Unfed Weight Research Articles

Infection with Borrelia afzelii and manipulation of the egg surface microbiota have no effect on the fitness of immature Ixodes ricinus ticks

Arthropod vectors carry vector-borne pathogens that cause infectious disease in vertebrate hosts, and arthropod-associated microbiota, which consists of non-pathogenic microorganisms. Vector-borne pathogens and the microbiota can both influence the fitness of their arthropod vectors, and hence the epidemiology of vector-borne diseases. The bacterium Borrelia afzelii, which causes Lyme borreliosis in Europe, is transmitted among vertebrate reservoir hosts by Ixodes ricinus ticks, which also harbour a diverse microbiota of non-pathogenic bacteria. The purpose of this controlled study was to test whether B. afzelii and the tick-associated microbiota influence the fitness of I. ricinus. Eggs obtained from field-collected adult female ticks were surface sterilized (with bleach and ethanol), which reduced the abundance of the bacterial microbiota in the hatched I. ricinus larvae by 28-fold compared to larvae that hatched from control eggs washed with water. The dysbiosed and control larvae were subsequently fed on B. afzelii-infected or uninfected control mice, and the engorged larvae were left to moult into nymphs under laboratory conditions. I. ricinus larvae that fed on B. afzelii-infected mice had a significantly faster larva-to-nymph moulting time compared to larvae that fed on uninfected control mice, but the effect was small (2.4% reduction) and unlikely to be biologically significant. We found no evidence that B. afzelii infection or reduction of the larval microbiota influenced the four other life history traits of the immature I. ricinus ticks, which included engorged larval weight, unfed nymphal weight, larva-to-nymph moulting success, and immature tick survival. A retrospective power analysis found that our sampling effort had sufficient power (> 80%) to detect small effects (differences of 5% to 10%) of our treatments. Under the environmental conditions of this study, we conclude that B. afzelii and the egg surface microbiota had no meaningful effects on tick fitness and hence on the R0 of Lyme borreliosis.

Salivary gland degeneration and ovarian development in the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae). I. Post-engorgement events

It is well known that female ixodid ticks undergo salivary gland degeneration and the greater part of ovarian development following engorgement. The process has been particularly well studied in Amblyomma hebraeum, including the hormonal control of these processes. The purpose of this study, and the second one in this series, is to compare the processes in Dermacentor andersoni with those of A. hebraeum. A major difference between the two species is that virgin female D. andersoni feed to a much higher fed-to-unfed weight ratio than do virgin female A. hebraeum, the former achieving an average of 67× the unfed weight in this study, the latter normally achieving an average of only about 10–15× the unfed weight. We show here that although engorged virgins (defined here as those that exceed a fed-unfed weight ratio of 50, even though they do not detach from the host spontaneously) degenerate their salivary glands and develop their ovaries, these processes proceed more slowly in virgins that they do in mated females, as is the case for A. hebraeum.

Salivary gland degeneration and ovary development in the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae). II. Determination of the ‘critical weight’

The feeding cycle of female ixodid ticks is divided into preparatory, slow, and rapid feeding phases. When a female Amblyomma hebraeum is removed from the host after achieving a minimum size of about 10–13× the unfed weight, various physiological and behavioural changes occur: (a) haemolymph ecdysteroid concentration rises dramatically, (b) the tick does not reattach to the host when given the opportunity, (c) its salivary glands degenerate within about 4 days (if mated) or 8 days (if virgin), and (d) oocyte maturation and oviposition occur (Kaufman and Lomas, 1996; Invert. Repr. Devel. 30: 191–198). None of these changes occur if the tick is removed from the host at smaller sizes. This transition, which occurs when the tick enters the rapid phase of engorgement, has been named the ‘critical weight’. To date, the critical weight has been determined for A. hebraeum only. The present study established that, in both mated and virgin D. andersoni, the critical weight is similar to that of A. hebraeum. Although a small percentage of virgin A. hebraeum do exceed the critical weight, achieving perhaps 20× the unfed weight, virgin D. andersoni regularly fed well beyond their CW (>50× the unfed weight) and occasionally engorged completely (100× the unfed weight), although they did not detach spontaneously from the host within 21 days of attachment.

