Control of Pyrethroid-Resistant Chagas Disease Vectors with Entomopathogenic Fungi

Chagas disease, also known as American Trypanosomiasis, is the most relevant parasitic disease in Latin America, being a major burden that affects mostly poor human populations living in rural areas. The kissing-bugs of the Triatominae family transmit the parasite Trypanosoma cruzi by infectious blood-sucking; Triatoma infestans is the vector of major relevance in the southern Cone of South America. Current control strategies, heavily based on residual insecticide spraying, are threatened by the emergence of pyrethroid-resistant bug populations. Furthermore, ensuring the long-term and sustainable control of this overwhelming disease remains a major challenge. Here we show the utility of a simple, low-cost, biological control methodology against T. infestans bugs, regardless of their susceptibility to pyrethroid insecticides. It is based on the understanding of the initial contact interactions between a mycoinsecticide agent—the fungus Beauveria bassiana—and the host defense barrier, the bug cuticle. The proposed methodology is also supported by present data showing a relationship between the triatomine cuticle width and its hydrocarbon surface components, with insecticide resistance. These results will help to provide a safe and efficient alternative to overcome pyrethroid-resilience of these noxious bugs. A high transfer potential to immediate application in rural communities located in remote areas inaccessible to sanitary control teams, and to the control of other Chagas disease vectors as well, is also envisaged

Infection of the malaria mosquito, Anopheles gambiae, with two species of entomopathogenic fungi: effects of concentration, co-formulation, exposure time and persistence

<p>Abstract</p> <p>Background</p> <p>Entomopathogenic fungi <it>Metarhizium anisopliae </it>and <it>Beauveria bassiana </it>isolates have been shown to infect and reduce the survival of mosquito vectors.</p> <p>Methods</p> <p>Here four different bioassays were conducted to study the effect of conidia concentration, co-formulation, exposure time and persistence of the isolates <it>M. anisopliae </it>ICIPE-30 and <it>B. bassiana </it>I93-925 on infection and survival rates of female <it>Anopheles gambiae sensu stricto</it>. Test concentrations and exposure times ranged between 1 × 10⁷- 4 × 10¹⁰conidia m^-2and 15 min - 6 h. In co-formulations, 2 × 10¹⁰conidia m^-2of both fungus isolates were mixed at ratios of 4:1, 2:1, 1:1,1:0, 0:1, 1:2 and 1:4. To determine persistence, mosquitoes were exposed to surfaces treated 1, 14 or 28 d previously, with conidia concentrations of 2 × 10⁹, 2 × 10¹⁰or 4 × 10¹⁰.</p> <p>Results</p> <p>Mosquito survival varied with conidia concentration; 2 × 10¹⁰conidia m^-2was the concentration above which no further reductions in survival were detectable for both isolates of fungus. The survival of mosquitoes exposed to single and co-formulated treatments was similar and no synergistic or additive effects were observed. Mosquitoes were infected within 30 min and longer exposure times did not result in a more rapid killing effect. Fifteen min exposure still achieved considerable mortality rates (100% mortality by 14 d) of mosquitoes, but at lower speed than with 30 min exposure (100% mortality by 9 d). Conidia remained infective up to 28 d post-application but higher concentrations did not increase persistence.</p> <p>Conclusion</p> <p>Both fungus isolates are effective and persistent at low concentrations and short exposure times.</p

Infection of Anopheles gambiae mosquitoes with entomopathogenic fungi: effect of host age and blood-feeding status

