Semi-field Experiments Research Articles

Evaluation of personal protection afforded by repellent-treated sandals against mosquito bites in south-eastern Tanzania

BackgroundOutdoor and early evening mosquito biting needs to be addressed if malaria elimination is to be achieved. While indoor-targeted interventions, such as insecticide-treated nets and indoor residual spraying, remain essential, complementary approaches that tackle persisting outdoor transmission are urgently required to maximize the impact. Major malaria vectors principally bite human hosts around the feet and ankles. Consequently, this study investigated whether sandals treated with efficacious spatial repellents can protect against outdoor biting mosquitoes.MethodologySandals affixed with hessian bands measuring 48 cm2 treated with 0.06 g, 0.10 g and 0.15 g of transfluthrin were tested in large cage semi-field and full field experiments. Sandals affixed with hessian bands measuring 240 cm2 and treated with 0.10 g and 0.15 g of transfluthrin were also tested semi field experiments. Human landing catches (HLC) were used to assess reduction in biting exposure by comparing proportions of mosquitoes landing on volunteers wearing treated and untreated sandals. Sandals were tested against insectary reared Anopheles arabiensis mosquitoes in semi-field experiments and against wild mosquito species in rural Tanzania.ResultsIn semi-field tests, sandals fitted with hessian bands measuring 48 cm2 and treated with 0.15 g, 0.10 g and 0.06 g transfluthrin reduced mosquito landings by 45.9%, (95% confidence interval (C.I.) 28–59%), 61.1% (48–71%), and 25.9% (9–40%), respectively compared to untreated sandals. Sandals fitted with hessian bands measuring 240 cm2 and treated with 0.15 g and 0.10 g transfluthrin reduced mosquito landings by 59% (43–71%) and 64% (48–74%), respectively. In field experiments, sandals fitted with hessian bands measuring 48 cm2 and treated with 0.15 g transfluthrin reduced mosquito landings by 70% (60–76%) against Anopheles gambiae sensu lato, and 66.0% (59–71%) against all mosquito species combined.ConclusionTransfluthrin-treated sandals conferred significant protection against mosquito bites in semi-field and field settings. Further evaluation is recommended for this tool as a potential complementary intervention against malaria. This intervention could be particularly useful for protecting against outdoor exposure to mosquito bites. Additional studies are necessary to optimize treatment techniques and substrates, establish safety profiles and determine epidemiological impact in different settings.

Chemical Mediation of Oviposition by Anopheles Mosquitoes: a Push-Pull System Driven by Volatiles Associated with Larval Stages

The oviposition behavior of mosquitoes is mediated by chemical cues. In the malaria mosquito Anopheles gambiae, conspecific larvae produce infochemicals that affect this behavior. Emanations from first instar larvae proved strongly attractive to gravid females, while those from fourth instars caused oviposition deterrence, suggesting that larval developmental stage affected the oviposition choice of the female mosquito.We examined the nature of these chemicals by headspace collection of emanations of water in which larvae of different stages were developing. Four chemicals with putative effects on oviposition behavior were identified: dimethyldisulfide (DMDS) and dimethyltrisulfide (DMTS) were identified in emanations from water containing fourth instars; nonane and 2,4-pentanedione (2,4-PD) were identified in emanations from water containing both first and fourth instars. Dual-choice oviposition studies with these compounds were done in the laboratory and in semi-field experiments in Tanzania.In the laboratory, DMDS and DMTS were associated with oviposition-deterrent effects, while results with nonane and 2,4-PD were inconclusive. In further studies DMDS and DMTS evoked egg retention, while with nonane and 2,4-PD 88% and 100% of female mosquitoes, respectively, laid eggs. In dual-choice semi-field trials DMDS and DMTS caused oviposition deterrence, while nonane and 2,4-PD evoked attraction, inducing females to lay more eggs in bowls containing these compounds compared to the controls. We conclude that oviposition of An. gambiae is mediated by these four infochemicals associated with conspecific larvae, eliciting either attraction or deterrence. High levels of egg retention occurred when females were exposed to chemicals associated with fourth instar larvae.

