economically important crop pests. Although Bt crops initially provided effective control of target pests such as H. zea, many insect pests have developed resistance to these Bt crops. Alternative approaches are needed, including biological control agents such as entomopathogenic nematodes (EPNs). However, the effectiveness of EPNs for aboveground applications can be limited due to issues such as desiccation and ultraviolet radiation. Effective adjuvants are needed to overcome these problems. Ten strains of EPNs were tested for virulence against eggs, first to fourth instars, fifth instars, and pupae of H. zea and C. includens in the laboratory. These 10 EPN strains were Heterorhabditis bacteriophora (HP88 and VS strains), H. floridensis (K22 strain), Hgkesha (Kesha strain), Steinernema carpocapsae (All and Cxrd strains), S. feltiae (SN strain), S. rarum (17c+e strain), and S. riobrave (355 and 7-12 strains). EPNs could infect eggs of H. zea or C. includens in the laboratory, but the infection was low. The mortality caused by 10 EPN strains in seven days was significantly higher for the first to fourth instars of H. zea compared to the control, as was the fifth instars of H. zea. Similarly, for the first to fourth and fifth instars of C. includens, the mortality was significantly higher compared to the controls, respectively. However, only S. riobrave (355) had significantly higher mortality than the control for the pupae of H. zea. For the pupae of C. includens, except for H. bacteriophora (HP88), S. rarum (17c+e), and H. floridensis (K22), the mortality of the other seven strains was significantly higher than the control. Subsequently, S. carpocapsae (All) and S. riobrave (7-12) were chosen for efficacy testing in the field with an adjuvant 0.066% Southern Ag Surfactant (SAg Surfactant). In field experiments, the SAg Surfactant treatment significantly increased the mortality and EPN infection for S. carpocapsae (All) on first instars of H. zea in corn plant whorls. On soybean plants, with the SAg Surfactant, S. carpocapsae (All) was more effective than S. riobrave (7-12) on fifth instars of C. includens. This study indicates that EPNs can control H. zea and C. includens, and SAg Surfactant can enhance EPN efficacy.

Enhancing entomopathogenic nematode efficacy with Pheromones: A field study targeting the pecan weevil.

Consistent efficacy is required for entomopathogenic nematodes to gain wider adoption as biocontrol agents. Recently, we demonstrated that when exposed to nematode pheromone blends, entomopathogenic nematodes showed increased dispersal, infectivity, and efficacy under laboratory and greenhouse conditions. Prior to this study, the impact of entomopathogenic nematode-pheromone combinations on field efficacy had yet to be studied. Steinernema feltiae is a commercially available entomopathogenic nematode that has been shown to increase mortality in insect pests such as the pecan weevil Curculio caryae. In this study, the pecan weevil was used as a model system to evaluate changes in S. feltiae efficacy when treated with a partially purified ascaroside pheromone blend. Following exposure to the pheromone blend, the efficacy of S. feltiae significantly increased as measured with decreased C. caryae survival despite unfavorable environmental conditions. The results of this study highlight a potential new avenue for using entomopathogenic nematodes in field conditions. With increased efficacy, using entomopathogenic nematodes will reduce reliance on conventional management methods in pecan production, translating into more environmentally acceptable practices.

Post-Application Field Persistence and Efficacy of Cordyceps javanica against Bemisia tabaci.

Previously, Cordyceps javanica Wf GA17, a causing agent of whitefly epizootics in southern Georgia, demonstrated superior temperature tolerance and higher virulence against the whitefly Bemisia tabaci than commercial strains in the laboratory. The post-application persistence and efficacy of this fungus against B. tabaci were compared with that of the commercially available C. javanica Apopka97 strain over a two-year field study in cotton and vegetable crops. When blastospores of both strains were applied alone, whitefly populations were not effectively suppressed. Thus, JMS stylet oil was added to fungal treatments for enhancing efficacy and persistence. For 0-day samples, all fungal treatments caused similar but significant levels of immature mortality regardless of fungal strain, propagule form (conidia vs. blastospores), and application method (alone or mixed with JMS). In follow-up samplings, Wf GA17 blastospores + JMS achieved higher control levels than other treatments in some trials, but the efficacy did not last long. The JMS oil alone caused significant mortality and suppressed whiteflies. Over 90% of spores lost viability 24 h after treatment in all fungal treatments. Across evaluation times, there was no difference between the two fungal strains (conidia or blastospores, alone or combined with JMS), but conidia persisted better than blastospores for both strains. Overall, the field persistence and efficacy of C. javanica did not last long; therefore, improved delivery methods and formulations are needed for enhancement.