Calcium regulates Na+:K+:2Cl− cotransporter function in Malpighian tubules of Rhodnius prolixus

Rhodnius prolixus is a haematophagous insect, vector of Chagas’ disease. During each blood meal the insect ingests large volumes of blood that may be up to 10 times its unfed weight. The excess of water and ion ingested is expelled thanks to a rapid post‐prandial diuresis triggered by the diuretic hormone serotonin, that stimulate the Malpighian (renal) tubules (MT). Until now, serotonin was believed to stimulate MTs via the second messenger cAMP and Ca2+ was considered to play no significant role. Here we tested the role of Ca2+ on serotonin‐stimulated MTs. Our results show that serotonin stimulation triggered Ca2+ waves in MTs. In addition, incubating tubules in Ca2+‐free saline containing BAPTA‐AM (3 μM) reduced fluid transport by 50%, decreased Na+ flux by 70% and decreased pH of the secreted fluid from 7.10±0.05 to 6.20±0.21. Measurements of transepithelial potential suggest a reduced activity of the basolateral Na+:K+:2Cl− cotransporter (NKCC) when chelating Ca2+. The results indicate that Ca2+ is important for normal functioning of the tubules. We hypothesize that Ca2+ may be involved in NKCC regulation. Disruption of Ca2+ signalling may alter NKCC activity by changing its phosphorylation state or its insertion to the membrane. Funded by a Natural Sciences and Engineering Research Council of Canada grant to JPI.

The Costs and Effects of Alternative Winter Feeding Strategies for Channel Catfish Ictalurus punctatus in Multiple-Batch Production

Previous work suggested that feeding catfish, Ictalurus punctatus, more frequently over the winter might reduce weight loss. Twelve 0.10-ha ponds were stocked with 987 kg/ha market-sized fish and 2,960 kg/ha sub-marketable fish in November 2008 with treatments of: (1) unfed, (2) fed daily (fed 90 d), and (3) temperature-threshold feeding (fed 62 d). Total gross yield was significantly greater for the temperature-threshold feeding treatment than the unfed control, but survival and mean weight of fish at harvest were not. Net yield was negative for all treatments, due primarily to mortality of market-sized fish. Plasma glucose and insulin-like growth factor-1 did not differ significantly, but plasma osmolality was significantly lower in fasted than in fed fish. Mean feed consumption rates in vats provided evidence to support more frequent feeding over the winter. Overwintering costs were $0.11/kg with temperature-threshold feeding. Research on strategies to reduce winter mortality has potential to reduce overwintering costs.

Salivary gland degeneration and vitellogenesis in the ixodid tick Amblyomma hebraeum: Surpassing a critical weight is the prerequisite and detachment from the host is the trigger

The normal engorged body weight of female ixodid ticks (Acari: Ixodidae) is about 100× the unfed weight. Virgin female Amblyomma hebraeum normally do not feed beyond 10× the unfed weight. However, about 10–20% of a population of virgins will feed to perhaps 20× the unfed weight, but not much beyond that. In A. hebraeum, when females surpass about 10× the unfed weight, the following changes in physiology occur if they are removed from the host: (a) they will not reattach if given the opportunity, (b) their salivary glands (SGs) will undergo autolysis within 4 days if they are mated or 8 days if they are virgin, and (c) egg maturation and oviposition will occur in due course. Mated or virgin female ticks removed from the host below about 10× the unfed weight do not experience the latter changes (Kaufman, W.R., Lomas, L., 1996. ‘Male Factors’ in ticks: their role in feeding and egg development. Invertebrate Reproduction and Development 30, 191–198). In 1984 we named this transitional weight, the ‘critical weight’ (CW). Its absolute value is probably a species-specific characteristic (Kaufman, W.R., 2007. Gluttony and sex in female ixodid ticks: how do they compare to other blood-sucking arthropods? Journal of Insect Physiology 53, 264–273). Although mated females tend to engorge within a day of surpassing the CW, virgin females surpassing the CW can remain attached to the host for at least several weeks more. It is not known whether the physiological changes in the SGs and ovaries listed above occur in those large virgins that remain attached, although we suppose that this would be maladaptive. Instead, we hypothesize in this study that surpassing the CW is only a prerequisite for inducing these changes, and that detachment is the actual trigger. We support our hypothesis by demonstrating that large virgins, remaining attached to a host for 8 days, did not undergo SG degeneration nor complete egg maturation during the attachment period. Those changes occurred only within 8 days following detachment. So some type of sensory information associated with attachment to the host, and still undefined, inhibits expression of the physiological changes hitherto associated merely with surpassing the CW.

