Evaluation of synergistic interactions between the Colorado potato beetle (Coleoptera: Chrysomelidae) pathogen Beauveria bassiana and the insecticides, imidacloprid, and cyromazine

Improved control of Trialeurodes vaporariorum using mixture combinations of entomopathogenic fungi and the chemical insecticide spiromesifen

Greenhouse whitefly (Trialeurodes vaporariorum) is a major global pest, causing direct damage to plants and transmitting viral plant diseases. Management of T. vaporariorum is problematic because of widespread pesticide resistance, and many greenhouse growers rely on biological control agents to regulate T. vaporariorum populations. However, these are often slow and vary in efficacy, leading to subsequent application of chemical insecticides when pest populations exceed threshold levels. Combining chemical and biological pesticides has great potential but can result in different outcomes, from positive to negative interactions. In this study, we evaluated co-applications of the entomopathogenic fungi (EPF) Beauveria bassiana and Cordyceps farinosa and the chemical insecticide spiromesifen in laboratory bioassays. Complex interactions between the EPFs and insecticide were described using an ecotoxicological mixtures model, the MixTox analysis. Depending on the EPF and chemical concentrations applied, mixtures resulted in additivity, synergism, or antagonism in terms of total whitefly mortality. Combinations of B. bassiana and spiromesifen, compared to single treatments, increased the rate of kill by 5 days. Results indicate the potential for combined applications of EPF and spiromesifen as an effective integrated pest management strategy and demonstrate the applicability of the MixTox model to describe complex mixture interactions.

Synergistic interactions between three insecticides and Beauveria bassiana (Bals.-Criv.) Vuill. (Ascomycota: Hypocreales) in lesser mealworm, Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae), larvae

Topical applications of insecticides β-cyfluthrin, imidacloprid, and spinosad in combination with Beauveria bassiana (topical and contact filter paper application) induced synergistic interactions in lesser mealworm larvae, increasing mortality and in some cases numbers of larval cadavers exhibiting conidiogenesis. Reduced concentrations (LC10, LC20, LC30) of the insecticides induced sublethal effects in lesser mealworm larvae, inhibiting development (mass, head-capsule width, moulting) after eight days' exposure and movement behaviour (area explored and distance travelled) after 3 h' exposure. The most potent synergist was ß-cyfluthrin, it strongly inhibited larval development and movement while significantly increasing mortality and conidiogenesis in B. bassiana-infected larvae. Imidacloprid also strongly inhibited larval development and movement, but only produced weak short-lived synergistic increases in mortality, with no increase in conidiogenesis. Spinosad induced no effect on development and limited effect on movement, but still induced moderate short-lived synergistic increases in mortality and conidiogenesis. Intoxicated larvae exposed to B. bassiana on filter paper for 3 h showed no synergistic interactions, except when intoxicated by spinosad.

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.

The Fungus Nosema ceranae and a Sublethal Dose of the Neonicotinoid Insecticide Thiamethoxam Differentially Affected the Health and Immunity of Africanized Honey Bees

Honey bees (Apis mellifera L.) are affected by different biotic and abiotic stressors, such as the fungus Nosema ceranae and neonicotinoid insecticides, that negatively impact their health. However, most studies so far conducted have focused on the effect of these stressors separately and in European honey bees. Therefore, this study was conducted to analyze the impact of both stressors, singly and in combination, on honey bees of African descent that have demonstrated resistance to parasites and pesticides. Africanized honey bees (AHBs, Apis mellifera scutellata Lepeletier) were inoculated with N. ceranae (1 × 10⁵ spores/bee) and/or chronically exposed for 18 days to a sublethal dose of thiamethoxam (0.025 ng/bee) to evaluate their single and combined effects on food consumption, survivorship, N. ceranae infection, and immunity at the cellular and humoral levels. No significant effects by any of the stressors were found for food consumption. However, thiamethoxam was the main stressor associated to a significant decrease in AHB survivorship, whereas N. ceranae was the main stressor affecting their humoral immune response by upregulating the expression of the gene AmHym-1. Additionally, both stressors, separately and combined, significantly decreased the concentration of haemocytes in the haemolymph of the bees. These findings indicate that N. ceranae and thiamethoxam differentially affect the lifespan and immunity of AHBs and do not seem to have synergistic effects when AHBs are simultaneously exposed to both stressors.

Effects of Low Doses of a Novel dsRNA-based Biopesticide (Calantha) on the Colorado Potato Beetle

The Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) is a destructive pest of the cultivated potato, Solanum tuberosum. Members of this species are well-suited to agricultural habitats because of a suite of physiological adaptations and their ability to evolve resistance to multiple insecticides. Recently, a novel double-stranded RNA (dsRNA) insecticide (Calantha, active ingredient ledprona) has been demonstrated as an effective tool to manage Colorado potato beetle populations through RNA interference (RNAi). Previous studies have demonstrated the lethality of the high doses of ledprona but had not assessed possible effects of low doses that may happen due to product degradation in the environment, incomplete spray coverage, and foliage growth. Exposure of fourth instar larvae to low concentrations of ledprona interfered with their pupation. Exposure of adults significantly reduced their mobility after seven days, as well as their fertility. Reproductive effects were stronger in females, especially when exposed before reaching sexual maturity. The observed effects of low doses of ledprona may aid in the overall management of Colorado potato beetles by reducing the size of resident populations, inhibiting beetle movement within and between fields, and reducing the population growth rate.

