Laboratory and field evaluation of entomopathogenic fungi for the control of amitraz-resistant and susceptible strains of Rhipicephalus decoloratus

Efficacy of Metarhizium anisopliae, Isolate ICIPE 7, against Anopheles arabiensis, Glossina fuscipes, and Rhipicephalus spp

Arthropod vectors are responsible for a multitude of human and animal diseases affecting poor communities in sub-Saharan Africa. Their control still relies on chemical agents, despite growing evidence of insecticide resistance and environmental health concerns. Biorational agents, such as the entomopathogenic fungus Metarhizium anisopliae, might be an alternative for vector control. Recently, the M. anisopliae isolate ICIPE 7 has been developed into a commercial product in Kenya for control of ticks on cattle. We were interested in assessing the potential of controlling not only ticks but also disease-transmitting mosquitoes and tsetse flies using cattle as blood hosts, with the aim of developing a product for integrated vector management. Laboratory bioassays were carried out with M. anisopliae, isolate ICIPE 7 and isolate ICIPE 30, to compare efficacy against laboratory-reared Anopheles arabiensis. ICIPE 7 was further tested against wild Glossina fuscipes and Rhipicephalus spp. Dose-response tests were implemented, period of mosquito exposure was evaluated for effects on time to death, and the number of spores attached to exposed vectors was assessed. Exposure to 109 spores/mL of ICIPE 7 for 10 min resulted in a similar mortality of An. arabiensis as exposure to ICIPE 30, albeit at a slower rate (12 vs. 8 days). The same ICIPE 7 concentration also resulted in mortalities of tsetse flies (LT50: 16 days), tick nymphs (LT50: 11 days), and adult ticks (LT50: 20 days). Mosquito mortality was dose-dependent, with decreasing LT50 of 8 days at a concentration of 106 spores/mL to 6 days at 1010 spores/mL. Exposure period did not modulate the outcome, 1 min of exposure still resulted in mortality, and spore attachment to vectors was dose-dependent. The laboratory bioassays confirmed that ICIPE 7 has the potential to infect and cause mortality to the three exposed arthropods, though at slower rate, thus requiring further validation under field conditions.

A comparison between the effectiveness of the fungi Beauveria bassiana and Metarhizium anisopliae for the control of Argas persicus with the emphasis of histopathological changes in the integument

Argas persicus is an important ectoparasite of domestic fowl that causes heavy economic losses to the poultry industry. The present study was carried out to compare and assess the effects induced by spraying the fungi Beauveria bassiana and Metarhizium anisopliae separately, on the mobility and viability of semifed adult A. persicus, also to follow the histopathological effect induced by a selected concentration of 10¹⁰ conidia/ml of B. bassiana on the integument. Biological studies revealed a more or less similar pattern of response in adults treated with either of the two fungi (Increasing concentration resulting in more death along with examined period). As the estimated LC50 and LC95 of B. bassiana were recorded 5 × 10⁹ and 4.6 × 10¹² conidia/ml, respectively, and for M. anisopliae were 3 × 10¹¹ and 2.7 × 10¹⁶ conidia/ml respectively, the fungus B. bassiana was more efficient than M. anisopliae when applied at the same concentrations. The study revealed that spraying of Beauveria at 10¹² conidia/ml is sufficient to control A. persicus as it recorded 100% efficacy, so it might be selected to be the effective dose. Histological investigation of the integument treated with B. bassiana revealed the dispersal of the hyphal network on the after 11 days of treatment, accompanied by other changes. Results from our study verify the susceptibility of A. persicus to the pathogenic effect induced by spraying B. bassiana, which is sufficient for its control with the recording better results.