The relationship between ‘critical weight’ and 20-hydroxyecdysone in the female ixodid tick, Amblyomma hebraeum

The feeding cycle of adult female ticks (Acari: Ixodidae) is divided into preparatory, slow and rapid feeding phases. At the transition from slow to rapid feeding, Amblyomma hebraeum (Koch) females reach a ‘critical weight’ (CW; approx. 10× the unfed weight) that is characterized by several behavioural and physiological changes. Five of these changes were used as criteria to establish a more precise estimate of CW than we have to date. The CW as defined by re-attachment to the host was 9× the unfed weight, while for haemolymph ecdysteroid titre, salivary gland degeneration, ovary weight, oocyte length and oocyte vitellin content the CW was 10×, 10×, 12×, 12× and 13×, respectively. CW thus varies depending on the parameter measured. Although previous studies have established the influence of ecdysteroids on salivary gland degeneration and vitellogenesis, here we demonstrate a further effect of ecdysteroids: inhibiting re-attachment to the host.

Responses of the tick, Amblyomma hebraeum (Acari: Ixodidae), to carbon dioxide

We investigated the effect of physiological state of adult ticks (Amblyomma hebraeum Koch; Acari: Ixodidae) on their responses to a CO2-enriched atmosphere. Ticks were exposed to CO2 or air in an experimental chamber; we measured the effects on questing, movement and latency (the time after exposure to CO2 or air when ticks began questing or moving). This study confirmed the hypothesis that responsiveness to CO2 is enhanced during host-seeking periods of the life cycle and reduced at other times. Thus, whereas newly moulted ticks quested infrequently when exposed to CO2, questing increased over the 6 week period following moulting. Likewise, in 6 week old ticks, movement in CO2 was significantly greater than in air. When a partially fed female below approximately ten times its unfed weight is removed from a host, it reattaches if subsequently presented to another host. Such females quested vigorously in CO2 but not in air. When a partially fed female above approximately ten times its unfed weight is removed from a host, it usually does not subsequently reattach. Such females quested infrequently, there being no significant difference between air and CO2. Males removed from a host at any stage of feeding reattach readily when given the opportunity. They quested frequently, moved readily and the latency was very low in air or CO2. Exp Appl Acarol 22: 667–681 © 1998 Kluwer Academic Publishers

Relationships Among Body Size, Blood Meal Size, Egg Volume, and Egg Production of Tabanus fuscicostatus (Diptera: Tabanidae)

Number of ovarioles, egg production, and weight of unfed and bloodfed Tabanus fuscicostatus Hine females were related linearly to wing length. Wing length did not change whether flies were freshly thawed, preserved in formalin solution, or oven dried. Left and right wings were similar in length. The length from the costa to the anterior cross vein or to the intersection of R4 and R5 veins was associated linearly to wing length. The number of eggs produced by flies bloodfed on one or two bovine hosts was similar when adjusted by wing length. The average number of ovarioles per female was 277 +/- 50 (+/- SD), and eggs developed in only 63% of the ovarioles after a bloodmeal. An estimated 3.1 eggs were produced for each milligram of blood ingested by a fly, and the average bloodmeal size was 110% of the unfed weight of the flies (49.7 mg). Egg volume was unrelated to body size, but was associated inversely with the number of eggs produced per female.

