Bacillus Thuringiensis Israelensis Research Articles

Combined use of long-lasting insecticidal nets and Bacillus thuringiensis israelensis larviciding, a promising integrated approach against malaria transmission in northern Côte d'Ivoire

BackgroundThe recent reduction in malaria burden in Côte d’Ivoire is largely attributable to the use of long-lasting insecticidal nets (LLINs). However, this progress is threatened by insecticide resistance and behavioral changes in Anopheles gambiae sensu lato (s.l.) populations and residual malaria transmission, and complementary tools are required. Thus, this study aimed to assess the efficacy of the combined use of LLINs and Bacillus thuringiensis israelensis (Bti), in comparison with LLINs.MethodsThis study was conducted in the health district of Korhogo, northern Côte d'Ivoire, within two study arms (LLIN + Bti arm and LLIN-only arm) from March 2019 to February 2020. In the LLIN + Bti arm, Anopheles larval habitats were treated every fortnight with Bti in addition to the use of LLINs. Mosquito larvae and adults were sampled and identified morphologically to genus and species using standard methods. The members of the An. gambiae complex were determined using a polymerase chain reaction technique. Plasmodium infection in An. gambiae s.l. and malaria incidence in local people was also assessed.ResultsOverall, Anopheles spp. larval density was lower in the LLIN + Bti arm 0.61 [95% CI 0.41–0.81] larva/dip (l/dip) compared with the LLIN-only arm 3.97 [95% CI 3.56–4.38] l/dip (RR = 6.50; 95% CI 5.81–7.29; P < 0.001). The overall biting rate of An. gambiae s.l. was 0.59 [95% CI 0.43–0.75] biting/person/night in the LLIN + Bti arm against 2.97 [95% CI 2.02–3.93] biting/person/night in LLIN-only arm (P < 0.001). Anopheles gambiae s.l. was predominantly identified as An. gambiae sensu stricto (s.s.) (95.1%, n = 293), followed by Anopheles coluzzii (4.9%; n = 15). The human-blood index was 80.5% (n = 389) in study area. EIR was 1.36 infected bites/person/year (ib/p/y) in the LLIN + Bti arm against 47.71 ib/p/y in the LLIN-only arm. Malaria incidence dramatically declined from 291.8‰ (n = 765) to 111.4‰ (n = 292) in LLIN + Bti arm (P < 0.001).ConclusionsThe combined use of LLINs with Bti significantly reduced the incidence of malaria. The LLINs and Bti duo could be a promising integrated approach for effective vector control of An. gambiae for elimination of malaria.

Influence of larval growth and habitat shading on retreatment frequencies of biolarvicides against malaria vectors

Effective larviciding for malaria control requires detailed studies of larvicide efficacies, aquatic habitat characteristics, and life history traits of target vectors. Mosquitoes with brief larval phases present narrower timeframes for biolarvicidal effects than mosquitoes with extended periods. We evaluated two biolarvicides, VectoBac (Bacillus thuringiensis israelensis (Bti)) and VectoMax (Bti and Bacillus sphaericus) against Anopheles funestus and Anopheles arabiensis in shaded and unshaded habitats; and explored how larval development might influence retreatment intervals. These tests were done in semi-natural habitats using field-collected larvae, with untreated habitats as controls. Additionally, larval development was assessed in semi-natural and natural habitats in rural Tanzania, by sampling daily and recording larval developmental stages. Both biolarvicides reduced larval densities of both species by >98% within 72 h. Efficacy lasted one week in sun-exposed habitats but remained >50% for two weeks in shaded habitats. An. funestus spent up to two weeks before pupating (13.2(10.4–16.0) days in semi-natural; 10.0(6.6–13.5) in natural habitats), while An. arabiensis required slightly over one week (8.2 (5.8–10.6) days in semi-natural; 8.3 (5.0–11.6) in natural habitats). The findings suggest that weekly larviciding, which is essential for An.arabiensis might be more effective for An. funestus whose prolonged aquatic growth allows for repeated exposures. Additionally, the longer residual effect of biolarvicides in shaded habitats indicates they may require less frequent treatments compared to sun-exposed areas.