Synergistic Interaction between the Entomopathogenic Fungus Akanthomyces attenuatus (Zare & Gams) and the Botanical Insecticide Matrine against Megalurothrips usitatus (Bagrall)

The excessive use of synthetic chemicals for Megalurothrips usitatus (Bagrall) management has resulted in the development of insecticide resistance as well as adverse effects to the natural ecosystem. This has driven the need to develop alternative pest control strategies. This study reports a synergistic interaction between the entomopathogenic fungus Akanthomyces attenuatus (Zare & Gams) and the botanical insecticide matrine against M. usitatus. The results revealed that the germination rate and colony growth of A. attenuatus were inhibited by higher matrine concentrations. Percentage mortalities of M. usitatus following application of A. attenuatus and matrine showed a dose mortality effect. After five days of treatment, all concentrations of matrine combined with different concentrations of A. attenuatus, except one combination (matrine 0.25 mg/mL + 1 × 10⁷ conidia/mL), showed synergistic effect. The activities of acetylcholinesterase and antioxidant enzymes (superoxide dismutase, catalase and peroxidase) in M. usitatus, in response to individual or combined application of A. attenuatus and matrine at the end of the experimental period, were significantly lower than controls. The findings confirm the synergistic action of A. attenuatus and matrine against M. usitatus along with the biochemical phenomenon possibly regulating the synergistic effect.

Studies on biochemical and synergistic effects of immunosuppressive concentration of imidacloprid with Beauveria bassiana and Metarhizium anisopliae for enhancement of virulence against vector mosquito Culex quinquefasciatus

In order to increase the virulence of two commonly used entomopathogens namely Beauveria bassiana and Metarhizium anisopliae for effective mosquito control programs, we developed new combined formulation by the use of immunosuppressive concentration of imidacloprid. Exposure of sublethal concentration (LC₁₀ 1.34 ppb) of imidacloprid to second instar larvae for 92 h that differently modulated the larval biochemical markers by decreasing the total protein (20.65% reduction), acetylcholinesterase (35.74% reduction) and increases the β-carboxylesterase (26.59% increase) and acid phosphatase (30.69% increase) levels while no significant difference was noticed in alkaline phosphatase of C. quinquefasciatus. Further we demonstrated that the imidacloprid exposure brings about reduction in phenoloxidase level (39.48% decrease) and nitric oxide production (37.64% decrease) in larval homogenate over control. The reduction in viability of hemocytes (15.37% decrease) and phagocytic activity of hemocytes (32.18% decrease) was noticed in imidacloprid treatment. Moreover in laboratory condition, exposure of 1 × 10⁷ spores/ml of B. bassiana (984) and M. anisopliae (6060) alone for 92 h cumulative toxicity assay exhibited larval mortality of 36.47% and 47.64% respectively against C. quinquefasciatus. However in the synergistic experimental studies with LC₁₀ of imidacloprid and 1 × 10⁷ spores/ml of B. bassiana or M. anisopliae to the larvae for 92 h cumulative assay brought 60% and 50.59% more insecticidal activity than the respective entomopathogens alone. The substantial increase of larvicidal activity noticed in the synergistic test conditions against larvae of C. quinquefasciatus revealed that the inclusion of sublethal concentration was proved to be useful for effective larval control.

Repellent activity of Tanacetum parthenium (L.) and Tanacetum vulgare (L.) essential oils against Leptinotarsa decemlineata (Say)

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is one of the most destructive pest species to have developed resistance to most chemical insecticides. We determined the composition and evaluated the potential of Tanacetum parthenium L. and Tanacetum vulgare L. (Asteraceae family) essential oil (EO) application as an alternative eco-friendly control strategy against L. decemlineata. We assessed the antifeedant activity for L. decemlineata larvae and adults by estimating the damage to potato leaves treated with three concentrations of EOs dissolved in ethanol (0.125, 0.25 and 0.5%). Results showed that T. parthenium EO was more effective against larvae, and T. vulgare was more effective against adults. In an olfactometer assay, the time required to choose an untreated leaf disc did not depend on the Tanacetum species, or life stage examined. However, the concentration of EO exhibited a significant effect on the behaviour of both developmental stages. At higher EO concentrations, both third instar larvae and adults require less time to choose an untreated leaf disc. Additionally, T. parthenium EO provoked more rapid movement away from the treated leaf disc than T. vulgare, especially at the highest concentration. Successful modification of L. decemlineata behaviour by the two Tanacetum oils suggests that they possess the potential for use in potato protection.

Influence of Bacillus thuringiensis and avermectins on gut physiology and microbiota in Colorado potato beetle: Impact of enterobacteria on susceptibility to insecticides

Gut physiology and the bacterial community play crucial roles in insect susceptibility to infections and insecticides. Interactions among Colorado potato beetle Leptinotarsa decemlineata (Say), its bacterial associates, pathogens and xenobiotics have been insufficiently studied. In this paper, we present our study of the survival, midgut histopathology, activity of digestive enzymes and bacterial communities of L. decemlineata larvae under the influence of Bacillus thuringiensis var. tenebrionis (morrissoni) (Bt), a natural complex of avermectins and a combination of both agents. Moreover, we estimated the impact of culturable enterobacteria on the susceptibility of the larvae to Bt and avermectins. An additive effect between Bt and avermectins was established regarding the mortality of the larvae. Both agents led to the destruction of midgut tissues, a decrease in the activity of alpha-amylases and alkaline proteinases, a decrease in the Spiroplasma leptinotarsae relative abundance and a strong elevation of Enterobacteriaceae abundance in the midgut. Moreover, an elevation of the enterobacterial CFU count was observed under the influence of Bt and avermectins, and the greatest enhancement was observed after combined treatment. Insects pretreated with antibiotics were less susceptible to Bt and avermectins, but reintroduction of the predominant enterobacteria Enterobacter ludwigii, Citrobacter freundii and Serratia marcescens increased susceptibility to both agents. We suggest that enterobacteria play an important role in the acceleration of Bt infection and avermectin toxicoses in L. decemlineata and that the additive effect between Bt and avermectin may be mediated by alterations in the bacterial community.