Inputs to the hormonal control of egg development in Rhodnius prolixus.

This paper re-examines existing data on the environmental inputs governing egg production in Rhodnius prolixus. Feeding has a direct effect on egg production such that the product of the unfed weight of the female times the weight of the blood meal is a good predictor of the number of eggs produced. Mating modifies this input, so that mated females produce more eggs. Egg production is governed by the corpus allatum, and indirect evidence suggests that the number of eggs producted by a female is a function of the length of time that juvenile hormone is secreted by the corpus allatum. The input which determines the times at which the corpus allatum is switched off originates in the stretch induced by the amount of the meal remaining in the crop, modified by the matedness status of the female. The precise nature of the sensors detecting stretch is not yet clear, but the integrity of the dorsal aorta is essential to the transmission of the information. These data are related to the survival strategy for Rhodnius.

The effect of size on feeding and breeding performance of Rhipicephalus appendiculatus Neumann

A positive mean correlation was observed between engorged larval weight and unfed nymphal weight. Similarly, positive linear correlations were observed between engorged nymphal weight and unfed adult weight, between unfed female weight and engorged female weight and between engorged female weight and egg batch weight. Positive linear correlations were also observed between scutal length and weight of unfed adult ticks and between the duration of survival and unfed weight of adult ticks at both 43 and 85% r.h. and 28°C. At 43% r.h. and 28°C, small ticks lost water faster than larger ones. At 96% r.h. and 28°C the small ticks also gained water faster than larger ones. For the sizes tested, all the male ticks were comparable in their ability to fertilize normal females, but the smallest females were incapable of reproduction.

The life cycle of Argas (Argas) africolumbae under constant abiotic and biotic conditions

The developmental and reproduction pattern as well as the nondiapause behaviour of Argas (Argas) africolumbae, reared on domestic chickens and held at 27°C and 90% RH, indicate that there may be 2–3 generations annually. The minimum incubation period of eggs requires 16.2 days (mean), irrespective of the day of oviposition. Larvae feed for 5–6 days and moult 10.2 days after detaching to N 1. Generally, there are only 2 nymphal instars. All N 1 develop to N 2 13.7 days after feeding. After repletion, N 2 moult to males and females within 28.3 days with a ratio of 1.12:1.0. Female determined N 1 and N 2 are always heavier (1.13 mg and 3.81 mg, respectively) and imbile larger bloodmeals (4.19 mg and 17.45 mg, respectively) than male N 1 and N 2 (0.9 mg and 2.71 mg unfed weight and 3.04 mg and 12.33 mg bloodmeal size, respectively). Fed females begin to oviposit 9.5 days after engorgement and produce 102.9 eggs during a 14-day oviposition period.

The biology of the tree-hole breeding mosquito Aedes geniculatus (Olivier) (Diptera: Culicidae) in southern England

AbstractThe biology of Aedes geniculatus (O1.) was studied in 1967–73 in Monks Wood National Nature Reserve, an oak-ash woodland, in southern England. Adult emergence from tree-holes occurred from May to September, and the sex ratio was approximately 1:1. Catches on man indicated that the maximum biting densities occurred in July and August and that females spend about two minutes obtaining a blood-meal. Significant positive correlations were found between their unfed weight and the weight of the blood-meal and also between female wing length and fecundity. The mean number of eggs per batch was 70. Studies with bamboo pots used as artificial oviposition sites in the field showed that the seasonal peak in oviposition spanned July and August, daily ovipositional activity was greatest in mid-afternoon and evening and ovipositing females preferred oviposition sites positioned within 4 m of the ground. A small proportion of eggs hatched during the summer in which they were laid, but most hatched in the following spring. Continuous or intermittent soaking failed to induce hatching until this time. In 'the laboratory, partially em'bryonated eggs required a minimum relative humidity of 88% to develop fully, but some embryonated eggs survived at 58%. Some eggs survived for 18–24 months in the field. The sampling of preadult stages dn tree-holes showed that larvae in the first two instars occurred almost throughout the year while third- and fourth-instar larvae were present in spring and summer. Pupae occurred only in the summer. It was concluded that A. geniculatus is univoltine in Monks Wood.

