The entomopathogenic fungus Beauveria bassiana reduces instantaneous blood feeding in wild multi-insecticide-resistant Culex quinquefasciatus mosquitoes in Benin, West Africa

Evaluation of In2Care mosquito stations for suppression of the Australian backyard mosquito, Aedes notoscriptus (Diptera: Culicidae)

Aedes notoscriptus (Skuse) is a container-inhabiting mosquito endemic to Australia that vectors arboviruses and is suspected to transmit Mycobacterium ulcerans, the cause of Buruli ulcer. We evaluated the effectiveness of the In2Care station, which suppresses mosquito populations via the entomopathogenic fungus, Beauveria bassiana, and the insect growth regulator pyriproxyfen, the latter of which is autodisseminated among larval habitats by contaminated mosquitoes. A field trial was conducted using 110 In2Care stations in a 50,000 m2 area and results were compared to 4 control areas that did not receive the treatment. Efficacy was evaluated by comparing egg counts and measuring larvicidal impact in surrounding breeding sites. Laboratory experiments validated the effect of B. bassiana on adult survival. Results of this field trial indicate that, 6 wk after the In2Care stations were deployed, treatment site ovitraps contained 43% fewer eggs than control site ovitraps, and 33% fewer eggs after 10 wk, suggesting that the In2Care station was able to reduce the egg density of Ae. notoscriptus. Population reduction remained evident for up to 3 wk after In2Care stations were removed. Treatment site ovitraps had significantly fewer Ae. notoscriptus eclosing than control site ovitraps, confirming the pyriproxyfen autodissemination feature of the stations. An average reduction of 50% in adult eclosion was achieved. Exposure to B. bassiana resulted in four-times higher mortality among adult mosquitoes. Additionally, using fresh In2Care nettings led to an 88% decrease in average survival compared to 4-wk-old nettings. The use of In2Care stations has potential for suppressing Ae. notoscriptus egg density.

Biotechnological Potential of Microorganisms for Mosquito Population Control and Reduction in Vector Competence

Mosquitoes transmit pathogens that cause human diseases such as malaria, dengue fever, chikungunya, yellow fever, Zika fever, and filariasis. Biotechnological approaches using microorganisms have a significant potential to control mosquito populations and reduce their vector competence, making them alternatives to synthetic insecticides. Ongoing research has identified many microorganisms that can be used effectively to control mosquito populations and disease transmission. However, the successful implementation of these newly proposed approaches requires a thorough understanding of the multipronged microorganism-mosquito-pathogen-environment interactions. Although much has been achieved in discovering new entomopathogenic microorganisms, antipathogen compounds, and their mechanisms of action, only a few have been turned into viable products for mosquito control. There is a discrepancy between the number of microorganisms with the potential for the development of new insecticides and/or antipathogen products and the actual available products, highlighting the need for investments in the intersection of basic research and biotechnology.

Chromobacterium Biopesticide Exposure Does Not Select for Resistance in Aedes Mosquitoes

Developing effective tools to control mosquito populations is essential for reducing the incidence of diseases like malaria and dengue. Biopesticides of microbial origin are a rich, underexplored source of mosquitocidal compounds. We previously developed a biopesticide from the bacterium Chromobacterium sp. Panama that rapidly kills vector mosquito larvae, including Aedes aegypti and Anopheles gambiae. Here, we demonstrate that two independent Ae. aegypti colonies exposed to a sublethal dose of that biopesticide over consecutive generations persistently exhibited high mortality and developmental delays, indicating that resistance did not develop during the study period. Critically, the descendants of biopesticide-exposed mosquitoes experienced decreased longevity and did not display increased susceptibility to dengue virus or decreased susceptibility to common chemical insecticides. Through RNA sequencing, we observed no link between biopesticide exposure and the increased activity of xenobiotic metabolism and detoxification genes typically associated with insecticide resistance. These findings indicate that the Chromobacterium biopesticide is an exciting, emerging mosquito control tool. IMPORTANCE Vector control is an essential part of mitigating diseases caused by pathogens that mosquitoes spread. Modern vector control is highly reliant on using synthetic insecticides to eliminate mosquito populations before they can cause disease. However, many of these populations have become resistant to commonly used insecticides. There is a strong need to explore alternative vector control strategies that aim to mitigate disease burden. Biopesticides, insecticides of biological origin, can have unique mosquitocidal activities, meaning they can effectively kill mosquitoes that are already resistant to other insecticides. We previously developed a highly effective mosquito biopesticide from the bacterium Chromobacterium sp. Csp_P. Here, we investigate whether exposure to a sublethal dose of this Csp_P biopesticide over 9 to 10 generations causes resistance to arise in Aedes aegypti mosquitoes. We find no evidence of resistance at the physiological or molecular levels, confirming that the Csp_P biopesticide is a highly promising new tool for controlling mosquito populations.

Entomopathogenic Fungi as a Potential Management Tool for the Control of Urban Malaria Vector, Anopheles stephensi (Diptera: Culicidae)

Anopheles stephensi (Diptera: Culicidae) is the vector of urban malaria in India and has a significant impact in transmitting infection in cities and towns. Further, WHO has also alarmed its invasive nature as a threat to African countries. Entomopathogenic fungi such as Beauveria bassiana and Metarhizium anisopliae have been found to be highly effective in controlling vector mosquito populations and therefore could be used in integrated vector control programs. Before employing the entomopathogenic fungi into the control programs, an effective isolate must be selected. Two separate experiments were conducted to evaluate the efficacy of Beauveria bassiana (Bb5a and Bb-NBAIR) and Metarhizium anisopliae (Ma4 and Ma-NBAIR) isolates against An. stephensi. Cement and mud panels were treated with fungal conidia with the concentration of 1 × 10⁷ conidia/mL and adult An. stephensi mosquitoes were exposed to the treated panels (24 h after conidia were applied) by conducting WHO cone bioassay tests. The survival of the mosquitoes was monitored daily until the 10th day. In the second experiment, second instar larvae of An. stephensi were treated with fungal (Bb5a, Bb-NBAIR, Ma4 and Ma-NBAIR) conidia and blastospores with the spore concentration of 1 × 10⁷ spores/mL. The survival of larvae was monitored until pupation. All the fungal isolates tested caused mortality in the adult mosquitoes, with varying median survival times. The Bb5a isolate reported lesser median survival times on both cement and mud panels (6 days). The treated mosquitoes showed similar survival rates for each fungal isolate irrespective of the panel type. There was no mortality in the treated larvae; however, a delay in larval development to pupae was observed compared with the untreated control larvae. Ma4-treated larvae took 11 days (95% CI = 10.7-11.2) to become pupae when compared with the untreated control larvae (6 days [95% CI = 5.6-6.3]). The findings of this study will be useful to consider EPF as a tool for the management of vector mosquitoes.

