Engorgement Rates Research Articles

Host-feeding patterns of Florida mosquitoes. V. Wyeomyia.

Two species of neotropical Wyeomyia constitute the main day-biting mosquitoes in the hardwood forests of southern Florida. Engorged females captured in daytime suction traps and tractor-aspirator collections were subjected to precipitin tests to determine their host-blood sources. Although both Wy. vanduzeei Dyar & Knab and Wy. mitchellii Lutz appear capable of attacking a variety of hosts, most blood meals were from rabbits. The late afternoon activity period of rabbits corresponded with the diurnal biting cycle of Wyeomyia , as revealed by 24-hr collections from animal-baited Lumsden traps. Engorgement rates, which were <5% for both species, were not indicative of the difference in autogeny reported for these 2 species.

Autogenous egg production in the salt-marsh mosquito, Aedes taeniorhynchus.

1. A total of 17 populations of Aedes taeniorhynchus were examined for the occurrence of autogeny. Every population contained some autogenous as well as some anautogenous females. In general, populations from the tropics and subtropics had higher rates of autogeny than did temperate zone populations. A major exception to this pattern was a Panama strain where less than 1% of the females were autogenous.2. Autogenous and anautogenous females occurred in the same reproductive populations. The progeny derived from individual, wild-caught females often contained both reproductive types.3. The mean fecundity was often less than 30 eggs per autogenous female in those populations where the occurrence of autogeny was rare or infrequent. In contrast, significantly higher levels of fecundity were associated with all populations that contained mostly autogenous females. Geographical variation in autogenous fecundity appears to be regulated by polygenic factors.4. We compared the blood-feeding characteristics and requirements of two mosquito populations in southern Florida. At Flamingo, Florida, only 8.1% of the females collected with power aspirators were engorged, whereas at Big Pine Key, Florida the engorgement rate was 20.9%. Approximately 80% of all females from the Flamingo collections were at a stage where they could be considered "blood-thirsty" mosquitoes. In contrast, only about 60% of the Big Pine Key females were in this category. Both the frequency and the fecundity of autogenous females were significantly greater at Flamingo.5. The higher engorgement rate for the Big Pine Key population when compared to the Flamingo population can be readily attributed to the differences in the availability of a single host species, the Key deer.6. Our findings support the hypothesis that autogenous females are abundant in some populations of A. taeniorhynchus because hosts are either unavailable or available on a very limited basis.

Effect of Host Defenses on the Feeding Pattern of Culex nigripalpus When Offered a Choice of Blood Sources

