Small-Molecule Agonists of Ae. aegypti Neuropeptide Y Receptor Block Mosquito Biting

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Comparative fecundity and survival rates of Phlebotomus papatasi sandflies membrane fed on blood from eight mammal species

Female sandflies, Phlebotomus papatasi (Scopoli) (Diptera: Psychodidae), were fed via chicken membrane on heparinized blood from eight species of mammal (human, horse, cow, pig, dog, rabbit, guinea-pig, hamster) and their reproductive success rates were compared. No appreciable differences between those fed on human and animal blood were detected with respect to the proportion of flies that fed successfully, mortality-rate within 24h, number of eggs laid per blood-fed female or egg viability. When mass-rearing sandflies for research purposes, membrane-feeding avoids practical difficulties encountered if sandflies are allowed to feed on live hosts (i.e. anaesthesia, distress from handling and postfeeding inflammation) and reduction of sandfly fecundity due to host antibody interference. Use of animal blood also eliminates risks of accidental transmission of human blood-borne pathogens, e.g. hepatitis B and human immunodeficiency virus (HIV), and is less expensive than maintenance of animals and their preparation for sandfly feeding.     

The calcium activated nucleotidases: A diverse family of soluble and membrane associated nucleotide hydrolyzing enzymes

It has long been known that the salivary glands of hematophagous (blood-feeding) arthropods secrete soluble apyrases, which are potent nucleotide hydrolyzing enzymes capable of hydrolyzing extracellular ATP and ADP, the latter being a major agonist contributing to platelet aggregation. Only recently, however, has the identification of proteins homologous to these apyrases been reported in non-blood-feeding organisms such as rodents and humans. In this review, we present an overview of the diverse family of apyrases first described in the blood-feeding arthropods, including the identification and characterization of the soluble and membrane-bound vertebrate enzymes homologous to these arthropod apyrases. We also describe the enzymatic properties and nucleotide specificities of the expressed enzymes, and insights gained into the structure and function of this calcium activated nucleotidase (CAN) family from biophysical, mutagenesis and crystallography studies. The potential therapeutic value of these proteins is also discussed.     

Endocrine aspects of mosquito reproduction

Blood ingestion by the female mosquito initiates a series of endocrine events that is dominated by juvenile hormone, ecdysteroids, and several peptide hormones, resulting in the maturation of a batch of eggs. The mechanisms of hormone release and their roles during the previtellogenic, vitellogenic, and postvitellogenic phases are discussed. Arch. Insect Biochem. Physiol. 35:491–512, 1997. © 1997 Wiley-Liss, Inc.     

Could insecticide‐treated cattle reduce Afrotropical malaria transmission? Effects of deltamethrin‐treated Zebu on Anopheles arabiensis behaviour and survival in Ethiopia

Anopheles arabiensis Patton (Diptera: Culicidae) is the most widespread vector of malaria in the Afrotropical Region. Because An. arabiensis feeds readily on cattle as well as humans, the insecticide-treatment of cattle--as employed to control tsetse (Diptera: Glossinidae) and ticks (Acari: Ixodidae)--might simultaneously affect the malaria vectorial capacity of this mosquito. Therefore, we conducted field experiments in southern Ethiopia to establish whether Zebu cattle (Bos indicus L.) treated with a pour-on pyrethroid formulation of 1% deltamethrin, widely used to control ticks and tsetse, would be effective against An. arabiensis or cause the female mosquitoes to feed more frequently on humans, due to behavioural avoidance of insecticide-treated cattle. Contact bioassays (3 min exposure) showed that the insecticide remained effective for about 1 month (kill rate > 50%) against mosquitoes feeding on the flanks of treated cattle. A novel behavioural assay demonstrated that An. arabiensis readily fed on insecticide-treated cattle and were not deflected to human hosts in the presence of treated cattle. DNA-fingerprinting of bloodmeals revealed that An. arabiensis naturally feeds most frequently on older animals, consistent with the established practice of applying insecticide only to older cattle, while allowing younger untreated animals to gain immunity against infections transmitted by ticks. These encouraging results were tempered by finding that > 90% of An. arabiensis, An. pharoensis and An. tenebrosus females feed on the legs of cattle, farthest from the site of pour-on application along the animal's back and where the treatment may be least residual due to weathering. Observations of mosquitoes feeding naturally on insecticide-treated cattle showed that the majority of wild female anophelines alighted on the host animal for less than 1 min to feed, with significantly shorter mean duration of feeding bouts on insecticide-treated animals, and the effective life of the insecticide was only 1 week. Thus the monthly application of deltamethrin to cattle, typically used to control tsetse and ticks, is unlikely to be effective against An. arabiensis populations or their vectorial capacity. Even so, it seems likely that far greater impact on anopheline mosquitoes could be achieved by applying insecticide selectively to the legs of cattle.     

Size variation and reproductive success of female Aedes punctor (Diptera: Culicidae)

Abstract. 1. Variation in size (wing length) of females and males within a population of Aedes punctor (Kirby) at emergence was recorded in northern Britain during 1984 and 1985.
2. Wing length correlated well with body dry weight, confirming its usefulness as a measure of body size. In 1984, but not in 1985, mean size decreased significantly as emergence progressed.
3. The size of host-seeking females caught at human bait varied seasonally. This was partly accounted for by size variation during emergence.
4. Of females which fed to repletion, the largest spent least time in contact with the host.
5. In the laboratory, wing length correlated well with potential fecundity (number of ovarioles) and less well with actual fecundity (number of matured follicles) after feeding on human blood.
6. In the field, larger females were more successful at locating hosts, developed more egg clutches in a lifetime and generally lived longer than did smaller ones. Larger females appear to enjoy greater reproductive success than do smaller females.     

