Evaluation of large volume yeast interfering RNA lure-and-kill ovitraps for attraction and control of Aedes mosquitoes

Aedes mosquitoes (Diptera: Culicidae), principle vectors of several arboviruses, typically lay eggs in man-made water-filled containers located near human dwellings. Given the widespread emergence of insecticide resistance, stable and biofriendly alternatives for mosquito larviciding are needed. Laboratory studies have demonstrated that inactivated yeast interfering RNA tablets targeting key larval developmental genes can be used to facilitate effective larvicidal activity while also promoting selective gravid female oviposition behaviour. Here we examined the efficacy of transferring this technology toward development of lure-and-kill ovitraps targeting Aedes aegypti (L.) and Aedes albopictus (Skuse) female mosquitoes. Insectary, simulated field and semi-field experiments demonstrated that two mosquito-specific yeast interfering RNA pesticides induce high levels of mortality among larvae of both species in treated large volume containers. Small-scale field trials conducted in Trinidad, West Indies demonstrated that large volume ovitrap containers baited with inactivated yeast tablets lure significantly more gravid females than traps containing only water and were highly attractive to both A. aegypti and A. albopictus females. These studies indicate that development of biorational yeast interfering RNA-baited ovitraps may represent a new tool for control of Aedes mosquitoes, including deployment in existing lure-and-kill ovitrap technologies or traditional container larviciding programs

Metarhizium anisopliae blastospores are highly virulent to adult Aedes aegypti, an important arbovirus vector

BackgroundThe use of entomopathogenic fungi (EPF) for the control of adult mosquitoes is a promising alternative to synthetic insecticides. Previous studies have only evaluated conidiospores against adult mosquitoes. However, blastospores, which are highly virulent against mosquito larvae and pupae, could also be effective against adults.MethodsMetarhizium anisopliae (ESALQ 818 and LEF 2000) blastospores and conidia were first tested against adult Aedes aegypti by spraying insects with spore suspensions. Blastospores were then tested using an indirect contact bioassay, exposing mosquitoes to fungus-impregnated cloths. Virulence when using blastospores suspended in 20% sunflower oil was also investigated.ResultsFemale mosquitoes sprayed with blastospores or conidia at a concentration of 108 propagules ml−1 were highly susceptible to both types of spores, resulting in 100% mortality within 7 days. However, significant differences in virulence of the isolates and propagules became apparent at 107 spores ml−1, with ESALQ 818 blastospores being more virulent than LEF 2000 blastospores. ESALQ 818 blastospores were highly virulent when mosquitoes were exposed to black cotton cloths impregnated with blastospores shortly after preparing the suspensions, but virulence declined rapidly 12 h post-application. The addition of vegetable oil to blastospores helped maintain virulence for up to 48 h.ConclusionThe results showed that blastospores were more virulent to adult female Ae. aegypti than conidia when sprayed onto the insects or applied to black cloths. Vegetable oil helped maintain blastospore virulence. The results show that blastospores have potential for use in integrated vector management, although new formulations and drying techniques need to be investigated

Evaluation of Bifenthrin and Deltamethrin Barrier Sprays for Mosquito Control in Eastern North Carolina

Mosquitoes can be a nuisance and also transmit pathogens causing numerous diseases worldwide. Homeowners and others may hire private companies to alleviate mosquito-related issues. Here, two pyrethroids (Suspend[registered] Polyzone[registered] [deltamethrin] and Bifen Insecticide/Termiticide [bifenthrin]) used in mosquito control were evaluated on blocks of properties in two neighborhoods (Magnolia Ridge: 1-6 lot blocks, 2,100 -- 7,500 m2/block and Cedar Ridge: 1-3 lot blocks, 1,300 -- 4,200 m2/block) in eastern North Carolina for 23 weeks from May 18 -- October 19, 2015. Properties were treated by Mosquito Authority operators using backpack mist blowers every 21 days. At 17 fixed sampling locations (13 treatment and four control lots), Centers for Disease Control and Prevention CO2-baited traps were deployed overnight once/week for the duration of the experiment (377 trap nights). Oviposition traps (ovitraps) were deployed weekly at the same 17 locations and ovistrips remained in the field for seven days as a measure of Aedes albopictus abundance. Mosquitoes were identified to species, quantified, and tabulated by location and week. Differences were observed in mosquito abundance between neighborhoods, treatments, and weeks and differences varied between species. Adult and egg abundance were generally significantly (P [less than] 0.05) higher in traps placed on control properties (no insecticide) compared to traps placed on treatment properties. In both neighborhoods, the abundance of Psorophora columbiae and Ae. vexans was significantly higher in control versus treatment traps. Bifenthrin and deltamethrin showed differences in efficacy (e.g. Ae. vexans, An. punctipennis, and Ps. ferox abundance was greater in traps placed on bifenthrin compared to deltamethrin and control properties), but this varied between neighborhoods and species