Evaluating the efficacy of Mazao Tickoff (Metarhizium anisopliae ICIPE 7) in controlling natural tick infestations on cattle in coastal Kenya: Study protocol for a randomized controlled trial

Ticks and tick-borne diseases cause substantial economic losses to the livestock industry in sub-Saharan Africa. Mazao Tickoff is a novel bioacaricide developed for tick control and is based on the entomopathogenic fungus Metarhizium anisopliae sensu lato (s.l.) isolate ICIPE 7. To date, no randomized controlled study has been undertaken to demonstrate the efficacy of this bioacaricide in reducing natural tick infestation on cattle. To this end, this field trial is designed to evaluate the anti-tick efficacy of Mazao Tickoff on cattle in coastal Kenya compared to a standard chemical tick control protocol. In this prospective, multi-center randomized controlled trial, eligible herds will be randomized by the herd size to the intervention arm in a 1:1:1 ratio to either Triatix® (active ingredient: amitraz); Mazao Tickoff (active ingredient: M. anisopliae ICIPE 7); or placebo (excipients of the Mazao Tickoff), with a total enrollment target of 1,077 cattle. Treatments will be dispensed on Day 0 (defined individually as the day each animal receives the first treatment) and thereafter every two weeks until Day 182. Ticks will be counted on every animal in each herd (herds to be included have at least one animal bearing at least one tick on Day 0), and thereafter on bi-weekly intervals until Day 182. The primary efficacy assessments of Mazao Tickoff will be based on the mean percentage reduction in tick counts at each post-treatment follow-up visit compared to the placebo group and the Triatix® arm. Further, the effect of Mazao Tickoff on the prevalence of common cattle pathogens, Anaplasma marginale and Theileria parva, will be determined by assessing incidence and seroprevalence at four different time points. This protocol describes the first rigorous evaluation of the efficacy of Mazao Tickoff and its potential as a viable alternative non-chemical acaricide tool for tick control in Kenya and elsewhere.

Identification and Pathogenicity of a New Entomopathogenic Fungus, Mucor hiemalis (Mucorales: Mucorales), on the Root Maggot, Bradysia odoriphaga (Diptera: Sciaridae)

Bradysia odoriphaga Yang and Zhang (Diptera: Sciaridae), the Chinese chive root maggot, is a destructive pest of Allium vegetables and flowers that causes severe losses in northern China. Novel biological control technologies are needed for controlling this pest. We identified a new entomopathogenic fungus isolated from infected B. odoriphaga larvae and evaluated the susceptibility of the biological stages of B. odoriphaga and the effects of temperature on fungus growth and pathogenicity. Based on morphological characteristics and molecular phylogeny, the fungus was identified as Mucor hiemalis BO-1 (Mucorales: Mucorales). This fungus had the strongest virulence to B. odoriphaga larvae followed by eggs and pupae, while B. odoriphaga adults were not susceptible. A temperature range of 18-28°C was optimum for the growth and sporulation of M. hiemalis BO-1 and virulence to B. odoriphaga larvae. At 3 and 5 d after inoculation with 105 spores/ml at 23°C, the survival rates were 24.8% and 4.8% (2nd instar larvae), respectively, and 49.6% and 12.8% (4th instar larvae), respectively. The potted plant trials confirmed that M. hiemalis BO-1 exerted excellent control efficiency against B. odoriphaga larvae, and the control exceeded 80% within 5 d when the spore concentration applied exceeded 107 spores/ml. In conclusion, these findings supported the hypotheses that this fungus could serve as an effective control agent against B. odoriphaga larvae and is worth being further tested to determine its full potential as a biocontrol agent.

Acaricidal and pathogenic effects of the entomopathogenic fungus Beauveria bassiana on engorged females of the fowl tick, Argas persicus (Argasidae)