Larval Mortality and Ovipositional Preference in Aedes albopictus (Diptera: Culicidae) Induced by the Entomopathogenic Fungus Beauveria bassiana (Hypocreales: Cordycipitaceae)

Entomopathogenic fungi allow chemical-free and environmentally safe vector management. Beauveria bassiana (Balsamo-Crivelli) Vuillemin is a promising biological control agent and an important component of integrated vector management. We investigated the mortality of Aedes albopictus (Skuse) larvae exposed to five concentrations of B. bassiana using Mycotrol ESO and adult oviposition behavior to analyze the egg-laying preferences of wild Ae. albopictus in response to different fungal concentrations. We examined the mortality of mid-instars exposed to B. bassiana concentrations of 1 × 104, 1 × 105, 1 × 106, 1 × 107, and 1 × 108 conidia/ml every 24 h for 12 d. In the oviposition behavior study, the fungus was applied to wooden paddles at 1 × 105, 1 × 107, and 1 × 109 conidia/ml, and the paddles were individually placed into quad-ovitraps. Both experiments contained control groups without B. bassiana. Kaplan-Meier survival analysis revealed that larval mortality was concentration dependent. The median lethal concentration was 2.43 × 105 conidia/ml on d 12. The median lethal time was 3.68 d at 1 × 106 conidia/ml. Oviposition monitoring revealed no significant difference in egg count between the control and treatment paddles. We observed an inverse relationship between the concentration of B. bassiana and the percentage of paddles with eggs. We concluded that concentrations above 1 × 106 conidia/ml are larvicidal, and Ae. albopictus laid similar numbers of eggs on fungus-impregnated and control wooden substrates; however, they were more likely to oviposit on substrates without B. bassiana. With these findings, we suggest that B. bassiana-infused ovitraps can be used for mosquito population monitoring while also delivering mycopesticides to adult mosquitoes.

A Field Efficacy Evaluation of In2Care Mosquito Traps in Comparison with Routine Integrated Vector Management at Reducing Aedes aegypti

Aedes aegypti is the predominant vector of dengue, chikungunya, and Zika viruses. This mosquito is difficult to control with conventional methods due to its container-inhabiting behavior and resistance to insecticides. Autodissemination of pyriproxyfen (PPF), a potent larvicide, has shown promise as an additional tool to control Aedes species in small-scale field trials. However, few large-scale field evaluations have been conducted. We undertook a 6-month-long large-scale field study to compare the effectiveness and operational feasibility of using In2Care Mosquito Traps (In2Care Traps, commercially available Aedes traps with PPF and Beauveria bassiana) compared to an integrated vector management (IVM) strategy consisting of source reduction, larviciding, and adulticiding for controlling Ae. aegypti eggs, larvae, and adults. We found that while the difference between treatments was only statistically significant for eggs and larvae (P < 0.05 for eggs and larvae and P > 0.05 for adults), the use of In2Care Traps alone resulted in 60%, 57%, and 57% fewer eggs, larvae, and adults, respectively, collected from that site compared to the IVM site. However, In2Care Trap deployment and maintenance were more time consuming and labor intensive than the IVM strategy. Thus, using In2Care Traps alone as a control method for large areas (e.g., >20 ha) may be less practical for control programs with the capacity to conduct ground and aerial larviciding and adulticiding. Based on our study results, we conclude that In2Care Traps are effective at suppressing Ae. aegypti and have the most potential for use in areas without sophisticated control programs and within IVM programs to target hotspots with high population levels and/or risk of Aedes-borne pathogen transmission.

Metarhizium Anisopliae Challenges Immunity and Demography of Plutella xylostella

Simple Summary

The diamondback moth, Plutella xylostella, is a destructive pest of cruciferous crops worldwide. Integrated pest management (IPM) strategies, largely involve the use chemical pesticides which are harmful for the environment and human health. In this study, the virulence of three species of entomopathogenic fungi were tested. Metarhizium anisopliae proved to be the most effective by killing more than 90% of the population. Based on which the fungus was selected to study the host-pathogen immune interactions. More precisely, after infection, superoxide dismutase (SOD) and phenoloxidase (PO), two major enzymes involved in immune response, were studied at different time points. The fungus gradually weakened the enzyme activities as the time progressed, indicating that physiological attributes of host were adversely affected. The expression of immune-related genes (Defensin, Spaetzle, Cecropin, Lysozyme, and Hemolin) varied on different time points. Moreover, the fungus negatively impacted the development of the host by reducing the life span and egg laying ability. Thus, M. anisopliae can become a potent prospect for the control of this pest. This information will also reinforce the development of policies for biocontrol-based pest management.

Abstract

Entomopathogenic fungi are naturally existing microbes, that can serve as a key regulator of insect pests in integrated pest management strategies. Besides having no hazardous effects on the environment, these entomopathogens are alternatives to synthetic insecticides that can control notorious insect-like Plutella xylostella, a destructive pest of cruciferous crops. Three different species of entomopathogenic fungi were evaluated before the selection (high larval mortality and least LC₅₀) of Metarhizum anisopliae. The study was designed to investigate the mortality, development, and immune responses of P. xylostella when challenged with M. anisopliae, a naturally existing soil-borne entomopathogenic fungus. M. anisopliae resulted in high pest mortality by killing 93% of larvae. However, no statistically significant effect on hemocyte concentration was observed. The activity of enzymes (Phenoloxidase and Superoxide dismutase) and immune genes (Defensin, Spaetzle, Cecropin, Lysozyme, and Hemolin) did vary at different time points (24, 48, 72 and 96 h) after exposure to M. anisopliae. Disturbance in the biological cycles of P. xylostella was also detected, significantly shorter adult life span (8.11:6.87, M:F) and reduced fecundity (101 eggs/female) were observed along with disturbed larval and pupal duration. Results suggest that M. anisopliae can efficiently hinder the P. xylostella defense and developmental system, resulting in mortality and disturbed demography.

Infection of highly insecticide-resistant malaria vector Anopheles coluzzii with entomopathogenic bacteria Chromobacterium violaceum reduces its survival, blood feeding propensity and fecundity

BACKGROUND

This is now a concern that malaria eradication will not be achieved without the introduction of novel control tools. Microbiological control might be able to make a greater contribution to vector control in the future. The interactions between bacteria and mosquito make mosquito microbiota really promising from a disease control perspective. Here, the impact of Chromobacterium violaceum infections, isolated from both larvae and adult of wild-caught Anopheles gambiae sensu lato mosquitoes in Burkina Faso, was evaluated on mosquito survival, blood feeding and fecundity.

METHODS

To assess entomopathogenic effects of C. violaceum infection on mosquitoes, three different types of bioassays were performed in laboratory. These bioassays aimed to evaluate the impact of C. violaceum infection on mosquito survival, blood feeding and fecundity, respectively. During bioassays mosquitoes were infected through the well-established system of cotton ball soaked with 6% glucose containing C. violaceum.

RESULTS

Chromobacterium violaceum kills pyrethroid resistant Anopheles coluzzii (LT80 of 8.78 days ± 0.18 at 10⁸ bacteria cell/ml of sugar meal). Interestingly, this bacterium had other negative effects on mosquito lifespan by significantly reducing (~ 59%, P < 0.001) the mosquito feeding willingness from day 4-post infection (~ 81% would seek a host to blood feed) to 9- day post infection (22 ± 4.62% would seek a host to blood feed). Moreover, C. violaceum considerably jeopardized the egg laying (~ 16 eggs laid/mosquito with C. violaceum infected mosquitoes vs ~ 129 eggs laid/mosquito with control mosquitoes) and hatching of mosquitoes (a reduction of ~ 22% of hatching rate with C. violaceum infected mosquitoes). Compared to the bacterial uninfected mosquitoes, mosquitoes infected with C. violaceum showed significantly higher retention rates of immature eggs and follicles.