Toxicity of the Locally Formulated Diesel Oil Alone and Mixed with Botanical Synthetic Materials against Mealybug Ferrisia virgate (Cockerell)

Physico-chemical properties of crude diesel oil and botanical synthetic materials (thymol and camphor) were studied and prepared as emulsifiable concentrate formulation (EC). Prepared formulations passed successfully specified testes, then their toxicity were investigated against different stages of mealybug Ferrisia virgata (Cockerell) under laboratory conditions. Results indicated that all tested formulations showed high toxicity against all tested insect stages. The mixing, thymol or camphor with diesel oil increased toxicity of oil against mealybug F. virgate, whereas mixture, thymol with diesel oil was more effective than camphor with diesel oil. LC50 values after two days of application were 4.02, 4.51, 4.86 and 5.33 ml/l for diesel oil, while it were 0.17, 0.17, 0.25, and 0.25ml/l for mixture of oil and thymol, and 0.88, 0.99, 1.12, and 1.24 ml/l for mixture of diesel oil and camphor for first, second, third and adult stages of F. virgate respectively. While LC50 values after three days of application were: 1.43, 1.49, 1.61 and 1.77 ml/l for diesel oil, while it were 0.03, 0.03, 0.08 and 0.11 ml/l for mixture of oil with thymol, and 0.14, 0.24, 0.21 and 0.16 ml/l for mixture of oil with camphor for 1st, 2nd, 3rd and adult of F. virgate respectively. Results showed, efficacy of tested materials increased by increasing concentration and period after application and mixing botanical synthetic materials with diesel oil increased toxicity against all tested stages; moreover, mixtures could be used for controlling mealybug in medical, aromatic and ornamental plants after conducting more semi-field and field experiments.

Use of Novaluron-Based Autocidal Gravid Ovitraps to Control Aedes Dengue Vector Mosquitoes in the District of Gampaha, Sri Lanka.

Dengue is the most important mosquito-borne viral infection in Sri Lanka causing an enormous social and economic burden in the country. In the absence of therapeutic drugs and the developed vaccines are under investigation, vector control is the best strategy to reduce the disease transmission. Therefore, the development of novel tools to control dengue vector mosquitoes has become the need of the hour. Novaluron is a recently developed Insect Growth Regulator (IGR) which inhibits chitin synthesis in immature stages of insects. The aim of the study was to identify the efficacy of a simple and cost-effective Autocidal Gravid Ovitrap (AGO) developed using Novaluron to control dengue outbreaks in the District of Gampaha, Sri Lanka. Laboratory and semifield experiments were performed to identify the activity range, optimum field dosage, and residual effects of Novaluron following the World Health Organization guidelines, and field experiments were performed in the Ragama Medical Officer of Health (MOH) area. Two study areas 800 m apart were selected and assigned as treated and control areas randomly. In each study area, 30 households were selected randomly. Each household was given two ovitraps, one placed indoors and the other placed outdoors. Mortality and survival counts were recorded separately for one-year time period and data were analyzed using a two-way repeated measures analysis of variance model. During the laboratory experiments, the adult emerging inhibition was 100% in all tested concentrations. The optimum field dosage was 2 ppm and the residual effect was 28 days. In the field experiments, significantly higher mortality counts were recorded in treated areas both indoor- and outdoor-placed AGOs. Two-factor repeated measures ANOVA followed by Tukey's test confirmed that the mean mortality count is high for the developed AGOs both indoor and outdoor settings. The developed AGO can be deployed to control both indoor and outdoor dengue vector mosquito populations, and in dengue-risk areas, the ovitrap will be supportive to local health authorities to enhance the efficiency of future vector control programs.

Ingested insecticide to control Aedes aegypti: developing a novel dried attractive toxic sugar bait device for intra-domiciliary control

