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Biomedical subjects

B Yuval

Publications and source records attributed to B Yuval.

At least 19 recordsLinked to original sources
PubMed2005

Enterobacteria-mediated nitrogen fixation in natural populations of the fruit fly Ceratitis capitata.

Nitrogen, although abundant in the atmosphere, is paradoxically a limited resource for multicellular organisms. In the Animalia, biological nitrogen fixation has solely been demonstrated in termites. We found that all individuals of field-collected Mediterranean fruit flies (Ceratitis capitata) harbour large diazotrophic enterobacterial populations that express dinitrogen reductase in the gut. Moreover, nitrogen fixation was demonstrated in isolated guts and in live flies and may significantly contribute to the fly's nitrogen intake. The presence of similar bacterial consortia in additional insect orders suggests that nitrogen fixation occurs in vast pools of terrestrial insects. On such a large scale, this phenomenon may have a considerable impact on the nitrogen cycle.

Animals↗
PubMed2003

Regulation of sexual receptivity of female Mediterranean fruit flies: old hypotheses revisited and a new synthesis proposed.

The objective of this study was to examine the relative contributions of copula duration and sperm transfer to the inhibition of sexual receptivity of female Mediterranean fruit flies (Ceratitis capitata, Diptera: Tephritidae). Females choosing to remate had significantly fewer sperm in their spermathecae than females who chose not to remate. Duration of a female's first copulation did not affect her subsequent receptivity. Furthermore, on the first day following copulation significantly more females whose first mate was sterile and from a laboratory strain (sterile males transfer fewer sperm than wild males) chose to copulate than did females whose mate was fertile and recently derived from wild stock. Finally, we offer a synthesis of the available information on remating in this species, and suggest that while females are facultatively polyandrous, copula duration, sperm transfer and male accessory gland secretions act in succession to inhibit female receptivity.

Animals↗
PubMed2000

Perimeter trapping strategy to reduce Mediterranean fruit fly (Diptera: Tephritidae) damage on different host species in Israel.

To evaluate the perimeter trapping strategy as a control method, field tests were conducted in three different host species of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), in Israel. Dry traps baited with a three component food-based synthetic attractant that were hung in the peripheral rows of a plum, a pear, and a persimmon orchard, caught female C. capitata (up to 20.1, 1.4, and 4.1 female C. capitata per trap per day, respectively). Fruit damage, estimated at harvest, indicated a negligible percentage for the plum orchard (< 1%), 3% for the persimmon orchard (compared with 9% at an untreated neighboring plot), and no damaged fruit in the pear orchard. Finally, dissections of female C. capitata caught in dry traps on different host plant species indicate that a high percentage (range, 84-100%) contained mature eggs. The attraction of mature females to the dry traps might explain the successful results. Future research, to determine precisely how many traps should be placed and how frequently they should be serviced, is necessary before applying this strategy on a commercial basis.

Animals↗
PubMed1999

Postcopulatory sexual selection in Mediterranean fruit flies: advantages for large and protein-fed males.

Previous laboratory studies of Mediterranean fruit flies, Ceratitis capitata (medflies), have identified large size and protein feeding as positive influences on the ability of males to secure copulations. In this study, we investigated whether large and protein-fed males experience additional advantages in terms of amount and distribution of sperm stored by mates. We also examined relationships between copula duration and sperm storage. Mates of large and protein-fed males were more likely to store sperm and to store more sperm than mates of small and protein-deprived males. Probability of sperm storage was associated with copula duration; all copulations lasting less than 100 min failed whereas 98% lasting longer than 100 min succeeded. Copulations involving sperm storage were longer if males were small or protein deprived or if the female was large, although there was no evidence of a relationship between copula duration and total sperm storage. Evidence from related studies suggests that variation in latency until sperm transfer, caused by size and diet, is a likely explanation for varying copula duration. Sperm tended to be stored asymmetrically between the female's two spermathecae, consistent with a mating system in which females maintain isolated populations of sperm from different males and later select between them. Storage was less asymmetric when large numbers of sperm were stored but there was little evidence that male size or diet affected this asymmetry. It is uncertain whether postcopulatory advantages of large and protein-fed male medflies arise from female preferences or male dominance through coercion or force. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1997