CONCLUSION

These data showed important properties of Burkina Faso C. violaceum strains, which are highly virulent against insecticide-resistant An. coluzzii, and reduce both mosquito blood feeding and fecundity propensities. However, additional studies as the sequencing of C. violaceum genome and the potential toxins secreted will provide useful information render it a potential candidate for the biological control strategies of malaria and other disease vectors.

Pathogenicity and Transgenerational Effects of Metarhizium anisopliae on the Demographic Parameters of Aedes albopictus (Culicidae: Diptera)

Dengue fever is a vector-borne infectious disease that spreads swiftly and threatens human lives in several tropical countries. Most of the strategies employed for the control of Aedes albopictus (Skuse) involve synthetic chemicals. The indiscriminate use of synthetic chemicals has led to the development of resistance and is unsafe for human and environmental health. Therefore, there is a need to develop ecologically safe tactics, such as the use of the entomopathogenic fungus (EPF) Metarhizium anisopliae (Metchnikoff 1879) (Met-11.1). The following study investigated the effectiveness of EPF-Met-11.1 on different demographic parameters of Ae. albopictus. Mortality bioassays showed 92.5% mortality when adult Ae. albopictus were treated with M. anisopliae. Metarhizium anisopliae absorbs the hemolymph sugar which results in retarded development. Metarhizium anisopliae LC50 not only affected the parental generation (F0) but also affected the demographic parameters of the offspring (F1). Transgenerational results (F1) with Met-11.1 showed decreased net reproductive rates (Ro), intrinsic rates of increase (r), and mean generation times (T) compared to those of uninfected controls. The larval developmental duration in the treatment group was 8.22 d, compared to 8.00 d in the control. There was a significant decrease in mean fecundity in the treated group (208.87 eggs) compared to that of the control group (360.27 eggs), and adult longevity was also significantly reduced in the treated group. Therefore, it is concluded that M. anisopliae can have lasting effects on the developmental parameters of Ae. albopictus, indicating that it can be an integral part of mosquito control strategies.

Mosquitoes (Diptera: Culicidae) and mosquito-borne diseases in Mali, West Africa

Mosquito-borne diseases cause major human diseases in almost every part of the world. In West Africa, and notably in Mali, vector control measures help reduce the impact of mosquito-borne diseases, although malaria remains a threat to both morbidity and mortality. The most recent overview article on mosquitoes in Mali was published in 1961, with a total of 88 species. Our present review focuses on mosquitoes of medical importance among which the Anopheles vectors of Plasmodium and filaria, as well as the Culex and Aedes vectors of arboviruses. It aims to provide a concise update of the literature on Culicidae, covering the ecological areas in which the species are found but also the transmitted pathogens and recent innovative tools for vector surveys. This review highlights the recent introduction of invasive mosquito species, including Aedes albopictus and Culex neavei. The comprehensive list of mosquito species currently recorded includes 106 species (28 species of the Anophelinae and 78 species of the Culicinae). There are probable gaps in our knowledge concerning mosquitoes of the subfamily Culicinae and northern half of Mali because most studies have been carried out on the genus Anopheles and have taken place in the southern part of the country. It is hoped that this review may be useful to decision makers responsible for vector control strategies and to researchers for future surveys on mosquitoes, particularly the vectors of emerging arboviruses.

The interplay between dose and immune system activation determines fungal infection outcome in the African malaria mosquito, Anopheles gambiae

The Toll pathway is a central regulator of antifungal immunity in insects. In mosquitoes, the Toll pathway affects infections with the fungal entomopathogen, Beauveria bassiana, which is considered a potential mosquito biopesticide. We report here the use of B. bassiana strain I93-825 in Anopheles gambiae to analyze the impact of Toll pathway modulation on mosquito survival. Exposure to a narrow dose range of conidia by direct contact decreased mosquito longevity and median survival. In addition, fungal exposure dose correlated positively and linearly with hazard ratio. Increased Toll signaling by knockdown of its inhibitor, cactus, decreased survivorship of uninfected females, increased mosquito survival after low dose B. bassiana exposure, but had little effect following exposure to higher doses. This observed trade-off could have implications for development of B. bassiana as a prospective vector control tool. On the one hand, selection for small increases in mosquito immune signaling across a narrow dose range could impair efficacy of B. bassiana. On the other hand, costs of immunity and the capacity for higher doses of fungus to overwhelm immune responses could limit evolution of resistance.

Evaluation of Two Entomopathogenic Fungi for Control of Culex quinquefasciatus (Diptera: Culicidae) in Underground Storm Drains in the Coachella Valley, California, United States

Commercially available formulations of two entomopathogenic fungi, Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Clavicipitaceae) and Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae), were assessed for control of Culex quinquefasciatus Say (Diptera: Culicidae) in underground storm drain systems (USDS) in the Coachella Valley of southern California. Each of three treatments, the two fungi or a water control, was applied to 1 m2 of vertical wall at eight USDS sites in spring and autumn of 2015. Fungal infectivity and lethality were assessed at 1 d and 1, 2, and 4 wk post-application. Overnight bioassays using adult lab-reared female mosquitoes were carried out on the treated USDS wall areas and then mosquitoes were held in the laboratory for up to 21 d to allow fungal infections to be expressed. Postmortem fungal sporulation was assessed up to 2 wk at 100% humidity. Mosquito-fungal interactions also were assessed in bioassays of the three treatments on filter paper exposed to USDS conditions during autumn. Metarhizium anisopliae killed mosquitoes faster than B. bassiana; nevertheless, both freshly applied formulations caused greater than 80% mortality. Fungal persistence declined significantly after 1 wk under USDS conditions, but some infectivity persisted for more than 4 wk. Beauveria bassiana was more effective against Cx. qinquefasciatus in the spring, while M. anisopliae was more effective in the cooler conditions during autumn. USDS environmental conditions (e.g., temperature, relative humidity, standing water) influenced fungal-related mortality and infection of Cx. quinquefasciatus. The utility of these fungal formulations for mosquito abatement in the Coachella Valley and implications for fungal control agents in USDS environments are discussed.