Phylogeny of a Mosquitocidal Bacillus thuringiensis var israelensis

Objectives: The study aims to compare the 16srRNA sequence of Bacillus thuringiensis var israelensis available in the National Center for Biotechnology Information, database, the sequence length, the relatedness, identity, and ancestral property by constructing a phylogenetic tree and by basic local alignment tool. Methods: The 16srRNA sequence of all the Bacillus thuringiensis var israelensis was retrieved from the database. A basic local alignment tool was used to study the description of the sequences, the percent identity, graphical summary, and alignment. Mega software was used to draw the phylogenetic tree. Results: The total number of mosquitocidal 16srRNA gene sequences was 19. One sequence VCRC-B17 strain was the complete genomic sequence deposited other 18 hits were partial sequences. The Expected value, percent identity, maximum, and total score of 18 hits shows a significant match with the query sequence VCRC-B17. The graphic summary result displays that the 18 hits align with the query sequence as they are coded with the highest score coding color bar, red with a ≥ 200 alignment score. The phylogenetic tree did not support the monophyletic status indicating there is a diversity in the strain. Conclusion: The 19 sequences deposited in the database are identified as a mosquito larvicidal Bacillus thuringiensis var israelensis based on the alignment score or match even though they do not possess an equal base pair length with the query sequence.

Morphological Features of Mosquito Larvicidal Bacillus Thuringiensis Isolated From Soil Samples of Nepal

Anopheles, Culex, and Aedes spp are the main vectors for transmitting malaria, Japanese encephalitis, lymphatics filariasis, dengue, zika, chikungunya, etc. Mosquito-borne diseases are increasing especially dengue in Nepal. Additional tools are required to decrease the disease rate. Biological control tools like Gambusia fish, Cyclopods, Bacillus thuringiensis, etc., have not been adopted and are unavailable in Nepal. The research aims to isolate mosquitocidal Bacillus thuringiensis a biological control tool from the soil samples of Nepal. Bacillus thuringiensis (Bt) was isolated from the soil samples of Nepal by the acetate selection method. The larvicidal bioassay of Bt was studied against the field-collected mosquito larvae. The isolate showing larvicidal activity was coded as Bacillus thuringiensis -14P2A (Bt-14P2A). The growth pattern of the positive control strain Bacillus thuringiensis var israelensis (Bti-IPS-82) and the test strain were studied in different types of culture media. The microscopic morphology was studied by using different staining techniques. Bt-14P2A and Bti -IPS-82 caused 100% mortality of field-collected larvae. Both the strains showed the same type of colony morphology in a standard culture media and uniform turbidity with sedimentation type of growth pattern in broth media. The strains were Gram-positive single rod-shaped of size 1.2X4.8µm in both negatively stained slides and Gram-stained slides. A slight difference in the endospore location was terminal in Bti-IPS-82 and subterminal in Bt-14P2A. The newly isolated Bt-14P2A differs from Bti-IPS-82 in arrangement and endospore location but harbors the same morphological characteristic and larvicidal activity as the positive control strain.

Enhanced Production of Bacillus Thuringiensis Israelensis using Solid State Fermentation Technique