BackgroundIllnesses transmitted by Aedes aegypti (Linnaeus, 1762) such as dengue, chikungunya and Zika comprise a considerable global burden; mosquito control is the primary public health tool to reduce disease transmission. Current interventions are inadequate and insecticide resistance threatens the effectiveness of these options. Dried attractive bait stations (DABS) are a novel mechanism to deliver insecticide to Ae. aegypti. The DABS are a high-contrast 28 inch2 surface coated with dried sugar-boric acid solution. Aedes aegypti are attracted to DABS by visual cues only, and the dried sugar solution elicits an ingestion response from Ae. aegypti landing on the surface. The study presents the development of the DABS and tests of their impact on Ae. aegypti mortality in the laboratory and a series of semi-field trials.MethodsWe conducted multiple series of laboratory and semi-field trials to assess the survivability of Ae. aegypti mosquitoes exposed to the DABS. In the laboratory experiments, we assessed the lethality, the killing mechanism, and the shelf life of the device through controlled experiments. In the semi-field trials, we released laboratory-reared female Ae. aegypti into experimental houses typical of peri-urban tropical communities in South America in three trial series with six replicates each. Laboratory experiments were conducted in Quito, Ecuador, and semi-field experiments were conducted in Machala, Ecuador, an area with abundant wild populations of Ae. aegypti and endemic arboviral transmission.ResultsIn the laboratory, complete lethality was observed after 48 hours regardless of physiological status of the mosquito. The killing mechanism was determined to be through ingestion, as the boric acid disrupted the gut of the mosquito. In experimental houses, total mosquito mortality was greater in the treatment house for all series of experiments (P < 0.0001).ConclusionsThe DABS devices were effective at killing female Ae. aegypti under a variety of laboratory and semi-field conditions. DABS are a promising intervention for interdomiciliary control of Ae. aegypti and arboviral disease prevention.

Field evaluation of Spalangia endius Walker in controlling Zeugodacus cucurbitae (Coquillett)

We designed a series of semifield experiments and two types of nylon cages to evaluate the control efficacy of Spalangia endius Walker in the field and to verify the possibility of using S. endius for the control of Zeugodacus cucurbitae (Coquillett) pupae. More hosts were killed by S. endius at higher parasitoid–host ratios. The effectiveness of S. endius was highest at a parasitoid–host ratio of 1:10, which caused 50.33% and 33% mortality in enclosed and semiopen conditions, respectively. The adult parasitoids supplemented with honey solution or water survived to 7 or 5 days at most, respectively. S. endius showed a low control efficacy for Z. cucurbitae pupae in the field. However, combined with the natural mortality of pupae and the effects of other natural enemies, the mortality of Z. cucurbitae pupae exceeded 85%. Thus, S. endius may help control Z. cucurbitae pupae in the field, but other control strategies need to be applied to kill the pupae in the soil which S. endius cannot reach and to control any remaining adult Z. cucurbitae.

Oviposition site attraction of Aedes albopictus to sites with conspecific and heterospecific larvae during an ongoing invasion in Medell\xedn, Colombia

BackgroundAedes aegypti and Aedes albopictus are two globally invasive vectors with similar ecological niches. Encounters between them can result in either competitive exclusion or stable co-existence, but it is unclear what drives these variable outcomes. Larval competition in favor of Ae. albopictus is a main hypothesis for the competitive exclusion of Ae. aegypti observed in some regions. However, the role of oviposition preference in determining the degree of competitive larval interactions in the field is not well understood. In this study, we used a combination of mark-release-recapture methods with ovitraps in the open-field and a semi-field cage to test whether gravid Ae. albopictus seek oviposition sites in response to the presence, species, and density of either conspecific or heterospecific Ae. aegypti larvae in the aquatic habitat. We conducted our study in Medellín, Colombia, where Ae. aegypti is a long-term resident and Ae. albopictus is a recent invader.ResultsIn the open-field and semi-field cage experiments, gravid Ae. albopictus showed strong preference for ovitraps with larvae over those without. They consistently preferred ovitraps with higher density of conspecific (Ae. albopictus) larvae and low density of heterospecific (Ae. aegypti) larvae over traps with no larvae or high density of heterospecific (Ae. aegypti) larvae. In the semi-field cage experiment, traps with low density of Ae. albopictus were not preferred more or less than any other trap, but in the open-field experiment they were preferred over traps without larvae.ConclusionsWe demonstrate, through open-field and semi-field cage experiments, that Ae. albopictus are more attracted to oviposition sites with larvae and that the combination of species and density of larvae influence attraction. This demonstrated preference could increase interspecific larval competition as Ae. albopictus actively seek containers with conspecific and heterospecific larvae. Any resulting competition with Ae. aegypti may favor one species over the other and alter the distribution or abundance of both. Because these species vary in vectorial capacity and insecticide resistance, effects of interspecific competition could ultimately impact arbovirus transmission rates and the success of vector control efforts.