Fungus Metarhizium robertsii and neurotoxic insecticide affect gut immunity and microbiota in Colorado potato beetles

Fungal infections and toxicoses caused by insecticides may alter microbial communities and immune responses in the insect gut. We investigated the effects of Metarhizium robertsii fungus and avermectins on the midgut physiology of Colorado potato beetle larvae. We analyzed changes in the bacterial community, immunity- and stress-related gene expression, reactive oxygen species (ROS) production, and detoxification enzyme activity in response to topical infection with the M. robertsii fungus, oral administration of avermectins, and a combination of the two treatments. Avermectin treatment led to a reduction in microbiota diversity and an enhancement in the abundance of enterobacteria, and these changes were followed by the downregulation of Stat and Hsp90, upregulation of transcription factors for the Toll and IMD pathways and activation of detoxification enzymes. Fungal infection also led to a decrease in microbiota diversity, although the changes in community structure were not significant, except for the enhancement of Serratia. Fungal infection decreased the production of ROS but did not affect the gene expression of the immune pathways. In the combined treatment, fungal infection inhibited the activation of detoxification enzymes and prevented the downregulation of the JAK-STAT pathway caused by avermectins. The results of this study suggest that fungal infection modulates physiological responses to avermectins and that fungal infection may increase avermectin toxicosis by blocking detoxification enzymes in the gut.

Biological Impact and Enzyme Activities of Spodoptera litura (Lepidoptera: Noctuidae) in Response to Synergistic Action of Matrine and Beauveria brongniartii

Matrine, a naturally occurring heterocyclic compound, has been shown to enhance the pathogenicity of the entomopathogenic fungus Beauveria brongniartii against Spodoptera litura. In the current study, the biological impacts and synergism activities of these two agents on nutritional efficiency and antioxidant enzymes in S. litura were explored. Our results showed a high antifeedant activity of B. brongniartii and matrine on S. litura. The S. litura larvae were unable to pupate and emerge when treated with combinations of matrine and B. brongniartii. Following on, we measured the activities of five important antioxidant enzymes [superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), acetylcholinesterase (AChE), and glutathione-S-transferase (GST)] when treated with B. brongniartii SB010 (1 × 109 spores/ml), matrine (0.5 mg/ml), and B. brongniartii SB010 (1 × 109 spores/ml) + matrine (0.5 mg/ml). The results indicated the detoxification activity of the five enzymes in the fat body and hemolymph of S. litura when facing a combined B. brongniartii and matrine challenge. The activities of the enzymes were significantly lower than that of the control group 7 days post-treatment, indicating the inhibitory effect of the two xenobiotics. Matrine had better inhibition effects than B. brongniartii in a majority of the trials. The improved detoxification activity of the five enzymes may be the internal mechanism of synergism of matrine on B. brongniartii.

Nosema ceranae causes cellular immunosuppression and interacts with thiamethoxam to increase mortality in the stingless bee Melipona colimana

The microsporidian parasite Nosema ceranae and neonicotinoid insecticides affect the health of honey bees (Apis mellifera). However, there is limited information about the effect of these stressors on other pollinators such as stingless bees (Hymenoptera: Meliponini). We examined the separate and combined effects of N. ceranae and the neonicotinoid thiamethoxam at field-exposure levels on the survivorship and cellular immunity (hemocyte concentration) of the stingless bee Melipona colimana. Newly-emerged bees were subjected to four treatments provided in sucrose syrup: N. ceranae spores, thiamethoxam, thiamethoxam and N. ceranae, and control (bees receiving only syrup). N. ceranae developed infections of > 467,000 spores/bee in the group treated with spores only. However, in the bees subjected to both stressors, infections were < 143,000 spores/bee, likely due to an inhibitory effect of thiamethoxam on the microsporidium. N. ceranae infections did not affect bee survivorship, but thiamethoxam plus N. ceranae significantly increased mortality. Hemocyte counts were significantly lower in N. ceranae infected-bees than in the other treatments. These results suggest that N. ceranae may infect, proliferate and cause cellular immunosuppression in stingless bees, that exposure to sublethal thiamethoxam concentrations is toxic to M. colimana when infected with N. ceranae, and that thiamethoxam restrains N. ceranae proliferation. These findings have implications on pollinators' conservation.

Pesticide-Virus Interactions in Honey Bees: Challenges and Opportunities for Understanding Drivers of Bee Declines

Honey bees are key agricultural pollinators, but beekeepers continually suffer high annual colony losses owing to a number of environmental stressors, including inadequate nutrition, pressures from parasites and pathogens, and exposure to a wide variety of pesticides. In this review, we examine how two such stressors, pesticides and viruses, may interact in additive or synergistic ways to affect honey bee health. Despite what appears to be a straightforward comparison, there is a dearth of studies examining this issue likely owing to the complexity of such interactions. Such complexities include the wide array of pesticide chemical classes with different modes of actions, the coupling of many bee viruses with ectoparasitic Varroa mites, and the intricate social structure of honey bee colonies. Together, these issues pose a challenge to researchers examining the effects pesticide-virus interactions at both the individual and colony level.

Timing of sub-lethal insecticide exposure determines parasite establishment success in an insect-helminth model

Environmental toxicants are pervasive in nature, but sub-lethal effects on non-target organisms and their parasites are often overlooked. Particularly, studies on terrestrial hosts and their parasites exposed to agricultural toxicants are lacking. Here, we studied the effect of sequence and timing of sub-lethal exposures of the pyrethroid insecticide alpha-cypermethrin on parasite establishment using the tapeworm Hymenolepis diminuta and its intermediate insect host Tenebrio molitor as a model system. We exposed T. molitor to alpha-cypermethrin (LD20) before and after experimental H. diminuta infection and measured the establishment success of larval tapeworms. Also, we conducted in vitro studies quantifying the direct effect of the insecticide on parasite viability. Our results showed that there was no direct lethal effect of alpha-cypermethrin on H. diminuta cysticercoids at relevant concentrations (LD10 to LD90 of the intermediate host). However, we observed a significantly increased establishment of H. diminuta in beetles exposed to alpha-cypermethrin (LD20) after parasite infection. In contrast, parasite establishment was significantly lower in beetles exposed to the insecticide before parasite infection. Thus, our results indicate that environmental toxicants potentially impact host-parasite interactions in terrestrial systems, but that the outcome is context-dependent by enhancing or reducing parasite establishment depending on timing and sequence of exposure.

