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Biomedical subjects

W A Foster

Publications and source records attributed to W A Foster.

At least 19 recordsLinked to original sources
PubMed2006

Diel timing and frequency of sugar feeding in the mosquito Anopheles gambiae, depending on sex, gonotrophic state and resource availability.

Little is known about the sugar-feeding behaviour of equatorial Africa's principal vector of malaria, Anopheles gambiae Giles (Diptera: Culicidae). It is suspected to feed on plant sugar infrequently, but possibly the timing depends on environmental circumstances, and males may differ markedly from females. These points of uncertainty were clarified in the laboratory, by monitoring both diel and longterm sugar-feeding activity in both sexes. Males fed on sugar in a nocturnal diel rhythm closely approximating non-specific flight activity. Female diel sugar-feeding patterns resembled published rhythms and cycles of host seeking. Males sugar fed nightly at an average frequency of about twice per night, sustained over 17 days. This was substantially higher than the sugar-feeding frequency of females that were allowed both blood and oviposition sites every night: they averaged about one sugar feed in every 4 nights. These females fed on sugar between gonotrophic cycles, after eggs were mature but before the next bloodmeal. They did not sugar feed during the 2 days after blood feeding, while blood was being digested and the eggs developed. A slight delay in the availability of either the oviposition site or blood led to an increase in female sugar-feeding frequency: they averaged more than once per night until the delayed resource was made available. These observations support the conclusion that sugar feeding is a normal part of the biology of both sexes of An. gambiae.

Animals↗
PubMed2005

Analysis of a complex vertical copulatory-courtship display in the yellow fever vector Sabethes chloropterus.

Sabethes chloropterus (Von Humboldt) (Diptera: Culicidae), an arboreal mosquito vector of the yellow fever virus, perches on vertical surfaces, where airborne males patrol for potential mates and mating occurs. Laboratory analysis of 26 virgin mating pairs partly confirms and greatly extends an earlier description suggesting that males perform a courtship ritual. A male approaches a female by hovering behind her, moving toward her from one side, reaching toward her and occasionally touching her with his closest midleg, and eventually seizing her wing with that midleg and inverting beneath her, forelegs against the substrate. Immediately after male alignment with the female, the pair enters a superficial genital-coupling phase, in which the male's extended gonostyli are linked to the female, and he proceeds sequentially through four stages of midleg oscillations (MLOs): Alternate I, Synchronous I, Double-flex, and Synchronous II. Following one or more genital thrusts, the pair shifts to a full-copulation phase, which lasts only up to 6 s, during which the genitalia are clasped and insemination occurs. The male raises his midlegs and hindlegs in succession, then performs Alternate II MLO until the female kicks him and he is released. Nineteen (73%) of the 26 pairs successfully completed the entire sequence, including genital shift and full copulation, taking an average of 3.7 min. Features of the display that might determine success were not evident. Reversions in the chain of events occurred, but linear progression of stages and phases was characteristic of nearly all matings. The male's approach, however, lacked stereotypic form and probably is not part of the courtship.

Animals↗
PubMed2004

Nectar-related vs. human-related volatiles: behavioural response and choice by female and male Anopheles gambiae (Diptera: Culicidae) between emergence and first feeding.

The close association of Anopheles gambiae Giles with humans and its females' ability to live on human blood alone suggest that females may ignore sources of sugar in favour of human blood as a source of energy. They have limited energy reserves at emergence, and at 27 degrees C both sexes generally die if they do not feed during night 1, 24-36 h after emergence. Food preferences during this critical period were tested by measuring responses to volatiles from honey and soiled socks, which served as surrogates for nectar-related and human-related volatiles in a wind-tunnel olfactometer. Both sexes responded more strongly to honey than to human volatiles, and given a choice, preferred honey over human volatiles. After 5 days of sugar access and maturation, males continued to prefer honey volatiles, whereas females changed behaviour, responding almost exclusively to human volatiles. Night 1 experiments also demonstrated that: (i). females previously having had sugar during the night of emergence responded more strongly to human volatiles; (ii). large-bodied mosquitoes of both sexes responded more strongly to honey than small-bodied ones; and (iii). females were equally responsive to honey in both early and late scotophase but were slightly more responsive to human volatiles in late scotophase. These results indicate that for a female's first meal, sugar is a viable option and is preferred when nectar-related stimuli are strong. This supports field evidence that sugar-feeding is a significant component of A. gambiae female behaviour.