Toxicity of Beauveria bassiana-28 Mycelial Extracts on Larvae of Culex quinquefasciatus Mosquito (Diptera: Culicidae)

Microbial-based pest control is an attractive alternative to chemical insecticides. The present study sought to evaluate the toxicity of the entomopathogenic fungus Beauveria bassiana-28 ethyl acetate extracts on different larval stages and pupae of Culex quinquefasciatus mosquitoes. B. bassiana-28 ethyl acetate mycelial extracts produced mosquitocidal activity against larvae and pupae which was comparable to that of the commercial insecticide B. bassiana-22 extract. The LC₅₀ (lethal concentration that kills 50% of the exposed larvae) values of B. bassiana-28 extracts for 1st to 4th instar larvae and pupae were 11.538, 6.953, 5.841, 3.581 and 9.041 mg/L respectively. Our results show that B. bassiana-28 ethyl acetate mycelial extract has strong insecticidal activity against larval and pupal stages of Cx. quinquefasciatus. Fourier transform infrared spectrum study of B. bassiana-28 extract shows peaks at 3226.91; 2927.94; 1593.13; 1404.18; 1224.18; 1247.94; 1078.21; 1018.41; 229.69; and 871.82 cm⁻¹. Major spectral peaks were observed at 3226.91 cm^−1, assigned to N–H stretching, 2927.94 cm⁻¹ assigned to C–H bonding and 1595.13 cm⁻¹ assigned to C–O stretching. Gas Chromatography-Mass Spectrometry studies of B. bassiana-28 ethyl acetate crude extract showed presence of six major compounds viz. N-hexadecanoic acids (13.6040%); Z,Z-9,12 octadecadienic acid (33.74%); 9-eicosyne (10.832%); heptacosane (5.148%); tetrateracontane (5.801%); and 7 hexyleicosane (5.723%). Histology of mosquito midgut tissue shows tissue lysis as a result of B.bassiana-28 extract exposure. The study shows that bioactive molecules obtained from B. bassiana-28 mycelial extract has insecticidal properties and can be used as alternative for mosquito control.

Biological control of human disease vectors: a perspective on challenges and opportunities

Chemical insecticides are the mainstay of contemporary control of human disease vectors. However, the spread of insecticide resistance and the emergence of new disease threats are creating an urgent need for alternative tools. This perspective paper explores whether biological control might be able to make a greater contribution to vector control in the future, and highlights some of the challenges in taking a technology from initial concept through to operational use. The aim is to stimulate a dialogue within biocontrol and vector control communities, in order to make sure that biological control tools can realize their full potential.

Lack of resistance development in Bemisia tabaci to Isaria fumosorosea after multiple generations of selection

The emergence of insecticide resistant insect pests is of significant concern worldwide. The whitefly, Bemisia tabaci, is an important agricultural pest and has shown incredible resilience developing resistance to a number of chemical pesticides. Entomopathogenic fungi such as Isaria fumosorosea offer an attractive alternative to chemical pesticides for insect control, and this fungus has been shown to be an effective pathogen of B. tabaci. Little is known concerning the potential for the development of resistance to I. fumosorosea by B. tabaci. Five generations of successive survivors of B. tabaci infected by I. fumosorosea were assayed with I. fumosorosea. No significant differences in susceptibility to I. fumosorosea, number of ovarioles, or ovipostioning were seen between any of the generations tested. Effects of I. fumosorosea and cell-free ethyl acetate fractions derived from the fungus on the B. tabaci fat body, ovary, and vitellogenin were also investigated. These data revealed significant deformation and degradation of ovary tissues and associated vitellogenin by the fungal mycelium as well as by cell-free ethyl acetate fungal extracts. These data indicate the lack of the emergence of resistance to I. fumosorosea under the conditions tested and demonstrate invasion of the insect reproductive tissues during fungal infection.

Screening of Fungi for Biological Control of a Triatomine Vector of Chagas Disease: Temperature and Trypanosome Infection as Factors

Entomopathogenic fungi have been investigated as an alternative tool for controlling various insects, including triatomine vectors of the protozoan Trypanosoma cruzi, the etiological agent of Chagas disease. Here we tested the pathogenicity and virulence of ten isolates of the fungi Metarhizium spp. and Beauveria bassiana against Rhodnius prolixus and found all of the isolates to be virulent. We used two isolates (URPE-11 Metarhizium anisopliae and ENT-1 Beauveria bassiana) for further screening based on their prolific sporulation in vitro (an important property of fungal biopesticides). We characterized their virulences in a dose-response experiment and then examined virulence across a range of temperatures (21, 23, 27 and 30°C). We found isolate ENT-1 to maintain higher levels of virulence over these temperatures than URPE-11. We therefore used B. bassiana ENT-1 in the final experiment in which we examined the survival of insects parasitized with T. cruzi and then infected with this fungus (once again over a range of temperatures). Contrary to our expectations, the survival of insects challenged with the pathogenic fungus was greater when they had previously been infected with the parasite T. cruzi than when they had not (independent of temperature). We discuss these results in terms of aspects of the biologies of the three organisms. In practical terms, we concluded that, while we have fungal isolates of potential interest for development as biopesticides against R. prolixus, we have identified what could be a critical problem for this biological tool: the parasite T. cruzi appears to confer a measure of resistance to the insect against the potential biopesticide agent so use of this fungus as a biopesticide could lead to selection for vector competence.

Efficacy of Tolypocladium cylindrosporum against Aedes aegypti eggs, larvae and adults

AIMS

The aim of this study was to test the activity of seven Tolypocladium cylindrosporum isolates against different developmental stages of Aedes aegypti.

METHODS AND RESULTS

Ovicidal activity (≤30% of eclosion; at a 84% eclosion of control eggs) and lowest cumulative emergence of adults (≤30%; at a 66·3% control emergence) originating from eclosing larvae was found 15 and 30 days, respectively, after applying conidia of ARSEF 962 or 1580 onto the eggs. All isolates induced larval mortality when third-instar larvae were treated with conidia (≤5% control mortality); the lowest lethal concentration (LC50) at 5 days after treatment was found with ARSEF 1580 (9·2 × 10(5) conidia ml(-1)), and the shortest lethal time (LT50 ) with ARSEF 2912 (2·8 days at 3·3 × 10(6) conidia ml(-1)). The pathogenicity of T. cylindrosporum to A. aegypti adults is corroborated. ARSEF 1027, 1580 and 2912 induced the highest cumulative mortality in adults (≥90%) 15 days after application (≤5% control mortality).

CONCLUSIONS

Findings emphasized an isolate- and developmental stage-related virulence of T. cylindrosporum.

SIGNIFICANCE AND IMPACT OF THE STUDY

ARSEF 1580, in the group of tested isolates, is the most promising isolate for use against terrestrial eggs, aquatic larvae and adults of this important vector.

Isolation and efficacy of entomopathogenic fungus (Metarhizium anisopliae) for the control of Aedes albopictus Skuse larvae: suspected dengue vector in Pakistan

OBJECTIVE

To isolate the entomopathogenic fungus Metarhizium anisopliae (M. anisopliae) in the local environment, and evaluate its efficacy against the suspected dengue vector Aedes albopictus in Pakistan.

METHODS

According to the standard procedure, M. anisopliae was isolated from the dead mosquitoes which were collected from the field or dead after the collection. Bioassay was performed to determine its efficacy.

RESULTS

The results indicated that M. anisopliae had larvicidal effect with LC50 value 1.09×10(5) and LC90 value 1.90×10(13) while it took 45.41 h to kill 50% of tested population.

CONCLUSIONS

Taking long time to kill 50% population when compare with the synthetic insecticides, is the only drawback for the use of entomopathogenic fungus but these bio-pesticides are safe for the use.

Fungal biological control agents for integrated management of Culicoides spp. (Diptera: Ceratopogonidae) of livestock

Aim:

Entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana had wide host range against insects and hence these are being exploited as fungal bio-pesticide on a large scale. Both fungi are proved pesticides against many crop pests and farmers are well acquainted with their use on the field. Thus, research was aimed to explore the potency of these fungal spores against larval and adult Culicoides midges, a pest of livestock.