Implications of sequence and timing of exposure for synergy between the pyrethroid insecticide alpha-cypermethrin and the entomopathogenic fungus Beauveria bassiana

BACKGROUND

Combining low doses of chemical insecticides with entomopathogens constitutes a sustainable pest control method, but the significance of the timing and sequence of exposures needs clarification. We studied lethal effects of combinations of the entomopathogenic fungus Beauveria bassiana (KVL03-122) and the pyrethroid alpha-cypermethrin on the beetle Tenebrio molitor under varying timing and sequence of exposure. Synergy over time was evaluated in relation to the model of independent action (IA). We expected that increased progression of disease caused by B. bassiana would make beetles more susceptible to the insecticide, leading to enhanced synergy.

RESULTS

Synergistic effects between B. bassiana and alpha-cypermethrin were observed when B. bassiana was applied first, but only when the interval between applications was >48 h. With 72 h between exposures, mortality had increased to 100% after 8 days, in contrast to the 60% mortality expected. No synergy was observed when the insecticide was applied prior to fungal exposure within 24 h.

CONCLUSION

The sequence and timing of exposure do matter to achieve synergistic mortality by combining B. bassiana and alpha-cypermethrin, and the IA model proved to be a strong tool with which to evaluate the interactions of the two stressors over time. Pest control strategies could include B. bassiana followed by low-dose exposures to alpha-cypermethrin after 2-3 days. © 2018 Society of Chemical Industry.

Effects of fluorine-containing usnic acid and fungus Beauveria bassiana on the survival and immune-physiological reactions of Colorado potato beetle larvae

BACKGROUND

The search for compounds that interact synergistically with entomopathogenic fungi is aimed at enhancing the efficacy and stability of biological products against pest insects, for example, against the Colorado potato beetle (CPB). We hypothesized that fluorine-containing derivatives of usnic acid (FUA) might be candidates for the development of multicomponent bio-insecticides. The aim of this study was to analyze the co-influence of FUA and Beauveria bassiana on the survival and immune-physiological reactions of CPB larvae.

RESULTS

Synergy between FUA and B. bassiana was observed after treatment of second, third and fourth larvae instars under laboratory conditions. Furthermore, synergy was observed in field trials in continental climate conditions in southeastern Kazakhstan. In a field experiment, the median lethal time was shortened three-fold, and cumulative mortality for 15 days increased by 36% in the combined treatment compared with a fungal infection alone. FUA treatment delayed larval development, decreased the total hemocyte count, and increased both the phenoloxidase activity in integuments and the detoxification enzyme rate in hemolymph. A combined treatment with fungus and FUA led to increases in the aforementioned changes.

CONCLUSION

Toxicosis caused by FUA provides a stable synergistic effect between FUA and B. bassiana. The combination can be promising for the development of highly efficient products against CPB. © 2017 Society of Chemical Industry.

Influence of entomopathogenic fungus, Metarhizium anisopliae, alone and in combination with diatomaceous earth and thiamethoxam on mortality, progeny production, mycosis, and sporulation of the stored grain insect pests

The stored grain insects cause great damage to grains under storage conditions. Synthetic insecticides and fumigants are considered as key measures to control these stored grain insect pests. However, the major issue with these chemicals is grain contamination with chemical residues and development of resistance by insect pests to these chemicals. Biological control is considered as a potential alternative to chemical control especially with the use of pathogens, alone or in combination with selective insecticides. The present study was conducted to evaluate the synergism of Metarhizium anisopliae with diatomaceous earth (DE) and thiamethoxam against four insect pests on the stored wheat grains. In the first bioassay, the M. anisopliae was applied at 1.4 × 10⁴ and 1.4 × 10⁶conidia/ml alone and in integration with two concentrations (250 and 500 ppm) of tested DE. The tested fungus when combined with DE and thiamethoxam possessed synergistic impact as compared to their individual efficacy. Adult mortality increased with respect to increased exposure interval and doses. In the second bioassay, M. anisopliae was applied at 1.4 × 10⁴ conidia/ml individually and in combination with three concentrations (0.50, 0.75, and 1.00 ppm) of thiamethoxam. Results concluded that M. anisopliae integrated with DE and thiamethoxam provides more effective control of stored grain insect pests.

Interaction Between Metarhizium anisopliae (Met.) and the Insecticides Used for Controlling House Fly (Diptera: Muscidae) in Poultry Farm of Malaysia

The potential of integrating the mycoinsecticide, Metarhizium anisopliae (Met.), into house fly control programs is tremendous. However, the interaction between the fungus and insecticide, when applied at poultry farms, remains poorly understood. This study investigated the interaction between M. anisopliae and two selected insecticides, cyromazine and ChCy (a mixture of chlorpyrifos and cypemethrin), with three objectives: to assess the compatibility of M. anisopliae and the insecticides by measuring fungal vegetative growth and conidia production in the presence of insecticides; to evaluate the effect of M. anisopliae on these insecticides by analyzing insecticidal residue using ultra performance liquid chromatography; and to study the synergistic effects of M. anisopliae and the insecticides by applying sublethal concentrations of insecticides with M. anisopliae to house fly larvae. Metarhizium anisopliae was more tolerant to ChCy than to cyromazine, as M. anisopliae showed significantly more growth when grown with this insecticide. The M. anisopliae + ChCy combination resulted in significantly less chlorpyrifos residues compared to the ChCy plate, and 62-72% house fly larva mortality occurred when M. anisopliae and sublethal concentrations of ChCy were combined, implicating synergistic effects of the fungus with low concentrations of ChCy. Integrating M. anisopliae with compatible chemical at right concentration is crucial for poultry farm house fly control programs.

