Environmental constraints on the physiology of transgenic mosquitoes

Insects have exploited and responded to their environment in a plethora of ways. Environmental changes are used to trigger short- and long-term physiological events and environmental stresses have resulted in evolution of gene families and resistance genes. This highly evolved, tight interaction between organism and environment will be altered in transgenic mosquitoes, and this paper reviews some potential considerations concerning the physiology of transgenic mosquitoes upon release. This papers examines a few of the recent discoveries in Plasmodium-mosquito interactions and discusses the impact upon them of the transgenic-mosquito approach. A complex interplay between vector and parasite occurs during transmission, including the exploitation of xanthurenic acid for triggering exflagellation, the induction of a mosquito immune response and its evasion by the invading ookinete, and the ability of the parasite to establish infections when major genes are knocked out. Such functional redundancy in parasite genes is also demonstrable in the immune and detoxification systems of insects. Consequently, where genes can substitute for one another in a given physiological process, there is potentially significant environmental pressure for differential gene expression. In the transgenic context, such compensatory regulation could work to down-regulate and/or select against a transgene. Conversely, additional environmental triggers could be exploited to select positively for a transgenic mosquito. There is potential for heterogeneity at each stage of the transgenic release strategy, and addressing this will be important if such approaches are not to be scuttled by unforeseen factors that could reduce expression of and selection for the beneficial transgene

Nondigestive Cell Types in the Midgut Epithelium of Rhodnius Prolixus (Hemiptera: Reduviidae)

The ultrastructure of regenerative cells and endocrine cells in the midgut epithelium of mated female Rhodnius prolixus is described. Regenerative cells are numerous, found in all midgut regions, and do not contain any of the normal secretory apparatus of a cell. Endocrine cells are less numerous, restricted to the intestine, and contain prominent Golgi complexes, electron-opaque vacuoles, and intermediate-staining secretory granules. Both cell types rest on the basal lamina of the midgut and are considerably smaller than the normal digestive epithelial cells. The structure of the endocrine cells is compared to those from other insects, and a role for the endocrine cell in the hormonal control of blood meal digestion is postulate

Survival and infection probabilities of anthropophagic anophelines from an area of high prevalence of Plasmodium falciparum in humans

Delayed and immediate oocyst rates; parous rates and sporozoite rates were obtained in Anopheles gambiae Giles, A. arabiensis Patten and A. funestus Giles from two villages in the Kilombero Valley, southern Tanzania during the wet season of 1991. Collection methods included light trap, indoor resting collection and nets with holes cut in their side. Mosquito survival estimates from parous rates obtained from light trap collections, were compared with estimates from capture-recapture experiments and from that obtained during a population decline. Methods of estimating the proportion of feeds infectious to mosquitoes, K, were also compared. This proportion varied between villages and species and was highest in the village with the greatest proportion of A. gambiae. We propose that absolute estimates of K should be obtained by determining the immediate oocyst rate and measuring the parous rate using the same host seeking mosquitoes. This estimate was only available from one village and ranged from 1.9% for A. gambiae s.l. to 3.4% for A. funestu

Density independent feeding success of malaria vectors (Diptera: Culicidae) in Tanzania

The possibility of density dependent feeding success in the African malaria vectors Anopheles gambiae Giles (sensu lato) and A. funestus Giles was investigated by examining the gonotrophic status of mosquitoes from 423 collections made in a Tanzanian village. Up to 500 mosquitoes were caught in any single 35 minute indoor resting collection. Estimates of the total numbers of mosquitoes resting were made by removal sampling. These indicated that the efficiency of resting collections decreased with increasing mosquito population. Of 1904 mosquito blood meals tested by ELISA, 95% were of human origin. There was no decrease in the proportion of mosquitoes fully fed at high population densities and the only demonstrable avoiding action by hosts in response to high densities of mosquitoes was the increased use of bednets during the wet season. The late biting cycle of these mosquitoes precludes many other density-dependent host defence mechanisms because the hosts are asleep at the time of attack. African malaria vectors have evolved with man and perhaps their evasion of density-dependent host responses has reinforced their preference for human bloo

The rise and fall of Anopheles arabiensis (Diptera: Culicidae) in a Tanzanian village

The continual recruitment of new individuals makes it difficult to study both the survival of multivoltine mosquitoes, and the size of the infectious reservoir in narural populations of malaria vectors. During long-term surveillance of a population of Anopheles gambiae Giles sensu lato in a Tanzanian village by daily light trapping, a temporary dry spell resulted in the cessation of recruitment for a period of 33 days, and a decline in numbers of A. arabiensis Patton caught from over 2000 to less than 10 in a sentinel house. Traps placed elsewhere in the village indicated similar proportionate declines although numbers caught varied according to location. A survival rate of 83% per day was estimated from the rate of population decline. Survival was unrelated to the size of the mosquitoes. The infectious reservoir (the chance of a mosquito acquiring an infection) was estimated to be 2% per feed. The exploitation of fortuitous events which temporarily eliminate a single stage in the life cycle has general applicability in the study of the bionomics of multivoltine insect

Larval nutrition differentially affects adult fitness and Plasmodium development in the malaria vectors Anopheles gambiae and Anopheles stephensi