Vectors play an important role in disease transmission, globally. Despite various advancements in vector management, mosquitoes are still prime vectors of dreadful diseases which influences human health and economy as well. Bacillus thuringiensis israelensis (Bti) is a major bacterium that produces δ-endotoxin, which can kill the certain strains of mosquito larvae. Bti based biopesticides can be used as an alternative technique to control insects. Biopesticides derived from Bti are the most prominent biological agents for selective control of insect pests. In this study we aim to produce Bti using different cost-effective medias based on the fruit, pulses and sea food waste and other such materials using solid state fermentation techniques (SSF). SSF has been described as the process that takes place in solid matrix in the absence or near absence of water, and the substrate requires less moisture to support the growth and metabolic activity of organisms. Here, in the present study we use different fruit wastes as carbon sources and other wastes as nitrogen source to optimize cost effective and efficient media for the growth and sporulation of Bti. Fruit juices of rotten fruits like pineapple, grapes, watermelon etc were used as a substrate for the production of Bti. Nitrogenous supplements like prawn peel powder, peanut meal extract, poultry manure was also used for the overproduction of Bti. Finally, the larvicidal efficiency of the novel media was also determined. This method was found to be cost effective and is functional also, and it can solve the problems caused by fruit waste accumulation. It can also reduce the problems inflicted by disease carrying vectors like mosquitoes.

Effect of predators on Anopheles arabiensis and Anopheles funestus larval survivorship in Homa Bay County Western Kenya

BackgroundThe rise of insecticide resistance against malaria vectors in sub-Saharan Africa has resulted in the need to consider other methods of vector control. The potential use of biological methods, including larvivorous fish, Bacillus thuringiensis israelensis (Bti) and plant shading, is sustainable and environmentally friendly options. This study examined the survivorship of Anopheles arabiensis and Anopheles funestus larvae and habitat productivity in four permanent habitat types in Homa Bay county, western Kenya.MethodsPredator densities were studied in a laboratory setup while habitat productivity and larval survivorship was studied in field setup.ResultsFish were observed as the most efficient predator (75.8% larval reduction rate) followed by water boatman (69%), and dragonfly nymph (69.5%) in predation rates. Lower predation rates were observed in backswimmers (31%), water beetles (14.9%), water spiders (12.2%), mayflies (7.3%), and tadpoles (6.9%). Increase in predator density in the field setup resulted in decreased Culex larval density. Larval and pupa age–specific distribution was determined and their survivorship curves constructed. Combined larvae (Stage I–IV) to pupa mortality was over 97% for An. arabiensis and 100% for An. funestus. The highest larval stage survival rate was from larval stages I to II and the lowest from larval stage IV to pupa. Stage-specific life tables indicated high mortality rates at every developmental stage, especially at the larval stage II and III.ConclusionDetermination of the efficiency of various larval predators and habitat productivity will help with the correct identification of productive habitats and selection of complementary vector control methods through environmental management and/or predator introduction (for instance fish) in the habitats.

A Novel Mosquiocidal Bacterium from Soils of Vellore, Tamil nadu, India

In this study, intensive screening for mosquitocidal bacteria from different agricultural soils of Vellore district of Tamil Nadu was carried out to isolate potential mosquitocidal bacteria. From a total of 315 soil samples, 945 bacterial isolates were cultured, out of which three isolates showed mosquitocidal activity. One most potential mosquitocidal isolate was selected out of these and studied further. The isolate was identified by ilvD primer and phylogenetic tree as Bacillus thuringiensis israelensis. This new isolate exhibited effective toxicity against Aed. aegypti, An. stephensi, and Cx. quinquefasciatus. The LC50 values were 0.757, 0.52 and 0.165 mg/ l respectively. Similarly, the LC90 values were 0.963, 0.794 and 0.355 mg/l, respectively. These results depict that the new isolate (Bti) VEVP-60 is a good candidate for mosquito control.

Resistance development to bioinsecticides in Aedes aegypti (Culicidae: Diptera), the vector of dengue fever in Saudi Arabia

A laboratory strain of Aedes aegypti (L) was subjected repeatedly to larval selection pressure with two bacterial insecticides, spinosad (Saccharopolyspora spinosa) and bacilod (Bacillus thuringiensis israelensis). The results indicated that the mosquito Ae. aegypti acquired low resistance to spinosad and bacilod by about 3.1 and 2.4-fold, respectively, due to selection pressure for fifteen successive generations. The slope values of the selected strains were increased gradually from one generation to the next, indicating moderate homogeneity between individuals in their response to the test bio-insecticide. Moreover, larval selection with current bacterial bioinsecticides prolonged the time required to digest a blood meal. It showed an evident decrease in the reproductive potential of adult mosquitoes surviving selected larvae.

