Arrested development of the rabbit stomach worm Obeliscoides cuniculi: resumption of development of arrested larvae throughout the course of a single infection

Arrested development of the rabbit stomach worm Obeliscoides cuniculi: resumption of development of arrested larvae throughout the course of a single infection. International Journal for Parasitology 16: 47–54. Twenty rabbits were inoculated once with cold treated L3s of Obeliscoides cuniculi with a high propensity for arrest and killed in pairs at intervals over 234 days post-infection. An exponential decline in numbers of adult worms and arrested larvae was observed. Arrested larvae resumed development at a rate seven times greater than adults were lost and appeared to replenish the adult population. More male than female arrested larvae were intially established in rabbits but males resumed development at a greater rate than females. Egg and larval production were correlated with the number of female worms present at any one time. In a subsidiary study, arrested larvae were recovered from one rabbit and transferred sequentially through two further rabbits. These larvae resumed development at the same rate as larvae in the 20 rabbits. Both studies suggest that resumption of development is an intrinsic characteristic of the larvae themselves and may be genetically controlled.     

The enhancement of muscle trichinosis in rabbits after immunization with heterologous serum proteins

The enhancement of muscle trichinosis in rabbits after immunization with heterologous serum proteins. International Journal for Parasitology4, 193–196. Rabbits were immunized with electrophoretically-purified rat serum albumin, β-globulin or γ-globulin in Freund's Complete Adjuvant and then inoculated with Trichinella spiralis larvae. Muscle parasitism was greatly enhanced in all the treated animals; this, plus the high levels of anti-rat and low levels of antiparasite antibody, indicates that antigenic competition can increase parasite numbers in trichinosis. Antigenic competition may play a role in the establishment of natural infections by T. spiralis by deflecting a protective immunological response by the host.     

Arrested development of the rabbit stomach worm Obeliscoides cuniculi: Manipulation of the ability to arrest through processes of selection

Through a process of selection in an isolate of O. cuniculi, the propensity for arrested development in response to cold treatment was increased from 15 to over 90% in five generations. In subsequent generations, the propensity for arrest remained high so long as selection pressure was maintained. The selected high arresting isolate exhibited a corresponding increase in ability to arrest without prior cold treatment of infective larvae. In the absence of selection for arrest, this isolate reverted to one with a lower propensity for arrest. These results indicate that arrested development has a genetic basis.

A hypothesis was developed which proposed that continuous variation in the rate of development is controlled by polygenes and that a worm will exhibit arrested developmet if its genotype has an enrichment of alleles for slow growth at the various polygenic loci.     

Kinetics of primary and secondary infections with Taenia crassiceps metacestodes (Zeder, 1800) rudolphi, 1810 (cestoda: cyclophyllidea)

Siebert A. E. Jr., Good A. H. & Simmons J. E. 1978. Kinetics of primary and secondary infections with Taenia crassiceps metacestodes (Zeder, 1800) Rudolphi, 1810 (Cestoda: Cyclophyllidea). International journal for Parasitology8: 39–43. When three T. crassiceps metacestodes were inoculated intraperitoneally in mice as a primary infection, approximately 50% of the larvae recovered during the first 4 weeks after inoculation were found to be dead, while in mice primed by previous subcutaneous inoculation, about 85% of the larvae died. Larvae which survived the first 4 weeks following primary intraperitoneal inoculation reproduced asexually by exogenous budding and produced viable infections within the host mice. But larvae in secondary infections were encapsulated by host granulomata, failed to reproduce asexually, and did not produce viable infections. In mice given intraperitoneal inoculations of seven, ten and twenty metacestodes, fewer larvae were killed and little encapsulation response was noted, though host cells were common at the budding region of the larvae. Such a biphasic host-response to the infection has not previously been reported for larval cestode infections, and the reduction in host response associated with increased worm burdens may indicate possible depression of the host immune system.     