Animals↗
PubMed2004

Anopheles gambiae feeding and survival on honeydew and extra-floral nectar of peridomestic plants.

It is widely believed that the malaria vector Anopheles gambiae Giles (Diptera: Culicidae) rarely or never feeds on sugar in nature. If so, the need for supplemental blood-feeding may be increased and this would help to explain why it is such an efficient malaria vector. Nonetheless, both sexes of this mosquito species readily imbibe and digest sugar solutions, and sugar is a staple of laboratory colonies. In this study, we investigated whether An. gambiae will feed on the extra-floral nectar of three common peridomestic plants in Africa, and on honeydew of the mealybug Pseudococcus longispinus (Targioni-Tozetti) (Hemiptera: Homoptera: Pseudococcidae), and how this affects survivorship. We found that both males and females of An. gambiae provided with vegetative parts of cassava (Manihot esculenta Crantz) survived as well (x = 26.3 and 19.2 days, respectively) as they did on 50% sucrose solution (x = 29.7 and 24.3 days, respectively) and much longer than they did on water alone (x = 1.8 days, both sexes). Females provided with mealybug honeydew also lived substantially longer (x = 16.5 days) than those on water alone. Males and females provided with vegetative parts of castorbean (Ricinus communis L.) also survived much longer (x = 12.7 and 7.8 days, respectively) than on water, but those provided with flowering lantana (Lantana camara L.) did not. Anthrone tests of females after one night of exposure to these potential energy sources confirmed that they obtained fructose from cassava, from mealybug honeydew, and from non-flowering castorbean, but not from lantana or from castorbean lacking its petiolar nectaries. Previous laboratory studies had shown that sugar availability affects the survival and biting frequency of An. gambiae. It now appears that this mosquito can locate natural sources of plant sugar readily and utilize them effectively. Nectar-producing plants in the domestic environment may play a significant role in this mosquito's energy budget and malaria vectorial capacity.

Animals↗
PubMed2004

Feeding and survival of the malaria vector Anopheles gambiae on plants growing in Kenya.

The propensity of the malaria vector mosquito Anopheles gambiae Giles (Diptera: Culicidae) to ingest sugars from various plants, and subsequent survival rates, were assessed with laboratory-reared males and females offered eight species of plants commonly cultivated and/or growing wild in western Kenya. In cages (no-choice bioassay), mosquitoes given the opportunity to feed on castorbean (Ricinus communis L.) had the longest survival times (mean and median survival time of 6.99 +/- 0.23 and 5.67 +/- 0.17 days, respectively), comparable to mosquitoes given 6% glucose (mean and median survival time of 8.70 +/- 0.23 and 6.67 +/- 0.33 days, respectively). Survival rates of An. gambiae were low on the other plants, comparable to mosquitoes given only water. Three plants: sweet potato (Ipomoea batatas L.), wild sage (Lantana camara L.) and castorbean provided levels of sugar ingestion by both sexes of An. gambiae detectable using the cold anthrone method, showing a positive correlation between median survival and sugar consumption (Spearman rank correlation coefficient = 0.905, P < 0.0001). Equal numbers of males and females were released in an enclosed semi-field screenhouse system containing a range of local plants, but no host for blood, and allowed to feed ad libitum: 6.7 +/- 0.5% (11/64) of those recaptured were found to contain detectable fructose (all females). Common plants are clearly a viable source of nutrition for adult female An. gambiae, as well as males, and may constitute and important resource for this important malaria vector.

Animals↗
PubMed2001

Effects of available sugar on the reproductive fitness and vectorial capacity of the malaria vector Anopheles gambiae (Diptera: Culicidae).

