Compatibility of the entomopathogenic fungus Beauveria bassiana with flufenoxuron and azadirachtin against Tetranychus urticae

Can Ivermectin kill Sarcoptes scabiei during the molting process?

BACKGROUND

Sarcoptes scabiei is a permanent obligate ectoparasite that lives and reproduces in the epidermis of humans and other mammals worldwide. There is a lack of information on the molting process of Sarcoptes scabiei. Ivermectin is widely used to treat Sarcoptes infection in humans and animals, while the survival of molting Sarcoptes mites in the presence of ivermectin is unknown. The aim of the present study is to investigate the molting process of Sarcoptes mites and assess the activity of ivermectin during the molting process of Sarcoptes mites.

METHODOLOGY/PRINCIPAL FINDINGS

molting Sarcoptes mites were incubated at 35°C and 80% relative humidity and observed hourly until complete molt. Of the 192 molting mites recorded, the longest molt periods for larvae and nymphs were 23 and 30 h, respectively. The activity of ivermectin on molting Sarcoptes mites was also assessed using two concentrations of the drug (0.1 and 0.05 mg/ml). The exposure time for molting mites was determined by 100% mortality of female mites exposed to the solution of ivermectin. While all female mites were killed after exposure to 0.1 mg/ml ivermectin for 2 h and and 0.05 mg/ml for 7 h, 32% and 36% of molting mites survived and successfully molted, respectively.

CONCLUSIONS/SIGNIFICANCE

The present study demonstrated that molting Sarcoptes mites are less susceptible to ivermectin than active mites. As a consequence, mites may survive after two doses of ivermectin given 7 days apart due not only to hatching eggs but also to the resistance of mites during their molting process. Our results provide insight into the optimal therapeutic regimens for scabies and highlight the need for further research on the molting process of Sarcoptes mites.

Compatibility of Beauveria bassiana and a Plant Secondary Metabolite: A Novel Modeling Approach to Invade Host Defense for Effective Control of Oligonychus afrasiaticus (McGregor) on Date Palms

Oligonychus afrasiaticus (McGregor) is an important pest causing substantial economic losses to date palm fruits (dates). The application of mycopathogens with plant secondary metabolites, which may proceed synergistically is thus essential to augment sustainable management strategy for O. afrasiaticus. In this regard, extensive laboratory experimentation involving compatibility, synergism, and host defense was performed to develop stable pest management option. The toxin-pathogen compatibility assay results revealed compatible interaction (biological index = 79–95) of B. bassiana ARSEF 8465 against each tested concentration of commercially available (+)-α-Pinene that provide the opportunity to further explore the time and concentration dependent mortality and defense related enzymatic regulation analysis. The time-mortality response assays that mainly comprised of various proportions of B. bassiana ARSEF 8465 and (+)-α-Pinene revealed that the sole application of B. bassiana ARSEF 8465 (LC₅₀ = 19.16 mg/mL), and (+)-α-Pinene (3.41 mg/mL) found to be least lethal compared with joint applications (LC₅₀ ranged from 1.32–7.06 mg/mL). The treatments complied under Scheme IV (80% (+)-α-Pinene: 20% B. bassiana ARSEF 8465 Conidia) led to strong synergistic interaction (joint toxicity = 755). In addition, synergistic interactions greatly induced enzymatic activities of the studied antioxidants (CAT and SOD), and defense-related enzymes (GST and AchE). We concluded that join application of B. bassiana ARSEF 8465 and (+)-α-Pinene is a promising option for controlling Oligonychus afrasiaticus populations.