Acquired resistance in sheep to infection with larvae of the blowfly, Lucilia cuprina

Acquired resistance in sheep to infection with larvae of the blowfly, Lucilia cuprina. International Journal for Parasitology16: 69–75. Resistance to blowfly larvae infections developed in sheep exposed to at least four consecutive infections. Half of the sheep treated showed significant levels of resistance, the others remained susceptible. This resistance took the form of a decreased yield of third instar larvae in comparison to controls and sheep which remained susceptible. In addition an increased sensitivity to larvae developed, as shown by the area of wound obtained per maggot recovered, by the early appearance in resistant sheep of exudate from the infection site and by skin reactions to larval products. Radioimmunoassays demonstrated high levels of serum antibody against larval excretory/secretory antigens, though the response did not peak until after four infections. Resistant animals showed somewhat lower antibody titres than susceptible sheep. Consecutive infections of only 50 larvae failed to induce resistance to larger challenge infections. It is suggested that consecutive infections of larger numbers of maggots induce a hypersensitivity response which may effect larval survival especially of first and second instar maggots.     

Immunological responses of rabbits artificially infested with the cattle grubs Hypoderma bovis (L.) and H. Lineatum (De Vill.) (Diptera: Oestridae)

Boulard Chantal and Weintraub J. 1973. Immunological responses of rabbits artificially infested with the cattle grubs Hypoderma bovis (L.) and H. lineatum (De Vill.) (Diptera : Oestridae). International Journal for Parasitology3: 379–386. Immunological responses against first-instar larvae of Hypoderma bovis (L.) and H. lineatum (De Vill.) were traced in artificially infested rabbits in which larvae grew normally in the first instar but did not survive to the second instar. Passive haemagglutination demonstrated a rapid rise in antibody titres during the first 2 months to maximum levels that persisted until about 200 days of the infestation. Immunoelectrophoretic analyses of the sera demonstrated that larval metabolic products were more important than breakdown products of dead larvae in stimulating the production of antibodies. Larval collagenase, which seemed to induce the most significant immune response, was inhibited by homologous antibodies in the serum of a hyperimmunized rabbit. The implications of these results for infestations in the normal bovine host were discussed, with emphasis on the need to identify antigenic fractions other than collagenase, which by itself had not produced total control of larvae in previous vaccination tests.     

Quantifying horizontal transmission of Nosema lymantriae, a microsporidian pathogen of the gypsy moth, Lymantria dispar (Lep., Lymantriidae) in field cage studies

Nosema lymantriae is a microsporidian pathogen of the gypsy moth, Lymantria dispar that has been documented to be at least partially responsible for the collapse of L. dispar outbreak populations in Europe. To quantify horizontal transmission of this pathogen under field conditions we performed caged-tree experiments that varied (1) the density of the pathogen through the introduction of laboratory-infected larvae, and (2) the total time that susceptible (test) larvae were exposed to these infected larvae. The time frame of the experiments extended from the early phase of colonization of the target tissues by the microsporidium to the onset of pathogen-induced mortality or pupation of test larvae. Upon termination of each experiment, the prevalence of infection in test larvae was evaluated. In the experiments performed over a range of pathogen densities, infection of test larvae increased with increasing density of inoculated larvae, from 14.2 ± 3.5% at density of 10 inoculated per 100 larvae to 36.7 ± 5.7% at 30 inoculated per 100 larvae. At higher densities, percent infection in test larvae appeared to level off (35.7 ± 5.5% at 50 inoculated per 100 larvae). When larval exposure to the pathogen was varied, transmission of N. lymantriae did not occur within the first 15 d post-inoculation (dpi) (11 d post-exposure of test larvae to inoculated larvae). We found the first infected test larvae in samples taken 20 dpi (16 d post-exposure). Transmission increased over time; in the cages sampled 25 dpi (21 d post-exposure), Nosema prevalence in test larvae ranged from 20.6% to 39.2%.     

Offspring dependence on parental care and the role of parental transfer of oral fluids in burying beetles

Background

Immature stages of many animals can forage and feed on their own, whereas others depend on their parents’ assistance to obtain or process food. But how does such dependency evolve, and which offspring and parental traits are involved? Burying beetles (Nicrophorus) provide extensive biparental care, including food provisioning to their offspring. Interestingly, there is substantial variation in the reliance of offspring on post-hatching care among species. Here, we examine the proximate mechanisms underlying offspring dependence, focusing on the larvae of N. orbicollis, which are not able to survive in the absence of parents. We specifically asked whether the high offspring dependence is caused by (1) a low starvation tolerance, (2) a low ability to self-feed or (3) the need to obtain parental oral fluids. Finally, we determined how much care (i.e. duration of care) they require to be able to survive.