Novel insecticides and application strategies for malaria vector control

Targeting malaria vector mosquitoes outdoors has become a research priority to address residual malaria transmission. Mosquito larval source management provides an excellent and well established tool. However, there is a need to reduce the cost and effort of larviciding programmes by testing persistent larvicides that reduce the frequency of application and by exploring novel strategies of application. This thesis aimed to evaluate two larval control agents, with unique mode of actions: the self-spreading silicone-based film Aquatain Mosquito Formulation (AMF) and the pyriproxyfen-based insect growth regulator Sumilarv®. Dose-response tests and standardized field tests were conducted to assess the susceptibility of Anopheles gambiae sensu stricto and An. arabiensis to the two insecticides and determine their residual activity. Adults that survived exposure to larvicide-treated water at the larval stages were assessed for possible effects on fecundity and fertility. Both species were highly susceptible to both control agents at very low doses. Both control agents provided residual control of up to six weeks. Adults that emerged from larvicide-treated water laid fewer eggs and had low egg hatching rates. Consequently, the impact of three-weekly operational application of pyriproxyfen to habitats in the western Kenya highlands was assessed by comparing adult vector emergences from aquatic habitats in intervention and non-intervention sites. Pyriproxyfen application led to over 80% adult vector emergence inhibition from treated aquatic habitats. To assess if larvicide-treated water could serve as ‘reproductive sinks’ for gravid mosquitoes, the oviposition response of gravid An. gambiae s.s. to water treated with pyriproxyfen or surface film was tested under semi-field conditions using squares of electrocuting nets. Larvicide-treated water did not affect the pre-oviposition behaviour of gravid females. This study however did not demonstrate that ‘attract and kill’ strategies could be used for control of malaria vectors as the addition of an oviposition attractant to ponds containing larvicide-treated water did not increase the proportion of gravid females orienting towards this pond. To explore the effect of pyriproxyfen exposure on adults, individual An. gambiae s.s. and Cx. quinquefasciatus females were exposed to pyriproxyfen at seven time points around blood feeding. Fecundity and ability to transfer pyriproxyfen to an oviposition substrate 4 were studied in the laboratory. The impact of pyriproxyfen was dependent on the time of exposure. Females were nearly completely sterilized when exposure occurred around the blood meal while pyriproxyfen was only transferred by females that were exposed while gravid and close to egg-laying time. Consequently, a baiting station for gravid females was developed and semi-field experiments implemented to explore the transfer of pyriproxyfen by gravid An. gambiae s.s. from the baiting station to aquatic habitats. Horizontal transfer was observed but the extent of emergence inhibition was dependent on the distance of the habitat from the baiting station. Only the closest habitats received sufficient pyriproxyfen to control significant numbers of offspring. In conclusion, this study demonstrated great potential of the two control agents for the control of vector immature stages and adults caused by sterilizing effects of pyriproxyfen. Results suggest that they are suitable for inclusion into integrated vector management programmes for malaria control. Auto-dissemination of pyriproxyfen however, appears not to be a feasible strategy for malaria vector control

Analysing the role of semiochemicals in the oviposition substrate choices of the malaria vector mosquito Anopheles gambiae sensu lato