Potential Synergy between Spores of Metarhizium anisopliae and Plant Secondary Metabolite, 1-Chlorooctadecane for Effective Natural Acaricide Development

Date palm dust mites are important pests severely infesting valuable nutritious fruits (dates) of date palm. In search of an alternative to acaricides, joint action of Metarhizium anisopliae EBCL 02049 spores and 1-Chlorooctadecane was evaluated as a potential candidate for the management of Oligonychus afrasiaticus through natural products. In this regard, in vitro tests were performed to evaluate the interaction of M. anisopliae spores with multiple doses of 1-Chlorooctadecane (0.8, 1.6, 2.4, 3.2, and 4.0 mg/mL). Compatibility bioassay results evidenced from vegetative growth (77.7–84.40 mm), sporulation (5.50–7.30 × 10⁶ spores/mL), and germination (96.70–98.20%), revealed that all the tested doses are compatible (biological index > 82) with the spores of M. anisopliae. The impact of combined treatment of spores with 1-Chlorooctadecane in different proportions (Scheme I, II, III, and IV) compared to their sole application against O. afrasiaticus was evaluated by concentration–mortality response bioassays. Results showed that all the combined treatments revealed high mortality compared to the sole application, which showed relatively slow mortality response over time. Toxicity recorded from Scheme IV combinations (80% 1-Chlorooctadecane: 20% Spores), exhibited strong synergistic interaction (joint toxicity = 713). Furthermore, potent interactions have overcome the host antioxidant defense at the final stage of infection by tremendously reducing catalase, and superoxide dismutase activities. These experiments demonstrated fungal–toxin joint synergistic interaction as a promising date palm dust mite management option.

Spinosad and Mixtures of an Entomopathogenic Fungus and Pyrethrins for Control of Sitona lineatus (Coleoptera: Curculionidae) in Field Peas

The pea leaf weevil, Sitona lineatus L., is an important pest of field peas and faba beans in most temperate regions. As no information is currently available on efficacy of biopesticides for S. lineatus control, laboratory bioassays were performed to evaluate the impact of biopesticides (spinosad, Beauveria bassiana strain GHA, pyrethrins, B. bassiana GHA + pyrethrins, and B. bassiana GHA + azadirachtin) against adults of this pest. The concentrations used in this bioassay were 0.1, 0.5, 1.0, and 2.0 times the lowest labeled application rate of each product. Results were further verified in cage experiments by assessing biopesticide effects on adult mortality and feeding damage in pea plants. The impact of biopesticides on mortality of larvae of two beneficial species, Chrysoperla carnea and Adalia bipunctata, was also tested in laboratory conditions. We found spinosad to be the most promising candidate, causing 100% adult mortality at high and medium concentrations. Beauveria bassiana and its combination with pyrethrins caused 60-62% adult mortality, but only at the highest concentration. In contrast, B. bassiana + azadirachtin and pyrethrins treatments caused only minimal adult mortality at all concentrations. In cage experiments, spinosad and B. bassiana + pyrethrins had significant effects on adult mortality and provided foliage protection from adult feeding. Conversely, the fungus treatment alone showed inconsistent performance. Beauveria bassiana and spinosad were generally harmless to C. carnea and A. bipunctata larvae, but B. bassiana + pyrethrins was toxic toward beneficial species. These results could help to improve integrated pest management programs intended to control S. lineatus.

Compatibility between the endoparasitoid Hyposoter didymator and the entomopathogenic fungus Metarhizium brunneum: a laboratory simulation for the simultaneous use to control Spodoptera littoralis

BACKGROUND

The cotton leafworm, Spodoptera littoralis, is one of the most destructive pests in the Mediterranean basin, being predominantly controlled using synthetic chemical pesticides. Strain EAMa 01/58-Su of the fungus Metarhizium brunneum and the parasitoid Hyposoter didymator are promising biological control agents for this pest. In this study, we assessed the compatibility between these two agents to control S. littoralis under joint attack scenarios.

RESULTS

Firstly, the direct and indirect effects of the fungus towards parasitoid adults were studied. The fungus significantly decreased life expectancy of the parasitoid (mortality = 62.5%; mean lethal concentration = 1.85 × 10⁶ conidia ml^-1 ; average survival time = 92.2 h) when applied at high concentrations (10⁸ conidia ml^-1 ), whereas it did not affect the reproductive potential of the parasitoid females during the 3 days after treatment. Secondly, the combinations between the two agents to control S. littoralis under different simultaneous use scenarios (inoculation of S. littoralis larvae with the fungus before being exposed to parasitoid females and vice versa) were investigated, with additive effect in all cases. A significant effect on fitness (preimaginal development time and reproductive potential) of the F1 parasitoid generation were detected. Moreover, parasitization significantly reduced the total hemocytes in S. littoralis hemolymph compared with the control, promoting fungal infection. Finally, parasitoids showed a significant preference for non-inoculated S. littoralis larvae.