Results

We demonstrate that N. orbicollis larvae are not characterized by a lower starvation tolerance than larvae of the more independent species. Hatchlings of N. orbicollis are generally able to self-feed, but the efficiency depends on the kind of food presented and differs from the more independent species. Further, we show that even when providing highly dependent N. orbicollis larvae with easy ingestible liquefied mice carrion, only few of them survived to pupation. However, adding parental oral fluids significantly increased their survival rate. Finally, we demonstrate that survival and growth of dependent N. orbicollis larvae is increased greatly by only a few hours of parental care.

Conclusions

Considering the fact that larvae of other burying beetle species are able to survive in the absence of care, the high dependence of N. orbicollis larvae is puzzling. Even though they have not lost the ability to self-feed, an easily digestible, liquefied carrion meal is not sufficient to ensure their survival. However, our results indicate that the transfer of parental oral fluids is an essential component of care. In the majority of mammals, offspring rely on the exchange of fluids (i.e. milk) to survive, and our findings suggest that even in subsocial insects, such as burying beetles, parental fluids can significantly affect offspring survival.

     

Nematospiroides dubius in mice selected for liability to infection: Modification of parasite biology through host selection

Brindley P. J. and Dobson C. 1982. Nematospiroides dubius in mice selected for liability to infection: modification of parasite biology through host selection. International Journal for Parasitology12: 573–578. Mice selected as liable (L) and refractory (R) over ten generations voided significantly more and less Nematospiroides dubius eggs compared with randomly mated (Rd) mice after primary infections with 100 larvae. There was little difference between the number of parasite eggs voided g^?1 faeces (epg) by individual mice on day 14 compared with day 15 after infection.However there was a significant diurnal variation in the egg values for individual mice but the mean differences observed between the R, Rd and L mice were maintained over a 24 h period. There was a strong correlation between both the total number and the number of female worms, surviving 21 days after infection, and the mean epg 14 and 15 days after infection. Female N. dubius produced more eggs in L mice and fewer eggs in R mice compared with worms in Rd mice. Similarly, worms grew longer in L mice and were shorter in R mice compared with parasites in Rd mice.     

Nematospiroides dubius: arrested development of larvae in immune mice.

When immune NIH mice were killed 10 days after a challenge infection with Nematospiroides dubius, approximately 10% of the inoculated larvae were recovered from the intestinal lumen, irrespective of the dose administered. When such mice were treated with cortisone from Day 10 for a period of 8 to 14 days and were subsequently killed for worm counts, it was found that they had significantly more worms than the immune control mice killed on Day 10. During the week following the beginning of treatment with cortisone there was little change in the low worm burdens in immune mice. However, 9 to 11 days after this treatment worm counts indicated that worms were accumulating in the intestinal lumen, and concurrently eggs were recorded in the feces of the mice. These observations indicated that a period of 9 to 11 days was required after the initiation of cortisone treatment on Day 10 for the worms in immune mice to complete their development to the adult lumen-dwelling stage. It is suggested that the larvae in the challenge infection became arrested early in their development in the intestinal wall and that growth resumed only after cortisone treatment. When treatment with cortisone was initiated later after challenge, it was still effective in reactivating arrested worms, but the lower worm recoveries in these mice indicated that the arrested larvae were being slowly rejected by the host. In subsequent experiments it was established that the arrested larvae of N. dubius were insusceptible to the activity of pyrantel embonate, an anthelmintic which is 99% effective against adult worms in the intestinal lumen. The mechanism whereby the larvae of N. dubius became arrested in immune mice and subsequently resumed their development after cortisone treatment is discussed.     