Nutritional correlates of reproductive success of male Mediterranean fruit flies (Diptera: Tephritidae)

We examined the hypothesis that adult diet affects the reproductive success of male Mediterranean fruit flies. In particular we determined whether protein-fed males copulated more frequently than protein-deprived males. Furthermore, we determined whether the nutritional status of their first sexual partner affects the renewal of female receptivity. Males fed no protein copulated at a significantly lower rate than did males fed protein. In both diet groups, size was significantly associated with copulatory success. Protein-deprived males transferred significantly more sperm to their mates than did protein-fed males. However, significantly more females mated to protein-deprived males re-mated on the following day. We conclude that male diet is a significant factor in determining male reproductive success. Male diet affects the ability to gain copulations with virgin females, and the receptivity of these females to further copulations.

Journal Article↗
PubMed1997

Multiple blood feeding by Anopheles freeborni and Culex tarsalis (Diptera:Culicidae): spatial and temporal variation.

Multiple blood feeding in field populations of Anopheles freeborni Aitken and Culex tarsalis Coquillet was detected using a histologic technique. Examination of 333 blood engorged An. freeborni and 41 Cx. tarsalis females revealed that 13 and 10% of these females imbibed multiple blood meals, respectively. Spatial and temporal distribution of multiple blood feeding events was evaluated against the percentage of blood fed females and the abundance of female mosquitoes. The percentage of blood fed An. freeborni females was higher among those collected in pasture and riparian habitats than those collected in rice field and mixed habitats. Conversely, spatial variation of multiple blood feeding in An. freeborni was not significantly associated with rice field, pasture, riparian, or mixed habitats. The decrease of multiple blood feeding for An. freeborni through the season was correlated inversely with the increase of the abundance of adult females; but not with the percentage of blood fed females. These results confirmed that multiple blood meals in An. freeborni, and perhaps in Cx. tarsalis, are a frequent phenomenon, and that the histologic procedure is an appropriate tool for longitudinal and region-wide detection of multiple blood feeding necessary in epidemiologic studies.

Animals↗
PubMed1997

Influence of plant abundance on nectar feeding by Aedes aegypti (Diptera: Culicidae) in southern Mexico.

The availability of flowering plants affected the sugar feeding rates of female Aedes aegypti (L.) in 4 areas of a small city in southern Mexico. The proportion of mosquitoes containing sugar varied from 8 to 21% in 4 areas in direct relation to blooming plant abundance. Human density was similar in the 4 areas (range, 3.9-5.4 per house), whereas the number of flowering plants per house increased on the outskirts (range, 3.1-5.4 plants per house). Equal proportions of sugar positive females were nulliparous or parous, indicating similar sugar feeding at any age. In addition, nearly 60% of positive females were at the Christophers stage II, indicating a greater need for flight fuel during the early stages of egg development. We conclude that Ae. aegypti feeds frequently on nectar and that this activity is modulated by nectar availability.

Aedes↗
PubMed1997

Energetics and sugar-feeding of field-collected anopheline females.

We studied the relationship between nutritional reserves and blood-feeding and sugar-feeding of Anopheles freeborni (Diptera: Culicidae) females in the field. In particular we determined whether (1) females feed on nectar before maturing eggs and initiating host-seeking and (2) the energy reserves of host-seeking females differ from those of non-fed resting females. Twenty-three percent of host-seeking females and 94 percent of gravid females were positive for nectar sugars (containing > 20 micrograms of fructose) versus 55 percent of empty (no blood or eggs) females collected in the morning and 36 percent of empty females collected in the evening. In addition, gravid females contained significantly more calories of nectar than empty, blood-fed, or partially blood-fed females collected in the morning. When the energy reserves of host-seeking and resting females were compared, no differences were found in lipid, trehalose, or glycogen. However, empty females collected in the evening contained more glycogen than empty females collected in the morning. We conclude that gravid females frequently feed on nectar and that fructose is metabolized into glycogen during the day.