Physiological characteristics of insects can influence their susceptibility to fungal infection of which age and nutritional status are among the most important. An understanding of host–pathogen interaction with respect to these physiological characteristics of the host is essential if we are to develop fungal formulations capable of reducing malaria transmission under field conditions. Here, two independent bioassays were conducted to study the effect of age and blood-feeding status on fungal infection and survival of Anopheles gambiae s.s. Giles. Mosquitoes were exposed to 2 × 1010 conidia m−2 of oil-formulated Metarhizium anisopliae ICIPE-30 and of Beauveria bassiana I93-825, respectively, and their survival was monitored daily. Three age groups of mosquitoes were exposed, 2–4, 5–8, and 9–12 days since emergence. Five groups of different feeding status were exposed: non-blood-fed, 3, 12, 36, and 72 h post-blood feeding. Fungal infection reduced the survival of mosquitoes regardless of their age and blood-feeding status. Although older mosquitoes died relatively earlier than younger ones, age did not tend to affect mosquito susceptibility to fungal infection. Non-blood-fed mosquitoes were more susceptible to fungus infection compared to all categories of blood-fed mosquitoes, except for those exposed to B. bassiana 72 h post-blood feeding. In conclusion, formulations of M. anisopliae and B. bassiana can equally affect mosquitoes of different age classes, with them being relatively more susceptible to fungus infection when non-blood-fed

Natural infection by the protozoan Leptomonas wallacei impacts the morphology, physiology, reproduction, and lifespan of the insect Oncopeltus fasciatus

Trypanosomatids are protozoan parasites that infect thousands of globally dispersed hosts, potentially affecting their physiology. Several species of trypanosomatids are commonly found in phytophagous insects. Leptomonas wallacei is a gut-restricted insect trypanosomatid only retrieved from Oncopeltus fasciatus. The insects get infected by coprophagy and transovum transmission of L. wallacei cysts. The main goal of the present study was to investigate the effects of a natural infection by L. wallacei on the hemipteran insect O. fasciatus, by comparing infected and uninfected individuals in a controlled environment. The L. wallacei-infected individuals showed reduced lifespan and morphological alterations. Also, we demonstrated a higher infection burden in females than in males. The infection caused by L. wallacei reduced host reproductive fitness by negatively impacting egg load, oviposition, and eclosion, and promoting an increase in egg reabsorption. Moreover, we associated the egg reabsorption observed in infected females, with a decrease in the intersex gene expression. Finally, we suggest alterations in population dynamics induced by L. wallacei infection using a mathematical model. Collectively, our findings demonstrated that L. wallacei infection negatively affected the physiology of O. fasciatus, which suggests that L. wallacei potentially has a vast ecological impact on host population growth

Can fungal biopesticides control malaria?

Recent research has raised the prospect of using insect fungal pathogens for the control of vector-borne diseases such as malaria. In the past, microbial control of insect pests in both medical and agricultural sectors has generally had limited success. We propose that it may now be possible to produce a cheap, safe and green tool for the control of malaria which, in contrast to most chemical insecticides, will not eventually be rendered useless by resistance evolution. Realising this potential will require lateral thinking by biologists, technologists and development agencie

Influence de la température sur la croissance in vitro d'hyphomycètes entomopathogènes