This study examined the acaricidal, histopathological and genotoxic effects of the entomopathogenic fungus Beauveria bassiana on engorged females of the fowl tick, Argas persicus. The acaricidal effect of B. bassiana (at 10⁶-10¹⁰ conidia/mL) was concentration- and time-dependent. At 10⁶ conidia/mL, the accumulated mortality of treated females ranged from 3.33 ± 3.3 to 13.33 ± 3.3% over 21 days. However, the mortality was remarkably increased after the application of 10¹⁰ conidia/mL, ranging from 6.67 ± 3.3 to 80 ± 5.8%. Females treated with various conidial concentrations exhibited complete inhibition of oviposition. Light and electron microscopic examination of the ovary of engorged female ticks at 3, 6 and 9 days after treatment with 10⁷ conidia/mL revealed that the oocytes exhibited drastic changes that affected their growth and development. The overall damage observed in the ovary included loss of grape-like appearance, distortion of oocytes, cytoplasmic vacuolation, degeneration of organelles and myelin figure formation. Previtellogenic oocyte progression was completely inhibited as the vitellogenic phase was not observed. Random amplified polymorphic DNA (RAPD-PCR) and inter simple sequence repeat (ISSR) methods were used to assess the genotoxic effects of B. bassiana at 10⁷ conidia/mL on engorged female A. persicus over 3 weeks. The lowest percentage of genomic template stability was recorded in paralyzed ticks after 3 weeks. The study demonstrated the efficacy of B. bassiana as a biocontrol agent against A. persicus as it interfered with its reproduction, movement and viability and disrupted its normal tissue and DNA integrity.

Entomopathogenic Fungi and Bacteria in a Veterinary Perspective

Simple Summary

Several fungal species are well suited to control arthropods, being able to cause epizootic infection among them and most of them infect their host by direct penetration through the arthropod’s tegument. Most of organisms are related to the biological control of crop pests, but, more recently, have been applied to combat some livestock ectoparasites. Among the entomopathogenic bacteria, Bacillus thuringiensis, innocuous for humans, animals, and plants and isolated from different environments, showed the most relevant activity against arthropods. Its entomopathogenic property is related to the production of highly biodegradable proteins. Entomopathogenic fungi and bacteria are usually employed against agricultural pests, and some studies have focused on their use to control animal arthropods. However, risks of infections in animals and humans are possible; thus, further studies about their activity are necessary.

Abstract

The present study aimed to review the papers dealing with the biological activity of fungi and bacteria against some mites and ticks of veterinary interest. In particular, the attention was turned to the research regarding acarid species, Dermanyssus gallinae and Psoroptes sp., which are the cause of severe threat in farm animals and, regarding ticks, also pets. Their impact on animal and human health has been stressed, examining the weaknesses and strengths of conventional treatments. Bacillus thuringiensis, Beauveria bassiana and Metarhizium anisopliae are the most widely employed agents. Their activities have been reviewed, considering the feasibility of an in-field application and the effectiveness of the administration alone or combined with conventional and alternative drugs is reported.

Combining insect pathogenic fungi and a pheromone trap for sustainable management of the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is a key invasive pest of maize and other crops in Africa. Entomopathogenic fungi play an important role in regulating the immature stages of this invasive pest as opposed to synthetic pesticides that are hazardous to human, environment and biodiversity. To tackle the adult stage of the pest (the moth) and to improve on the application strategy of the fungal-based biopesticides, this study evaluated the effect of various entomopathogenic fungi isolates on S. frugiperda moths. Twenty-two isolates (16 Metarhizium anisopliae and 6 Beauveria bassiana) were screened in the laboratory to assess their pathogenicity and virulence against S. frugiperda moths. The compatibility of the most pathogenic isolates with S. frugiperda pheromone FALLTRACT lure, the horizontal transmission of the inoculum among S. frugiperda moths, and the effect on oviposition were also determined under laboratory conditions. All 22 fungal isolates screened were pathogenic to the moths, but the mortality varied significantly among the isolates (P < 0.0001) seven days post-treatment. Beauveria bassiana ICIPE 621 and M. anisopliae ICIPE 7 outperformed all the other isolates by causing 100% mortality of the moths with the lowest LT₅₀ values of 3.6 ± 0.1 and 3.9 ± 0.0 days, respectively. Both isolates were also found compatible with FALLTRACT lure, as the lure had no effect on the conidial germination in the laboratory. Male and female moths were able to horizontally transmit conidia of both fungal isolates to untreated moths, causing high mortality of S. frugiperda in 'donor' and 'recipient' groups. In addition, the oviposition, hatchability of eggs and longevity of larvae were significantly affected on the fungal infected females. Although single moths still retained high conidial numbers 72 h post-inoculation, the number of conidia decreased with time. These results suggest that ICIPE 7 and ICIPE 621 could be used in combination with S. frugiperda pheromone in an autodissemination approach to suppress S. frugiperda population.