Assessment of the impact of the biological larvicide VectoMax G: Combination of Bacillus thuringiensis and Lysinibacillus sphaericus on non-target aquatic organisms in Yaoundé-Cameroon

There has been a renewed interest for larviciding during the recent decade. Although biological larvicides are considered not to be harmful to non-target organisms, there is still not sufficient data on the effect of new long-lasting larvicide formulations such as VectoMax G combining Bacillus thuringiensis israelensis and Lysinibacullus sphaericus on the environment especially on non-target organisms. The present study aimed to assess the possible influence of VectoMax G on the diversity and abundance of the aquatic fauna cohabiting with mosquito larvae in breeding habitats during a larviciding trial in the city of Yaoundé.Twelve districts of the city of Yaoundé divided into 6 intervention and 6 control sites were chosen for the study. In each district 4 semi-permanent or permanent aquatic habitats were followed. VectoMax G application was done once every two weeks during 6 months and aquatic organisms were collected 48 h after each treatment. All collected organisms were brought to the laboratory for identification. Physico-chemical parameters were recorded as well.A high diversity of the zooplankton was recorded in the intervention areas with 28 species collected against 14 species in the control areas. Cladocerans were the most represented group in both sites while Ostracods were found only in control sites. A total of 19 macro-invertebrates species were recorded in the control areas vs 16 species in the intervention areas. Gasteropods were the most represented groups of macro-invertebrates. Vertebrates such as larvivorous fishes and amphibians larvae were also found in approximately similar densities in both sites.The study indicated no significant influence of larviciding with VectoMax G on the diversity and abundance of the non-target aquatic fauna in the city of Yaoundé.

The NF-κB factor Relish is essential for the epithelial defenses protecting against δ-endotoxin dependent effects of Bacillus thuringiensis israelensis infection in the Drosophila model

Bacillus thuringiensis israelensis is largely regarded as the most selective, safe and ecofriendly biopesticide used for the control of insect vectors of human diseases. Bti enthomopathogenicity relies on the Cry and Cyt δ-endotoxins, produced as crystalline inclusions during sporulation. Insecticidal selectivity of Bti is mainly ascribed to the binding of the Cry toxins to receptors in the gut of target insects. However, the contribution of epithelial defenses in limiting Bti side effects in non-target species remains largely unexplored. Here, taking advantage of the genetically tractable Drosophila melanogaster model and its amenability for deciphering highly conserved innate immune defenses, we unravel a central role of the NF-κB factor Relish in the protection against the effects of ingested Bti spores in a non-susceptible host. Intriguingly, our data indicate that the Bti-induced Relish response is independent of its canonical activation downstream of peptidoglycan sensing and does not involve its longstanding role in the regulation of antimicrobial peptides encoding genes. In contrast, our data highlight a novel enterocyte specific function of Relish that is essential for preventing general septicemia following Bti oral infections strictly when producing δ-endotoxins. Altogether, our data provide novel insights into Bti-hosts interactions of prominent interest for the optimization and sustainability of insects’ biocontrol strategies.

Does biocide treatment for mosquito control alter carbon dynamics in floodplain ponds?