Animals↗
PubMed1996

Spatial distribution of adult mosquitoes (Diptera:Culicidae) in habitats associated with the rice agroecosystem of northern California.

The objective of this study was to determine whether abundance, blood feeding rates, and sex ratios of adult Anopheles freeborni Aitken and Culex tarsalis Coquillett were associated significantly with either rice field, pasture, riparian, or mixed habitats found within the rice culture agroecosystem of northern California. Significantly higher numbers of adult An. freeborni occurred in riparian and mixed habitats compared with rice and pasture habitats. Such a pattern was not evident for Cx. tarsalis. Riparian and pasture habitats contained significantly higher proportions of blood fed An. freeborni females than did rice and mixed habitats; however, the proportions of blood fed Cx. tarsalis females did not vary significantly among habitat types. The proportions of blood fed An. freeborni and Cx. tarsalis females in riparian habitats decreased with increasing abundance. There was no correlation between blood feeding rates and abundance for An. freeborni and Cx. tarsalis females in the other habitat types. The sex ratio of An. freeborni in pasture and riparian habitats was significantly female biased, unlike the other habitats which did not differ significantly from unity (1:1). Overall, riparian and mixed habitats contained greater numbers of adults mosquitoes; therefore, surveillance and control efforts of these mosquito species should be focused on such habitats.

Agriculture↗
PubMed1995

Multiple blood feeding in Anopheles freeborni (Diptera: Culicidae).

The frequency of multiple blood feeding in field populations of Anopheles freeborni was determined. Fifty-six laboratory-reared mosquitoes, all known to have taken two blood meals, were used to define the limits of the histologic procedure we used. Seventy-eight percent of known double meals were detected when the interval between meals was from 1 to 24 hr, and the time from the second meal until fixation ranged from 0 to 24 hr. At intervals outside this range, 50% of multiple meals were detected. In field-collected An. freeborni, the most important histologic parameters for determination of multiple feeding were the amount of heme that developed around each meal, the peritrophic membrane, partially digested blood meals, and physical blood meal separation. Examination of 134 blood-engorged An. freeborni collected in the field showed that 9.7% had imbibed multiple blood meals. These results suggest that multiple blood meals in An. freeborni are more frequent than previously thought, perhaps with significant epidemiologic implications.

Animals↗
PubMed1994

Low rates of multiple fertilization in parous Anopheles albimanus.

We determined how frequently parous female Anopheles albimanus fertilize their eggs with sperm from more than one male. To establish paternity we relied on 2 phenotypically distinct laboratory strains. Nulliparous females were allowed to mate freely with males from one strain, and after oviposition they were offered a 2nd mating with males of the other strain. Fertilization patterns were determined by the phenotypes of offspring. Only 0.6% of females ovipositing for a 2nd time (n = 312) used sperm from the 2nd male, as did 4% of females completing a 3rd gonotrophic cycle (n = 25). In this species receptivity is not routinely renewed following oviposition.

Aedes↗
PubMed1991

Populations of Phlebotomus papatasi (Diptera: Psychodidae) and the risk of Leishmania major transmission in three Jordan Valley habitats.

The abundance, population structure, and Leishmania infection rates of Phlebotomus papatasi were studied at two villages, a 10-yr old date plantation, and an undisturbed natural habitat in the Jordan Valley throughout one season. On 109 trap nights in the villages, 53 female and 61 male P. papatasi were caught, whereas in burrows in the natural and agriculturally modified habitat, greater than 3,500 sandflies were trapped on 157 trap nights. Burrows in the data plantation produced larger numbers of males and females significantly more frequently than burrows in the natural habitat. The sex ratio in the natural habitat and the date plantation was significantly male biased. Parous rates were similar among habitats, whereas gravid females were significantly more active in the modified habitat. Leishmania infected females were not collected in the villages, yet close to 10% of females collected in the two other habitats were infected. Risk of transmission to humans in the villages was negligible, but people working in the date plantation were exposed to Leishmania infected sandflies.