Synergistic Combinations of a Pyrethroid Insecticide and an Emulsifiable Oil Formulation of Beauveria bassiana to Overcome Insecticide Resistance in Listronotus maculicollis (Coleoptera: Curculionidae)

The annual bluegrass weevil, Listronotus maculicollis (Kirby), is a major pest of golf course turf in eastern North America and has become particularly problematic owing to widespread development of insecticide resistance. As an alternative option to manage resistant adult L. maculicollis, we explored combinations of the pyrethroid insecticide bifenthrin with an emulsifiable oil formulation of the entomopathogenic fungus Beauveria bassiana strain GHA (Bb ES). Combinations synergistically enhanced mortality in both insecticide-susceptible and insecticide-resistant L. maculicollis adults in the laboratory when bifenthrin was used at LC50s for each population. To determine the component behind the synergism, technical spores of B. bassiana GHA and the emulsifiable oil carrier in the fungal formulation were tested separately or in combination with bifenthrin. In both separate and combined applications, the emulsifiable oil carrier was responsible for high mortality within 3 d after treatment and interacted synergistically with bifenthrin, whereas fungus-induced mortality started later. Strong synergism was also observed in three field experiments with a relatively resistant L. maculicollis population. Combinations of Bb ES and bifenthrin hold promise as an effective L. maculicollis management tool, particularly of pyrethroid-resistant populations.

Starvation and Imidacloprid Exposure Influence Immune Response by Anoplophora glabripennis (Coleoptera: Cerambycidae) to a Fungal Pathogen

In several insect systems, fungal entomopathogens synergize with neonicotinoid insecticides which results in accelerated host death. Using the Asian longhorned beetle, Anoplophora glabripennis (Motschulsky), an invasive woodborer inadvertently introduced into North America and Europe, we investigated potential mechanisms in the synergy between the entomopathogenic fungus Metarhizium brunneum Petch and the insecticide imidacloprid. A potential mechanism underlying this synergy could be imidacloprid's ability to prevent feeding shortly after administration. We investigated whether starvation would have an impact similar to imidacloprid exposure on the mortality of fungal-inoculated beetles. Using real-time PCR to quantify fungal load in inoculated beetles, we determined how starvation and pesticide exposure impacted beetles' ability to tolerate or resist a fungal infection. The effect of starvation and pesticide exposure on the encapsulation and melanization immune responses of the beetles was also quantified. Starvation had a similar impact on the survival of M. brunneum-inoculated beetles compared to imidacloprid exposure. The synergy, however, was not completely due to starvation, as imidacloprid reduced the beetles' melanotic encapsulation response and capsule area, while starvation did not significantly reduce these immune responses. Our results suggest that there are multiple interacting mechanisms involved in the synergy between M. brunneum and imidacloprid.

Toxicological and biochemical basis of synergism between the entomopathogenic fungus Lecanicillium muscarium and the insecticide matrine against Bemisia tabaci (Gennadius)

The sweetpotato whitefly Bemisia tabaci (Gennadius) was challenged with different combinations of matrine (insecticide) and Lecanicillium muscarium (entomopathogenic fungus). Our results revealed a synergistic relationship between matrine and L. muscarium on mortality and enzyme activities of B. tabaci. To illustrate the biochemical mechanisms involved in detoxification and immune responses of B. tabaci against both control agents, activities of different detoxifying and antioxidant enzymes were quantified. After combined application of matrine and L. muscarium, activities of carboxylestrease (CarE), glutathione-s-transferase (GSTs) and chitinase (CHI) decreased during the initial infection period. Acetylcholinestrase (AChE) activities increased during the entire experimental period, whereas those of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) decreased during the later infection period. The increased mortality and suppression of enzymatic response of B. tabaci following matrine and L. muscarium application suggests a strong synergistic effect between both agents. The strong synergistic effect is possibly related to the disturbance of acetylcholine balance and changes in AchE activities of the whitefly as both matrine and L. muscarium target insect acetylcholine (Ach) receptors which in turn effects AchE production. Therefore, our results have revealed the complex biochemical processes involved in the synergistic action of matrine and L. muscarium against B. tabaci.

The production and uses of Beauveria bassiana as a microbial insecticide

Among invertebrate fungal pathogens, Beauveria bassiana has assumed a key role in management of numerous arthropod agricultural, veterinary and forestry pests. Beauveria is typically deployed in one or more inundative applications of large numbers of aerial conidia in dry or liquid formulations, in a chemical paradigm. Mass production is mainly practiced by solid-state fermentation to yield hydrophobic aerial conidia, which remain the principal active ingredient of mycoinsecticides. More robust and cost-effective fermentation and formulation downstream platforms are imperative for its overall commercialization by industry. Hence, where economics allow, submerged liquid fermentation provides alternative method to produce effective and stable propagules that can be easily formulated as dry stable preparations. Formulation also continues to be a bottleneck in the development of stable and effective commercial Beauveria-mycoinsecticides in many countries, although good commercial formulations do exist. Future research on improving fermentation and formulation technologies coupled with the selection of multi-stress tolerant and virulent strains is needed to catalyze the widespread acceptance and usefulness of this fungus as a cost-effective mycoinsecticide. The role of Beauveria as one tool among many in integrated pest management, rather than a stand-alone management approach, needs to be better developed across the range of crop systems. Here, we provide an overview of mass-production and formulation strategies, updated list of registered commercial products, major biocontrol programs and ecological aspects affecting the use of Beauveria as a mycoinsecticide.