An improved bioassay for the testing of entomopathogenic nematode virulence to the western corn rootworm (Diabrotica virgifera virgifera) (Coleoptera: Chrysomelidae): with focus on neonate insect assessments.

Bioassays involving newly hatched larval insects can be limited by the larvae's feeding state. Assays attempting to monitor mortality effects can be negatively affected by starvation effects on the larvae. Neonate western corn rootworms have significant reductions in viability if not provided food within 24 h post hatch. The recent development of an improved artificial diet for western corn rootworm larvae provides a new bioassay type for evaluating entomopathogenic nematodes that also makes the testing arena easy to observe. Here, we evaluated four species of entomopathogenic nematodes including Heterorhabditis bacteriophora Poinar, Steinernema carpocapsae (Weiser), Steinernema diaprepesi Nguyen & Duncan, and Steinernema rarum (de Doucet) against neonate western corn rootworm, Diabrotica virgifera virgifera LeConte, in 96-well plate diet bioassays. Nematode inoculation levels were 0, 15, 30, 60, and 120 nematodes per larva. Percentage mortality increased for each species as the rate of inoculation increased. Overall, H. bacteriophora and S. carpocapsae caused the greatest amount of larval mortality. The diet-based bioassays were shown to be an effective method for nematode exposure to insect pests. The assays provided adequate moisture to keep nematode from desiccating while also allowing freedom of movement around the arenas. Both rootworm larvae and nematodes were contained within the assay arenas. The addition of nematodes did not cause any significant deterioration of the diet within the three-day period of testing. Overall, the diet bioassays worked well as a measure of entomopathogenic nematode virulence.

Efficacy of entomopathogenic fungi, nematodes and spinetoram combinations for integrated management of Thrips tabaci.

BACKGROUND: Two consecutive field trials using a blend of entomopathogens in combination with a new chemistry insecticide were conducted to determine treatment effects on onion thrips (Thrips tabaci Lindeman) populations, crop damage, plant development, crop yield and impact on natural enemies. Products were tested in an onion cropping system and included the insect pathogenic fungus Beauveria bassiana (isolate WG-11), an entomopathogenic nematode Heterorhabditis bacteriophora (strain VS) and the new-chemistry chemical insecticide spinetoram. RESULTS: In all treatments, a significant decrease in thrips per plant population was detected in both trials. Overall, dual application of entomopathogens and insecticide was more effective than singly applied treatments. The lowest number of thrips larvae (1.96 and 3.85) and adults (0.00 and 0.00) were recorded when treated with dual application of B. bassiana and spinetoram at 7 days post application (DPA) after the second spray application in 2017and 2018, respectively. Damage on onion plants was considerably decreased in all treatments relative to the control. The lowest damage was observed on onion plants treated with B. bassiana + spinetoram at 7 DPA after the second spray application during both years. A significant decrease in the number of natural enemies (beetles, spiders, mites, lacewings, ants and bugs) on onion plants was recorded during both years. Insect pathogens when applied alone and in combination with each other considerably protected arthropod natural enemies compared to insecticide application applied alone. Significant increase in plant agronomic traits was observed compared to the control. Among all the treatments, B. bassiana + spinetoram produced maximum leaf length, leaf weight, total leaves, neck diameter, bulb diameter, number of rings per bulb, bulb weight, dry matter and plant yield following the 2017and 2018 applications, respectively. CONCLUSION: The findings of the study reveal the potential of using insect pathogens and insecticide for control of T. tabaci. However, combinations containing spinetoram are harmful to nontarget organisms, whereas biological control agents help in protecting biodiversity in onion agroecosystems. © 2023 Society of Chemical Industry.