Although females of most mosquito species are known to use sugar as a necessary source of energy, female Anopheles gambiae Giles sensu stricto are thought to use it facultatively or not at all. However, field evidence of sugar-free living is inconclusive, and the implications for reproductive fitness and vectorial capacity are unknown. To evaluate the role that sugar may play in the ecology of these mosquitoes, mated female An. gambiae in the laboratory were given access to either no food (water only), 10% sucrose, human blood, or human blood + 10% sucrose, and comparisons of daily mortality, fecundity, and biting frequency were made. The effect of sugar availability on vectorial capacity and the intrinsic rate of increase, a measure of fitness, then were determined. Females (pooled and individual) given blood + sugar lived significantly longer than did those on the other diets. Daily fecundity was higher for females given blood alone than for those fed blood + sugar (13 versus 9 eggs per female daily). However, total fecundity and intrinsic rate of increase were not affected by sugar availability. Biting frequency was significantly higher (0.41 versus 0.26 bites per female per day) for females given blood alone. Despite the reduced survivorship, exclusive blood-feeding led to a theoretically higher vectorial capacity for Plasmodium falciparum at 27 degrees C. These data indicate that female An. gambiae could replace sugar with increased blood feeding without suppressing reproductive fitness. Increased blood feeding could, in turn, increase the rate of malaria transmission and may explain the unusual efficiency of this vector.

Animals↗
PubMed2001

Eye of the beholder.

Three first semester nursing students collaborate to present their interpretations of their first observations in the operating room. This article includes a true story and topics addressing the operating room environment, the surgical team members, and the learning experience.

Adaptation, Psychological↗
PubMed2000

Ant tending influences soldier production in a social aphid.

The aphid Pseudoregma sundanica (Van der Goot) (Homoptera: Aphididae) has two defence strategies. It is obligatorily tended by various species of ant and also produces sterile soldiers. We investigated how they allocate their investment in these two strategies. We measured the size, number of soldiers, number and species of tending ant, and number and species of predators in P. sundanica populations. We found that the level of ant tending correlated negatively with soldier investment in P. sundanica. The species of tending ant also influenced soldier investment. We excluded ants from aphid populations and recorded changes in population size and structure over four weeks. Ant exclusion led to population decline and extinction. At the same time, surviving populations showed a significant increase in soldier investment. The data demonstrate that social aphids can adjust their investment in soldiers in direct response to environmental change.

Animals↗
PubMed2000

Exogenous juvenile hormone and methoprene, but not male accessory gland substances or ovariectomy, affect the blood/nectar choice of female Culex nigripalpus mosquitoes.

When newly emerged females of the mosquito Culex nigripalpus Theobald (Diptera: Culicidae) take a sugar meal, they develop both a propensity to seek a host and resting-stage ovarian follicles. As follicle growth is indicative of Juvenile Hormone (JH) activity, we searched for possible roles of JH in the behavioural shift from nectar to blood-host odour preference by Cx. nigripalpus after emergence, using an olfactometer-choice assay. Topically applied or injected methoprene (a JH analogue) resulted in a behavioural shift and follicular growth in unfed females that increased with increasing dosages. Topical methoprene 500 ng and 4 microg resulted in a switch to bird-odour preference. JH III injection resulted in a lesser shift from honey responses to bird responses. Methoprene application caused no detectable changes in glycogen, total sugars or total lipid when assayed 24h after treatment. Additionally, as male accessory glands (MAG) have been shown to synthesize JH, we implanted intact paired MAGs from either conspecific or Aedes aegypti (L.) donors, or injected 1/3 gland pair equivalents of conspecific MAG homogenate into unfed newly emerged females. All MAG treatments failed to induce behavioural or ovarian modifications. Ovariectomy had no effect on the sugar-induced shift from nectar to host preference in the olfactometer. Thus JH, but not MAG, mimicked the effects of a sugar meal by causing both follicular growth and the shift to preference for a host.

Animals↗
PubMed1997

Larval and adult nutrition effects on blood/nectar choice of Culex nigripalpus mosquitoes.