Materials and Methods:

In-vitro testing of both fungal biological control agents was undertaken in Petri dishes against field collected Culicoides larvae, while in plastic beakers against field collected blood-engorged female Culicoides midges. In-vivo testing was undertaken by spraying requisite concentration of fungal spores on the drainage channel against larvae and resting sites of adult Culicoides midges in the cattle shed. Lethal concentration 50 (LC₅₀) values and regression equations were drawn by following probit analysis using SPSS statistical computerized program.

Results:

The results of this study revealed LC₅₀ values of 2692 mg and 3837 mg (10⁸ cfu/g) for B. bassiana and M. anisopliae, respectively, against Culicoides spp. larvae. Death of Culicoides larvae due to B. bassiana showed greenish coloration in the middle of the body with head and tail showed intense blackish changes, while infection of M. anisopliae resulted in death of Culicoides larvae with greenish and blackish coloration of body along with total destruction, followed by desquamation of intestinal channel. The death of adult Culicoides midges were caused by both the fungi and after death growth of fungus were very well observed on the dead cadavers proving the efficacy of the fungus.

Conclusion:

Preliminary trials with both funguses (M. anisopliae, B. bassiana) showed encouraging results against larvae and adults of Culicoides spp. Hence, it was ascertained that, these two fungal molecules can form a part of biological control and alternative to chemical control and, therefore, can be inducted in integrated management programs.

Interactions between a fungal entomopathogen and malaria parasites within a mosquito vector

BACKGROUND

Mosquitoes are becoming increasingly resistant to the chemical insecticides currently available for malaria vector control, spurring interest in alternative management tools. One promising technology is the use of fungal entomopathogens. Fungi have been shown to impact the potential for mosquitoes to transmit malaria by reducing mosquito longevity and altering behaviour associated with flight and host location. Additionally, fungi could impact the development of malaria parasites within the mosquito via competition for resources or effects on the mosquito immune system. This study evaluated whether co-infection or superinfection with the fungal entomopathogen Beauveria bassiana affected malaria infection progress in Anopheles stephensi mosquitoes.

METHODS

The study used two parasite species to examine possible effects of fungal infection at different parasite development stages. First, the rodent malaria model Plasmodium yoelii was used to explore interactions at the oocyst stage. Plasmodium yoelii produces high oocyst densities in infected mosquitoes and thus was expected to maximize host immunological and resource demands. Second, fungal interactions with mature sporozoites were evaluated by infecting mosquitoes with the human malaria species Plasmodium falciparum, which is highly efficient at invading mosquito salivary glands.

RESULTS

With P. yoelii, there was no evidence that fungal co-infection (on the same day as the blood meal) or superinfection (during a subsequent gonotrophic cycle after parasite infection) affected the proportion of mosquitoes with oocysts, the number of oocysts per infected mosquito or the number of sporozoites per oocyst. Similarly, for P. falciparum, there was no evidence that fungal infection affected sporozoite prevalence. Furthermore, there was no impact of infection with either malaria species on fungal virulence as measured by mosquito survival time.

CONCLUSIONS

These results suggest that the impact of fungus on malaria control potential is limited to the well-established effects on mosquito survival and transmission behaviour. Direct or indirect interactions between fungus and malaria parasites within mosquitoes appear to have little additional influence.

Effects of fungal infection on feeding and survival of Anopheles gambiae (Diptera: Culicidae) on plant sugars

BACKGROUND

The entomopathogenic fungus Metarhizium anisopliae shows great promise for the control of adult malaria vectors. A promising strategy for infection of mosquitoes is supplying the fungus at plant feeding sites.

METHODS

We evaluated the survival of fungus-exposed Anopheles gambiae mosquitoes (males and females) fed on 6% glucose and on sugars of Ricinus communis (Castor oil plant) and Parthenium hysterophorus (Santa Maria feverfew weed). Further, we determined the feeding propensity, quantity of sugar ingested and its digestion rate in the mosquitoes when fed on R. communis for 12 hours, one and three days post-exposure to fungus. The anthrone test was employed to detect the presence of sugar in each mosquito from which the quantity consumed and the digestion rates were estimated.

RESULTS

Fungus-exposed mosquitoes lived for significantly shorter periods than uninfected mosquitoes when both were fed on 6% glucose (7 versus 37 days), R. communis (7 versus 18 days) and P. hysterophorus (5 versus 7 days). Significantly fewer male and female mosquitoes, one and three days post-exposure to fungus, fed on R. communis compared to uninfected controls. Although the quantity of sugar ingested was similar between the treatment groups, fewer fungus-exposed than control mosquitoes ingested small, medium and large meals. Digestion rate was significantly slower in females one day after exposure to M. anisopliae compared to controls but remained the same in males. No change in digestion rate between treatments was observed three days after exposure.

CONCLUSIONS

These results demonstrate that (a) entomopathogenic fungi strongly impact survival and sugar-feeding propensity of both sexes of the malaria vector An. gambiae but do not affect their potential to feed and digest meals, and (b) that plant sugar sources can be targeted as fungal delivery substrates. In addition, targeting males for population reduction using entomopathogenic fungi opens up a new strategy for mosquito vector control.

Natural variation in virulence of the entomopathogenic fungus Beauveria bassiana against malaria mosquitoes

Background

Insecticide resistance is greatly hampering current efforts to control malaria and therefore alternative methods are needed. Entomopathogenic fungi have been proposed as an alternative with a special focus on the cosmopolitan species Beauveria bassiana. However, few studies have analysed the effects of natural variation within fungal isolates on mosquito survival, and the implications and possible exploitation for malaria control.

Methods

Laboratory bioassays were performed on adult female mosquitoes (Anopheles coluzzii) with spores from 29 isolates of B. bassiana, originating from different parts of the world. In addition, phenotypic characteristics of the fungal isolates such as sporulation, spore size and growth rate were studied to explore their relationship with virulence.

Results

All tested isolates of B. bassiana killed An. coluzzii mosquitoes, and the rate at which this happened differed significantly among the isolates. The risk of mosquitoes dying was around ten times higher when they were exposed to the most virulent as compared to the least virulent isolate. There was significant variation among isolates in spore size, growth rate and sporulation, but none of these morphological characteristics were correlated, and thus predictive, for the ability of the fungal isolate to kill malaria mosquitoes.

Conclusions

This study shows that there is a wide natural variation in virulence of isolates of B. bassiana, and that selecting an appropriate fungal isolate is highly relevant in killing and thus controlling malaria mosquitoes, particularly if used as part of an integrated vector management strategy. Also, the wide variation observed in virulence offers the opportunity to better understand the molecular and genetic mechanisms that drive this variation and thus to address the potential development of resistance against entomopathogenic fungi.

