Are herders protected by their herds? An experimental analysis of zooprophylaxis against the malaria vector Anopheles arabiensis

Background The number of Anopheles arabiensis (Diptera: Culicidae) and Anopheles pharoensis caught by human and cattle baits was investigated experimentally in the Arba Minch district of southern Ethiopia to determine if attraction to humans, indoors or outdoors, was affected by the presence or absence of cattle. Methods Field studies were made of the effect of a surrounding ring (10 m radius) of 20 cattle on the numbers of mosquitoes collected by human-baited sampling methods (i) inside or (ii) outside a hut. Results The numbers of An. arabiensis caught outdoors by a human landing catch (HLC) with or without a ring of cattle were not significantly different (2 × 2 Latin square comparisons: means = 24.8 and 37.2 mosquitoes/night, respectively; n = 12, P > 0.22, Tukey HSD), whereas, the numbers of An. pharoensis caught were significantly reduced (44%) by a ring of cattle (4.9 vs. 8.7; n = 12, P 0.999) or An. pharoensis (n = 48, P > 0.870). The HLC catches indoors vs. outdoors were not significantly different for either An. arabiensis or An. pharoensis (n = 12, P > 0.969), but for An. arabiensis only, the indoor catch was reduced significantly by 49% when the hut was surrounded by cattle (Tukey HSD, n = 12, P > 0.01). Conclusions Outdoors, a preponderance of cattle (20:1, cattle:humans) does not provide any material zooprophylactic effect against biting by An. arabiensis. For a human indoors, the presence of cattle outdoors nearly halved the catch. Unfortunately, this level of reduction would not have an appreciable impact on malaria incidence in an area with typically > 1 infective bite/person/night. For An. pharoensis, cattle significantly reduced the human catch indoors and outdoors, but still only by about half. These results suggest that even for traditional pastoralist communities of East Africa, the presence of large numbers of cattle does not confer effective zooprophylaxis against malaria transmitted by An. arabiensis or An. pharoensis

Mosquito hearing is the most sensitive among arthropods — But is the sound level of a male swarm loud enough to be picked up by the female’s particle-velocity sensor?

Males of many mosquito species aggregate in station-keeping swarms, waiting for the arrival of conspecific females to mate with. We test whether audition could be used by a female to locate male swarms and to assess whether the males are conspecific. The sound level resulting from thousands of wing flaps could be loud enough to be heard at long range (~1m) via the antennal flagellum (particle velocity sensor, primarily designed for close-range communication). A mosquito hears a conspecific by adjusting its own wing-beat frequency so that the difference tone between its own and the opposite-sex frequencies falls into a narrow band to which the auditory organ is tuned. Indeed, the antennal flagella produce distortion products resulting in difference tones of the nearby soundscape. Swarms of males were recorded and played-back to females in a 2m–sided flight chamber. The natural sounds of the males of two species (Anopheles coluzzii and An. gambiae) and related synthetic sounds were played at different sound levels to individual free- ying An. coluzzii females. The mosquitoes’ responses were investigated by analysing changes in 3D-tracked flight trajectories and wing-beat frequencies. The results show: 1) females do respond to the sound of swarming males, 2) a qualitative difference between female and male behaviour, 3) a quantitative effect of the sound stimulus of conspecific males, and 4) verification of previous results suggesting the importance of the first harmonic of their wing beats in mosquito acoustic communication

Field study of the repellent activity of ‘Lem-ocimum’-treated double bags against the insect pests of stored sorghum, Tribolium castaneum and Rhyzopertha dominica, in northern Nigeria

A field study of the efficacy of a novel use of repellent plant material to protect stored sorghum from pest damage was conducted in Kebbi State, Nigeria. A combination of Ocimum basilicum (Sweet basil) and Cymbopogon nardus (Lemongrass) powdered dried leaves (‘Lem-ocimum’) was found to be significantly more repellent to the most common grain pest, Tribolium castaneum, when applied as a water-based paste between the layers of double storage-bags at a dose of 1% w/w (plant powder/grain) than untreated double bags (n = 30, P < 0.001). The efficacy of protecting a given percentage of grain in Lem-ocimum treated double-bags was tested in 120 store-rooms, each of which contained 15–35 × 60 kg single bags of sorghum that initially had moderate levels of beetle infestation (26–50 T. castaneum/bag). After 5 months in storage, the percent change in grain weight and levels of infestation by the two most prevalent pests, T. castaneum and Rhyzopertha dominica, inside treated double-bags were significantly lowest in the store-rooms with the highest percentage of all grain (4%) kept in treated double-bags (P < 0.01, n = 120 store-rooms). This result may have been due to the mass fumigation effect of adding 400–900 g Lem-ocimum to each of the store-rooms with 4% treated grain. Only the participant farmers that had stored 4% of their grain in treated double-bags felt the treatment provided significant protection. The findings suggest Lem-ocimum treated double-bags could improve the chances that a proportion of a farmer's grain would be of good enough quality to sell in the market mid-way through the storage season, when the price of grain would earn a good profit