Immune-physiological aspects of synergy between avermectins and the entomopathogenic fungus Metarhizium robertsii in Colorado potato beetle larvae

The interaction between the entomopathogenic fungus Metarhizium robertsii and natural avermectin metabolites of the actinomycete Streptomyces avermitilis were investigated on Colorado potato beetle larvae. A synergy in the mortality of larvae was detected after simultaneous treatment with half-lethal doses of avermectins (commercial name actarophit) 0.005% and fungus (5×10⁵conidia/ml). The treatment with avermectins led to rapid fungal colonization of the hemolymph. The defense strategies of insects infected by fungus and treated with avermectins and untreated insects were compared to investigate the mechanisms of this synergy. We have shown an increase in hemocytes, especially immunocompetent cells - plasmatocytes and granular cells in the initial stages of mycosis (third day post inoculation). In contrast, avermectins suppressed cellular immunity in hemolymph. Specifically, avermectins dramatically decreased the count of granular cells in larvae infected and uninfected with fungus. Apoptosis inducement and hemocyte necrosis under the influence of avermectins has been shown in vitro as one of the possible reasons for hemocyte mortality. In addition, avermectins enhanced the activity of phenoloxidases in integuments and hemolymph and increased the activity of glutathione-S-transferases activity in the fat body and hemolymph of infected and uninfected larvae, thereby intensifying the development of fungal infection by M. robertsii in Colorado potato beetle larvae. The combination of fungal infection and avermectins constitutes a new perspective for developing multicomponent bioinsecticides.

Biochemical basis of synergism between pathogenic fungus Metarhizium anisopliae and insecticide chlorantraniliprole in Locusta migratoria (Meyen)

We challenged Locusta migratoria (Meyen) grasshoppers with simultaneous doses of both the insecticide chlorantraniliprole and the fungal pathogen, Metarhizium anisopliae. Our results showed synergistic and antagonistic effects on host mortality and enzyme activities. To elucidate the biochemical mechanisms that underlie detoxification and pathogen-immune responses in insects, we monitored the activities of 10 enzymes. After administration of insecticide and fungus, activities of glutathione-S-transferase (GST), general esterases (ESTs) and phenol oxidase (PO) decreased in the insect during the initial time period, whereas those of aryl acylamidase (AA) and chitinase (CHI) increased during the initial period and that of acetylcholinesterase (AChE) increased during a later time period. Activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) decreased at a later time period post treatment. Interestingly, treatment with chlorantraniliprole and M. anisopliae relieved the convulsions that normally accompany M. anisopliae infection. We speculate that locust mortality increased as a result of synergism via a mechanism related to Ca²⁺ disruption in the host. Our study illuminates the biochemical mechanisms involved in insect immunity to xenobiotics and pathogens as well as the mechanisms by which these factors disrupt host homeostasis and induce death. We expect this knowledge to lead to more effective pest control.

Evaluation of the time-concentration-mortality responses of Plutella xylostella larvae to the interaction of Isaria fumosorosea with the insecticides beta-cypermethrin and Bacillus thuringiensis

BACKGROUND

Entomopathogenic fungi are potential candidates for controlling Plutella xylostella, a cosmopolitan pest of crucifers. In this study, bioassays were conducted to evaluate the interaction between Isaria fumosorosea and sublethal doses of two insecticides, beta-cypermethrin and Bacillus thuringiensis, against P. xylostella.

RESULTS

Data of each assay were in good agreement with the time-concentration-mortality model, indicating a strong dependence of the fungus and insecticide interaction on both concentration and post-exposure time. Using beta-cypermethrin 58-116 µg mL(-1) or B. thuringiensis 222.5-890 µg mL(-1) with the fungus significantly enhanced fungal efficacy. The LC50 values of the fungus declined over a 1-7 day period after exposure, and the LT50 values decreased with increasing concentration. Based on LC50 or LC90 estimates, synergism between the fungus and beta-cypermethrin resulted in a 2.7-28.3-fold reduction in LC50 values and a 12.1-19.6-fold reduction in LC90 values, while synergism of the fungus with B. thuringiensis led to a 2.4-385.0-fold reduction in LC50 values and a 4.4-151.7-fold reduction in LC90 values.

CONCLUSION

Results show that sublethal doses of B. thuringiensis and beta-cypermethrin can synergise I. fumosorosea activity on P. xylostella, suggesting that combination of I. fumosorosea with the two insecticides might offer an integrated approach to controlling P. xylostella in practice. © 2014 Society of Chemical Industry.

Compatibility of Isaria fumosorosea (Hypocreales: Cordycipitaceae) Blastospores with Agricultural Chemicals Used for Management of the Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Liviidae)

Biorational insecticides are being increasingly emphasized for inclusion in integrated pest management programs for invasive insects. The entomopathogenic fungus, Isaria fumosorosea, can be used to help manage the Asian citrus psyllid with minimal impact on beneficial arthropods, but its effectiveness may be compromised by agrochemicals used to control concurrent arthropod pests and diseases. We evaluated the compatibility of I. fumosorosea blastospores with a range of spray oils and copper-based fungicides registered for use in citrus groves. Results of laboratory and greenhouse tests showed a range of responses of the fungus to the different materials, including compatibility and incompatibility. Overall, I. fumosorosea growth in vitro was reduced least by petroleum-based materials and most by botanical oils and borax, and some of the copper-based fungicides, suggesting that tank mixing of I. fumosorosea with these latter products should be avoided. However, equivalent negative effects of test materials on fungal pathogenicity were not always observed in tests with adult psyllids. We hypothesize that some oils enhanced adherence of blastospores to the insect cuticle, overcoming negative impacts on germination. Our data show that care should be taken in selecting appropriate agrochemicals for tank-mixing with commercial formulations of entomopathogenic fungi for management of citrus pests. The prospects of using I. fumosorosea for managing the invasive Asian citrus psyllid and other citrus pests are discussed.

Exposure to sublethal doses of fipronil and thiacloprid highly increases mortality of honeybees previously infected by Nosema ceranae

Background

The honeybee, Apis mellifera, is undergoing a worldwide decline whose origin is still in debate. Studies performed for twenty years suggest that this decline may involve both infectious diseases and exposure to pesticides. Joint action of pathogens and chemicals are known to threaten several organisms but the combined effects of these stressors were poorly investigated in honeybees. Our study was designed to explore the effect of Nosema ceranae infection on honeybee sensitivity to sublethal doses of the insecticides fipronil and thiacloprid.