Transfer of inoculum of Metarhizium anisopliae between adult Glossina morsitans morsitans and effects of fungal infection on blood feeding and mating behaviors

The transfer of conidia of Metarhizium anisopliae between tsetse flies Glossina morsitans and the effects of fungal inoculation on mating and blood meal feeding behaviors were investigated in the laboratory. Male or female flies were inoculated with fungal conidia ("donors") and allowed to pair with fungus-free mate of opposite sex ("recipients") at 1-day-interval up to three mates. Fungus-treated male or female "donor" flies as well as their mates "recipients" died from fungal infection. However, mortality in male "recipient" flies declined with successive mating, from 82.5 to 32.5 %. Fungus-treated males readily located female flies and mating was successful in most cases comparable to the controls. There were no significant differences (P > 0.05) in mean duration of mating, number of jerking movements between fungus-treated and fungus-free males for all the mating lines, except in the number of jerking movements when male flies mated with the 3rd line female flies. Fungus-treated and fungus-free female flies previously mated with treated and non-treated males showed refractoriness during subsequent pairings. The number of fertile female flies was higher (P < 0.05) in fungus-free than in fungus-treated treatments, thus producing more pupae. High concentration of fungus (3.0 × 10⁶ conidia ml^-1) significantly (P < 0.05) reduced blood meal intake of flies. This study has shown that fungal infection does not affect the mating behavior of tsetse flies and fly-to-fly contamination does occur during matings. These are important attributes if entomopathogenic fungi have to be used in auto-dissemination strategy and be integrated into sterile insect technique.

Malaria mosquitoes attracted by fatal fungus

Insect-killing fungi such as Beauveria bassiana are being evaluated as possible active ingredients for use in novel biopesticides against mosquito vectors that transmit malaria. Fungal pathogens infect through contact and so applications of spores to surfaces such as walls, nets, or other resting sites provide possible routes to infect mosquitoes in and around domestic dwellings. However, some insects can detect and actively avoid fungal spores to reduce infection risk. If true for mosquitoes, such behavior could render the biopesticide approach ineffective. Here we find that the spores of B. bassiana are highly attractive to females of Anopheles stephensi, a major anopheline mosquito vector of human malaria in Asia. We further find that An. stephensi females are preferentially attracted to dead and dying caterpillars infected with B. bassiana, landing on them and subsequently becoming infected with the fungus. Females are also preferentially attracted to cloth sprayed with oil-formulated B. bassiana spores, with 95% of the attracted females becoming infected after a one-minute visit on the cloth. This is the first report of an insect being attracted to a lethal fungal pathogen. The exact mechanisms involved in this behavior remain unclear. Nonetheless, our results indicate that biopesticidal formulations comprising B. bassiana spores will be conducive to attraction and on-source visitation by malaria vectors.

Decreased proportions of indoor feeding and endophily in Anopheles gambiae s.l. populations following the indoor residual spraying and insecticide-treated net interventions in Benin (West Africa)

Background

In many parts of Africa as in Benin, the main strategies of vector control are based on the scaling-up of Long Lasting Insecticide Treated Nets (LLITNs) and indoor residual spraying (IRS). The need to understand the biological implications of IRS in large scale and full coverage of LLITNs is paramount. It is in this context that the present study was conducted. It aims to evaluate the effect of a large scale IRS using a non-pyrethroid insecticide and full coverage of deltamethrin treated nets on the behavior of An. gambiae s.l. in the intervention areas compared to untreated areas used as controls.

Methods

Mosquitoes were collected using human landing catches, pyrethrum spray catches and window exit traps to assess reduction of entry rate, endophily rate, endophagy rate and overall mortality rate in natural populations of An. gambiae s.l. before IRS and LLITNs intervention (2007) and after in 2008 and 2010.

Results

In the IRS arm, endophily rate was 67.13% before intervention and 4.5% after intervention, whereas in the control arm it was stable at 51.67% (P > 0 .05). In the LLITN arm endophily rates also decreased after intervention. After the IRS, no gravid mosquitoes were collected from all treated localities, but LLITN performance was not that spectacular. The proportion of mosquitoes biting indoors in the IRS arm decreased from 67.09% before intervention to 42.85% after intervention, compared to a low but significant decrease (71.31% to 57. 46%) in the LLITN arm.

The use of vector control tools and behavior of the host would be the main factors that modify the behavior of taking a human blood meal observed on An. gambiae s.l. inside human dwellings.

Conclusion

The impact on the behavior of An. gambiae s.l. observed with the bendiocarb used in IRS was highly effective compared with the free distribution of LLITNs in terms of mortality and the decrease of proportions of indoor feeding. Despite this efficacy, there is a need for complementary tools and research of alternative strategy oriented on effective health education, and the use of powerful tools such as IRS, LLITNs, larviciding and repellents.

Evaluating the lethal and pre-lethal effects of a range of fungi against adult Anopheles stephensi mosquitoes

BACKGROUND

Insecticide resistance is seriously undermining efforts to eliminate malaria. In response, research on alternatives to the use of chemical insecticides against adult mosquito vectors has been increasing. Fungal entomopathogens formulated as biopesticides have received much attention and have shown considerable potential. This research has necessarily focused on relatively few fungal isolates in order to 'prove concept'. Further, most attention has been paid to examining fungal virulence (lethality) and not the other properties of fungal infection that might also contribute to reducing transmission potential. Here, a range of fungal isolates were screened to examine variation in virulence and how this relates to additional pre-lethal reductions in feeding propensity.

METHODS

The Asian malaria vector, Anopheles stephensi was exposed to 17 different isolates of entomopathogenic fungi belonging to species of Beauveria bassiana, Metarhizium anisopliae, Metarhizium acridum and Isaria farinosus. Each isolate was applied to a test substrate at a standard dose rate of 1×109 spores ml-1 and the mosquitoes exposed for six hours. Subsequently the insects were removed to mesh cages where survival was monitored over the next 14 days. During this incubation period the mosquitoes' propensity to feed was assayed for each isolate by offering a feeding stimulant at the side of the cage and recording the number probing.

RESULTS AND CONCLUSIONS

Fungal isolates showed a range of virulence to A. stephensi with some causing >80% mortality within 7 days, while others caused little increase in mortality relative to controls over the study period. Similarly, some isolates had a large impact on feeding propensity, causing >50% pre-lethal reductions in feeding rate, whereas other isolates had very little impact. There was clear correlation between fungal virulence and feeding reduction with virulence explaining nearly 70% of the variation in feeding reduction. However, there were some isolates where either feeding decline was not associated with high virulence, or virulence did not automatically prompt large declines in feeding. These results are discussed in the context of choosing optimum fungal isolates for biopesticide development.

The use of entomopathogenic fungi in the control of tsetse flies

Tsetse flies harbor a number of pathogens in nature; but their potential as biological control agents has not been fully exploited, especially due to the difficulty of their application in the field. Since entomopathogenic fungi infect their target organisms through the cuticle, it has been possible to develop a device that deliver and autodisseminate inoculum among tsetse in the field, resulting in population reduction, comparable to mass-trapping technology. However, the success of this technology depends on the effective horizontal transmission of the inoculum between insects. We present an overview of the prospects of entomopathogenic fungi for the control of tsetse flies and highlight the challenges.