Effects of Aqueous Extracts from Amazon Plants on Plutella xylostella (Lepidoptera: Plutellidae) and Brevicoryne brassicae (Homoptera: Aphididae) in Laboratory, Semifield, and field trials.

We evaluated the insecticide activities of aqueous extracts of five species of plants from the Ecuadorian Amazon (Deguelia utilis (ACSm.) AMGAZEVEDO (Leguminosae: Papilionoideae), Xanthosoma purpuratum K. Krause (Alismatales: Araceae), Clibadium sp. (Asteracea: Asterales), Witheringia solanacea L'Hér (Solanales: Solanaceae), and Dieffenbachia costata H. Karst. ex Schott (Alismatales: Araceae)) plus Cymbopogon citratus Stapf. (Poales: Poaceae) under laboratory, open-field conditions in Plutella xylostella L. (diamondback moth), and semifield conditions in Brevicoryne brassicae L. Tap water was used as a negative control, and synthetic insecticides were used as positive controls. In a laboratory bioassay, aqueous extracts of D. utilis resulted in P. xylostella larval mortality. In contrast to chlorpyrifos, all botanicals were oviposition deterrents. All extracts except Clibadium sp. decreased leaf consumption by P. xylostella larvae. In semifield experiments, D. utilis, Clibadium sp., D. costata, and X. purpuratum initially controlled the population of B. brassicae, but 7 d after application, all botanicals except the D. utilis lost their ability to control the pest. In field experiments on broccoli crops in both dry and rainy seasons, the extracts did not control the abundance of P. xylostella, where as a mixture of two insecticides (chlorpyrifos + lambda cyhalothrin) did. These results show some incongruences from laboratory to semifield and field conditions, indicating that more studies, including the identification of the chemicals responsible for the biological activity, its stability, and the effects of chemotypes on insecticidal activity, are needed to understand the potential of these plant species as botanical insecticides.

Olfactory responses of Amblyomma maculatum to rumen fluid and other odourants that attract blood‐seeking arthropods

Amblyomma maculatum Koch (Ixodida: Ixodidae) has emerged as a significant vector of human and companion animal diseases in the U.S.A. When expanding in range, A.maculatum can be difficult to collect in the field and control on livestock. A novel method is needed to improve the field collection of A. maculatum, as well as to control their effects as ectoparasites of livestock and companion animals. The present study aimed to test the effects of known volatiles on the activation and selection choices of A. maculatum in a laboratory-based Y-tube assay and field-based assays. Although the majority of adult A. maculatum were activated to move by five of the seven semiochemicals tested, only rumen fluid significantly attracted ticks to make a selection in the Y-tube apparatus. Rumen fluid attracted the most A. maculatum in the laboratory, with 56% (84/150) making it to the rumen Y-tube arm, although the results were not replicated in semi-field experiments. These studies highlight the need for continued work to identify attractants for tick vectors that will assist field collections. These attractants could also be incorporated into management strategies that lead to prevention technologies to reduce tick burdens on cattle or in risk areas of humans.

Too \u201csexy\u201d for the field? Paired measures of laboratory and semi-field performance highlight variability in the apparent mating fitness of Aedes aegypti transgenic strains

BackgroundEvaluating and improving mating success and competitive ability of laboratory-reared transgenic mosquito strains will enhance the effectiveness of proposed disease-control strategies that involve deployment of transgenic strains. Two components of the mosquito rearing process, larval diet quantity and aquatic environment - which are linked to physiological and behavioural differences in adults - are both relatively easy to manipulate. In mosquitoes, as for many other arthropod species, the quality of the juvenile habitat is strongly associated with adult fitness characteristics, such as longevity and fecundity. However, the influence of larval conditioning on mating performance is poorly understood. Here, we investigated the combined effects of larval diet amount and environmental water source on adult male mating success in a genetically modified strain of Aedes aegypti mosquitoes in competition with wild-type conspecifics. Importantly, this research was conducted in a field setting using low generation laboratory and wild-type lines.ResultsBy controlling larval diet (high and low) and rearing water source (field-collected and laboratory water), we generated four treatment lines of a genetically modified strain of Ae. aegypti tagged with fluorescent sperm. Laboratory reared mosquitoes were then competed against a low generation wild-type colony in a series of laboratory and semi-field mating experiments. While neither food quantity nor larval aquatic environment were found to affect male mating fitness, the transgenic lines consistently outperformed wild-types in laboratory competition assays, an advantage that was not conferred to semi-field tests.ConclusionsUsing a model transgenic system, our results indicate that differences in the experimental conditions of laboratory- and field-based measures of mating success can lead to variation in the perceived performance ability of modified strains if they are only tested in certain environments. While there are many potential sources of variation between laboratory and field lines, laboratory adaptation - which may occur over relatively few generations in this species - may directly impact mating ability depending on the context in which it is measured. We suggest that colony-hybridization with field material can potentially be used to mitigate these effects in a field setting. Release programs utilising mass-produced modified laboratory strains should incorporate comparative assessments of quality in candidate lines.