BACKGROUND: Mosquito fitness is determined largely by body size and nutritional reserves. Plasmodium infections in the mosquito and resultant transmission of malaria parasites might be compromised by the vector's nutritional status. We studied the effects of nutritional stress and malaria parasite infections on transmission fitness of Anopheles mosquitoes. METHODS: Larvae of Anopheles gambiae sensu stricto and An. stephensi were reared at constant density but with nutritionally low and high diets. Fitness of adult mosquitoes resulting from each dietary class was assessed by measuring body size and lipid, protein and glycogen content. The size of the first blood meal was estimated by protein analysis. Mosquitoes of each dietary class were fed upon a Plasmodium yoelii nigeriensis-infected mouse, and parasite infections were determined 5 d after the infectious blood meal by dissection of the midguts and by counting oocysts. The impact of Plasmodium infections on gonotrophic development was established by dissection. RESULTS: Mosquitoes raised under low and high diets emerged as adults of different size classes comparable between An. gambiae and An. stephensi. In both species low-diet females contained less protein, lipid and glycogen upon emergence than high-diet mosquitoes. The quantity of larval diet impacted strongly upon adult blood feeding and reproductive success. The prevalence and intensity of P. yoelii nigeriensis infections were reduced in low-diet mosquitoes of both species, but P. yoelii nigeriensis impacted negatively only on low-diet, small-sized An. gambiae considering survival and egg maturation. There was no measurable fitness effect of P. yoelii nigeriensis on An. stephensi. CONCLUSIONS: Under the experimental conditions, small-sized An. gambiae expressed high mortality, possibly caused by Plasmodium infections, the species showing distinct physiological concessions when nutrionally challenged in contrast to well-fed, larger siblings. Conversely, An. stephensi was a robust, successful vector regardless of its nutrional status upon emergence. The data suggest that small-sized An. gambiae, therefore, would contribute little to malaria transmission, whereas this size effect would not affect An. stephensi

Safety, Immunogenicity, and Protective Efficacy of Intradermal Immunization with Aseptic, Purified, Cryopreserved Plasmodium falciparum Sporozoites in Volunteers Under Chloroquine Prophylaxis

Immunization of volunteers under chloroquine prophylaxis by bites of *Plasmodium falciparum* sporozoite (PfSPZ)–infected mosquitoes induces > 90% protection against controlled human malaria infection (CHMI). We studied intradermal immunization with cryopreserved, infectious PfSPZ in volunteers taking chloroquine (PfSPZ chemoprophylaxis vaccine [CVac]). Vaccine groups 1 and 3 received 3x monthly immunizations with 7.5 x 10^4 PfSPZ. Control groups 2 and 4 received normal saline. Groups 1 and 2 underwent CHMI (#1) by mosquito bite 60 days after the third immunization. Groups 3 and 4 were boosted 168 days after the third immunization and underwent CHMI (#2) 137 days later. Vaccinees (11/20, 55%) and controls (6/10, 60%) had the same percentage of mild to moderate solicited adverse events. After CHMI #1, 8/10 vaccinees (group 1) and 5/5 controls (group 2) became parasitemic by microscopy; the two negatives were positive by quantitative real-time polymerase chain reaction (qPCR). After CHMI #2, all vaccinees in group 3 and controls in group 4 were parasitemic by qPCR. Vaccinees showed weak antibody and no detectable cellular immune responses. Intradermal immunization with up to 3 x 10^5 PfSPZ-CVac was safe, but induced only minimal immune responses and no sterile protection against Pf CHMI. INTRODUCTIO

Constraints on the cosmic expansion history from GWTC–3

We use 47 gravitational wave sources from the Third LIGO–Virgo–Kamioka Gravitational Wave Detector Gravitational Wave Transient Catalog (GWTC–3) to estimate the Hubble parameter H(z), including its current value, the Hubble constant H0. Each gravitational wave (GW) signal provides the luminosity distance to the source, and we estimate the corresponding redshift using two methods: the redshifted masses and a galaxy catalog. Using the binary black hole (BBH) redshifted masses, we simultaneously infer the source mass distribution and H(z). The source mass distribution displays a peak around 34 M⊙, followed by a drop-off. Assuming this mass scale does not evolve with the redshift results in a H(z) measurement, yielding ${H}_{0}={68}_{-8}^{+12}\,\mathrm{km}\ \,\ {{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ (68% credible interval) when combined with the H0 measurement from GW170817 and its electromagnetic counterpart. This represents an improvement of 17% with respect to the H0 estimate from GWTC–1. The second method associates each GW event with its probable host galaxy in the catalog GLADE+, statistically marginalizing over the redshifts of each event's potential hosts. Assuming a fixed BBH population, we estimate a value of ${H}_{0}={68}_{-6}^{+8}\,\mathrm{km}\ \,\ {{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ with the galaxy catalog method, an improvement of 42% with respect to our GWTC–1 result and 20% with respect to recent H0 studies using GWTC–2 events. However, we show that this result is strongly impacted by assumptions about the BBH source mass distribution; the only event which is not strongly impacted by such assumptions (and is thus informative about H0) is the well-localized event GW190814