Effects of Beauveria bassiana on survival, blood-feeding success, and fecundity of Aedes aegypti in laboratory and semi-field conditions

The fungus Beauveria bassiana reduces Aedes aegypti longevity in laboratory conditions, but effects on survival, blood-feeding behavior, and fecundity in realistic environmental conditions have not been tested. Adult, female Ae. aegypti infected with B. bassiana (FI-277) were monitored for blood-feeding success and fecundity in the laboratory. Fungal infection reduced mosquito-human contact by 30%. Fecundity was reduced by (mean ± SD) 29.3 ± 8.6 eggs per female per lifetime in the laboratory; egg batch size and viability were unaffected. Mosquito survival, blood-feeding behavior, and fecundity were also tested in 5 meter × 7 meter × 4 meter semi-field cages in northern Queensland, Australia. Fungal infection reduced mosquito survival in semi-field conditions by 59-95% in large cages compared with 61-69% in small cages. One semi-field cage trial demonstrated 80% reduction in blood-feeding; a second trial showed no significant effect. Infection did not affect fecundity in large cages. Beauveria bassiana can kill and may reduce biting of Ae. aegypti in semi-field conditions and in the laboratory. These results further support the use of B. bassiana as a potential biocontrol agent against Ae. aegypti.

A preliminary evaluation of the potential of Beauveria bassiana for bed bug control

Residual biopesticide treatments of Beauveria bassiana were tested against the bed bug Cimex lectularius. An oil formulation of conidia was applied to different substrates. Bed bugs were exposed for 1 h, transferred to an unsprayed environment and monitored for mortality. Separate bioassays evaluated the effect of bed bug strain, sex, life stage, and exposure substrate on mortality. Rapid mortality was observed in all bioassays, with bed bugs exposed to treated jersey knit cotton dying most rapidly. A further assay demonstrated efficient autodissemination of conidia from exposed bed bugs to unexposed bed bugs within artificial harborages.

Culex genome is not just another genome for comparative genomics

Formal publication of the Culex genome sequence has closed the human disease vector triangle by meeting the Anopheles gambiae and Aedes aegypti genome sequences. Compared to these other mosquitoes, Culex quinquefasciatus possesses many specific hallmark characteristics, and may thus provide different angles for research which ultimately leads to a practical solution for controlling the ever increasing burden of insect-vector-borne diseases around the globe. We argue the special importance of the cosmopolitan species- Culex genome sequence by invoking many interesting questions and the possible of potential of the Culex genome to answer those.

The entomopathogenic fungus Beauveria bassiana activate toll and JAK-STAT pathway-controlled effector genes and anti-dengue activity in Aedes aegypti

Here we investigated the effect of Beauveria bassiana infection on the survival of Aedes aegypti mosquitoes and the modulation of their susceptibility to dengue virus infection. Application of B. bassiana caused a reduction in the life span of A. aegypti and hindered dengue virus replication in the mosquito midgut. Fungus infection induced the expression a variety anti-microbial and dengue virus restriction factor genes. Transient reverse genetic analyses showed that the JAK-STAT pathway is implicated anti-fungal defense of Aedes mosquitoes. Our data suggest that this B. bassiana-mediated anti-dengue activity is likely to be at least partly indirectly mediated through the activation of the mosquito's anti-dengue Toll and JAK-STAT pathways.

Molecular cloning and preliminary function study of iron responsive element binding protein 1 gene from cypermethrin-resistant Culex pipiens pallens

Background

Insecticide resistance jeopardizes the control of mosquito populations and mosquito-borne disease control, which creates a major public health concern. Two-dimensional electrophoresis identified one protein segment with high sequence homology to part of Aedes aegypti iron-responsive element binding protein (IRE-BP).

Method

RT-PCR and RACE (rapid amplification of cDNA end) were used to clone a cDNA encoding full length IRE-BP 1. Real-time quantitative RT-PCR was used to evaluate the transcriptional level changes in the Cr-IRE strain Aedes aegypti compared to the susceptible strain of Cx. pipiens pallens. The expression profile of the gene was established in the mosquito life cycle. Methyl tritiated thymidine (³H-TdR) was used to observe the cypermethrin resistance changes in C6/36 cells containing the stably transfected IRE-BP 1 gene of Cx. pipiens pallens.

Results

The complete sequence of iron responsive element binding protein 1 (IRE-BP 1) has been cloned from the cypermethrin-resistant strain of Culex pipiens pallens (Cr-IRE strain). Quantitative RT-PCR analysis indicated that the IRE-BP 1 transcription level was 6.7 times higher in the Cr-IRE strain than in the susceptible strain of 4th instar larvae. The IRE-BP 1 expression was also found to be consistently higher throughout the life cycle of the Cr-IRE strain. A protein of predicted size 109.4 kDa has been detected by Western blotting in IRE-BP 1-transfected mosquito C6/36 cells. These IRE-BP 1-transfected cells also showed enhanced cypermethrin resistance compared to null-transfected or plasmid vector-transfected cells as determined by ³H-TdR incorporation.

Conclusion

IRE-BP 1 is expressed at higher levels in the Cr-IRE strain, and may confer some insecticide resistance in Cx. pipiens pallens.

The role of cow urine in the oviposition site preference of culicine and Anopheles mosquitoes

Background

Chemical and behavioural ecology of mosquitoes plays an important role in the development of chemical cue based vector control. To date, studies available have focused on evaluating mosquito attractants and repellents of synthetic and human origins. This study, however, was aimed at seasonal evaluation of the efficiency of cow urine in producing oviposition cues to Anopheles gambiae s.l. and Culex quinquefasciatus in both laboratory and field conditions.

Methods

Oviposition response evaluation in laboratory conditions was carried out in mosquito rearing cages. The oviposition substrates were located in parallel or in diagonal positions inside the cage. Urine evaluation against gravid females of An. arabiensis and Cx. quinquefasciatus was carried out at Day 1, Day 3 and Day 7. Five millilitres (mls) of cow urine was added to oviposition substrate while de-chlorinated water was used as a control. In field experiments, 500 mls of cow urine was added in artificial habitats with 2500 mls of de-chlorinated water and 2 kgs of soil. The experiment was monitored for thirty consecutive days, eggs were collected daily from the habitats at 7.00 hrs. Data analysis was performed using parametric and non-parametric tests for treatments and controls while attraction of the oviposition substrate in each species was presented using Oviposition Activity Index (OAI).

Results

The OAI was positive with ageing of cattle urine in culicine species in both laboratory and field experiments. The OAI for anopheline species was positive with fresh urine. The OAI during the rainy season was positive for all species tested while in the dry season the OAI for culicine spp and Anopheles gambiae s.l., changed with time from positive to negative values.

Based on linear model analysis, seasons and treatments had a significant effect on the number of eggs laid in habitats, even though the number of days had no effect.

Conclusion

Oviposition substrates treated with cow urine in both laboratory and field conditions have shown that cow urine left to age from 1-7 days has an influence on oviposition behavioural response in mosquitoes. The analysis of microbial colonies for decaying urine should be investigated along with its associated by-products.

Reduction in host-finding behaviour in fungus-infected mosquitoes is correlated with reduction in olfactory receptor neuron responsiveness

BACKGROUND

Chemical insecticides against mosquitoes are a major component of malaria control worldwide. Fungal entomopathogens formulated as biopesticides and applied as insecticide residual sprays could augment current control strategies and mitigate the evolution of resistance to chemical-based insecticides.