Methodology/Finding

Five days after their emergence, honeybees were divided in 6 experimental groups: (i) uninfected controls, (ii) infected with N. ceranae, (iii) uninfected and exposed to fipronil, (iv) uninfected and exposed to thiacloprid, (v) infected with N. ceranae and exposed 10 days post-infection (p.i.) to fipronil, and (vi) infected with N. ceranae and exposed 10 days p.i. to thiacloprid. Honeybee mortality and insecticide consumption were analyzed daily and the intestinal spore content was evaluated 20 days after infection. A significant increase in honeybee mortality was observed when N. ceranae-infected honeybees were exposed to sublethal doses of insecticides. Surprisingly, exposures to fipronil and thiacloprid had opposite effects on microsporidian spore production. Analysis of the honeybee detoxification system 10 days p.i. showed that N. ceranae infection induced an increase in glutathione-S-transferase activity in midgut and fat body but not in 7-ethoxycoumarin-O-deethylase activity.

Conclusions/Significance

After exposure to sublethal doses of fipronil or thiacloprid a higher mortality was observed in N. ceranae-infected honeybees than in uninfected ones. The synergistic effect of N. ceranae and insecticide on honeybee mortality, however, did not appear strongly linked to a decrease of the insect detoxification system. These data support the hypothesis that the combination of the increasing prevalence of N. ceranae with high pesticide content in beehives may contribute to colony depopulation.

Interactions between imidacloprid and Metarhizium brunneum on adult Asian longhorned beetles (Anoplophora glabripennis (Motschulsky)) (Coleoptera: Cerambycidae)

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae), a longhorned beetle species native to Asia, has been introduced into several North American and European cities. Currently eradication and preventive measures are limited to identifying and destroying infested trees and protecting uninfested trees with trunk or soil-injections of the systemic insecticide imidacloprid. Because entomopathogenic fungi like Metarhizium brunneum Petch have been identified as virulent against these beetles we conducted several tests to determine the compatibility of the two agents in combination. Radial hyphal growth and the sporulation capacity of M. brunneum on Sabouraud dextrose agar with yeast were not significantly affected by the presence of imidacloprid. In a 2×3 factorial experiment investigating interactions between exposure to imidacloprid and M. brunneum we observed no effect of imidacloprid alone on beetle survival when beetles were given a single dose of 10 or 100 ppm compared to control insects. We observed a significant effect of exposure to M. brunneum, and a significant interaction between imidacloprid and M. brunneum representing a synergistic effect of dual treatment. Beetles exposed to the fungus alone lived significantly longer compared to insects treated with a single dose of 100 ppm imidacloprid (9.5 vs. 6.5d). Consumption of striped maple twigs by beetles exposed to imidacloprid, across concentrations, was reduced 48% compared to control insects, where as consumption by M. brunneum-exposed beetles was reduced by 16% over the first 6-days of the test period. Beetles fed 100 ppm imidacloprid consumed 32% less over the first 3d compared to beetles not exposed to imidacloprid and thereafter consumed as much as beetles not fed 100 ppm imidacloprid. M. brunneum-exposed beetles consumed significantly less food than control insects throughout the test period, and beetles treated with imidacloprid produced significantly fewer conidia compared to beetles not treated with imidacloprid.

Fungal infection counters insecticide resistance in African malaria mosquitoes

The evolution of insecticide resistance in mosquitoes is threatening the effectiveness and sustainability of malaria control programs in various parts of the world. Through their unique mode of action, entomopathogenic fungi provide promising alternatives to chemical control. However, potential interactions between fungal infection and insecticide resistance, such as cross-resistance, have not been investigated. We show that insecticide-resistant Anopheles mosquitoes remain susceptible to infection with the fungus Beauveria bassiana. Four different mosquito strains with high resistance levels against pyrethroids, organochlorines, or carbamates were equally susceptible to B. bassiana infection as their baseline counterparts, showing significantly reduced mosquito survival. Moreover, fungal infection reduced the expression of resistance to the key public health insecticides permethrin and dichlorodiphenyltrichloroethane. Mosquitoes preinfected with B. bassiana or Metarhizium anisopliae showed a significant increase in mortality after insecticide exposure compared with uninfected control mosquitoes. Our results show a high potential utility of fungal biopesticides for complementing existing vector control measures and provide products for use in resistance management strategies.

Evaluation of the time-concentration-mortality responses of Plutella xylostella larvae to the interaction of Beauveria bassiana with a nereistoxin analogue insecticide

Six bioassays were conducted to evaluate the interaction between Beauveria bassiana SG8702 and a nereistoxin analogue insecticide, diammonium S,S'-(2-dimethylaminotrimethylene)di(thiosulfate), which is highly compatible with the fungal biocontrol agent against diamondback moth Plutella xylostella (L.). Second-instar larvae were exposed to sprays of B. bassiana alone (assay 1) at concentrations of 21-38, 157-232 and 822-1133 conidia mm(-2) or together with the insecticide at the low application rates of 5, 10, 25, 50 and 100 microg AI ml(-1) (assays 2-6), and then maintained at 25 degrees C and 12:12 h light:dark photoperiod for daily monitoring of mortality for 8 days. Based on the modelling of the resultant time-concentration-mortality data sets, the fungal agent was highly virulent to P. xylostella with an LC50 decreasing from 269 conidia mm(-2) on day 4 to 107 on day 8. Lower lethal concentrations or shorter median lethal times resulted from fungal sprays including the tested chemical rates; the latter never caused higher mortalities than the fungal treatments alone. The fungal action over 3-7 days after spray was significantly enhanced by including in the fungal sprays the chemical at rates of > or =25 microg ml(-1) for 2.6- to 1756-fold reduction of LC50 values, > or =50 microg ml(-1) for 4- to 274-fold reduction of LC70 values and 100 microg ml(-1) for 9- to 33-fold reduction of LC90 values respectively. These rates were equivalent to 5-20% of the chemical rate labelled for field application. The fungal and chemical interaction outlined above highlights the feasibility of combined formulation or application of B. bassiana and the chemical insecticide for P. xylostella control.