Host defensive behavior was examined in several avian and mammalian species. Visual observations of activity indicated that low mosquito feeding rates were caused by defenses and not by a lack of attraction. Feeding rates were enhanced when this behavior was suppressed by immobilization. Several experiments were conducted in outdoor cages using paired combinations of different species which were situated in close horizontal proximity to each other (3 to 5 ft). Similar feeding rates were obtained when both hosts were immobilized. When only one was restrained the feeding ratio always shifted in favor of the immobilized host. This shift was greatest when the free was very defensive. If neither was restrained, mosquitoes always fed to a lesser extent on the more defensive host. No evidence of any active diversion from defensive to tolerant hosts was observed in tests where hosts were vertically separated 8 ft apart. When mosquito densities were gradually increased, there was a corresponding increase in the proportion of the engorged feeding on the tolerant host. But at the same time there was a decrease in the overall engorgement rate. The engorgement rates remained relatively stable on the tolerant but decreased on defensive hosts. In our previous studies of defensive behavior different ciconiiform birds were exposed individually to predetermined numbers of mosquitoes in large outdoor cages. We demonstrated that the defensive behavior exhibited by different species has a marked effect on the feeding success and mortality of mosquitoes attempting to bite (Edman and Kale, 1971). Variation in feeding success was also influenced by the age of the bird, i.e., whether nestling or adult, and to a lesser extent, by certain individual characteristics (Kale et al., 1972). In addition, we found, as did Reeves (1972), that the density of biting mosquitoes directly affects the intensity of defensive activity and thereby influences the interruption and success of feeding by the parasites as well (Edman et al., 1972). In the present study, hosts were tested in pairs or groups to determine if the behavior of different animals, when spaced or in close proximity, also influences the selection of a host by Culex nigripalpus. Numerous species of birds and mammals were first screened to establish their relative tolerance to mosquito attack. Then several species, manageable in captivity and yet representing a wide range of defensive behavior from intensely intolerant to tolerant, were selected for choice tests. Received for publication 9 August 1973. * Supported by National Institutes of Health Grants No. AI-06587 and AI-11201. t Florida Medical Entomology Laboratory, P.O. Box 520, Vero Beach, Florida 32960, U.S.A. MATERIALS AND METHODS Test mosquitoes were reared from eggs of wild females as previously described (Edman and Kale, 1971). Non-blood-fed unmated females 6 to 12 days old, the number varying with the experiment, were automatically released from electrically timed holding boxes (1 ft3) mounted inside the test cages containing hosts. All surviving mosquitoes were recovered from the cages the following morning with an aspirator, then counted and examined for blood. Partial or incomplete blood meals were also categorized as in past studies (Edman and Kale, 1971). In experiments with multiple hosts, engorged mosquitoes were individually extracted in buffered saline and precipitin tested (Edman, 1971) to determine which of the 2 or 3 host-bloods they contained. We employed the experimental cage apparatus previously described (Edman and Kale, 1971) as well as 2 modifications. Initial screening tests with individual birds were carried out in the original 4-cage (each 8 by 8 by 8 ft) system. In tests with paired hosts, cages 8 by 4 by 8 ft were used. Reducing the size allowed the utilization of 8 test cages per night and these were arranged in a circular pattern under the same rainproof canopy used previously. Two species of herons were tested using 2 of the original cages and 2 cages of the reduced size. Feeding success in the smaller cages was comparable to that in the larger cages. For the final test with 3 species, a single large cage 20 by 20 by 16 ft was assembled under the elevated canopy. Unrestrained hosts were held in portable, wire cages varying in volume from about 1 ft3 for the sparrow and mouse to 22 ft3 for large birds. These cages allowed for movement of the animals within and mosquitoes could readily fly in and out. In tests with immobilized hosts, small birds were restrained in nylon stockings and mammals in tight-fitting hardware cloth tubes. Egrets were

Effect of mosquito density on the interrelationship of host behavior and mosquito feeding success.

A night heron, a green heron, a white ibis, and a cattle egret were individually exposed overnight in 8-ft cages to densities of Culex nigripalpus ranging from 25 to 1,200 per cage. Surviving mosquitoes were examined the following morning and engorgement rates were determined as a measure of effect of antimosquito activity. In addition, the behavior of each bird was recorded for 2-hr periods at three different mosquito densities. Results indicated an inverse relationship between the density of mosquitoes and the proportion that successfully obtained blood. This relationship was ascribed to the increase in defensive activity displayed by the birds (differing in degree according to species) when exposed to increases in mosquito density. The frequency of interrupted feeding (= partial blood meals) was also related to host behavior and mosquito density.

Associations of Wiscosin mosquitoes and woodland vertebrate hosts.

Host-feeding associations of mosquitoes were determined by exposing 20 species of woodland vertebrates to natural mosquito populations. Only Culex pipiens (L.) and C. restuans (Theobald) showed a definite host preference to the avian hosts. However, C. pipiens fed also on several of the mammal hosts. Aedes and Psorophora showed a preference for mammal hosts especially nonrodents. Aedes vexans Meigen, A. stimulans group, and Psorophora ferox (Humboldt) exhibited little response to rodents or cold-blooded vertebrates. Aedes trivittatus (Coquillett); A. sticticus (Meigen); and Mansonia perturbans (Walker) were general feeders. Aedes canadensis (Theobald) had a high attraction and engorgement rate on turtles as well as on some mammals, while A. cincreus Meigen showed a strong association with chipmunks and ground squirrels. Of the 7 rodent hosts the 13-lined ground squirrel, Citellus tridecemlincatus (Metchill), was the most acceptable. Most of the Aedes mosquitoes appeared to attack the most available host in an area.