Shallow lentic aquatic ecosystems, such as ponds, are important repositories of carbon (C) and hotspots of C cycling and greenhouse gas emission. Tube-dwelling benthic invertebrates, such as chironomids, may be key players in C dynamics in these water bodies, yet their role in the C-budget at ecosystem level remains unclear. We tested whether a 41 % reduction in chironomid abundance after application of the mosquito control biocide Bacillus thuringiensis israelensis (Bti) had implications for the C-fluxes to the atmosphere, C-pools, and C-transformation (i.e. organic matter decomposition) in ponds. Data were collected over one year in the shallow, deep and riparian zones of 12 experimental floodplain pond mesocosms (FPMs), half of them treated with Bti. C-fluxes were measured as CO2 and CH4 emissions, atmospheric deposition, and emerging insects. C-pools were measured as dissolved inorganic and organic C in surface and porewater, sediment organic C, C in plant and in macroinvertebrate biomass. Despite seasonal variability, treated FPMs, for which higher CH4 emissions have been reported, showed a trend towards less dissolved organic C in porewater, while no effect was observed for all remaining components of the C-budget. We attribute the effect of Bti on the C-budget to the reduction in macroinvertebrates biomass, the increase in CH4 emissions, and the input of C from the Bti excipients. This finding suggests that changes in tube-dwelling macroinvertebrates have a weak influence on C cycling in ponds and confirms the existence of long-lasting effects of Bti on specific components of C-budgets.

Testing the susceptibility of larval stages of Simulium to temephos and Bacillus thuringiensis var israelensis in Germany and Northern Cameroon.

Assays to evaluate the susceptibility of Simulium larvae to temephos and Bacillus thuringiensis var israelensis (Bti) were carried out by setting-up an in vitro laboratory test ('bio assay') and a semi-natural test ('système de goutières') to assess the LC50/LC90 values. Larvae of Simulium species in Cameroon (S. damnosum s.l., S. hargreavesi, S. vorax and S. cervicornutum) and (S. (Odagmia) ornatum and S. latipes) in Germany were identified and tested. In the bio-assay, 50 larvae were exposed for 10min to concentrations from 0.01 to 10ppm. For the Simulium from Germany, the LC50 (LC90) values after 3 and 6h were 3.1 (27.9) and 0.14 (1.26) ppm for temephos and for Bti 7.8 (70.2) and 1.7 (15.3) ppm, respectively. For Cameroonian species, the values of LC50 (LC90) were lower, that is, 0.42 (8.04), 0.14 (2.70) and 0.073 (1.38) ppm, respectively, after 3, 6 and 12 h for temephos. In a semi natural condition, the LC50 of 10min of application of temephos was 0.84 ppm after 3h and a working solution (2.6 L) of Bti killed 50% after 6h. To detect an upcoming of any resistance as it happened in Ivory Coast, a study of the occurrence resistance genes should be implemented.

The need for larval source management accompanying urban development projects in malaria endemic areas: a case study on Bioko Island

BackgroundIn 2017, several new housing districts were constructed on Bioko Island, Equatorial Guinea. This case study assessed the impact construction projects had on mosquito larval habitats and the effectiveness of larval source management in reducing malaria vector density within the surrounding area.MethodsAnopheline larval presence was assessed at 11 new construction sites by the proportion of larval habitats containing Anopheline pupae and late instar larval stages. Bacillus thuringiensis israelensis (Bti) larvicide was applied weekly to nine locations for 30 weeks, while two locations received no larvicide and acted as controls. Adult mosquito density was monitored via human landing collections in adjacent communities of six construction sites, including the two control sites.ResultsThe sites that received Bti had significantly lower observation rates of both pupae (3.2% vs. 18.0%; p < 0.001) and late instar Anopheles spp. mosquitoes (14.1 vs. 43.6%; p < 0.001) compared to the two untreated sites. Anopheles spp. accounted for 67% of mosquitoes collected with human landing collections and were captured at significantly lower levels in communities adjacent to treated construction sites compared to untreated sites (p < 0.001), with an estimated 38% reduction in human biting rate (IRR: 0.62, 95% CI IRR: 0.55, 0.69). Seven months after the start of the study, untreated sites were treated due to ethical concerns given results from treatment sties, necessitating immediate Bti application. The following week, the number of habitats, the proportion of larval sites with Anopheles spp. pupae, late instars, and adult biting rates in adjacent communities to these sites all decreased to comparable levels across all sites.ConclusionFindings suggest larval source management represents an effective intervention to suppress mosquito populations during infrastructure development. Incorporating larval source management into ongoing and planned construction initiatives represents an opportunity to fine tune vector control in response to anthropogenetic changes. Ideally, this should become standard practice in malaria-endemic regions in order to reduce viable mosquito habitats that are common by-products of construction.