L'influence de la température sur la croissance in vitro des principales espèces d'hyphomycètes entomopathogènes a été étudiée avec 31 isolats fongiques : 3 souches de Beauveria bassiana (Balsamo) Vuillemin, 3 souches de B brongniartii (= tenella) (Saccardo) Petch, 8 souches de Metarhizium anisopliae (Metschnikoff) Sorokin, 1 souche de M flavoviride Gams et Rozsypal, 6 souches de Nomuraea rileyi (Farlow) Samson et 10 souches de Paecilomyces fumosoroseus (Wize) Brown et Smith. L'analyse des vitesses de croissance radiale à 10 niveaux de température compris entre 8 et 37 °C montre une variabilité à la fois inter- et intraspécifique, liée à l'origine géoclimatique des isolats fongiques. Les champignons provenant de zones subtropicales humides sont relativement thermophiles avec des gammes d'activité significative de 11 ° et 32 °C (isolats de N rileyi) ou 35 °C (isolats de M anisopliae). Inversement, les souches originaires de zones tempérées et surtout du sol de ces régions (isolats issus d'insectes vivants dans le sol ou d'échantillons de sol) présentent une croissance non négligeable aux basses températures (8 °C pour les isolats de B bassiana et ceux de B brongniartii). Néanmoins, l'optimum thermique de croissance de la plupart des isolats (26 sur 31) se situe à 25 °C. Enfin, si certains isolats ont une gamme thermique d'activité végétative relativement étroite (chez B brongniartii et P fumosoroseus) d'autres sont très thermotolérants (la plupart des isolats de M anisopliae). La tolérance thermique des champignons entomopathogènes apparaît donc comme un critère de sélection des isolats fongiques candidats à la lutte microbiologique mieux adaptés au biotope de l'insecte-hôte visé.Influence of temperature on in vitro growth of entomopathogenic hyphomycetes. Thirty-one isolates of 6 entomopathogenic hyphomycetes, Beauveria bassiana (Balsamo) Vuillemin, B brongniartii (= tenella) (Saccardo) Petch, Metarhizium anisopliae (Metschnikoff) Sorokin, M flavoviride Gams et Rozsypal, Nomuraea rileyi (Farlow) Samsom and Paecilomyces fumosoroseus (Wize) Brown et Smith, were grown in vitro to determine growth rates and ranges of growth at 10 temperatures from 8 to 37 °C in the dark. Radial growth of surface colonies on semisynthetic nutrient agar was recorded by daily measurement of 2 cardinal diameters. Because radial measurements (from day 3 to 12) of surface colonies for each temperature fit a linear model (y = vt+b), growth rates (v in mm x day-1) were used as the main growth parameter to evaluate the influence of temperature. The fungal isolates under study exhibited a wide diversity of responses to temperature according to their provenance. Isolates originating from tropical areas showed a remarkable growth at 35 °C (eg, M anisopliae isolates). By contrast, isolates originating from soil-inhabiting insects of temperate areas (eg B brongniartii isolates) exhibited high growth rates at 8 °C. However, the optimal growth was found at 25 °C for 26 isolates. Upper temperature limits of growth varied from 28-37 °C according to both fungal species and isolates. M anisopliae isolates exhibited an almost ideal combination of high growth rates and in particular a wide temperature range (8-11° to 35-37 °C); only one B bassiana isolate showed similar responses to temperature stimuli. Although the optimal temperature for fungal growth is not necessarily the same as that for fungal infection in insects, temperature ranges established according to in vitro growth data might be used for selecting fungal candidates for microbial control

Compatibility of Metarhizium anisopliae with Calpurnia aurea leaf extracts and virulence against Rhipicephalus pulchellus

Leaf extracts of Capurnia aurea (Fabaceae) have been reported to attract ticks and can be considered for use in combination with entomopathogenic fungus in an autodissemination approach, whereby ticks that are attracted to baited traps are infected with the inoculum. Bioassays were undertaken to assess the compatibility of aqueous, methanol and acetone extracts of C. aurea with conidia of Metarhizium anisopliae sensu stricto (ss) (Hypocreales: Clavicipitaceae) isolate ICIPE 7 in terms of mycelial growth, conidial production and spore viability. Aqueous extract of C. aurea was compatible with the fungus at all the concentrations tested whereas methanol and acetone extracts inhibited all the fungal growth parameters. The virulence of M. anisopliae formulated in different extracts of C. aurea was also tested against different developmental stages of Rhipicephalus pulchellus in laboratory bioassays. No significant differences in virulence were observed between M. anisopliae applied alone and M. anisopliae formulated in different concentrations of extracts of C. aurea among the larvae, nymphs and adults. However, mortality varied according to the developmental stage, with larval stage being the most susceptible. Aqueous extract was compatible with M. anisopliae and could be therefore mixed together for ‘spot-spray’ treatments as low cost and environmentally friendly technology for tick control in grazing pasture