The impact of nutritional variables on the development of host-seeking and biting behaviours after emergence by female Culex nigripalpus mosquitoes were studied using air-flow olfactometer and close-range biting assays, respectively. Unfed females failed to develop resting stage ovarian follicles. When offered a bird host in the absence of competing stimuli, sugar-fed mosquitoes were significantly more responsive in both host-seeking and biting than unfed controls. In a choice olfactometer assay using nectar odours (honey scented with artificial apple-blossom oil) versus host odours (a bird), unfed females preferred honey over bird odours except when honey odour was weak. After sucrose feeding, females switched from honey to bird preference. This change in behaviour was accompanied by significant accumulation of lipid and by follicular growth to the resting stage. Elevation of host responsiveness after sugar feeding was reversible; starvation ultimately resulted in females preferring honey over bird odours. When the larval diet was restricted by crowding, the wing-length and total lipid of resultant adult females were reduced. Although differences were subtle, unfed bird-responding females tended to have longer wings and more lipid than their honey-responding counterparts.

Animal Nutritional Physiological Phenomena↗
PubMed1996

The evolution of soldiers in aphids.

1. Defensive individuals, termed soldiers, have recently been discovered in aphids, Soldiers are typically early instar larvae, and in many species the soldiers are reproductively sterile and morphologically and behaviourally specialized. 2. Since aphids reproduce parthenogenetically, we might expect soldier production to be more widespread in aphids than it is. We suggest that a more useful way to think about these problems is to attempt to understand how a clone (rather than an individual) should invest in defence and reproduction. 3. Known soldiers are currently restricted to two families of aphids, the Pemphigidae and Hormaphididae, although they are distributed widely among genera within these families. We discuss the use of a phylogenetic perspective to aid comparative studies of soldier production and we demonstrate this approach using current estimates of phylogenetic affinities among aphids. We show that the distribution of soldier production requires a minimum of six to nine evolutionary origins plus at least one loss. 4. At least four main types of soldiers exist and we present and discuss this diversity of soldiers. 5. Most soldier-producing species produce soldiers within plant galls and we discuss the importance of galls for the evolution of soldiers. 6. We summarize the evidence on the interactions between soldiers and predators and between soldier-producing aphids and ants. 7. We present an optimality model for soldier investment strategies to help guide investigations of the ecological factors selecting for soldiers. 8. The proximate mechanisms of soldier production are currently very poorly understood and we suggest several avenues for further research.

Animals↗
PubMed1995

Mosquito sugar feeding and reproductive energetics.

Sugar feeding is a fundamental characteristic of mosquito life. Most evidence indicates frequent ingestion by both sexes and all ages of mosquitoes of plant sugar, usually as floral and extrafloral nectar and honeydew. Energetically, sugar and blood are interchangeable; females of some species have evolved independence from one or the other, but most need blood to develop eggs and sugar to survive, to fly, and to enhance reproduction. Mosquitoes' commitment to sugar is further illustrated by a wealth of behavioral, structural, and physiological specializations for finding, feeding on, and processing it. Blood and sugar feeding activities are antagonistic and mutually exclusive, owing to conflicting demands, yet they support the same goals and often share the same activity period. The rules by which females make food-choice decisions have been inadequately explored, and we still lack convincing evidence that sugar availability in nature varies sufficiently to affect mosquito populations.

Animals↗
PubMed1994

Nectar-related olfactory and visual attractants for mosquitoes.

Mosquitoes commonly feed on plant nectar and other sugar sources, which they locate chiefly by visual and chemical cues. A summary of current evidence indicates that nectar sources are not as attractive as blood sources at specific times in a mosquito's life but that sugar feeding is usually necessary and more frequent than bloodfeeding. Plant attractants used in traps would have the advantage of being effective for both sexes, starting soon after emergence, and for blood-digesting, gravid, and gonoinactive females. Field studies suggest that mosquitoes are most attracted to light-colored flowers, but the independence of appearance from fragrance has not been firmly established. Volatile components of flowers and honey have been proven to be attractive, but in a preliminary field trial honey extract was less attractive than some blood-host kairomones. Terpenoids and aromatics provide many of the distinctive and dominant volatiles of flowers; they elicit both chemosensory and behavioral responses in mosquitoes.

