Tolerance and Excretion of the Mycotoxins Aflatoxin B1, Zearalenone, Deoxynivalenol, and Ochratoxin A by Alphitobius diaperinus and Hermetia illucens from Contaminated Substrates.

This study aimed to investigate the potential accumulation of mycotoxins in the lesser mealworm (Alphitobius diaperinus, LMW) and black soldier fly (Hermetia illucens, BSF) larvae. Feed was spiked with aflatoxin B1, deoxynivalenol (DON), ochratoxin A or zearalenone, and as a mixture of mycotoxins, to concentrations of 1, 10, and 25 times the maximum limits set by the European Commission for complete feed. This maximum limit is 0.02 mg/kg for aflatoxin B1, 5 mg/kg for DON, 0.5 mg/kg for zearalenone and 0.1 mg/kg for ochratoxin A. The mycotoxins and some of their metabolites were analysed in the larvae and residual material using a validated and accredited LC-MS/MS-based method. Metabolites considered were aflatoxicol, aflatoxin P1, aflatoxin Q1, and aflatoxin M1, 3-acetyl-DON, 15-acetyl-DON and DON-3-glycoside, and α- and ß-zearalenol. No differences were observed between larvae reared on mycotoxins individually or as a mixture with regards to both larvae development and mycotoxin accumulation/excretion. None of the mycotoxins accumulated in the larvae and were only detected in BSF larvae several orders of magnitude lower than the concentration in feed. Mass balance calculations showed that BSF and LMW larvae metabolized the four mycotoxins to different extents. Metabolites accounted for minimal amounts of the mass balance, except for zearalenone metabolites in the BSF treatments, which accounted for an average maximum of 86% of the overall mass balance. Both insect species showed to excrete or metabolize the four mycotoxins present in their feed. Hence, safe limits for these mycotoxins in substrates to be used for these two insect species possibly could be higher than for production animals. However, additional analytical and toxicological research to fully understand the safe limits of mycotoxins in insect feed, and thus the safety of the insects, is required.

Eave tubes for malaria control in Africa: prototyping and evaluation against Anopheles gambiae s.s. and Anopheles arabiensis under semi-field conditions in western Kenya.

BACKGROUND: Whilst significant progress has been made in the fight against malaria, vector control continues to rely on just two insecticidal methods, i.e., indoor residual spraying and insecticidal bed nets. House improvement shows great potential to complement these methods and may further reduce indoor mosquito biting and disease transmission. Open eaves serve as important mosquito house entry points and provide a suitable location for intercepting host-seeking anophelines. This study describes semi-field experiments in western Kenya with eave tubes, a household protection product that leverages the natural behaviour of host-seeking malaria mosquitoes. METHODS: Semi-field experiments were conducted in two screen-houses. In both of these a typical western Kenyan house, with mud walls and corrugated iron sheet roofing, was built. Eave tubes with bendiocarb- or deltamethrin-treated eave tube inserts were installed in the houses, and the impact on house entry of local strains of Anopheles gambiae and Anopheles arabiensis was determined. Experiments with open eave tubes (no netting) were conducted as a control and to determine house entry through eave tubes. Insecticidal activity of the inserts treated with insecticide was examined using standard 3-min exposure bioassays. RESULTS: Experiments with open eave tubes showed that a high percentage of released mosquitoes entered the house through tubes during experimental nights. When tubes were fitted with bendiocarb- or deltamethrin-treated inserts, on average 21% [95% CI 18-25%] and 39% [CI 26-51%] of An. gambiae s.s. were recaptured the following morning, respectively. This contrasts with 71% [CI 60-81%] in the treatment with open eaves and 54% [CI 47-61%] in the treatment where inserts were treated with fluorescent dye powder. For An. arabiensis recapture was 21% [CI 14-27%] and 22% [CI 18-25%], respectively, compared to 46% [CI 40-52%] and 25% [CI 15-35%] in the treatments with open tubes and fluorescent dye. CONCLUSIONS: Insecticide-treated eave tubes resulted in significant reductions in recapture rates for both malaria vector species, representing the first and promising results with this novel control tool against Kenyan malaria vectors. Further field evaluation of eave tubes under more realistic field conditions, as well as their comparison with existing approaches in terms of cost-effectiveness and community acceptance, is called for.