Tolerance of Steinernema carpocapsae infective juveniles in novel nanoparticle formulations to ultraviolet radiation.

Entomopathogenic nematodes (EPNs) are susceptible to abiotic environmental factors including ultraviolet (UV) radiation, which affects the survival and efficacy. This study evaluated nanoparticle (NP) formulations for protecting Steinernema carpocapsae infective juveniles (IJs) from UV radiation. First, silica-NH2 NPs at oil-to-water ratios of 2:8, 3:7 and 4:6 were compared with Barricade Fire Gel (1 % and 2 %) and a water control (aqueous IJs) by exposing IJs to UV light (254 nm) for 0, 10 and 20 min. Barricade gel (especially 2 % Barricade) significantly improved IJs viability after UV treatment, while all three NPs had adverse effects on IJ viability after UV radiation. Subsequently, two silica (SiO2 basic and advanced) and one titania (TiO2) based formulations were tested with Barricade (1 % and 2 %) and a water control. The titania-NH2 NPs provided the highest UV protection, and IJ viability and virulence were not reduced even after 20-min UV. Except TiO2, only 2 % Barricade at 10-min UV and SiO2 basic at 20-min UV had lower IJ mortality than the water control. Only TiO2 formulated IJs caused higher insect mortality and infection levels than aqueous IJs after UV treatment. The UV tolerance of TiO2 was further examined by assessing the number of nematodes invading the hosts. Consistent with virulence tests, the number of invading nematodes in titania-NH2 NPs did not decrease after UV radiation for 10 or 20 min compared with the no-UV control. The anti-UV capability of titania-NH2 NPs has promise as a tool to enhance biocontrol efficacy of EPNs under field conditions.

Toxicity of Photorhabdus luminescens and Xenorhabdus bovienii bacterial metabolites to pecan aphids (Hemiptera: Aphididae) and the lady beetle Harmonia axyridis (Coleoptera: Coccinellidae).

Toxicity of the metabolites of two bacteria, Photorhabdus luminescens and Xenorhabdus bovienii, symbionts of entomopathogenic nematodes, were tested in the laboratory against the multicolored Asian lady beetle, Harmonia axyridis, the black pecan aphid, Melanocallis caryaefoliae, and the blackmargined aphid, Monellia caryella. Bacterial broth prepared from both P. luminescens and X. bovienii demonstrated high levels of toxicity equivalent to the pyrethroid insecticide bifenthrin and caused higher insect mortality than tryptic soy broth plus yeast extract (TSY) (blank control) against M. caryella; broth culture of P. luminescens was more effective than TSY against M. caryaefoliae. At the levels tested, the metabolites were not toxic to H. axyridis.

Combined application of entomopathogenic nematodes and fungi against fruit flies, Bactrocera zonata and B. dorsalis (Diptera: Tephritidae): laboratory cups to field study.

BACKGROUND: The peach fruit fly, Bactrocera zonata, and the Oriental fruit fly, B. dorsalis (Diptera: Tephritidae), are economically important fruit fly species in various regions of the world. We evaluated the effects of separate and combined applications of the entomopathogenic fungi (EPF) Beauveria bassiana (WG-18) and Metarhizium anisopliae (WG-02), and the entomopathogenic nematodes (EPNs) Heterorhabditis bacteriophora (VS strain) and Steinernema carpocapsae (ALL strain) against larvae, pupae and pharate adults, of B. zonata and B. dorsalis under laboratory, glasshouse and field cage conditions. RESULTS: Combined applications of EPF and EPNs produced greater mortality than individual treatments under all conditions. Against both species, the combination of B. bassiana and H. bacteriophora consistently exerted strong effects that were similar to the combined application of B. bassiana and S. carpocapsae whereas M. anisopliae applied with S. carpocapsae was least effective in all combinations. In a laboratory bioassay, synergistic interactions were detected between B. bassiana and H. bacteriophora applied against larvae and pharate adults of both fly species, between B. bassiana and S. carpocapsae against larvae of both species and pharate adults of B. zonata, and between M. anisopliae and H. bacteriophora against B. zonata larvae. Other combined treatments resulted in additive effects, especially against fly pupae. In a potted soil bioassay, there were only additive interactions in all combinations against different stages of both flies. The 3rd instar of both flies was more susceptible than pharate adult and pupal stages. Additive interactions between EPNs and EPF were detected in the glasshouse against 3rd instars and pupae, and under field conditions against 3rd instars of both fly species. CONCLUSION: These results indicate how particular combinations of entomopathogenic fungi and nematodes could be deployed in integrated pest management of tephritid fruit flies in orchard agro-ecosystems. © 2022 Society of Chemical Industry.