Phenotypic insecticide resistance status of the Culex pipiens complex: a European perspective

BackgroundThe common house mosquito Culex pipiens is known to be a major vector for West Nile virus. In order to decrease risks of West Nile virus outbreaks in Europe, insecticides and the bio-larvicide Bacillus thuringiensis israelensis (Bti) are commonly used for vector control. Alarmingly, insecticide resistance has been reported in Cx. pipiens populations from Southern Europe and several countries neighbouring Europe. For Central and Northern Europe, however, the phenotypic insecticide resistance status of Cx. pipiens has not yet been investigated.MethodsA literature review was performed to assess the geographical distribution of insecticide resistance in Cx. pipiens. To fill the gap of knowledge for Central and Northern Europe, WHO susceptibility tests with permethrin, deltamethrin, malathion, bendiocarb and DDT and a larval toxicity test with Bti were performed with a Cx. pipiens population from Belgium, a country in Central Europe.ResultsThis research provides the first evidence of widespread phenotypic insecticide resistance in Cx. pipiens. In general, Cx. pipiens developed resistance against multiple insecticides in several countries. Another Cx. pipiens population from Belgium was tested and showed insecticide resistance against deltamethrin, permethrin, DDT and possibly against bendiocarb. The bio-larvicide Bti caused lower mortality than reported for other Cx. pipiens populations in the literature.ConclusionsThese results indicate the urgent need for insecticide resistance monitoring against commonly used adulticides and larvicides in Europe, for the translation of knowledge gained regarding the limited efficiency and availability of insecticide into EU legislation and the need for innovative non-chemical vector control tools in order to counter the widespread insecticide resistance in Culex populations.Graphical abstract

Lethal and Sublethal Concentrations of Formulated Larvicides Against Susceptible Aedes aegypti.

Chemical control of vectors depends on the effective application of formulated insecticides. In this study we evaluated formulated larvicides using a larval bioassay against susceptible Aedes aegypti. The estimated larvicide lethal concentrations for 50% mortality (LC50s) were 25.7 μg/liter (Natular 2EC), 3.13 μg/liter (Abate 4E), 0.43 μg/liter (Altosid), 0.03 μg/liter (Nyguard), and 500.6 ITU/liter (VectoBac12AS containing Bacillus thuringiensis israelensis). Sublethal effects were identified and documented from adults that survived exposure to these estimated LC50s (body size and sex proportion). We observed changes in net growth as measured by adult wing lengths. For those larvae exposed to estimated LC50s, the average size of adults was between 0.1% and 10.6% smaller for males and between 1.1% and 13.6% smaller for females compared to controls. Sex proportions varied between larvicides, but some were significantly different from the control, favoring greater survival of females than males.

A review of vectors, vector borne diseases, vector control and their impact on public health

Mosquitoes are most important insect vectors for human disease transmission. Dengue, yellow fever, chikungunya, and zika are all spread by Aedes mosquitoes in many parts of the world. The primary vector of human malaria transmission is Anopheles. Culex is responsible for the transmission of Japanese encephalitis, lymphatic filariasis and West Nile virus fever. Synthetic pesticides have been successfully utilized in mosquito-control programmes for several decades. However, there are a number of disadvantages to the chemical method. As a result, there has been a rise in concern in the usage of biological agents for mosquito control in recent years. Because of their highly effective mosquitocidal activity, Bacillus sphaericus and Bacillus thuringiensis israelensis have been utilized extensively. While insecticide-based interventions have successfully reduced mosquito populations for a number of years, the reliance on a few number of insecticides has now led to the evolution of resistance. So there is a need to search for novel mosquitocidal bacteria for control the mosquito species. Since soil is one of the world's most diversified environments in which bacteria and fungi are abundant, screening of soil samples for isolation of novel mosquitocidal bacteria is attempted.