CONCLUSIONS

We demonstrated compatibility (additive effect) between fungus and parasitoid under different joint attack scenarios to control S. littoralis in laboratory conditions. However, this will be supported by our ongoing greenhouse and field studies. © 2019 Society of Chemical Industry.

Toxin-Pathogen Synergy Reshaping Detoxification and Antioxidant Defense Mechanism of Oligonychus afrasiaticus (McGregor)

Current study reveals the likelihood to use pathogen and toxin mutually as an effective and eco-friendly strategy for Oligonychus afrasiaticus (McGregor) management, which could reduce toxicant dose and host killing time. Therefore, phytol and Beauveria bassiana in different proportions were evaluated to determine their effectiveness. Prior to ascertaining host mortality and defense mechanisms, we have recorded in vitro action of phytol using different concentrations (0.70, 1.40, 2.10, 2.80, and 3.50 mg/mL) against B. bassiana suspension. In vitro compatibility assays revealed that growth parameters (vegetative growth, sporulation, and viability) of B. bassiana were least affected by the action of phytol at all tested concentrations. Biological Index of B. bassiana exhibited compatibility with phytol allowed us to conduct Joint toxicity bioassays in which phytol and spores mixed in different proportions in order to attain maximum treatment effect in terms of high mortality at low concentration under short time. Results revealed that joint-application exhibited both synergistic (treatments with higher proportions of phytol), and antagonistic interaction (treatments with higher proportions of spores) interactions. Biochemical mechanisms involved in host antioxidant and detoxification response were explored by quantifying their respective enzymatic activities. Lethality of different treatments induced different patterns of detoxification enzymes including glutathione S-transferase (GST) and acetylcholinesterase (AchE). Overall, the least potent treatments (20% phytol:80% spores, and 40% phytol:60% spores) established in the current study induced relatively higher GST and AchE activities. On the other hand, the most potent treatment (80% phytol:20% spores) at its maximum concentration exhibited negligible relative GST and AchE activities. Antioxidant enzyme activities of CAT and SOD measured in the current study showed moderate to complex interaction might because of toxin-pathogen remarkable synergy. This study suggested that joint application of phytol with B. bassiana spores have shown tremendous acaricidal potential and found to be promising new strategy for controlling old world date mites.

Synergistic and additive interactions of Serratia marcescens S-JS1 to the chemical insecticides for controlling Nilaparvata lugens (Hemiptera: Delphacidae)

The combined use of entomopathogens and chemical agents has been suggested as an alternative strategy to control pest insects. However, the effectiveness of combinations of entomopathogenic bacteria and insecticides against rice planthoppers is largely unknown. Here, we evaluated the separate and combined effects of an entomopathogenic bacterium, Serratia marcescens S-JS1, and spirotetramat or thiamethoxam insecticides against third-instar nymphs of Nilaparvata lugens Stål (Hemiptera: Delphacidae) under laboratory and greenhouse conditions. Under laboratory conditions, the combinations caused higher mortality in the third-instar nymphs of N. lugens and produced a synergistic or additive effect compared with the treatments with either bacterial suspension or insecticide alone. Application of S-JS1 (1 × 109 cfu/ml) in combination with 20 mg/liter spirotetramat resulted in 80.5% of N. lugens nymphal mortality, compared with 52.7% in spirotetramat alone treatments, and interactions resulted in a synergistic responses. Other combination treatments of S-JS1 with either insecticide concentration all exhibited additive interactions. In further greenhouse tests, S-JS1 (1 × 109 cfu/ml) + spirotetramat (20 mg/liter) and S-JS1 (1 × 109 cfu/ml) + thiamethoxam (5 mg/liter) showed additive effects against the nymphs, and were found to be most effective relative to their individual treatments on days 5 and 9. Our results indicate that S. marcescens S-JS1 combined with insecticide may provide a promising new strategy for controlling N. lugens.