The nutritional importance of dietary blood components for reproduction in the tsetse fly, Glossina morsitans

Females of Glossina morsitans morsitans were fed diets of different composition and their performance in terms of survival, fecundity and offspring size, used as a basis for assessing the nutritional importance of the dietary constituents for reproduction. Diets comprised defibrinated bovine blood from which individual components had been removed, or various fractions of bovine blood mixed in different ratios and combinations.Flies fed serum-free diets (comprising saline-washed bovine erythrocytes) failed to reproduce and their ovaries were atrophied. Attempts were made to correct these symptoms by adding serum components to washed erythrocytes. Results showed that serum albumin and lipoproteins were vital for ovarian growth. The erythrocytes in defibrinated bovine blood could be replaced by preparations of haemoglobin. Dialysis against isotonic sodium chloride, removal of gamma globulins, removal of lymphocytes or heating to 55°C for 2 h did not alter the nutritional quality of defibrinated bovine blood. The qualitative importance of dietary albumin associated lipids and lipoproteins for oöcyte growth suggests a specialisation which may be peculiar to viviparous Diptera. Results are discussed in terms of the development of synthetic diets for tsetse.     

Understanding host utilization by mosquitoes: determinants,challenges and future directions

Mosquito host utilization is a key factor in the transmission of vector-borne pathogens given that it greatly influences host–vector contact rates. Blood-feeding patterns of mosquitoes are not random, as some mosquitoes feed on particular species and/or individuals more than expected by chance. Mosquitoes use a number of cues including visual, olfactory, acoustic, and thermal stimuli emitted by vertebrate hosts to locate and identify their blood meal sources. Thus, differences in the quality/intensity of the released cues may drive host selection by mosquitoes at both inter- and intra-specific levels. Such patterns of host selection by mosquitoes in space and time can be structured by factors related to mosquitoes (e.g. innate host preference, behavioural plasticity), to hosts (e.g. emission of host-seeking cues, host availability) or to both (e.g. pathogen infection). In this study, we review current evidence, from phenomena to mechanisms, of how these factors influence host utilization by mosquitoes. We also review the methodologies commonly used in this research field and identify the major challenges for future studies. To bridge the knowledge gaps, we propose improvements to strengthen traditional approaches and the use of a functional trait-based approach to infer mosquito host utilization in natural communities.     

Feeding patterns revealed host partitioning in a community of frog-biting mosquitoes

1. Resource partitioning is a critical component in competing species that coexist in a community. The biting behaviour of coexisting frog-biting mosquito species associated with a tropical anuran community is investigated. 2. Monthly samplings were taken for 2 years at two study sites in central Sri Lanka to collect frog-biting mosquitoes, anuran abundance, environmental data, and interactions between mosquitoes and anuran hosts. Mosquitoes were collected using mouth-operated aspirators and sound traps broadcasting anuran calls. Mosquitoes were identified using taxonomic keys and DNA barcodes. 3. A total of 1079 frog-biting mosquitoes from four species belonging to two genera were collected [Uranotaenia rutherfordi (5%), Ur. morphotype 1 (67%), Ur. morphotype 2 (21%), and Mansonia uniformis (7%)]. Species-specific interactions between Uranotaenia mosquitoes and their anuran host were found. Uranotaenia morphotype 1, the most common species, was mainly attracted (99%) to Duttaphrynus melanostictus. Uranotaenia rutherfordi was mainly attracted (95%) to Pseudophilautus rus, while Ur. morphotype 2 was attracted (97%) to Polypedates cruciger. These Uranotaenia species are active at different hours at night that correspond to the peak calling activity of their anuran host. Each Uranotaenia species was active at heights that coincide with the calling sites of their host. In contrast, Ma. uniformis was non-specific in host choice and was equally distributed in space and time with respect to host feeding. 4. Here, previously unknown feeding patterns of co-occurring frog-biting mosquito species and their interactions with anurans present in their community are reported, highlighting the existence of complex behavioural patterns of these mosquito communities.     

Feeding behaviour of the horsefly Tabanus nigrovittatus (Diptera: Tabanidae): effects of dissolved solids on ingestion and destination of sucrose or ATP diets

Abstract Wild caught female horseflies, Tabanus nigrovittatus Macq. (Diptera: Tabanidae), were fed solutions containing either sucrose or ATP as a phagostimulant. The sucrose diets were presented as free liquids at room temperature. The ATP in the other diets was dissolved in 0.15 M NaCl, or in 0.3 M or 1 M cellobiose and was presented covered with a Parafilm membrane at 38^oC. The content of dissolved solids in some diets was adjusted with added cellobiose, which had no phago-stimulatory effect. Diets of 1 M or 0.6 M sucrose were ingested in large amounts and were directed to the crop. Diets of 0.3 M or 0.1 M sucrose induced lower levels of ingestion, and the diet was directed to the midgut. The addition of cellobiose to give a 1 M total concentration of dissolved solids in these sucrose diets induced many insects responding to the lower concentrations of sucrose to direct the diet to the crop. Diets of ATP in saline or in 0.3 M cellobiose were directed to the midgut. ATP in 1 M cellobiose caused many of the insects to put the diet in both the crop and the midgut. Two behavioural models are presented that integrate interactions between the level of phagostimulation, the concentration of dissolved solids, and an endogenous feeding factor. The dissolved solids effect is most likely a response to osmotic pressure.