Eave tubes for malaria control in Africa: an introduction.

In spite of massive progress in the control of African malaria since the turn of the century, there is a clear and recognized need for additional tools beyond long-lasting insecticide-treated bed nets (LLINs) and indoor residual spraying (IRS) of insecticides, to progress towards elimination. Moreover, widespread and intensifying insecticide resistance requires alternative control agents and delivery systems to enable development of effective insecticide resistance management strategies. This series of articles presents a novel concept for malaria vector control, the 'eave tube', which may fulfil these important criteria. From its conceptualization to laboratory and semi-field testing, to demonstration of potential for implementation, the stepwise development of this new vector control approach is described. These studies suggest eave tubes (which comprise a novel way of delivering insecticides plus screening to make the house more 'mosquito proof') could be a viable, cost-effective, and acceptable control tool for endophilic and endophagic anophelines, and possibly other (nuisance) mosquitoes. The approach could be applicable in a wide variety of housing in sub-Saharan Africa, and possibly beyond, for vectors that use the eave as their primary house entry point. The results presented in these articles were generated during an EU-FP7 funded project, the mosquito contamination device (MCD) project, which ran between 2012 and 2015. This was a collaborative project undertaken by vector biologists, product developers, modellers, materials scientists, and entrepreneurs from five different countries.

Electrostatic coating enhances bioavailability of insecticides and breaks pyrethroid resistance in mosquitoes.

Insecticide resistance poses a significant and increasing threat to the control of malaria and other mosquito-borne diseases. We present a novel method of insecticide application based on netting treated with an electrostatic coating that binds insecticidal particles through polarity. Electrostatic netting can hold small amounts of insecticides effectively and results in enhanced bioavailability upon contact by the insect. Six pyrethroid-resistant Anopheles mosquito strains from across Africa were exposed to similar concentrations of deltamethrin on electrostatic netting or a standard long-lasting deltamethrin-coated bednet (PermaNet 2.0). Standard WHO exposure bioassays showed that electrostatic netting induced significantly higher mortality rates than the PermaNet, thereby effectively breaking mosquito resistance. Electrostatic netting also induced high mortality in resistant mosquito strains when a 15-fold lower dose of deltamethrin was applied and when the exposure time was reduced to only 5 s. Because different types of particles adhere to electrostatic netting, it is also possible to apply nonpyrethroid insecticides. Three insecticide classes were effective against strains of Aedes and Culex mosquitoes, demonstrating that electrostatic netting can be used to deploy a wide range of active insecticides against all major groups of disease-transmitting mosquitoes. Promising applications include the use of electrostatic coating on walls or eave curtains and in trapping/contamination devices. We conclude that application of electrostatically adhered particles boosts the efficacy of WHO-recommended insecticides even against resistant mosquitoes. This innovative technique has potential to support the use of unconventional insecticide classes or combinations thereof, potentially offering a significant step forward in managing insecticide resistance in vector-control operations.

Development and evaluation of a novel contamination device that targets multiple life-stages of Aedes aegypti.

BACKGROUND: The increasing global threat of Dengue demands new and easily applicable vector control methods. Ovitraps provide a low-tech and inexpensive means to combat Dengue vectors. Here we describe the development and optimization process of a novel contamination device that targets multiple life-stages of the Aedes aegypti mosquito. Special focus is directed to the diverse array of control agents deployed in this trap, covering adulticidal, larvicidal and autodissemination impacts. METHODS: Different trap prototypes and their parts are described, including a floater to contaminate alighting gravid mosquitoes. The attractiveness of the trap, different odor lures and floater design were studied using fluorescent powder adhering to mosquito legs and via choice tests. We demonstrate the mosquitocidal impacts of the control agents: a combination of the larvicide pyriproxyfen and the adulticidal fungus Beauveria bassiana. The impact of pyriproxyfen was determined in free-flight dissemination experiments. The effect on larval development inside the trap and in surrounding breeding sites was measured, as well as survival impacts on recaptured adults. RESULTS: The developmental process resulted in a design that consists of a black 3 Liter water-filled container with a ring-shaped floater supporting vertically placed gauze dusted with the control agents. On average, 90% of the mosquitoes in the fluorescence experiments made contact with the gauze on the floater. Studies on attractants indicated that a yeast-containing tablet was the most attractive odor lure. Furthermore, the fungus Beauveria bassiana was able to significantly increase mortality of the free-flying adults compared to controls. Dissemination of pyriproxyfen led to >90% larval mortality in alternative breeding sites and 100% larval mortality in the trap itself, against a control mortality of around 5%. CONCLUSION: This ovitrap is a promising new tool in the battle against Dengue. It has proven to be attractive to Aedes aegypti mosquitoes and effective in contaminating these with Beauveria bassiana. Furthermore, we show that the larvicide pyriproxyfen is successfully disseminated to breeding sites close to the trap. Its low production and operating costs enable large scale deployment in Dengue-affected locations.

