Nolleria pulicis N. Gen., N. Sp. (Microsporida: Chytridiopsidae), a Microsporidian Parasite of the Cat Flea, Ctenocephalides felis (Siphonaptera: Pulicidae)

A new species of microsporidium, Nolleria pulicis, is described and named here from the cat flea, Ctenocephalides felis. The genus Nolleria is created and placed within the family Chytridiopsidae. The family is slightly modified to accommodate certain features of intracellular development seen in N. pulicis, which is otherwise very similar to other species in the family Chytridiopsidae. Sporulation is described from ultrastructural analysis of infected midgut epithelial cells of adult C. felis. The term “multiple division by vacuolation” is proposed for describing sporogony as it occurs in this species and certain related species of microsporidia. The probable mode of transmission and apparent absence of merogony are discussed.     

Amblyospora trinus N. Sp. (Microsporida: Amblyosporidae) in the Australian Mosquito Culex halifaxi (Diptera: Culicidae)

ABSTRACT. A new species of Amblyospora , a parasite found in wild populations of the predacious Australian mosquito Culex halifaxi , was investigated with light and electron microscopy. This species was found to be heterosporous with two concurrent sporulation sequences in the host larvae, both arising from diplokaryotic meronts and ending with haploid spores. One sequence was dominant and involved meiosis to produce eight thick-walled, broadly oval meiospores in a sporophorous vesicle (SV). The other sequence involved nuclear dissociation to produce lanceolate, thin-walled spores in a subpersistent SV. Horizontal transmission to the mosquito host, by one or both of two distinctly different pathways (one via an intermediate host, the other by cannibalism of infected individuals) and by vertical transmission, are postulated but have not been demonstrated. A new species, Amblyospora trinus , is proposed and its affinities to other heterosporous microsporidia in mosquitoes are discussed.     

Brood size manipulations in Great Horned Owls Bubo virginianus: are predators food limited at the peak of prey cycles?

The reproduction of raptors strongly depends on food resources. It is unclear whether predators experience superabundant food during cyclic peaks of prey populations. In order to test this hypothesis, four pairs of Great Horned Owls Bubo virginianus with two young were subjected to brood size manipulations during high densities of cyclic Snowshoe Hare Lepus americanus populations in southwestern Yukon, Canada. Broods older than 35 days were temporarily enlarged by one, and then by two, young. No effects were observed when one owlet was added, but the addition of two young resulted in significant weight losses in manipulated broods. Females with enlarged broods moved farther from their nest sites at night, presumably reflecting increased hunting effort, and also spent less time near the nest during the day. Food additions to enlarged broods returned the parental behaviour to normal. We conclude that these large predators did not experience superabundant food at this stage of the breeding season during a peak in cyclic prey.     

Comparison of ELISA and immunoblotting techniques for the detection of cherry mottle leaf virus

Formaldehyde treated cherry mottle leaf virus (ChMLV) and the isolated coat protein were used successfully for the production of polyclonal and monoclonal antibodies. The monoclonal antibodies had a titre of 1:51 200 and consisted of IgG1 and IgG2. The antibodies reacted with all 11 isolates of ChMLV, from five locations in Canada and the USA, included in this study. Several serological procedures were assessed to compare their sensitivity for detecting ChMLV. Plate-trapped antigen ELISA (PTA-ELISA) and dot-blot immunobinding assay (DBIA), using virus specific MAbs, were the most sensitive tests in this study. Triple antibody sandwich ELISA (TAS-ELISA) and Western blot were found to be less sensitive. Dilution of the samples appeared to increase the sensitivity of both PTA-ELISA and Western blot detection. Young leaves and flowers of Prunus avium were the best tissue for detecting the virus which could also be detected in the fruit and leaves of P. tomentosa. April and May were optimal for detection of the virus in the field, whereas both April to May and August to September were optimal for screenhouse-grown plants.     

Ovule abortion in white clover (Trifolium repens L.)

Plants of white clover ( Trifolium repens L.) cv. Olwen were grown in an open glasshouse maintained at a mean temperature of 20^oC and ovule growth and seed production measured. Differences in the rate of growth of ovules within ovaries were observed as early as 2 days after pollination. Ovules reached a maximum size after 8 days with the smallest only half the size of the largest. After 8 days, the smallest ovules became flaccid and shrivelled. Ovule position within the ovary had little effect on the frequency of seed set and although there was an apparently higher probability that central ovules produced a seed than those nearer the peduncle or style this was not statistically significant. Inflorescence position and floret position on the inflorescence had a significant effect on the number of seeds per floret and seed weight; the first formed inflorescences and the first florets to be pollinated on each inflorescence had more seeds per floret and heavier seeds and fewer florets with no seed than later pollinated florets. There were also differences between florets within the same whorl. The role of a number of factors which may influence floret site utilisation are discussed.     

Recurrent response patterns of a zooplankton community to whole-lake fish manipulation

1. In a series of whole-lake manipulations conducted from 1984 to 1991, planktivorous fishes were alternately removed and restocked in a small mesotrophic lake, resulting in dramatic changes in the zooplankton community. 2. Response patterns in the zooplankton community, which include species and size structure, and within-year community variability, were examined. Variation in the zooplankton community in unmanipulated years was much lower than that in manipulated years, regardless of direction of the manipulation (i.e. decreasing or increasing planktivory). 3. The succession of zooplankton species abundance was repeated in the second removal of planktivorous fishes. The community shifted from small-bodied cladocerans, copepods and rotifers, through an intermediate state with high abundance of Holopedium, to an assemblage dominated by large-bodied daphnids.