Animals↗
PubMed1993

Effects of preblood-meal sugar on sugar seeking and upwind flight by gravid and parous Aedes aegypti (Diptera: Culicidae).

Sugar seeking and upwind flight of gravid and parous female Aedes aegypti (L.) was measured by their attraction to honey in a dual-port airflow olfactometer at selected time intervals after a blood meal. Comparisons were made between pre-blood-meal sugar-fed and unfed females. Sugar-fed females had greater total energy reserves, mostly because of elevated lipid levels. Gravid mosquitoes in both groups showed a strong tendency to fly upwind. This appears to be a pre-ovipositional response. Gravid female orientation to honey was greater in unfed females than in sugar-fed females. After oviposition, parous females became more strongly attracted to honey, if their honey response was not already high.

Aedes↗
PubMed1993

Records of mosquito-parasitic mermithid nematodes in the northcentral United States.

Mermithid parasites (Nematoda: Mermithidae) were observed in 11 mosquito species in 22 counties of Indiana, Michigan, Minnesota, Ohio and Wisconsin. Natural hosts included adult Aedes vexans, Ae. canadensis, Ae. cinereus, Ae. diantaeus, Ae. punctor, Anopheles punctipennis and Coquillettidia perturbans and larvae of Ae. abserratus, Ae. canadensis, Ae. cinereus, Ae. communis, Ae. diantaeus, Ae. provocans, Ae. punctor, Ae. stimulans and Cq. perturbans. These are the first records of such parasites in Indiana, Minnesota, Ohio and Wisconsin.

Aedes↗
PubMed1992

Simultaneous field comparison of evening temporal distributions of nectar and blood feeding by Aedes vexans and Ae. trivittatus (Diptera: Culicidae) in Ohio.

Nectar- and blood-feeding time distributions of Aedes vexans (Meigen) and Aedes trivittatus (Coquillett) were determined from collections of mosquitoes attempting to feed on flowers and human bait during six nights in an Ohio field. Distributions of nectar and blood feeding were different in Ae. vexans on three of five nights when analyses were possible, and they were different in pooled Ae. trivittatus data. Higher proportions of blood feeders appeared in earlier time intervals, but both nectar and blood feeding had broadly overlapping peaks and distributions. These results suggest that the nectar- and blood-feeding rhythms are probably in phase in Ae. vexans females, and that possibly the earlier onset of blood feeding reflects a strategy taking advantage of blood when it is available. Male Ae. vexans had later peak nectar-feeding times than females. Nectar feeding in males may be delayed by mating activity early in the activity period.

Aedes↗
PubMed1992

Diel sugar-feeding and host-seeking rhythms in mosquitoes (Diptera: Culicidae) under laboratory conditions.

Mosquito sugar-feeding and host-seeking rhythms were recorded in the laboratory using remote sensors. In all five species studied, the two rhythms were nearly synchronous. In Anopheles quadrimaculatus Say, Culex quinquefasciatus Say, and Aedes triseriatus (Say), host-seeking activity increased slightly earlier than sugar feeding in the evening. The evening sugar-feeding period was longer than the evening host-seeking period in Aedes aegypti (L.), but the two periods were of similar duration in Aedes albopictus (Skuse). In the morning, the only clear difference between the two behaviors occurred in Cx. quinquefasciatus, which had a host-seeking peak but lacked a sugar-feeding peak. When exposed concurrently to both host and sugar stimuli, sugar feeding practically ceased in Ae. albopictus and Ae. aegypti. In the presence of host stimuli, the sugar-feeding rhythms of An. quadrimaculatus, Cx. quinquefasciatus, and Ae. triseriatus differed from those obtained in the absence of host stimuli by having an earlier onset of evening activity, a relatively smaller evening activity peak, and a more irregular activity pattern during early scotophase, respectively. We concluded that inseminated, nulliparous females have nonspecific appetitive feeding periods, and that the order in which sugar and blood are sought largely may be a function of factors other than differences in diel rhythms.

Animals↗