Carbon dioxide baited trap catches do not correlate with human landing collections of Anopheles aquasalis in Suriname.

Three types of carbon dioxide-baited traps, i.e., the Centers for Disease Control Miniature Light Trap without light, the BioGents (BG) Sentinel Mosquito Trap (BG-Sentinel) and the Mosquito Magnet® Liberty Plus were compared with human landing collections in their efficiency in collecting Anopheles (Nyssorhynchus) aquasalis mosquitoes. Of 13,549 total mosquitoes collected, 1,019 (7.52%) were An. aquasalis. Large numbers of Culex spp were also collected, in particular with the (BG-Sentinel). The majority of An. aquasalis (83.8%) were collected by the human landing collection (HLC). None of the trap catches correlated with HLC in the number of An. aquasalis captured over time. The high efficiency of the HLC method indicates that this malaria vector was anthropophilic at this site, especially as carbon dioxide was insufficiently attractive as stand-alone bait. Traps using carbon dioxide in combination with human odorants may provide better results.

Carbon dioxide baited trap catches do not correlate with human landing collections of Anopheles aquasalis in Suriname

Three types of carbon dioxide-baited traps, i.e., the Centers for Disease Control Miniature Light Trap without light, the BioGents (BG) Sentinel Mosquito Trap (BG-Sentinel) and the Mosquito Magnet® Liberty Plus were compared with human landing collections in their efficiency in collecting Anopheles (Nyssorhynchus) aquasalis mosquitoes. Of 13,549 total mosquitoes collected, 1,019 (7.52 percent) were An. aquasalis. Large numbers of Culex spp were also collected, in particular with the (BG-Sentinel). The majority of An. aquasalis (83.8 percent) were collected by the human landing collection (HLC). None of the trap catches correlated with HLC in the number of An. aquasalis captured over time. The high efficiency of the HLC method indicates that this malaria vector was anthropophilic at this site, especially as carbon dioxide was insufficiently attractive as stand-alone bait. Traps using carbon dioxide in combination with human odorants may provide better results.

Differential attraction of malaria mosquitoes to volatile blends produced by human skin bacteria.

The malaria mosquito Anopheles gambiae sensu stricto is mainly guided by human odour components to find its blood host. Skin bacteria play an important role in the production of human body odour and when grown in vitro, skin bacteria produce volatiles that are attractive to A. gambiae. The role of single skin bacterial species in the production of volatiles that mediate the host-seeking behaviour of mosquitoes has remained largely unknown and is the subject of the present study. Headspace samples were taken to identify volatiles that mediate this behaviour. These volatiles could be used as mosquito attractants or repellents. Five commonly occurring species of skin bacteria were tested in an olfactometer for the production of volatiles that attract A. gambiae. Odour blends produced by some bacterial species were more attractive than blends produced by other species. In contrast to odours from the other bacterial species tested, odours produced by Pseudomonas aeruginosa were not attractive to A. gambiae. Headspace analysis of bacterial volatiles in combination with behavioural assays led to the identification of six compounds that elicited a behavioural effect in A. gambiae. Our results provide, to our knowledge, the first evidence for a role of selected bacterial species, common on the human skin, in determining the attractiveness of humans to malaria mosquitoes. This information will be used in the further development of a blend of semiochemicals for the manipulation of mosquito behaviour.