Metarhizium anisopliae and Beauveria bassiana: Pathogenicity, Horizontal Transmission, and Their Effects on Reproductive Potential of Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

The polyphagous moth, Thaumatotibia leucotreta (Meyrick) is among the major constraints to the horticultural industry in East Africa. In a search of sustainable control methods, the pathogenicity of the dry conidia of 17 Metarhizium anisopliae (Metschn.) and five Beauveria bassiana (Bals.) (Vuill.) isolates were tested against T. leucotreta moths. The conidial uptake by a single moth, horizontal transmission, and effect of fungal inoculant on egg-laying and hatchability for the pest were also assessed. The findings from this study showed that tested fungi were virulent to the moths, with 12 isolates causing mortality that ranged between 58.8 and 94.2% for M. anisopliae and three isolates between 57.6 and 84.6% for B. bassiana. The entomopathogenic fungi isolates, M. anisopliae ICIPE 69 and B. bassiana ICIPE 279 were highly virulent with low lethal times to 50% mortality (LT50) of 3.81 and 5.13 d, respectively. The isolate, ICIPE 69 conidia acquisition by a single moth were approximately 4.58 × 106 and 3.51 × 106 for males and females, respectively. The lowest survival rate (3.33 %) caused by inoculum transmission was recorded in donor males compared to 16.67% in recipient males. Fecundity was reduced by 33.6 and 25.9% for donor and recipient females, respectively. The pest can acquire conidia from the treated substrate and transmission is then possible between adults. ICIPE 69 is virulent and reduces the reproduction potential of the pest after transmission. The findings are discussed in the prospects of microbial control of this pest using an autodissemination technique.

Use of Metarhizum aniopliae s.l. to control soil-dwelling longhorned tick, Haemaphysalis longicornis

The longhorned tick (bush tick),Haemaphysalis longicornis (Ixodida: Ixodidae), is a serious pest; it transmits the severe fever with thrombocytopenia syndrome (SFTS) virus to humans and has a wide distribution. The use of chemical control is not favored for environmental and health reasons, so more environmentally sound management methods need to be developed. Herein, we describe the use of an entomopathogenic fungal library to develop a fungus-mediated tick management system. Field-collected nymphs were assayed for their susceptibility to entomopathogenic fungi belonging to genera Beauveria, Metarhizium, Cordyceps, and Akanthomyces. Three M. anisopliae s.l. isolates, JEF-214, -279, and -290 showed high virulence in a dose-dependent manner. One Cordyceps isolate was pathogenic but virulence was much lower than the M. anisopliae isolates. Beauveria isolates were not pathogenic to the tick. Because the longhorned tick dwells on the soil surface except for blood-feeding periods, the soil surface was sprayed with conidial suspensions of the isolates after the release of longhorned ticks. The treatments resulted in 60-90% mortality after 30 days. M. anisopliae s.l. isolates were highly virulent against longhorned tick, and the application of fungus-based biopesticides on the soil surface could be an effective control strategy to reduce the tick population for long-term tick management.

Mosquitoes of Etiological Concern in Kenya and Possible Control Strategies

Kenya is among the most affected tropical countries with pathogen transmitting Culicidae vectors. For decades, insect vectors have contributed to the emergence and distribution of viral and parasitic pathogens. Outbreaks and diseases have a great impact on a country's economy, as resources that would otherwise be used for developmental projects are redirected to curb hospitalization cases and manage outbreaks. Infected invasive mosquito species have been shown to increasingly cross both local and global boarders due to the presence of increased environmental changes, trade, and tourism. In Kenya, there have been several mosquito-borne disease outbreaks such as the recent outbreaks along the coast of Kenya, involving chikungunya and dengue. This certainly calls for the implementation of strategies aimed at strengthening integrated vector management programs. In this review, we look at mosquitoes of public health concern in Kenya, while highlighting the pathogens they have been linked with over the years and across various regions. In addition, the major strategies that have previously been used in mosquito control and what more could be done to reduce or combat the menace caused by these hematophagous vectors are presented.