Transgenerational effects modulate density-dependent prophylactic resistance to viral infection in a lepidopteran pest

There is an increasing appreciation of the importance of transgenerational effects on offspring fitness, including in relation to immune function and disease resistance. Here, we assess the impact of parental rearing density on offspring resistance to viral challenge in an insect species expressing density-dependent prophylaxis (DDP); i.e. the adaptive increase in resistance or tolerance to pathogen infection in response to crowding. We quantified survival rates in larvae of the cotton leafworm (Spodoptera littoralis) from either gregarious- or solitary-reared parents following challenge with the baculovirus S. littoralis nucleopolyhedrovirus. Larvae from both the parental and offspring generations exhibited DDP, with gregarious-reared larvae having higher survival rates post-challenge than solitary-reared larvae. Within each of these categories, however, survival following infection was lower in those larvae from gregarious-reared parents than those from solitary-reared, consistent with a transgenerational cost of DDP immune upregulation. This observation demonstrates that crowding influences lepidopteran disease resistance over multiple generations, with potential implications for the dynamics of host–pathogen interactions.     

Order of Inoculation Affects the Success of Co-Invading Entomopathogenic Fungi

The effect of order of inoculation of Pandora blunckii and Zoophthora radicans co-infecting Plutella xylostella (L.) (Lepidoptera: Plutellidae) was investigated. After co-inoculation, the proportion of larvae infected by either species was greatly reduced compared to when they were inoculated singly. The order of inoculation influenced the final outcome; the isolate inoculated last always killed more larvae than the isolate inoculated first.     

Developmental arrest of Haemonchus contortus in sheep treated with a corticosteroid

Adams D. B. 1986. Developmental arrest of Haemonchus contortus in sheep treated with a corticosteroid. International Journal for Parasitology16: 659–664. Developmental arrest of the nematode, Haemonchus contortus, at the fourth larval stage within sheep appears to be controlled by a complex of signals and events in which both host-associated and parasite-associated factors are essential participants. Treatment of worm-free sheep with the corticosteroid, dexamethasone, during infection demonstrated the existence of an arrest-prone state in infective larvae and a host-associated influence actuating the phenomenon of arrest. Not all subpopulations of the parasite responded to the influence of dexamethasone and a selection experiment in which the parasite was passaged through immune and non-immune sheep showed that the arrest-prone state was largely determined by genetic factors. The host-associated factor initiating or actuating arrest and identified by dexamethasone-treatment could be ascribed more satisfactorily to a manifestation of immune responsiveness than to a direct effect of the corticosteroid.     

Cold stored ectoparasitoid of Cydia fruit moths released under different temperature regimes

Cold storage of parasitoids to be used in biological control programs is desirable but risky for the performance of the stored parental generation as well as for its offspring. We studied the performance of cold stored and unstored parasitoids after release at different temperature regimes in the laboratory at the level of two subsequent generations in Hyssopus pallidus (Askew) (Hymenoptera: Eulophidae). This gregarious ectoparasitoid is a candidate biocontrol agent of Cydia pomonella L. (Lepidoptera: Tortricidae) and Cydia molesta (Busck) (Lepidoptera: Tortricidae) larvae, two fruit pests of high economic significance in apple cultivation. Cold storage for 14 days at 4°C imposed to the pupal stage of the parasitoid did not reduce the parasitism capacity of the parental generation, nor did it alter the female biased sex ratio of the progeny. Remarkably, this short-term storage of the parental generation exhibited a significant and consistently positive effect on offspring weight throughout all ambient temperature regimes, resulting in an increased offspring weight. Furthermore, offspring number was only reduced after release at low ambient temperatures, but not at 25°C and 30°C. Irrespective of whether the parasitoids originated from the stored or unstored group, highest parasitism rate was achieved at temperatures above 20°C. In conclusion, this candidate biocontrol agent can be cold stored for short periods without any measurable quality loss after release at most except at low ambient temperatures. Our findings suggest that H. pallidus is a thermophilous parasitoid that will perform best when applied at warm ambient temperatures in fruit orchards.     

Ancylostoma duodenale: maintenance through six generations in helminth-native pups.