Digestive Processes Of Hematophagous Insects: VIII. Estimation of meal size and demonstration of trypsin in horse flies and deer flies (Diptera: Tabanidae)

Blood-meal sizes are given for 12 species of tabanids (2 Chrysops and 10 Hybomitra ). In each species the average amount of blood ingested by the females was approximately equal to their average unfed weight. However, there was no significant intraspecific correlation between the unfed weight of a female and the amount of blood ingested. Females of Hybomitra affinis (Kirby), Hybomitra arpadi (Szilady), and Hybomitra lasiophthalma (Macquart) took larger meals when they fed upon man than when they fed upon rabbit or upon defibrinated beef blood through a Silverlight membrane. Under certain circumstances the diverticulum was used as a reservoir lor blood. Trypsin was demonstrated in 13 species (5 Chrysops , 7 Hybomitra and Haematopota americana Osten Sacken). In H. affinis (at 25°C), the maximum amount of trypsin occurred 24 to 48 hr after ingestion and there was a significant correlation between trypsin activity and protein content of the midgut.

Diuresis in the tsetse fly Glossina austeni.

After taking a blood meal, the tsetse fly Glossina austeni excretes the excess water and salts of the meal in approximately 30 min. During this period a volume of fluid equivalent to 80% of the unfed weight of the fly passes through the haemolymph, whose composition nevertheless remains almost constant. The fluid excreted has a higher sodium and lower potassium concentration than the haemolymph, indicating that sodium may be the prime mover in urine formation in Glossina.

Ion and Water Balance in the Ixodid Tick Dermacentor Andersoni

ABSTRACT Of the total meal imbibed by female Dermacentor andersoni during the normal adult feeding cycle, about 80% is excreted. Of the total water excreted by the tick, 75 % is removed by salivation, less than 3 % is evaporated from the integument and spiracles, and the remainder is lost via the anus. Of the total excreted sodium and potassium, 4 and 82 % respectively are lost via the anus. The remainder in each case is presumed excreted via the salivary glands. The ionic and osmotic concentrations of the haemolymph and saliva stabilize at constant values by the third or fourth day of feeding. The volume of extracellular fluid is constantly maintained at 23 % of the body weight, even though the total body weight increases 75 times over the unfed weight, and the volume of excreted fluid passing through the haemolymph is about ten times the haemolymph volume at repletion.

The cuticle as a template for growth in Rhodnius prolixus

The variation in size that occurs in Rhodnius has been examined and it is found that while the size of the head in any instar is almost constant, the dimensions of the abdomen vary as weight 3 . The meal that is taken is 5·7 times the unfed weight, suggesting that the abdomen stretches by a standard ratio regardless of size. In the adult the size of the abdomen is neither constant nor varies as weight 3 and the size is difficult to predict from the size of the fifth instar larva. Experiments with dilute meals and constraints on the size of the cuticle showed that the size of the larval abdomen is affected by the size of the cuticle in the previous instar; the effect of nutrition on the size of the head, however, is far less great. Experiments with fifth instar bugs showed that the size of the abdomen of the adult was directly related to the size of the larval abdomen at about the time of the deposition of the epicuticle. A model has been suggested to describe the growth of Rhodnius which proposes that the size in the next instar is the product of the existing size and a local growth factor. The local growth factor may change at metamorphosis and is probably expressed at the cellular level in terms of cell density and the area of epicuticle deposited per cell.