Malaria mosquito control in rice paddy farms using biolarvicide mixed with fertilizer in Tanzania: semi-field experiments

BackgroundThe wide distribution of malaria mosquito breeding sites within tropical environments limits the mosquito larval source management efforts to control malaria. Rice farming contributes substantially in supporting malaria mosquito productivity in tropical countries. To overcome this challenge, this study was carried out to determine the effect of applying a mixture of biolarvicide and fertilizer on mosquito larvae density in rice farms under semi-field conditions in Tanzania.MethodsA semi-field experiment was designed to determine the timing of application of a biolarvicide, Bacillus thuringiensis israelensis (Bti) and fertilizer (di-ammonium phosphate-DAP or urea) and assess their effect on mosquito larvae density and rice grain outputs. The experiment had five blocks (4 treatment arms and one control arm) and each had four replicates. Treatment arms had different intervals of days between treatments for mixtures of fertilizer and biolarvicides. The dosages used were 10 g of Bti/16 M2 and 160 g of DAP/Urea/16 m2.ResultsIn overall, the intervention blocks (with biolarvicide) had lowest mean mosquito larvae abundance compared to control block (F = 22.42, P < 0.001). Similarly, the control arm maintained highest density of Anopheles gambiae sensu lato larvae compared to interventions blocks (F = 21.6, P < 0.001). The best determined timing for application of Bti was in 7 and in 10 days (F = 3.753, P < 0.001). There was neither significant different in mean rice grain harvest per ten panicle (F = 1.453, P = 0.27) nor mean difference in rice grain harvest (F = 1.479, P = 0.26) per intervention arms.ConclusionThe findings of this study have shown that application of a mixture of Bti and fertilizer have impact on both mosquito larvae density and maintaining yield rice harvest. Thus, application of a combination of biolarvicide and fertilizer can be an alternative approach in malaria mosquito intervention among rice farming communities of rural Tanzania.

Potential of the European earwig (Forficula auricularia) as a biocontrol agent of the soft and stone fruit pest Drosophila suzukii.

The unintentional introduction of Drosophila suzukii (Matsumura) from Asia has caused global economic losses in the soft and stone fruit industries. Pesticide use can have unintended negative impacts on natural enemies, disrupting attempts to incorporate integrated pest management programmes. Generalist predators could potentially act as biocontrol agents of D. suzukii. In this context, the predatory capabilities of the European earwig (Forficula auricularia) were investigated. In semi-field conditions, F. auricularia were effective at reducing the reproductive rate of D. suzukii in more densely populated enclosures. In controlled laboratory conditions, significant negative effects of earwigs were observed for both low (three breeding pairs) and high (six breeding pairs) D. suzukii densities. Both semi-field and laboratory experiments revealed that F. auricularia predation on adult D. suzukii could not account for the subsequent reductions in population density. Reductions in both larval and adult offspring in the presence of earwigs indicate an impact on D. suzukii via predation prior to metamorphosis or disruption of oviposition. Although F. auricularia may predate D. suzukii populations, its capacity to act as a biocontrol agent may be limited. However, results suggest that F. auricularia may be a more effective biocontrol agent earlier in the growing season. © 2019 Society of Chemical Industry.