An Indian strain of Ancylostoma duodenale with a known propensity for arrested development in man was passaged serially in 2-month-old, helminth-naive, male beagles. The sixth passage was initiated about 500 days after laboratory maintenance began. Experimental animals were infected by stomach tube with 1500 larvae each. These infections became patent in 22–31 days. In a line passaged in dogs without the use of a corticosteroid (prednisolone), adaptation, as judged by fecal egg count, increased through the first three generations and then declined sharply. This line appears destined for extinction. In another line passaged in prednisolone-treated pups, the strain's original viability is being maintained. Infections were long lived, frequently surviving for 90 days or more. Maximum egg output in terms of eggs per gram of feces (EPG) was highly variable between generations and between individuals within generations, but commonly exceeded 1500 EPG. In pups necropsied between 44 and 55 days, harboring fifth- and sixth-generation infections, adult worm burdens ranged from 47–146 and 34–128 in the nonprednisolone and prednisolone lines, respectively. Arrested larvae have been found in the same pups and apparently contribute to a turnover in the population of adult worms. Although A. duodenale has yet to be fully adapted to dogs in the sense that indefinite survival without prednisolone is assured, the present system yields a variety of life history stages in quantities suitable for many experimental purposes. Thus it provides a utilitarian laboratory model for the investigation of one of man's major hookworms.     

Divergent selection in a maize population for germination at low temperature in controlled environment: study of the direct response, of the trait inheritance and of correlated responses in the field

Improving cold tolerance in maize (Zea mays L.) is an important breeding objective, allowing early sowings which result in many agronomic advantages. Using as source the F₂ population of B73 × IABO78 single cross, we previously conducted four cycles of divergent recurrent selection for high (H) and low (L) cold tolerance level, evaluated as the difference (DG) between germination at 9.5 °C and at 25 °C in the germinator. Then, we pursued the divergent selection in inbreeding from S₁ to S₄. This research was conducted to study (1) the direct response to selection (by testing ten S₄ L and ten S₄ H lines), (2) the trait inheritance (in a complete diallel scheme involving four L and four H lines), (3) the associated responses for cold tolerance in the field (at early and delayed sowings) and (4) the responses for other traits, by testing the ten L and the ten H lines at usual sowing. Selection was effective, leading to appreciable and symmetric responses for DG. Variation among crosses was mainly due to additive effects and the ability to predict hybrid DG based on parental lines DG was appreciable. Associated responses for cold tolerance traits in the field were noticeable, though the relationship between DG and these traits was not outstanding. High tolerance was also associated with early flowering, short plants, less leaves, low kernel moisture, red and thin cob, and flint kernels. These divergently selected lines can represent valuable materials for undertaking basic studies and breeding works concerning cold tolerance.     

East Coast fever: the infectivity for cattle of infective particles of Theileria parva harvested in various substrates

Cunningham M.P., Brown C.G.D., Burridge M.J., Joyner L.P. and Purnell R.E. 1973. East Coast fever : the infectivity for cattle of infective particles of theileria parva harvested in various substrates. International Journal for Parasitology3: 335–338. Female Rhipicephalus appendiculatus ticks infected with Theileria parva were pre-fed on rabbits for 4 days before being removed and restrained on ‘plasticine’. They were then fed for 2-h periods on capillary tubes containing various substrates, the contents of which were subsequently inoculated into East Coast fever-susceptible cattle. Using this technique, precolostral calf serum and Eagle's Minimum Essential Medium, with the addition of Bovine Albumin Powder, were selected as substrates suitable for further laboratory investigation on East Coast fever as they were acceptable to the ticks and supported the viability of the parasites.     

Ecdysteroid-titre reduction and developmental arrest of last-instar Heliothis virescens larvae by calyx fluid from the parasitoid Campoletis sonorensis

Fifth-instar Heliothis virescens larvae did not pupate after injections of Campoletis sonorensis calyx fluid in or before the burrow-digging stage of development. Arrested development occurred in 40% of larvae injected at the cell-formation stage. Further experiments showed that the particles in calyx fluid were responsible for developmental arrest. Arrested development due to calyx fluid could be reversed by injecting 10 μg of either ecdysone or 20-hydroxyecdysone, although a second injection of 20-hydroxyecdysone was needed for some larvae 3 days after the first treatment. Ecdysteroid production ceased for up to 10 days in 5th-instar H. virescens after calyx-fluid injection. After 10 days, some experimental larvae began to produce ecdysteroids again but remained developmentally arrested. The head, thorax, or abdomen of larvae were isolated by ligations and calyx fluid injected into the isolated body region. After 24 h, ligatures were released and the larvae observed for developmental arrest. Only injections into the isolated thorax stopped development. This, along with ecdysteroid data, indicated that C. sonorensis calyx fluid may directly affect the prothoracic glands of 5th-instar H. virescens.