The search for tools that target malaria vector that resist insecticides and bite outdoors has become a research priority. Such tools will be necessary for managing residual malaria transmission and hastening the eradication of this devastating disease. This study investigated chemicals that potentially affect the oviposition substrate choices of Anopheles gambiae sensu lato (s.l.). It is foreseen that increased knowledge of the oviposition behaviour of this major malaria vectors and chemicals cues that mediate oviposition site-selection can be applied in the development of additional sampling methods and alternative interventions that to trap gravid malaria mosquitoes outdoors. To achieve a reproducible high egg-laying success of An. gambiae sensu stricto (s.s.) and An. arabiensis four factors were evaluated: (1) the time provided for mating; (2) the impact of cage size, mosquito age and female body size on insemination; (3) the peak oviposition time; and, (4) the host source of blood meals. Then four bioassays were optimised for studying oviposition responses of An. gambiae s.s. in the laboratory and semi-field conditions: a WHO-tube bioassay and a wind-tunnel that detected short-range attraction in the laboratory; a two-tier choice egg-count bioassay that compared the relative proportion of eggs laid in substrates in the laboratory; and a modified BG Sentinel mosquito gravid trap that evaluated long-range attraction of gravid females to olfactory cues in the semi-field. Finally, the oviposition responses of gravid An. gambiae s.s. mosquitoes to water vapour, Bermuda grass hay infusion (hay infusion), and putative semiochemicals identified from the hay infusion and a soil infusion previously shown to elicit higher egg deposition compared to filtered Lake Victoria water (lake water) in two choice egg-count bioassays (Herrera-Varela et al. 2014), were evaluated. High oviposition rates [84%, 95% confidence interval (CI) 77-89%] were achieved when 300 male and 300 blood-fed female An. gambiae s.s. were held together in a cage for four days. The chance of oviposition in the mosquitoes dropped when human host source of blood-meal was substituted with a rabbit (Odds ratio (OR) 0.30, 95% CI 0.14-0.66) but egg-numbers per female were not affected. All four optimised oviposition bioassays effectively showed between 15-20% shifts in oviposition substrate choices of mosquitoes with 80% statistical power and 5% significance. Using the WHO-tube bioassay, gravid An. gambiae s.s. were shown to be 2.4 times (95% CI 1.3-4.7 times) more likely to move towards high humidity in still air compared to non-gravid Preamble mosquitoes. This was more pronounced in the airflow olfactometer where the gravid mosquitoes were 10.6 times (95% CI 5.4-20.8 times) more likely to fly into a chamber with water than a dry chamber. Two-choice egg-count bioassays showed that An. gambiae s.s. were less likely to lay eggs in six-day old hay infusion (OR 0.10, 95% CI 0.03-0.33) compared to lake water. Ten putative semiochemicals were identified from the hay infusion using mass spectrometry and published electrophysiology data: 4-hepten-1-ol, 4-ethylphenol, phenylmethanol, 2-phenylethanol, indole, phenol, 3-methylindole, 3-methyl-1-butanol, 4-ethylphenol, and nonanal. Tested in two-choice egg-count bioassays, the first four listed compounds had no effect on egg deposition at the tested concentrations (between 0.01-5 parts per million) but mosquitoes were less likely to lay eggs in at least one concentration of 3-methylindole (OR 0.39, 95% CI 0.21-0.71), indole (OR 0.57, 95% CI 0.37-0.87), 3-methyl-1-butanol (OR 0.32, 95% CI 0.22-0.47), phenol (OR 0.55, 0.32-0.95), 4-methylphenol (OR 0.32, 0.18-0.57) and nonanal (OR 0.66, 95% CI 0.47-0.91) compared to lake water. In contrast to the hay infusion and hay infusion volatiles, An. gambiae s.s. were about two times more likely to lay eggs in cedrol, a sesquiterpene alcohol identified from the soil infusion, compared to lake water (OR 1.84, 95% CI 1.16-2.91). Cedrol attracted twice as many gravid mosquitoes in the semi-field also (OR 1.92, 95% CI 1.63-2.27). In the field, modified BG-Sentinel traps, electrocuting nets and OviART gravid traps with lake water and cedrol were three times more likely to trap malaria mosquitoes compared to traps with water only (OR 3.3, 95% CI 1.4-7.9). In conclusion, water vapour was shown to be a strong, non-specific pre-oviposition attractant for gravid An. gambiae s.s. in still air and moving air. It is probably the long range cue that gravid An. gambiae s.l. use to detect the presence aquatic habitats beyond the range of chemical cues. Evidence showed that An. gambiae s.s. discriminate between potential oviposition substrates and that this selective process is in-part mediated by volatile organic compounds originating from the site. Water vapour leads gravid mosquitoes to aquatic sites but semiochemicals enable the mosquitoes to discriminate and select between potential habitats. It was demonstrated that synthetic equivalents of semiochemicals found to attract gravid mosquitoes such as cedrol can be used to trap malaria mosquitoes outdoors