Comparing Production and Efficacy of Cordyceps javanica With Cordyceps fumosorosea.

A newly discovered entomopathogenic fungus Cordyceps javanica (Friedrichs & Bally) Samson & Hywel-Jones (Hypocreales: Cordycipitaceae) strain Wf GA17 was compared with the commercial Cordyceps fumosorosea Wize (Hypocreales: Cordycipitaceae) Apopka 97 strain for liquid-culture production, formulation, insecticidal efficacy, and storage stability under laboratory conditions. We compared culture media with carbon:nitrogen (C:N) ratios of 10:1, 30:1, and 50:1 for these two isolates. A third strain, C. fumosorosea strain ARSEF 3581, had previously been optimized for liquid-culture production of blastospores at 10:1 C:N served as an added control. These seven cultures were processed by spray drying with skim milk powder, stored at 25oC to evaluate storage stability, and assayed for insecticidal activity against Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) neonates. Final blastospore concentrations were not significantly different among cultures, ranging from 4.47 to 9.88 × 108 spores/ml. Fungal biomass decreased and final glucose concentrations increased with increasing C:N ratios, indicating better fungal growth with higher nitrogen concentrations. Product yields from the spray dryer (grams per liter culture) increased with increased C:N ratios while spore concentrations decreased, ranging from 2.27 to 7.17 × 109 spores/g. There were no significant differences for insecticidal efficacy among the seven treatments. Spores produced in 10:1 C:N ratio media retained viability longer than spores produced in other media. Cost of ingredients decreased with increasing C:N ratios, such that the 30:1 media may yield the most economical product. The raw material cost needed for application was 1.4× greater for Wf GA17 compared with Apopka 97, a difference that could be erased by optimization of culture conditions.

Laboratory virulence of entomopathogenic nematodes to the sweetpotato whitefly, Bemisia tabaci.

The sweetpotato whitefly, Bemisia tabaci Middle East-Asia Minor 1 (MEAM1), is a major insect pest on vegetable crops worldwide. Enormous economic losses result from direct and indirect plant damage caused by MEAM1. Biological control using entomopathogenic nematodes (EPN) may be an effective alternative strategy against MEAM1 because this pest has developed resistance to most insecticides. First, nine EPN species (Heterorhabditis bacteriophora, H. indica, H. georgiana, H. floridensis, Steinernema feltiae, S. carpocapsae, S. riobrave, S. glaseri, and S. rarum) were investigated for virulence to MEAM1 third instar nymphs on snap bean leaves under laboratory conditions. The mortality of MEAM1 nymphs was evaluated at 3 days post-inoculation (dpi). Compared to the water control, the application of the nine EPN species except S. glaseri resulted in significantly higher mortality of MEAM1 nymphs, such as H. bacteriophora (66.31%), H. floridensis (56.38%), S. carpocapsae (54.54%), and S. rarum (57.80%). Subsequently, the four virulent EPN species, H. bacteriophora, H. floridensis, S. carpocapsae, and S. rarum were evaluated further for virulence to MEAM1 nymphs on snap bean and tomato leaves. The mortality of MEAM1 nymphs was assessed at 3 dpi and 7 dpi. There were no significant differences in MEAM1 nymphal mortality between tomato and snap bean at either 3 dpi or 7 dpi. The mortality of MEAM1 nymphs caused by the application of H. floridensis (99.25%) was significantly higher than the other three EPN species and the water control at 7dpi. The results indicate that H. floridensis is a very promising biocontrol agent for B. tabaci management.