Benthic macroinvertebrate community shifts based on Bti-induced chironomid reduction also decrease Odonata emergence

Chironomid larvae (Diptera: Chironomidae) often dominate aquatic macroinvertebrate communities and are a key food source for many aquatic predators, such as dragonfly and damselfly larvae (Odonata). Changes in aquatic macroinvertebrate communities may propagate through terrestrial food webs via altered insect emergence. Bacillus thuringiensis israelensis (Bti)-based larvicides are widely used in mosquito control but can also reduce the abundance of non-biting chironomid larvae. We applied the maximum field rate of Bti used in mosquito control three times to six mesocosms in a replicated floodplain pond mesocosm (FPM) system in spring for two consecutive years, while the remaining six FPMs were untreated. Three weeks after the third Bti application in the first year, we recorded on average a 41% reduction of chironomid larvae in Bti-treated FPMs compared to untreated FPMs and a shift in benthic macroinvertebrate community composition driven by the reduced number of chironomid, Libellulidae and Coenagrionidae larvae (Odonata). Additionally, the number of emerging Libellulidae (estimated by sampling of exuviae in the second year) was reduced by 54% in Bti-treated FPMs. Since Odonata larvae are not directly susceptible to Bti, our results suggest indirect effects due to reduced prey availability (i.e., chironomid larvae) or increased intraguild predation. As Libellulidae include species of conservation concern, the necessity of Bti applications to their habitats, e.g. floodplains, should be carefully evaluated.

Efficacy Evaluation of Oregano Essential Oil Mixed with Bacillus thuringiensis israelensis and Diflubenzuron against Culex pipiens and Aedes albopictus in Road Drains of Italy.

Mosquito management programs in the urban environment of Italian cities mainly rely on larval control with conventional insecticides, primarily targeting the road drains that constitute the principal mosquito breeding sites encountered in public. The repeated utilization of synthetic insecticides may have adverse effects on non-targets and lead to resistance development issues, while the performance of biopesticides encounters limitations in field use. Botanical insecticides as single larval control agents or in binary mixtures with conventional insecticides have been extensively studied in the laboratory as an effective and eco-friendly alternative mosquito control method with promising results. The study herein concerns the investigation, for the first time under realistic conditions in the field, of the joint action of a carvacrol-rich oregano Essential Oil (EO) with two conventional insecticides, namely, the insect growth regulator diflubenzuron and the bio-insecticide Bacillus thuringiensis israelensis (B.t.i.), in road drains in Crevalcore city, Italy, against Culex pipiens and Aedes albopictus. According to the obtained results, the application of both plain EO and its mixtures with diflubenzuron and B.t.i. exerted very high efficacy in terms of immature mosquito population reduction over a two-week period. Three weeks after treatment, the performance of the oil and its mixtures diminished but remained high, while the addition of diflubenzuron potentiated the persistent action of the oil against Cx. pipiens. These findings are indicative of the potential of mixing carvacrol-rich EO with diflubenzuron and B.t.i. as an efficient eco-friendly alternative to mono-insecticide applications in road drains against Cx. pipiens and Ae. albopictus larvae.