Environmental Aspects of Zoonotic Diseases

Environmental Aspects of Zoonotic Diseases provides a definitive description, commentary and research needs of environmental aspects related to zoonotic diseases. There are many interrelated connections between the environment and zoonotic diseases such as: water, soil, air and agriculture. The book presents investigations of these connections, with specific reference to environmental processes such as: deforestation, floods, draughts, irrigation practices, soil transfer and their impact on bacterial, viral, fungal, and parasitological spread. Environmental aspects such as climate (tropical, sub-tropical, temperate, arid and semi-arid), developed and undeveloped countries, animal traffic animal border crossing, commercial animal trade, transportation, as well geography and weather on zoonosis, are also discussed and relevant scientific data is condensed and organized in order to give a better picture of interrelationship between the environment and current spread of zoonotic diseases

An investigation into the effects of Plasmodium parasite infection on the human odour profile

Some studies suggest that Plasmodium parasites can change the attractiveness of their vertebrate hosts to Anopheles vectors. This is suggestive of parasite manipulation, where the parasite alters a host phenotype to the parasite’s own fitness benefit. In this instance, Plasmodium parasites may benefit from increased transmission via a greater number of vector-host contacts. Despite evidence that variation in human host attractiveness to biting insects is manifest through differences in the human odour profile (volatile compounds produced by the skin), the association between odour profile and Plasmodium infection has never been studied in humans. The skin odour profile of individuals infected with Plasmodium in both experimental- and natural-infection settings was investigated using gas chromatography (GC). In the experimentally-infected (EI) cohort, adults were infected with Plasmodium falciparum and their odour profile sampled before, during and after infection. In the naturally-infected (NI) cohort, children aged 5-12 years with Plasmodium infections of varied parasite density, stage and species were sampled before and after treatment with antimalarials. Odour samples from both cohorts were further screened for infection-associated compounds using coupled GC-electroantennography (GC-EAG). In both EI and NI cohorts, changes in the production of several compounds in skin odour were found to be associated with the presence of Plasmodium parasites. Of these, production of the aldehydes heptanal, octanal and nonanal (C7-C9) was both increased in association with the presence of parasites in a density-dependent manner, and found to induce antennal response in Anopheles coluzzi. The production of C7-C9 and other infection-associated compounds via malaria-induced oxidative stress is a suggested mechanism. Malaria remains one of the most important diseases worldwide. As the global strategy for malaria control and elimination evolves, to combat both parasite and vector resistance to drugs and insecticides, the need for innovative tools intensifies. If malaria parasites can alter the human odour profile and attractiveness to mosquitoes, the repercussions would be far reaching: this would likely have a profound influence on the way that malaria spreads through populations, and malaria-specific volatile biomarkers could provide a basis for novel diagnostic tools

Federal Register

Daily publication of the U.S. Office of the Federal Register contains rules and regulations, proposed legislation and rule changes, and other notices, including "Presidential proclamations and Executive Orders, Federal agency documents having general applicability and legal effect, documents required to be published by act of Congress, and other Federal agency documents of public interest" (p. ii). Table of Contents starts on page iii