Characterization of a broad-based mosquito yeast interfering RNA larvicide with a conserved target site in mosquito semaphorin-1a genes

BackgroundRNA interference (RNAi), which has facilitated functional characterization of mosquito neural development genes such as the axon guidance regulator semaphorin-1a (sema1a), could one day be applied as a new means of vector control. Saccharomyces cerevisiae (baker’s yeast) may represent an effective interfering RNA expression system that could be used directly for delivery of RNA pesticides to mosquito larvae. Here we describe characterization of a yeast larvicide developed through bioengineering of S. cerevisiae to express a short hairpin RNA (shRNA) targeting a conserved site in mosquito sema1a genes.ResultsExperiments conducted on Aedes aegypti larvae demonstrated that the yeast larvicide effectively silences sema1a expression, generates severe neural defects, and induces high levels of larval mortality in laboratory, simulated-field, and semi-field experiments. The larvicide was also found to induce high levels of Aedes albopictus, Anopheles gambiae and Culex quinquefasciatus mortality.ConclusionsThe results of these studies indicate that use of yeast interfering RNA larvicides targeting mosquito sema1a genes may represent a new biorational tool for mosquito control.

Biological Activity of Sumilarv 0.5G against Anopheles gambiae sensu stricto and Anopheles arabiensis in Northern Tanzania

Background: Sumilarv 0.5G (Sumitomo Chemical Co., Ltd., Tokyo, Japan) is a granular insecticide developed for the control of mosquito and fly aquatic stages. The active ingredient is pyriproxyfen (4-phenoxyphenyl (RS)-2-(2 – pyridyloxy) propyl ether), a juvenile hormone analogue that acts as an insect growth regulator. Sumilarv 0.5G functions by inhibition of adult emergence from pupae. In this study, the Tropical Pesticides Research Institute in Tanzania carried out laboratory, semifield, and full-field evaluation on a new candidate of pupicide, Sumilarv 0.5G. The present study, therefore, sought to test the bioefficacy of Sumilarv 0.5G in laboratory, semifield, and full-field conditions in Mabogini, northern Tanzania. Methods: Standard World Health Organization laboratory bioefficacy evaluations of Sumilarv 0.5G and untreated microcosms were prepared and monitored for inhibition of the larvae introduced to the habitats, while field plots were monitored for 5 weeks after the introduction of Sumilarv 0.5G using manufacturer-recommended doses. Results: Sumilarv 0.5G biolarvicide was highly efficacious in its pupicidal effect, with an adult emergence inhibition rate of up to 90% in all conditions. In both laboratory and semifield experiments, the emergence inhibition was dose-dependent, with the lowest adult emergence being recorded in association with the highest Sumilarv 0.5G dose of 0.03 ppm of active ingredient. Under field conditions, the application rate recommended by the manufacturer – 5 mg ai per m2 – reduced the adult emergence rate by 90% to 96% for up to 5 weeks. Conclusion: We demonstrated the long-lasting biological activity of Sumilarv 0.5G under field conditions. Notably, the field efficacy was attained using the recommended dose of 5 mg per m2, thus making it economical to apply this product, which is capable of inhibiting mosquito productivity in natural habitats for longer periods than achieved by existing products, the efficacy of which is usually about 1 week.

Biological Activity of Sumilarv 0.5G against Anopheles gambiae sensu stricto and Anopheles arabiensis in Northern Tanzania

Background: Sumilarv 0.5G (Sumitomo Chemical Co., Ltd., Tokyo, Japan) is a granular insecticide developed for the control of mosquito and fly aquatic stages. The active ingredient is pyriproxyfen (4-phenoxyphenyl (RS)-2-(2 – pyridyloxy) propyl ether), a juvenile hormone analogue that acts as an insect growth regulator. Sumilarv 0.5G functions by inhibition of adult emergence from pupae. In this study, the Tropical Pesticides Research Institute in Tanzania carried out laboratory, semifield, and full-field evaluation on a new candidate of pupicide, Sumilarv 0.5G. The present study, therefore, sought to test the bioefficacy of Sumilarv 0.5G in laboratory, semifield, and full-field conditions in Mabogini, northern Tanzania. Methods: Standard World Health Organization laboratory bioefficacy evaluations of Sumilarv 0.5G and untreated microcosms were prepared and monitored for inhibition of the larvae introduced to the habitats, while field plots were monitored for 5 weeks after the introduction of Sumilarv 0.5G using manufacturer-recommended doses. Results: Sumilarv 0.5G biolarvicide was highly efficacious in its pupicidal effect, with an adult emergence inhibition rate of up to 90% in all conditions. In both laboratory and semifield experiments, the emergence inhibition was dose-dependent, with the lowest adult emergence being recorded in association with the highest Sumilarv 0.5G dose of 0.03 ppm of active ingredient. Under field conditions, the application rate recommended by the manufacturer – 5 mg ai per m2 – reduced the adult emergence rate by 90% to 96% for up to 5 weeks. Conclusion: We demonstrated the long-lasting biological activity of Sumilarv 0.5G under field conditions. Notably, the field efficacy was attained using the recommended dose of 5 mg per m2, thus making it economical to apply this product, which is capable of inhibiting mosquito productivity in natural habitats for longer periods than achieved by existing products, the efficacy of which is usually about 1 week.