Efficacy of native cyclopoid copepods in biological vector control with regard to their predatory behavior against the Asian tiger mosquito, Aedes albopictus

BackgroundThe control of the Asian tiger mosquito Aedes albopictus (Diptera: Culicidae) is crucial owing to its high vector competence for more than 20 arboviruses—the most important being dengue, chikungunya and Zika virus. Aedes albopictus has an enormous adaptive potential, and its invasive spreading across urban and suburban environments poses challenges for its control. Therefore, all suitable, cost-effective and eco-friendly control tools should be put into practice. In this context, cyclopoid copepods are already known as effective predators of mosquito larvae. This study reports an essential preliminary step towards the integration of copepods into the vector control strategy in Germany, in order to provide a sustainable tool in an integrated control strategy based on the elimination or sanitation of breeding sites, the use of formulations based on Bacillus thuringiensis israelensis (Bti.) and the sterile insect technique (SIT).MethodsThe predatory potential of native cyclopoid copepods, namely the field-derived species Megacyclops viridis (Crustacea: Cyclopidae), was examined against the larvae of Ae. albopictus, and for comparison, against the larvae of the common house mosquito, Culex pipiens sensu lato (Diptera: Culicidae). The use of different larval instars as prey, and various predator-to-prey ratios, were examined under laboratory and semi-field conditions. The compatibility of Bti. applications along with the use of copepods was assessed in the laboratory.ResultsHigh predation efficiency of M. viridis upon first-instar larvae of Ae. albopictus was observed under laboratory (up to 96%) and semi-field conditions (65.7%). The copepods did not prey upon stages further developed than the first instars, and in comparison with Ae. albopictus, the predation rates on the larvae of Cx. pipiens s.l. were significantly lower.ConclusionsThe results indicate a high predation potential of M. viridis against Ae. albopictus larvae, even though strong larval stage and mosquito species preferences were implicated. The integration of copepods as a promising biocontrol agent to the vector control strategy in Germany is therefore highly recommended, especially because of the excellent compatibility of copepods with the use of Bti. However, further research is required, concerning all the probable parameters that may impact the copepod performance under natural conditions.Graphical

SCG Mosquito Trap: A New Lethal Ovitrap for Controlling Aedes aegypti (L.) and Ae. albopictus (Skuse); the Vectors of Dengue Haemorrhagic Fever, and Chikungunya and Zika Fever

Aedes aegypti (L.) and Ae. albopictus (Skuse) are known to be the vectors of dengue haemorrhagic fever (DHF), and chikungunya and zika fever. Of these diseases, DHF is the most dangerous because it has high incidence and mortality in many countries worldwide, especially in Asia. As there is currently no effective vaccine available to prevent these diseases, vector control is the best strategy for controlling them. Therefore, the SCG Mosquito Trap: a new lethal ovitrap combined with attractant and biological larvicide, was developed in this study for controlling Ae. aegypti and Ae. albopictus mosquitoes. The trap without attractant showed significantly higher oviposition efficacy than that of a conventional one in luring gravid Ae. aegypti and Ae. Albopictus to lay their eggs under laboratory conditions by approximately 3.1 and 2.6 times, respectively. The attractant derived from carpet shell extract increased the oviposition efficacy of the SCG Mosquito Trap by about 1.7 and 4.1 times against Ae. aegypti and Ae. albopictus, respectively, under laboratory conditions. Bacillus thuringiensis israelensis (Bti) was the biological larvicide used in the SCG Mosquito Trap. It provided a complete killing effect (100% mortality) against the larvae of Ae. aegypti and Ae. albopictus for 4 weeks post single application, as no larvae hatched from sponge sheets applied with Bti, which were obtained from the SCG Mosquito Trap. In the field study against Ae. aegypti, the SCG Mosquito Trap could reduce the number of houses infested from 80% (with 75% from the positive trap and an average of 242 eggs/trap) to 30% (with 22.5% from the positive trap and an average of 64 eggs/trap) by the fourth week after initiation. In conclusion, the SCG Mosquito Trap developed from this study could be used additionally as an effective device for controlling Ae. aegypti and Ae. albopictus mosquitoes, in order to prevent the diseases that are transmitted by these vectors.&nbsp; &nbsp