METHODS

Anopheles stephensi mosquitoes were exposed to Beauveria bassiana or Metarhizium acridum fungal spores and sub-lethal effects of exposure to fungal infection were studied, especially the potential for reductions in feeding and host location behaviours related to olfaction. Electrophysiological techniques, such as electroantennogram, electropalpogram and single sensillum recording techniques were then employed to investigate how fungal exposure affected the olfactory responses in mosquitoes.

RESULTS

Exposure to B. bassiana caused significant mortality and reduced the propensity of mosquitoes to respond and fly to a feeding stimulus. Exposure to M. acridum spores induced a similar decline in feeding propensity, albeit more slowly than B. bassiana exposure. Reduced host-seeking responses following fungal exposure corresponded to reduced olfactory neuron responsiveness in both antennal electroantennogram and maxillary palp electropalpogram recordings. Single cell recordings from neurons on the palps confirmed that fungal-exposed behavioural non-responders exhibited significantly impaired responsiveness of neurons tuned specifically to 1-octen-3-ol and to a lesser degree, to CO2.

CONCLUSIONS

Fungal infection reduces the responsiveness of mosquitoes to host odour cues, both behaviourally and neuronally. These pre-lethal effects are likely to synergize with fungal-induced mortality to further reduce the capacity of mosquito populations exposed to fungal biopesticides to transmit malaria.

First report of the infection of insecticide-resistant malaria vector mosquitoes with an entomopathogenic fungus under field conditions

Background

Insecticide-resistant mosquitoes are compromising the ability of current mosquito control tools to control malaria vectors. A proposed new approach for mosquito control is to use entomopathogenic fungi. These fungi have been shown to be lethal to both insecticide-susceptible and insecticide-resistant mosquitoes under laboratory conditions. The goal of this study was to see whether entomopathogenic fungi could be used to infect insecticide-resistant malaria vectors under field conditions, and to see whether the virulence and viability of the fungal conidia decreased after exposure to ambient African field conditions.

Methods

This study used the fungus Beauveria bassiana to infect the insecticide-resistant malaria vector Anopheles gambiae s.s (Diptera: Culicidae) VKPER laboratory colony strain. Fungal conidia were applied to polyester netting and kept under West African field conditions for varying periods of time. The virulence of the fungal-treated netting was tested 1, 3 and 5 days after net application by exposing An. gambiae s.s. VKPER mosquitoes in WHO cone bioassays carried out under field conditions. In addition, the viability of B. bassiana conidia was measured after up to 20 days exposure to field conditions.

Results

The results show that B. bassiana infection caused significantly increased mortality with the daily risk of dying being increased by 2.5× for the fungus-exposed mosquitoes compared to the control mosquitoes. However, the virulence of the B. bassiana conidia decreased with increasing time spent exposed to the field conditions, the older the treatment on the net, the lower the fungus-induced mortality rate. This is likely to be due to the climate because laboratory trials found no such decline within the same trial time period. Conidial viability also decreased with increasing exposure to the net and natural abiotic environmental conditions. After 20 days field exposure the conidial viability was 30%, but the viability of control conidia not exposed to the net or field conditions was 79%.

Conclusions

This work shows promise for the use of B. bassiana fungal conidia against insecticide-resistant mosquitoes in the field, but further work is required to examine the role of environmental conditions on fungal virulence and viability with a view to eventually making the fungal conidia delivery system more able to withstand the ambient African climate.

The combination of the entomopathogenic fungus Metarhizium anisopliae with the insecticide Imidacloprid increases virulence against the dengue vector Aedes aegypti (Diptera: Culicidae)

Background

Dengue fever transmitted by the mosquito Aedes aegypti, is one of the most rapidly spreading insect borne diseases, stimulating the search for alternatives to current control measures. The dengue vector A. aegypti has received less attention than anophelene species, although more than 2.5 billion people are at risk of infection worldwide. Entomopathogenic fungi are emerging as potential candidates for the control of mosquitoes. Here we continue our studies on the pathogenicity of the entomopathogenic fungus Metarhizium anisopliae against adult A. aegypti females. With the aim of further reducing mean survival times of A. aegypti exposed to fungus impregnated surfaces, a sub-lethal concentration of the neonicotinoid insecticide Imidacloprid (IMI) was added to fungal suspensions.

Results

A sub-lethal concentration of IMI that did not significantly alter the daily survival rates or mean survival percentages of mosquitoes was identified to be 0.1 ppm. This sub-lethal concentration was combined with M. anisopliae conidia (1 × 10⁹ conidia mL^-1). Both the combined treatment and the conidia alone were able to reduce the survival of A. aegypti compared with untreated or IMI treated mosquitoes. Importantly, mosquito survival following exposure to the combined treatment for 6 and 12 hrs was significantly reduced when compared with mosquitoes exposed to conidia alone.

Conclusions

This is the first time that a combination of an insecticide and an entomopathogenic fungus has been tested against A. aegypti. Firstly, the study showed the potential of IMI as an alternative to the currently employed pyrethroid adulticides. Secondly, as an alternative to applications of high concentrations of chemical insecticides, we suggest that adult A. aegypti could be controlled by surface application of entomopathogenic fungi and that the efficiency of these fungi could be increased by combining the fungi with ultra-low concentrations of insecticides, resulting in higher mortality following relatively short exposure times.

Entomopathogenic fungus as a biological control for an important vector of livestock disease: the Culicoides biting midge

BACKGROUND

The recent outbreak of bluetongue virus in northern Europe has led to an urgent need to identify control measures for the Culicoides (Diptera: Ceratopogonidae) biting midges that transmit it. Following successful use of the entomopathogenic fungus Metarhizium anisopliae against larval stages of biting midge Culicoides nubeculosus Meigen, we investigated the efficacy of this strain and other fungi (Beauveria bassiana, Isaria fumosorosea and Lecanicillium longisporum) as biocontrol agents against adult C. nubeculosus in laboratory and greenhouse studies.

METHODOLOGY/FINDINGS

Exposure of midges to 'dry' conidia of all fungal isolates caused significant reductions in survival compared to untreated controls. Metarhizium anisopliae strain V275 was the most virulent, causing a significantly decrease in midge survival compared to all other fungal strains tested. The LT(50) value for strain V275 was 1.42 days compared to 2.21-3.22 days for the other isolates. The virulence of this strain was then further evaluated by exposing C. nubeculosus to varying doses (10(8)-10(11) conidia m(-2)) using different substrates (horse manure, damp peat, leaf litter) as a resting site. All exposed adults were found to be infected with the strain V275 four days after exposure. A further study exposed C. nubeculosus adults to 'dry' conidia and 'wet' conidia (conidia suspended in 0.03% aq. Tween 80) of strain V275 applied to damp peat and leaf litter in cages within a greenhouse. 'Dry' conidia were more effective than 'wet' conidia, causing 100% mortality after 5 days.

CONCLUSION/SIGNIFICANCE

This is the first study to demonstrate that entomopathogenic fungi are potential biocontrol agents against adult Culicoides, through the application of 'dry' conidia on surfaces (e.g., manure, leaf litter, livestock) where the midges tend to rest. Subsequent conidial transmission between males and females may cause an increased level of fungi-induced mortality in midges thus reducing the incidence of disease.