Animals↗
PubMed1991

Leishmania-sandfly interactions: an empirical field study.

Phlebotomus papatasi is the sandfly vector of Leishmania major in the Jordan Valley. The objective of this study was to characterize vector-parasite relations in an active zoonotic focus. Seasonality and intensity of promastigote infection rates in female sandflies and the developmental stage of these hosts were established. On 153 trap-nights, 641 female P. papatasi were caught and examined. Of these, 48 (7.4%, range 12.9-4.8%) were infected with L. major promastigotes. Correlating the number of parasites with the gonotrophic age of the vector revealed that most infections initially are light ones, and those that survive in the vector generally prosper and proliferate. Comparing infection rates in parous and gravid flies revealed that similar proportions of gravid and parous flies are found infected. Thus, Leishmania infections do not appear to affect sandfly survival.

Animals↗
PubMed1990

Duration and regulation of the developmental cycle of Ixodes dammini (Acari: Ixodidae).

To determine how long the various developmental stages of the deer tick (Ixodes dammini Spielman, Clifford, Piesman & Corwin) survive in nature and to establish the interval between blood feeding and ecdysis or oviposition as well as subsequent larval eclosion, we observed ticks confined in the field. Unless adults feed during their first season (fall through spring) of activity, they die and do not survive the summer. Nonfed nymphs survive through two seasons (May through August) of feeding activity such that annual cohorts overlap. Nonfed larvae survive less than one year, and because they hatch toward the end of the summer, cohorts of this developmental stage do not overlap. Larvae that feed before September molt promptly and overwinter as nymphs; those that feed later overwinter engorged and ecdyse during the following spring. Fed nymphs fail to survive the winter, and thus must feed before late summer. They develop to the adult stage in the same year in which they feed. Regardless of time of feeding, females lay eggs in early summer, and the resulting larvae synchronously eclose late in that season. Although the cycle of this tick can be completed in nature in two years, it may extend to four years when hosts are relatively scarce. The seasonal inversion of larvae and nymphs appears to be regulated by physiological mechanisms and by host abundance.

Animals↗
PubMed1989

Leishmaniasis in the Jordan Valley: differential attraction of dispersing and breeding site populations of Phlebotomus papatasi (Diptera: Psychodidae) to manure and water.

The response of Phlebotomus papatasi Scopoli to traps baited with manure or water was used to compare the behavior of flies near rodent burrows (breeding sites) and dispersing flies in fallow fields. The degree of response in each biotype was defined for each bait by the difference between catches in baited and unbaited traps. Manure bait attracted twice as many flies near the burrows and 2.7 times more flies in the field compared with unbaited traps. In both locations, the manure bait increased the capture of males and nongravid females, whereas gravid females were attracted only near burrows and not in the fields. The catch in the fields with water bait was similar to the unbaited control. However, near burrows, water bait captured more males and gravid females, but not nongravid females. These results demonstrate specific behavioral patterns of the dispersing P. papatasi population.

Animals↗
PubMed1988

Leishmaniasis in the Jordan Valley. V. Dispersal characteristics of the sandfly Phlebotomus papatasi.

Several characteristics of dispersing and non-dispersing Phlebotomus papatasi (Scopoli) were quantified and compared. The majority of dispersing sandflies, trapped crossing fallow fields, were females (68.5% v. 51.1%); of the dispersing females, 55.4% were parous, 48.1% were inseminated and 11.6% were gravid. In the population of sandflies sampled exiting from burrows of the sand rat Psammomys obesus Cretschmar, these categories, respectively, represented 39%, 90% and 26% of the females examined. Leishmania promastigotes were found in 9% of females exiting from P. obesus burrows, and in 2.7% of the dispersing females. The anthrone test established that the reason for activity of gravid females is sugar feeding. These females do not disperse and are suitable targets for future control measures.

Animals↗