Comment l’entomologie et la musique peuvent se nourrir l’une de l’autre: le cas de la communication acoustique des moustiques

Les dernières décennies ont vu de nombreuses avancées dans la compréhension de la communication sonore chez les moustiques, possédant une sensibilité auditive inégalée chez les arthropodes. Nous discutons ici un possible biais anthropocentrique vis-à-vis des recherches scientifiques et leur interprétation, lié à un imaginaire musical de la fonction sonore. Nous verrons que malgré certaines interprétations discutables, elles ont stimulé la recherche et participent à leur tour à la création musicale. En 2006, une étude décrit l’habilité de certaines espèces à ajuster à l’unisson leurs battements d’ailes [Gibson & Russel 2006], exploitée par des artistes faisant réagir des moustiques à de la musique tonale [Meier & Momeini 2009]. Plus tard, cette découverte s’enrichit d’autres espèces qui accordent leurs tonalités de vol respectives à la quarte ou la quinte avant la copulation. On parle alors de « convergence harmonique dans les chants d’amour des moustiques », corrélée aux chances d’accouplement [Cator et al 2009] ou à la reconnaissance inter-espèces [Pennetier et al 2010]. Puis, vient une étude montrant que cette convergence pourrait n’être qu’un épiphénomène du fonctionnement particulier du système auditif et avoir pour but indirect de localiser son partenaire [Warren et al 2009]. Cette étude n’aura pas le même retentissement scientifique et médiatique que celle invoquant l’image du chant d’amour. Aujourd’hui, il semblerait qu’un artefact expérimental soit en partie à l’origine de ces convergences et qu’elles se produisent peu dans des conditions moins artificielles [Aldersley & Cator 2019, Pantoja- Sanchez et al 2019]. La tentation de prêter aux moustiques une capacité à échanger des sons jugés harmonieux a tout de même permis de mieux comprendre le fonctionnement auditif de certains insectes. Toujours est-il que ces phénomènes de convergence harmonique existent dans des conditions particulières. Ainsi, nous présenterons pour finir un projet basé sur l’interaction musicale avec un essaim d’espèces mixtes réagissant sélectivement à des stimuli sonores

Potential vector for West Nile virus prevalent in Kent

THE mosquito Culex modestus is considered the main bridge vector of West Nile virus in continental Europe, responsible for transmitting the virus from birds to humans (Balenghien and others 2008). Cx modestus was reported in three nature reserves in north Kent in 2010 (Golding and others 2012) – 60 years after the previous UK report. Isolated specimens were then reported from Dorset and Cambridgeshire (Medlock and Vaux 2012)

Comment l’entomologie et la musique peuvent se nourrir l’une de l’autre : le cas de la communication acoustique des moustiques

Les dernières décennies ont vu de nombreuses avancées dans la compréhension de la communication sonore chez les moustiques, arthropodes possédant une sensibilité auditive inégalée dans ce groupe phylogénétique. Nous discutons ici d’un possible biais anthropocentrique des recherches scientifiques et de leurs interprétations lié à un imaginaire musical de la fonction sonore. Nous verrons que malgré le caractère discutable de ces interprétations, ce biais a stimulé la recherche et a participé à son tour à la création musicale. En 2006, une étude décrit l’habilité de certaines espèces à ajuster à l’unisson leurs battements d’ailes, travail exploité par des artistes faisant réagir des moustiques à de la musique tonale. Plus tard, cette découverte s’enrichit à d’autres espèces qui accordent leurs tonalités de vol respectives à la quarte ou la quinte avant la copulation. On parle alors de « convergence harmonique dans les chants d’amour des moustiques », corrélée aux chances d’accouplement ou à la reconnaissance inter- espèces. Puis, vient une étude montrant que cette convergence pourrait n’être qu’un épiphénomène du fonctionnement particulier du système auditif et avoir pour but indirect de localiser son partenaire. Cette étude n’aura pas le même retentissement scientifique et médiatique que celle invoquant l’image du chant d’amour. Aujourd’hui, il semblerait qu’un artefact statistique soit en partie à l’origine de ces convergences. La tentation de prêter aux moustiques une capacité à échanger des sons jugés harmonieux a tout de même permis de mieux comprendre le fonctionnement auditif des moustiques. Toujours est-il que ces phénomènes de convergence harmonique peuvent exister dans des conditions particulières, même s’ils n’ont pas le rôle qui leur ait a été attribué initialement. Ainsi, nous présenterons pour finir un projet basé sur l’interaction musicale avec un essaim d’espèces mixtes réagissant sélectivement à des stimuli sonores. Nous conclurons par une critique du système de la recherche scientifique actuel basé sur la bibliométrie, en l’illustrant par les travaux sur la théorie de la « convergence harmonique » chez les moustiques