Feeding Behavior and Host Preferences of Some Black Flies (Diptera:Simuliidae) in Wisconsin1

A rapid method for capturing simuliids attracted to and feeding on hosts is described. Engorged and nonengorged specimens readily entered the trap. The method was superior to human visual observation in detecting black fly feeding activity on avian hosts. The blood-sucking females were divided into two categories, those feeding on birds (ornithophilic) and those feeding on mammals (mammalophilic). Most avian feeders exhibited marked habitat and stratification preferences. Differences in the number of flies attracted to various sizes of simultaneously exposed birds were significant at the 5% level. Except for the ornithophilic species occurring in woodland habitats, preferences for mammals and birds were (within the habitats studied) generally related more closely to host size than to any other apparent factor. Engorgement rates were closely related to the attractiveness of the hosts. Simulium meridionale Riley and Eusimulium aureum (Fries) were vectors of Leucocytozoon parasites to turkeys, as was S. rugglesi N. & M. to ducks. Prosimulium magnum D. & S., S. decorum Walk., S. luggeri N. & M., S. jenningsi Mall., S. venustum Say, and S. vittatum Zett. were occasional livestock pests.

Field tests of avian host preference of Culex tarsalis Coq.

SummaryIn comparative tests with baited traps slowly rotated about a common vertical axis, comparable numbers of Culex tarsalis were attracted to birds of the same size whether of the same or different species, while the number attracted to birds of different size was proportional to their size.C. tarsalis engorgement rates were independent of attraction rates and size of bird, but they varied for different bird species and for different individuals of the same species. Engorgement rates on individual birds were usually consistent, with only a few instances of night-to-night differences. A combination of the host's attractiveness and acceptability to C. tarsalis undoubtedly influences the biting attack rates on avian hosts.A depression of the engorgement of C. tarsalis on chickens was found to be correlated with increased numbers of mosquitoes.C. tarsalis is attracted to and feeds on a wide range of avian and mammalian species exposed in traps under field conditions.

The influence of mating on egg production by Aedes aegypti.

SummaryThe egg production of individual virgin and mated female Aedes aegypti was investigated under laboratory conditions. No differences in the engorgement rates were observed. However, the continuously mated females deposited a statistically and significantly greater number of eggs per mosquito than did the virgin and partially mated females. These differences were attributable to the large proportion of females in the latter groups which laid few or no eggs. In these experiments, therefore, almost all ovipositing females, regardless of their mating conditioning, laid approximately the same number of eggs. An additional finding of this study was the delayed oviposition times of virgin mosquitoes.