Biological Activity of Sumilarv 0.5G against Anopheles gambiae sensu stricto and Anopheles arabiensis in Northern Tanzania

Background: Sumilarv 0.5G (Sumitomo Chemical Co., Ltd., Tokyo, Japan) is a granular insecticide developed for the control of mosquito and fly aquatic stages. The active ingredient is pyriproxyfen (4-phenoxyphenyl (RS)-2-(2 – pyridyloxy) propyl ether), a juvenile hormone analogue that acts as an insect growth regulator. Sumilarv 0.5G functions by inhibition of adult emergence from pupae. In this study, the Tropical Pesticides Research Institute in Tanzania carried out laboratory, semifield, and full-field evaluation on a new candidate of pupicide, Sumilarv 0.5G. The present study, therefore, sought to test the bioefficacy of Sumilarv 0.5G in laboratory, semifield, and full-field conditions in Mabogini, northern Tanzania. Methods: Standard World Health Organization laboratory bioefficacy evaluations of Sumilarv 0.5G and untreated microcosms were prepared and monitored for inhibition of the larvae introduced to the habitats, while field plots were monitored for 5 weeks after the introduction of Sumilarv 0.5G using manufacturer-recommended doses. Results: Sumilarv 0.5G biolarvicide was highly efficacious in its pupicidal effect, with an adult emergence inhibition rate of up to 90% in all conditions. In both laboratory and semifield experiments, the emergence inhibition was dose-dependent, with the lowest adult emergence being recorded in association with the highest Sumilarv 0.5G dose of 0.03 ppm of active ingredient. Under field conditions, the application rate recommended by the manufacturer – 5 mg ai per m2 – reduced the adult emergence rate by 90% to 96% for up to 5 weeks. Conclusion: We demonstrated the long-lasting biological activity of Sumilarv 0.5G under field conditions. Notably, the field efficacy was attained using the recommended dose of 5 mg per m2, thus making it economical to apply this product, which is capable of inhibiting mosquito productivity in natural habitats for longer periods than achieved by existing products, the efficacy of which is usually about 1 week.

Biological Activity of Sumilarv 0.5G against Anopheles gambiae sensu stricto and Anopheles arabiensis in Northern Tanzania

Background: Sumilarv 0.5G (Sumitomo Chemical Co., Ltd., Tokyo, Japan) is a granular insecticide developed for the control of mosquito and fly aquatic stages. The active ingredient is pyriproxyfen (4-phenoxyphenyl (RS)-2-(2 – pyridyloxy) propyl ether), a juvenile hormone analogue that acts as an insect growth regulator. Sumilarv 0.5G functions by inhibition of adult emergence from pupae. In this study, the Tropical Pesticides Research Institute in Tanzania carried out laboratory, semifield, and full-field evaluation on a new candidate of pupicide, Sumilarv 0.5G. The present study, therefore, sought to test the bioefficacy of Sumilarv 0.5G in laboratory, semifield, and full-field conditions in Mabogini, northern Tanzania. Methods: Standard World Health Organization laboratory bioefficacy evaluations of Sumilarv 0.5G and untreated microcosms were prepared and monitored for inhibition of the larvae introduced to the habitats, while field plots were monitored for 5 weeks after the introduction of Sumilarv 0.5G using manufacturer-recommended doses. Results: Sumilarv 0.5G biolarvicide was highly efficacious in its pupicidal effect, with an adult emergence inhibition rate of up to 90% in all conditions. In both laboratory and semifield experiments, the emergence inhibition was dose-dependent, with the lowest adult emergence being recorded in association with the highest Sumilarv 0.5G dose of 0.03 ppm of active ingredient. Under field conditions, the application rate recommended by the manufacturer – 5 mg ai per m2 – reduced the adult emergence rate by 90% to 96% for up to 5 weeks. Conclusion: We demonstrated the long-lasting biological activity of Sumilarv 0.5G under field conditions. Notably, the field efficacy was attained using the recommended dose of 5 mg per m2, thus making it economical to apply this product, which is capable of inhibiting mosquito productivity in natural habitats for longer periods than achieved by existing products, the efficacy of which is usually about 1 week.