Novel associations in antibiosis stemming from an insect pupal cell.

The pupal soil cell of the pecan weevil, Curculio caryae (Coleoptera: Curculionidae), was reported previously to exhibit antibiosis to an entomopathogenic fungus, Beauveria bassiana. The objectives of this study were to examine 1) if the antimicrobial effect occurs in other insects that form pupal cells, 2) whether the effect extends to plant pathogenic fungi, and 3) identify the source of antibiosis in pupal soil cells of C. caryae. Antibiosis of pupal cells against B. bassiana was confirmed in-vitro in three additional curculionids, Diaprepes abbreviatus, Conotrachelus nenuphar, and Pissodes nemorensis, all of which had fewer fungal colonies relative to controls. Pupal soil cells were found to suppress phytopathogenic fungi in-vitro, including suppression of Alternaria solani by D. abbreviatus pupal cell, and that of Monilinia fructicola by C. caryae. The detection of antibiosis of soil cells formed by surface-sterilized insects using sterile soil implies the antimicrobial effect stemmed from inside the insect. Further, a novel biotic mechanism was identified: a bacterium related to Serratia nematodiphila was isolated from C. caryae pupal soil cells and was found to be associated with antibiosis. The bacterial cultures with or without autoclave had similar effects but were not as potent as pupal soil cells for suppressing B. bassiana. Also, autoclaved soil cells and autoclaved bacterial culture suppressed M. fructicola but were not as inhibitory as non-autoclaved soil cells. This indicates that antibiosis may be due to bacterial metabolites, although other factors may also be involved. Our findings suggest potential to develop the antibiotic compounds as novel bio-fungicides to control plant diseases.

Quantification of pH tolerance levels among entomopathogenic nematodes.

Soil pH affects the availability of nutrients, which impacts plant growth and development. Similarly, soil pH may also influence microorganisms in the soil, either beneficial or nonbeneficial. One such group of beneficial microorganisms is entomopathogenic nematodes (EPN), parasites of soil-inhabiting insects. Entomopathogenic nematodes have a number of attributes that make them good alternatives to chemical insecticides. The objective of this study was to investigate pH tolerance of 11 steinernematids and six heterorhabditids post exposure to different pH levels. Entomopathogenic nematode populations were exposed to varying pH levels (pH2 to pH11) made up from two different chemical solutions (ammonium-acetate and citrate-phosphate). Entomopathogenic nematode populations are expected to have varying tolerance to different pH levels. The highest infective juvenile survival was obtained from pH3 to pH10 in citrate-phosphate, where all populations displayed >50% survival. Steinernema carpocapsae populations had >90% survival at pH3 to pH11 in citrate-phosphate solutions. Overall, the steinernematids had a higher survival range in ammonium-acetate pH solutions compared with the heterorhabditids. Moreover, Steinernema spp., S. carpocapsae (ScCxrd, ScAll, and ScItalian) and S. riobrave showed consistently higher survival in both acidic and alkaline solutions, when compared to the other steinernematids, suggesting that they may be applied in both acidic and alkaline soils. These findings can be of use when selecting EPNs for biological control purposes in the two countries, respectively.

Combined Effect of Entomopathogens against Thrips tabaci Lindeman (Thysanoptera: Thripidae): Laboratory, Greenhouse and Field Trials.

Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae) is one of the most damaging insect pests of onions, Allium cepa L., which is an economically important agricultural crop cultivated worldwide. In this study, the combined application of entomopathogenic nematodes with entomopathogenic fungi against different soil dwelling stages of T. tabaci was evaluated. The nematodes included Heterorhabditis bacteriophora (VS strain) and Steinernema feltiae (SN strain), and fungi included Beauveria bassiana (WG-11) and Metarhizium anisopliae (WG-02); all four paired combinations (nematode + fungus) were included. In a small cup bioassay, only the combined application of H. bacteriophora and B. bassiana (WG-11) caused a synergistic interaction against pre-pupae, while all other combinations were compatible in an additive manner against pupae and late second instars. In a larger arena, a potted soil bioassay, again, combined applications of both pathogens produced greater mortality compared to single applications of each pathogen; all the combinations exhibited additive interactions, with the highest mortality observed in pre-pupae, followed by pupae and late second instar larvae using H. bacteriophora and B. bassiana (WG-11). Additionally, in the potted plant bioassay, lower adult emergence was observed from treated groups compared to control groups. Under field conditions, lower numbers of adults and larvae were found in treated groups relative to controls. Overall, the pre-pupal stage was more susceptible to the pathogen treatments, followed by pupae and late second instar larvae, and also combined applications of both pathogens suppressed the adult population. Combined application of entomopathogenic nematodes and fungi could be used for integrated pest management (IPM) of T. tabaci in onion production systems.

Identification and Virulence of Cordyceps javanica Strain wf GA17 Isolated From a Natural Fungal Population in Sweetpotato Whiteflies (Hemiptera: Aleyrodidae).

A new strain of the entomopathogenic fungus, identified as Cordyceps javanica (Frieder. & Bally) Kepler, B. Shrestha & Spatafora (Hypocreales: Cordycipitaceae) wf GA17, was found naturally infecting the sweetpotato whitefly, Bemisia tabaci (Gennadius) MEAM1 in southern Georgia, US, in September 2017. The fungus was tested for pathogenicity and virulence in comparison with commercially available entomopathogenic fungal strains against several insect species in the laboratory. In specific, it was compared with Cordyceps fumosorosea (Wize) Kepler, B. Shrestha & Spatafora (Hypocreales: Cordycipitaceae) Apopka 97, Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) strain GHA, and Metarhizium brunneum Petch (Hypocreales: Clavicipitaceae) strain F52 for virulence against B. tabaci (4th instars) and cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) (4th instars with or without wingbuds), on leaf-discs, and against last instars of pecan weevil Curculio caryae (Horn) (Coleoptera: Curculionidae) and citrus root weevil Diaprepes abbreviatus (L.) (Coleoptera: Curculionidae) in soil cups. Against B. tabaci, C. javanica exhibited higher mortality and mycosis development at 5 d post inoculation than other fungi. In assays against A. gossypii with and without wingbuds, C. javanica and C. fumosorosea had the highest mortality and mycosis levels and B. bassiana had the lowest; nymphs with wingbuds were more susceptible to some fungal infection than those without. Against C. caryae, B. bassiana was more effective than other fungi. For D. abbreviatus, B. bassiana also caused the highest mortality while M. brunneum had the lowest, with Cordyceps spp. being intermediate. Overall, the findings suggest high potential of the new strain, C. javanica wf GA17, for managing whiteflies and aphids, while it was not as effective as B. bassiana against the curculionids.

Evaluation of Barricade® to enhance survival of entomopathogenic nematodes on cowhide.