A role for acoustic distortion in novel rapid frequency modulation behaviour in free-flying male mosquitoes

We describe a new stereotypical acoustic behaviour by male mosquitoes in response to the fundamental frequency of female flight-tones during mating sequences. This male-specific free-fight behaviour consists of phonotactic flight beginning with a steep increase in wing-beat frequency (WBF) followed by Rapid Frequency Modulation (RFM) of WBF in the lead-up to copula formation. Male RFM behaviour involves remarkably fast changes in WBF and can be elicited without acoustic feedback or physical presence of the female. RFM features are highly consistent, even in response to artificial tones that do not carry the multi-harmonic components of natural female flight-tones. Comparison between audiograms of the robust RFM behaviour and the electrical responses of the auditory Johnston's organ (JO) reveals that the male JO is tuned not to the female WBF per se, but, remarkably, to the difference between the male and female WBFs. This difference is generated in the JO responses due to intermodulation distortion products (DPs) caused through nonlinear interaction between male-female flight-tones in the vibrations of the antenna. We propose that male mosquitoes rely on their own flight-tones in making use of DPs to acoustically detect, locate and orientate towards flying females. We argue that the previously documented flight-tone harmonic convergence of flying male and female mosquitoes could be a consequence of WBF adjustments so that DPs generated through flight-tone interaction fall within the optimal frequency ranges for JO detection

Measuring Infrared SurfaceBrightness Fluctuation Distances with HST WFC3: Calibration and Advice

We present new calibrations of the near-infrared (near-IR) surface brightness fluctuation (SBF) distance method for the F110W ( ) and F160W ( ) bandpasses of the Wide Field Camera 3 Infrared Channel (WFC3/IR) on the Hubble Space Telescope. The calibrations are based on data for 16 early-type galaxies in the Virgo and Fornax clusters observed with WFC3/IR and are provided as functions of both the optical and near-infrared colors. The scatter about the linear calibration relations for the luminous red galaxies in the sample is approximately 0.10 mag, corresponding to a statistical error of 5% in distance. Our results imply that the distance to any suitably bright elliptical galaxy can be measured with this precision out to about 80 Mpc in a single-orbit observation with WFC3/IR, making this a remarkably powerful instrument for extragalactic distances. The calibration sample also includes much bluer and lower-luminosity galaxies than previously used for IR SBF studies, revealing interesting population differences that cause the calibration scatter to increase for dwarf galaxies. Comparisons with single-burst population models show that as expected, the redder early-type galaxies contain old, metal-rich populations, while the bluer dwarf ellipticals contain a wider range of ages and lower metallicities than their more massive counterparts. Radial SBF gradients reveal that IR color gradients are largely an age effect; the bluer dwarfs typically have their youngest populations near their centers, while the redder giant ellipticals show only weak trends and in the opposite sense. Because of the population variations among bluer galaxies, distance measurements in the near-IR are best limited to red early-type galaxies. We conclude with some practical guidelines for using WFC3/IR to measure reliable SBF distances

Decoding the biomechanics of flight-tone based acoustic communication in mosquitoes

The aerial courtship dance of mosquitoes involves controlled variations in the frequency and intensity of flight-tones, with concurrent changes in flight speed and direction. This behavior enables detection of conspecifics, leading to competitive flight and acoustic displays of fitness, with successful copulation under the right circumstances. However, despite >150 years of research, it is not clear how the 6-D soundscape (3D space, time, intensity, and frequency) generated by flying mosquitoes is actively modified during courtship. Also, not known are the energetic costs of this courtship behavior, nor the degree to which exogenous sounds can alter and even disrupt courtship. In the current phase of the project, we integrate computational biomechanics and acoustics with biological assays and measurement of sensory-controlled behaviors, to generate unprecedented data and provide insights into courtship-associated acoustic communication in mosquitoes. We have developed a computational tool to predict the aerodynamics, energetics and soundscape mapping of mosquito flight-tones. Wing kinematics extracted from high-speed images of flying mosquitoes have provided input for simulations. The current focus is on comparison of simultaneous measurements of wing-kinematics, flight-tone intensity and directivity from tethered and free-flying mosquitoes, male and female alone or in pairs. Analysis of the computational and experimental results will provide insights into the mechanisms of flight control and scaling of energetic costs, and efficiency of flight-tone generation. 6D sound maps of flight-tones for flying mosquitoes are being constructed to enable quantitative analyses of acoustic communication between mosquitoes during each stage of mating: from the onset of male mating-swarms to the interactions within male-female dyads. The success of this novel approach could be transformative for many pest species of flying insects that employ similar modes of mating communication; our results could form the scientific foundation for exploitation of sound-stimuli that we now know control the success/failure of mating for each generation of mosquitoes. Such technologies have the potential to significantly reduce vector populations and lead to environmentally friendly strategies by diminishing mating success in vectors of malaria, Zika fever and other devastating mosquito-borne diseases