Interacting stressors matter: diet quality and virus infection in honeybee health.

Honeybee population declines have been linked to multiple stressors, including reduced diet diversity and increased exposure to understudied viral pathogens. Despite interest in these factors, few experimental studies have explored the interaction between diet diversity and viral infection in honeybees. Here, we used a mixture of laboratory cage and small semi-field nucleus hive experiments to determine how these factors interact. In laboratory experiments, we found that high-quality diets (polyfloral pollen and high-quality single-source pollen) have the potential to reduce mortality in the face of infection with Israeli acute paralysis virus (IAPV). There was a significant interaction between diet and virus infection on mortality, even in the presence of high virus titres, suggesting that good diets can help bees tolerate virus infection. Further, we found that extreme stress in the form of pollen starvation in conjunction with IAPV infection increase exiting behaviour from small experimental hives. Finally, we showed that higher-quality pollen diets have significantly higher iron and calcium content, suggesting micronutrient deficiencies could be an under-explored area of bee nutrition.

Potential surrogate plants for use in semi-field pesticide risk assessment with Megachile rotundata.

BackgroundCurrent regulatory pesticide risk assessments for bees are based primarily on the honey bee (Apis mellifera) and may not always be protective of solitary bees. To incorporate solitary bees into the risk assessment process, standardized methods to assess the hazard of pesticides under semi-field (Tier II) conditions will be needed. We conducted a series of experiments over 2 years to assess potential surrogate plants and adult release rates for use in semi-field experiments with the alfalfa leafcutting bee (ALB, Megachile rotundata).MethodsWe compared ALB foraging activity and reproduction on 12 m2 plots of flowering alfalfa (Medicago sativa) and buckwheat (Fagopyrum esculentum) at low (10♀/20♂) and high (20♀/40♂) adult release rates. The following year, we assessed the same endpoints on plots of purple tansy (Phacelia tanacetifolia) at a release rate of 10♀/15♂.ResultsAlthough ALB foraging activity was high on buckwheat plots, fewer adults were produced compared to alfalfa plots. On alfalfa, there were no differences in foraging activity, nesting, or reproduction between the low and high release rates. ALB readily foraged from purple tansy flowers, but females avoided purple tansy leaves for leaf cell construction.DiscussionOur study suggests that buckwheat alone cannot support ALB during semi-field studies on small plots. For alfalfa, we recommend a maximum release rate of 10♀/20♂ in 12 m2 plots. Further study of higher ALB release rates on purple tansy is warranted. A mixed planting of purple tansy and a plant suitable for leaf piece collection (e.g., buckwheat) may provide favorable conditions for ALB activity and reproduction during semi-field testing.

A short note on extreme sex ratio in solitary bees Osmia cornuta in semi-field trials testing the impact of neonicotinoids

The widespread prophylactic use of neonicotinoids has severe negative effects on non-target organisms that provide ecosystem services. Chronic neonicotinoid exposure led to a male-biased offspring sex ratio in the solitary bee species Osmia bicornis in laboratory experiments, but semi-field or field data are largely lacking. Here, we used semi-field experiments to investigate the potential impact of the neonicotinoid clothianidin on the sex ratio of the closely related species Osmia cornuta. Male and female individuals of O. cornuta were held in flight cages with fully blooming winter oilseed rape, treated or not with clothianidin. After hibernation, sex ratio of emerging offspring and overwintering mortality was determined. A total of 191 male and 4 female, and 203 male and 2 female O. cornuta emerged in the control and the clothianidin treatment, respectively, thereby clearly showing an extremely male-biased sex ratio. However, there was no significant clothianidin treatment effect. As sex ratio was strongly biased in both, the clothianidin and the control treatment, our data can obviously not explain the underlying mechanism. Such extreme sex ratios require more attention in semi-field studies assessing the impacts of pesticides and other stressors on solitary bees.