Entomopathogenic nematodes (EPNs), Steinernema riobrave and Heterorhabditis floridensis are under evaluation for eradication of the southern cattle fever tick, Rhipicephalus microplus infesting nilgai antelope, in South Texas. Cattle fever ticks are a significant threat to the U.S. livestock industry. Although they have been eradicated in the U.S. they frequently re-invade along the Texas-Mexico border. Remotely operated field sprayers have been developed to directly treat nilgai antelope with EPNs as they transit fence crossings and as they contact wetted foliage and soil from the surrounding area. EPNs are known to be susceptible to mortality from ultraviolet light (UV) and desiccation. A sprayable fire gel, Barricade®, has been reported to protect EPNs from UV and desiccation but has not been tested on animal hides. Barricade® at 1 and 2 percent rates was mixed with the water solution of S. riobrave and H. floridensis and applied to cowhides (to mimic direct treatment of nilgai) and filter paper and then these substrates were placed out of doors in 0, 30, 60 or 120 min of sunlight. Wax moth larvae, Galleria mellonella, were exposed to the cowhides and filter paper to determine efficacy of the EPNs. Efficacy of S. riobrave with 1 and 2% Barricade® gel applied to cowhides was significantly improved at 30 and 60 min as compared to the control. At 120 min mortality of the wax moth larvae was near zero for both the control and the treatments. Similar results were found with the filter paper test. In contrast, efficacy of H. floridensis with Barricade® applied to cowhides or filter paper was not significantly improved at 30, 60 or 120 min as compared to the water only control. Barricade® has the potential to improve the efficacy of S. riobrave and other EPNs by reducing mortality and desiccation, especially when used in the remotely operated sprayer developed for treatment of cattle fever tick infested nilgai.

Bemisia tabaci on Vegetables in the Southern United States: Incidence, Impact, and Management.

Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is among the most economically important insect pests of various vegetable crops in the Southern United States. This insect is considered a complex of at least 40 morphologically indistinguishable cryptic species. Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) was initially introduced in the United States around 1985 and has since rapidly spread across the Southern United States to Texas, Arizona, and California, where extreme field outbreaks have occurred on vegetable and other crops. This pest creates extensive plant damage through direct feeding on vegetables, secreting honeydew, causing plant physiological disorders, and vectoring plant viruses. The direct and indirect plant damage in vegetable crops has resulted in enormous economic losses in the Southern United States, especially in Florida, Georgia, and Texas. Effective management of B. tabaci on vegetables relies mainly on the utilization of chemical insecticides, particularly neonicotinoids. However, B. tabaci has developed considerable resistance to most insecticides. Therefore, alternative integrated pest management (IPM) strategies are required, such as cultural control by manipulation of production practices, resistant vegetable varieties, and biological control using a suite of natural enemies for the management of the pest.

Mortality of native and invasive ladybirds co-infected by ectoparasitic and entomopathogenic fungi.

Harmonia axyridis is an invasive alien ladybird in North America and Europe. Studies show that multiple natural enemies are using Ha. axyridis as a new host. However, thus far, no research has been undertaken to study the effects of simultaneous infection by multiple natural enemies on Ha. axyridis. We hypothesized that high thallus densities of the ectoparasitic fungus Hesperomyces virescens on a ladybird weaken the host's defenses, thereby making it more susceptible to infection by other natural enemies. We examined mortality of the North American-native Olla v-nigrum and Ha. axyridis co-infected with He. virescens and an entomopathogenic fungus-either Beauveria bassiana or Metarhizium brunneum. Laboratory assays revealed that He. virescens-infected O. v-nigrum individuals are more susceptible to entomopathogenic fungi, but Ha. axyridis does not suffer the same effects. This is in line with the enemy release hypothesis, which predicts that invasive alien species in new geographic areas experience reduced regulatory effects from natural enemies compared to native species. Considering our results, we can ask how He. virescens affects survival when confronted by other pathogens that previously had little impact on Ha. axyridis.

Antifungal activity of Xenorhabdus spp. and Photorhabdus spp. against the soybean pathogenic Sclerotinia sclerotiorum.