Synergistic interaction between Beauveria bassiana- and Bacillus thuringiensis tenebrionis-based biopesticides applied against field populations of Colorado potato beetle larvae

Commercial biopesticides based on the fungal pathogen Beauveria bassiana strain GHA and the bacterial pathogen Bacillus thuringiensis tenebrionis were applied alone and in combination (tank mixed) against larval populations of the Colorado potato beetle, Leptinotarsa decemlineata, in small plots of potatoes over three field seasons. Interactions between the two products were evaluated in terms of pest-control efficacy. B. bassiana (formulated as Mycotrol) was applied at low and medium label rates of 1.25 and 2.5 x 10(13) conidia/ha, and B. thuringienis (formulated as Novodor) was applied at low and high label rates of 40.3 and 120.8 x 10(6) Leptinotarsa units/ha. Two weekly applications of the bacterial pesticide alone provided 50-85% control of beetle larvae within 14 days after the initial application, while applications of the mycopesticide alone produced no greater than 25% control. Maximum control, in nearly all tests, was produced by the combination of the two products. The combined treatments produced a statistically significant 6-35% greater reduction in larval populations than would have been predicted had the two biopesticides acted independently. This low-level synergistic interaction was observed during all field seasons and resulted from combinations at all rates, including, in one of two tests, the low rates of each product. These results indicate that B. thuringiensis and B. bassiana have strong potential for integrated biologically based management of Colorado potato beetle.

Time-concentration-mortality modeling of the synergistic interaction of Beauveria bassiana and imidacloprid against Nilaparvata lugens

Interactions between the entomopathogenic fungus, Beauveria bassiana SG8702, and imidacloprid on Nilaparvata lugens (Homoptera: Delphacidae) were studied in laboratory bioassays by spraying suspensions of unformulated conidia (assay 1) and aqueous dilutions of emulsifiable conidia formulation alone (assay 2) or together with imidacloprid at the sub-lethal rates of 0.5, 1.0 and 2.0 microg ml(-1) (assays 3-5). Each assay consisted of five conidia concentrations plus an appropriate control and three replicates, each including 30-40 third-instar nymphs, so as to generate time-concentration-mortality data for modeling analysis. A mineral oil-based emulsion used to formulate B bassiana slightly enhanced fungal activity but had no significant impact on the background mortality of N lugens. On the basis of LC50 estimates and associated variances on days 4-12 after spraying, synergistic interactions of both agents or formulations were determined by estimating relative potencies of assay 2 over assay 1 (1.2-9.0), assay 3 over assay 2 (1.3-1.7), assay 4 over assay 2 (7.5-9.6), assay 5 over assay 2 (22.7-101), assay 4 over assay 3 (3.8-5.8), assay 5 over assay 3 (16.1-61.0), and assay 5 over assay 4 (3.0-10.5). The time-concentration-mortality modeling method was not only mathematically but also biologically robust to evaluate the interactions of B bassiana and imidacloprid on N lugens. Compared with their counterparts, enhanced fungal formulations displayed consistently earlier or greater activities against the pest species based on LC50 and LT50 estimates determined from their time-concentration-mortality relationships. The results highlight a potential for pest control by combined formulation or application of B bassiana and imidacloprid.

Diatomaceous earth increases the efficacy of Beauveria bassiana against Tribolium castaneum larvae and increases conidia attachment

This research tested the suppressive ability of Beauveria bassiana (Balsamo) Vuillemin alone and in combination with diatomaceous earth against the red flour beetle, Tribolium castaneum (Herbst). Adults did not show a dose response to B. bassiana, and the addition of diatomaceous earth (DE) did not result in a significant increase in mortality. Against larvae, however, DE at 190 mg/kg grain enhanced the efficacy of B. bassiana at all concentrations ranging from 33 to 2,700 mg of conidia per kilogram of grain. The presence of DE resulted in 17- and 16-fold decreases in the median lethal concentration of B. bassiana at 56 and 75% RH, respectively. No significant differences in larval mortality in response to B. bassiana and diatomaceous earth alone or in combination were found between 56 and 75% RH. Conidial attachment to larvae was significantly greater with 190 mg/kg DE than without it. The partial analysis of lipids taken up by DE from the larvae revealed the removal of phospholipids and long-chain fatty acids. These results support the hypothesis that diatomaceous earth enhances the efficacy of B. bassiana against larval T. castaneum, at least in part by damaging the insect cuticle, thus increasing conidial attachment and making nutrients more available to conidia for their germination.

Starvation induced stress and the susceptibility of the Colorado potato beetle, Leptinotarsa decemlineata, to infection by Beauveria bassiana

Starvation of second instar Colorado potato beetle larvae for 24h immediately after treatment with Beauveria bassiana conidia increased susceptibility to the pathogen and subsequent sporulation of cadavers but decreased time to larval death. In feeding studies, B. bassiana-treatment had no effect on subsequent larval development, and mortality occurred 5-6 days after treatment. Twenty-four hours of starvation alone retarded subsequent larval development but did not affect mortality. Mortality of B. bassiana-treated starvation stressed larvae occurred 4-5 days after treatment. Both B. bassiana treatment and 24h starvation significantly reduced total foliage consumption and daily weight gains. On the day of treatment, B. bassiana had no effect on the efficiency with which food was converted to biomass (ECI). ECI was not affected by B. bassiana or starvation alone on the day following treatment but was significantly affected by a combination of both. When larvae were exposed to a range of limited food quantities, ECI decreased with decreasing food availability but only extreme stress (starvation for 24h) increased susceptibility to B. bassiana. Topical application of Dacryodes excelsa resin (an antifeedant) to potato leaves caused a concentration dependent reduction in foliage consumption and weight gain by second instar larvae but did not affect larval mortality. When larvae were exposed to a fixed concentration of B. bassiana and a range of antifeedant concentrations there were significant linear relationships between 24h larval weight gain and mortality and 24h larval weight gain and sporulation. The interaction between starvation stress and the susceptibility to B. bassiana infection is discussed and its possible implications in pest management considered.