AN EXPERIMENTAL STUDY OF TICK PARALYSIS IN AUSTRALIA.*

1. Tick paralysis occurs in man, the dog, and other domesticated animals on the East Coast of Australia.2. As far as is known, the disease in Australia is only conveyed by the mature female of Ixodes holocyclus. The immature stages and the male of this species of ticks are non-pathogenic.3. A similar disease, induced in a like manner by females of other species of ticks, has been observed by various authors in South Africa, Canada and Crete.4. A single tick, as shown by experiment, may cause fatal paralysis in man and the dog in Australia, the death-rate in dogs being very high.5. The main symptoms of tick paralysis in Australia do not differ materially from those observed in other countries. They begin with loss of coordination commencing in the hind legs in dogs, the fore legs, head and neck becoming subsequently affected. Death in all cases appears to be due to respiratory paralysis.6. The onset of symptoms has not been observed to occur in less than 5 days from the time the tick or ticks have attached themselves to a dog.7. Some of the ticks do not produce paralysis and others do, as shown repeatedly from my experiments on dogs. This requires explanation. It does not depend on the time that has elapsed between the tick having moulted and its attacking the dog.8. Paralysis has never been seen to occur when ticks were removed from dogs before the time when symptoms usually appear.9. It is impossible to transmit the disease from affected to healthy animals by the inoculation of blood, cerebro-spinal fluid or nervous tissue. Nor can the disease be transmitted by the injection of the body contents of ticks removed from affected animals. The examination of the fluids and organs of affected animals has failed to reveal the presence of pathogenic organisms.10. It is considered that the causal factor in the production of the disease is a tick-derived toxin, this toxin being secreted by the salivary glands.11. During the process of engorgement the salivary glands develop greatly, pouring out a maximum amount of secretion during the 2 days before the female tick drops.12. An emulsion of salivary glands of I. holocyclus proved to be toxic for when injected into a dog (Experiment V, p. 424) it caused fever, vomiting, etc. The salivary secretion contains anticoagulins. As Nuttall and Strickland found for anticoagulins, individual ticks may vary in toxicity.13. The period which elapses between the attachment of a tick to the host and the first signs of an attack of tick paralysis cannot be regarded in the light of an incubation period; it is dependent on the rate and stage of the tick's engorgement.14. If it be accepted that the causal agent of the disease is a tick-derived toxin, it remains to be shown how such a toxin is produced.15. There is some evidence that immunity to the disease may be acquired after recovering from previous attacks.16. There is no evidence of season having an influence on tick paralysis. It was induced experimentally both in winter (June–August) and summer (November–December) in Sydney.

An Experimental Study of Tick Paralysis in Australia

1. Tick paralysis occurs in man, the dog, and other domesticated animals on the East Coast of Australia.2. As far as is known, the disease in Australia is only conveyed by the mature female ofIxodes holocyclus. The immature stages and the male of this species of ticks are non-pathogenic.3. A similar disease, induced in a like manner by females of other species of ticks, has been observed by various authors in South Africa, Canada and Crete.4. A single tick, as shown by experiment, may cause fatal paralysis in man and the dog in Australia, the death-rate in dogs being very high.5. The main symptoms of tick paralysis in Australia do not differ materially from those observed in other countries. They begin with loss of coordination commencing in the hind legs in dogs, the fore legs, head and neck becoming subsequently affected. Death in all cases appears to be due to respiratory paralysis.6. The onset of symptoms has not been observed to occur in less than 5 days from the time the tick or ticks have attached themselves to a dog.7. Some of the ticks do not produce paralysis and others do, as shown repeatedly from my experiments on dogs. This requires explanation. It does not depend on the time that has elapsed between the tick having moulted and its attacking the dog.8. Paralysis has never been seen to occur when ticks were removed from dogs before the time when symptoms usually appear.9. It is impossible to transmit the disease from affected to healthy animals by the inoculation of blood, cerebro-spinal fluid or nervous tissue. Nor can the disease be transmitted by the injection of the body contents of ticks removed from affected animals. The examination of the fluids and organs of affected animals has failed to reveal the presence of pathogenic organisms.10. It is considered that the causal factor in the production of the disease is a tick-derived toxin, this toxin being secreted by the salivary glands.11. During the process of engorgement the salivary glands develop greatly, pouring out a maximum amount of secretion during the 2 days before the female tick drops.12. An emulsion of salivary glands ofI. holocyclusproved to be toxic for when injected into a dog (Experiment V, p. 424) it caused fever, vomiting, etc. The salivary secretion contains anticoagulins. As Nuttall and Strickland found for anticoagulins, individual ticks may vary in toxicity.13. The period which elapses between the attachment of a tick to the host and the first signs of an attack of tick paralysis cannot be regarded in the light of an incubation period; it is dependent on the rate and stage of the tick's engorgement.14. If it be accepted that the causal agent of the disease is a tick-derived toxin, it remains to be shown how such a toxin is produced.15. There is some evidence that immunity to the disease may be acquired after recovering from previous attacks.16. There is no evidence of season having an influence on tick paralysis. It was induced experimentally both in winter (June–August) and summer (November–December) in Sydney.