The fungus, Sclerotinia sclerotiorum, causes white mold disease and infects a broad spectrum of host plants (> 500), including soybean with yield losses of up to 70%. Biological control is a potential alternative for management of this severe plant pathogen, and relative to chemical fungicides, provides broad benefits to the environment, farmers and consumers. The symbiotic bacteria of entomopathogenic nematodes, Xenorhabdus spp. and Photorhabdus spp., are characterized by the production of antimicrobial compounds, which could serve as potential sources for new bio-fungicides. The objectives of this study were to assess cell-free supernatants (CFS) of 16 strains of these bacteria cultures on S. sclerotiorum mycelium growth; assess the volatiles of X. szentirmaii cultures on the fungus mycelium and sclerotium inhibition; and evaluate the X. szentirmaii cultures as well as their CFS on the protection of soybean seeds against the white mold disease. Among the 16 strains, the CFS of X. szentirmaii showed the highest fungicidal effect on growth of S. sclerotiorum. The CFS of X. szentirmaii inhibited > 98% of fungus growth from mycelium and sclerotia, whereas the volatiles generated by the bacterium culture inhibited to 100% of fungus growth and 100% of sclerotia production. The bacterial culture diluted to 33% in water and coated on soybean seeds inhibited S. sclerotiorum and protected soybean plants, allowing 78.3% of seed germination and 56.6% of plant development. Our findings indicate potential for a safe and novel control method for S. sclerotiorum in soybean. Moreover, this is the first study to indicate that volatile organic compounds from Xenorhabdus spp. can be used in plant disease suppression.

Environmental Tolerance of Entomopathogenic Fungi: A New Strain of Cordyceps javanica Isolated from a Whitefly Epizootic Versus Commercial Fungal Strains.

A new strain of Cordyceps javanica (wf GA17) was observed causing widespread epizootics among whiteflies in Southern Georgia in 2017. The tolerance of conidia to environmental factors including variable temperature and ultraviolet (UV) light was compared between this strain and three commercial strains of entomopathogenic fungi (Metarhizium brunneum F52, Cordyceps fumosorosea Apopka97, and Beauveria bassiana GHA). Under 10-30 °C, C. javanica wf GA17 responded similarly to other fungi, with the highest virulence against Galleria mellonella at 25 °C, followed by 20, 30, and 15 °C; lowest virulence was observed at 10 °C. At 35 °C and 40 °C, C. javanica wf GA17 had lower tolerance than M. brunneum F52 and B. bassiana GHA, but was superior to C. fumosorosea Apopka97 in conidia viability and post-treatment virulence. After exposure to -20 °C for 56 d, C. javanica wf GA17 exhibited lower germination than M. brunneum F52 and lower virulence than M. brunneum F52 and B. bassiana GHA, but higher germination and virulence than C. fumosorosea Apopka97. Following exposure to strong UV light, viability and virulence of all fungi were reduced with increasing exposure periods. Increased environmental tolerance of C. javanica wf GA17 over C. fumosorosea Apopka97 suggests that the new strain could have applicability for commercial pest management.

Environmental tolerance of entomopathogenic nematodes differs among nematodes arising from host cadavers versus aqueous suspension.

Environmental factors such as temperature and desiccation impact the survival and efficacy of entomopathogenic nematodes (EPNs). Most studies on environmental tolerance have focused on EPNs applied in aqueous suspension. Another approach for EPN application is via infected host cadavers. Emergence in host cadavers is also more representative of nematodes in natural populations. In prior studies, certain advantages in fitness have been observed with the cadaver application approach relative to aqueous application, yet the impact of environmental stress on these approaches requires investigation. In this study, we compared the effects of various temperatures (heat and cold) and desiccation intervals (48 and 72 hr) on the survival, virulence and reproductive capacity of Heterorhabditis bacteriophora and Steinernema glaseri when applied via cadaver versus aqueous suspension. In the heat tolerance bioassays, following exposure to 30 °C, 35 °C and 37. 5 °C, nematodes (from both species) in the cadaver treatments exhibited higher survival, and reproductive capacity compared with aqueous application. No survival was observed above 37.5 °C regardless of species or application approach. In cold tolerance, no differences were observed between the cadaver and aqueous treatments after a sequence of exposures from 10 °C to -2 °C. In desiccation assays, following exposure to 85% relative humidity for 2 or 3 days, nematodes (from both species) exhibited higher survival and reproduction in the cadaver treatment than in the aqueous treatment, whereas no differences were observed in virulence. This is the first study to find differential stress tolerance among nematodes emerged from infected host cadavers versus those applied in aqueous suspension. Our findings indicate additional advantages when using the cadaver approach for biocontrol applications, and suggest EPNs existing in natural populations may have broader environmental tolerance than those applied via aqueous suspension.