Potential of Entomopathogenic Fungi as Biological Control Agents of Diamondback Moth (Lepidoptera: Plutellidae) and Compatibility With Chemical Insecticides

The objectives were to evaluate the efficiency of entomopathogenic fungi against Plutella xylostella (L.) and the compatibility of the most virulent isolates with some of the insecticides registered for use on cabbage crops. Pathogenicity tests used isolates of Beauveria bassiana, Metarhizium rileyi, Isaria fumosorosea, Isaria sinclairii, and Lecanicillium muscarium standardized at a concentration of 10(7) conidia/ml. Cabbage leaf discs were immersed in these suspensions, and after evaporation of the excess water, were placed 10 second-instar larvae of P. xylostella, totaling 10 leaf discs per treatment. Mortality was assessed 7 d after treatment, and the isolates that caused mortality>80% were used to estimate LC50 and LT50. The compatibilities of the most virulent isolates and the insecticides were tested from the mixture of these into the culture medium, and after solidifying, the medium was inoculated with an aliquot of the isolated suspension. The following parameters were evaluated: growth of the colony, number and viability of conidia after 7 d. The isolated IBCB01, IBCB18, IBCB66, and IBCB87 of B. bassiana, LCMAP101 of M. rileyi, and ARSEF7973 of I. sinclairii caused mortality between 80 and 100%, with LC50 and LT50 between 2.504 to 6.775×10(4) conidia/ml and 52.22 to 112.13 h, respectively. The active ingredients thiamethoxam and azadirachtin were compatible with the entomopathogenic fungi. The results suggest that the use of these isolates is an important alternative in the pesticidal management of P. xylostella, with the possible exception of the associated use of chemical controls using the active ingredients thiamethoxam or azadirachtin.

Insecticide Rotation Programs with Entomopathogenic Organisms for Suppression of Western Flower Thrips (Thysanoptera: Thripidae) Adult Populations under Greenhouse Conditions

Western flower thrips, Frankliniella occidentalis (Pergande), is one of the most destructive insect pests of greenhouse production systems with the ability to develop resistance to a wide variety of insecticides. A common resistance management strategy is rotating insecticides with different modes of action. By incorporating entomopathogenic organisms (fungi and bacteria), which have discrete modes of action compared to standard insecticides, greenhouse producers may preserve the effectiveness of insecticides used for suppression of western flower thrips populations. The objective of this study was to determine how different rotation programs that include entomopathogenic organisms (Beauveria bassiana, Isaria fumosoroseus, Metarhizium anisopliae, and Chromobacterium subtsugae) and commonly used standard insecticides (spinosad, chlorfenapyr, abamectin, and pyridalyl) may impact the population dynamics of western flower thrips adult populations by means of suppression. Eight-week rotation programs were applied to chrysanthemum, Dendranthema x morifolium plants and weekly counts of western flower thrips adults captured on yellow sticky cards were recorded as a means to evaluate the impact of the rotation programs. A final quality assessment of damage caused by western flower thrips feeding on foliage and flowers was also recorded. Furthermore, a cost comparison of each rotation program was conducted. Overall, insecticide rotation programs that incorporated entomopathogenic organisms were not significantly different than the standard insecticide rotation programs without entomopathogenic organisms in suppressing western flower thrips adult populations. However, there were no significant differences among any of the rotation programs compared to the water control. Moreover, there was no differential effect of the rotation programs on foliage and flower quality. Cost savings of up to 34% (in US dollars) are possible when including entomopathogenic organisms in the rotation program. Therefore, by incorporating entomopathogenic organisms into insecticide rotation programs, greenhouse producers can decrease costs without affecting suppression, as well as diminish selection pressure on western flower thrips adult populations, which may avoid or delay resistance development.