Fast accumulation of few polyhedra mutants during passage of a Spodoptera frugiperda multicapsid nucleopolyhedrovirus (Baculoviridae) in Sf9 cell cultures

Baculoviruses are a group of viruses that infect invertebrates and that have been used worldwide as a biopesticide against several insect pests of the Order Lepidoptera. In Brazil, the baculovirus Spodoptera frugiperda multicapsid nucleopolyhedrovirus (SfMNPV; Baculoviridae) has been used experimentally to control S. frugiperda (Lepidoptera: Noctuidae), an important insect pest of corn (maize) fields and other crops. Baculoviruses can be produced either in insect larvae or in cell culture bioreactors. A major limitation to the in vitro production of baculoviruses is the rapid generation of mutants when the virus undergoes passages in cell culture. In order to evaluate the potential of in vitro methods of producing SfMNPV on a large-scale, we have multiplied a Brazilian isolate of this virus in cell culture. Extensive formation of few polyhedra mutants was observed after only two passages in Sf9 cells.     

Description of the Oocysts of Two New Species of Eimeria (Apicomplexa: Eimerüdae) from the Florida Manatee, Trichechus manatus (Sirenia: Trichechidae)

Two new species of Eimeria (Apicomplexa: Eimerüdae) are described from the feces of the Florida manatee, Trichechus manatus latirostrts (Sirenia: Trichechidae). Oocysts of Eimeria manatus n. sp. are spherical to subsphencal, 11.8 × 10.7 (10.5–13.5 × 9.0–13.5) μ m , with a smooth, thin, bilayered wall; shape index (length/width) 1.1 (1.0–1.3). Micropyle and oocyst residuum absent; polar granule(s) usually present. Sporocysts are ovoid, 8.6 × 5.1 (8.0–9.5 × 5.0–5.5) μm, with thin, membrane–like walls and a knoblike Stieda body; shape index 1.7 (1.4–1.8). Sporozoites elongate, each with a large posterior refractile body. The sporocyst residuum consists of a small cluster or row of few to many small granules. Oocysts of Eimeria nodulosa n. sp. are spherical to subspherical, 15.6 × 14.7 (14.5–17.5 × 13.0–16.0) μm, with a distinctly bilayered wall; shape index 1.1 (1.0–1.2). Unsporulated and freshly sporulated oocysts often possess large, knob–like structures on the external surface of the oocyst wall that support a thin membrane or filament. Micropyle, oocyst residuum and polar granule absent. Sporocysts are ovoid, 10.6 × 5.9 (9.5–12.0 × 5.0–6.5) μm, with a smooth, thin wall and knob–like Stieda body; shape index 1.8 (1.5–2.1). Sporozoites granular and elongate, each with a large posterior refractile body. The sporocyst residuum consists of a loose aggregate or scattered mass of moderately sized granules.     

Ultrastructural Observations on Renal Schizogony of Leucocytozoon dubreuili in the American Robin

SYNOPSIS. The schizogonic development of Leucocytozoon dubreuili in the kidney proximal tubule cells of the American robin, Turdus migratorius , was studied by electron microscopy. Renal schizogony is initiated by the entry of certain hepatic merozoites into cells of the proximal tubules. Development of the schizont consists of a coordinated sequence of events including extensive mitotic nuclear division, multiplication of mitochondria, increase in endoplasmic reticulum and ribosomes, differentiation of membranes, microtubules, micronemes and rhoptries, and cytoplasmic segmentation (cytomere formation). Merozoites form by budding around numerous centers in the schizont and, when mature, are bounded by a single plasma membrane subtended by microtubules. Each merozoite contains a large nucleus, a mitochondrion, and a well developed apical complex consisting of 3 polar rings, paired rhoptries, and numerous micronemes.
An atypical nuclear division observed in some maturing schizonts was characterized by the multiple fission of a nucleus within a persistent outer nuclear membrane and the absence of mitotic spindle apparatus. Alterations in infected renal cells consisted of disorganization and loss of cytoplasmic organelles and the accumulation of lipofuscin-like inclusions.     

Relationships between host blood factors and proteases in Glossina morsitans subspecies infected with Trypanosoma congolense

Abstract. Host blood effects on Trypanosoma congolense establishment in Glossina morsitans morsitans and Glossina morsitans centralis were investigated using goat, rabbit, cow and rhinoceros blood. Meals containing goat erythrocytes facilitated infection in G. m. morsitans , whereas meals containing goat plasma facilitated infection in G. m. centralis. Goat blood effects were not observed in the presence of complementary rabbit blood components. N-acetyl-glucosamine (a midguMectin inhibitor) increased infection rates in some, but not all, blood manipulations. Cholesterol increased infection rates in G. m. centralis only. Both compounds together added to cow blood produced superinfection in G. m. centralis , but not in G. m. morsitans. Midgut protease levels did not differ 6 days post-infection in flies maintaining infections versus flies clearing infections. Protease levels were weakly correlated with patterns of infection, but only in G. m. morsitans. These results suggest that physiological mechanisms responsible for variation in infection rates are only superficially similar in these closely-related tsetse.     

Geographic parthenogenesis and the common tea‐tree stick insect of New Zealand

Worldwide, parthenogenetic reproduction has evolved many times in the stick insects (Phasmatidae). Many parthenogenetic stick insects show the distribution pattern known as geographic parthenogenesis, in that they occupy habitats that are at higher altitude or latitude compared with their sexual relatives. Although it is often assumed that, in the short term, parthenogenetic populations will have a reproductive advantage over sexual populations; this is not necessarily the case. We present data on the distribution and evolutionary relationships of sexual and asexual populations of the New Zealand stick insect, Clitarchus hookeri. Males are common in the northern half of the species’ range but rare or absent elsewhere, and we found that most C. hookeri from putative‐parthenogenetic populations share a common ancestor. Female stick insects from bisexual populations of Clitarchus hookeri are capable of parthenogenetic reproduction, but those insects from putative‐parthenogenetic populations produced few offspring via sexual reproduction when males were available. We found similar fertility (hatching success) in mated and virgin females. Mated females produce equal numbers of male and female offspring, with most hatching about 9–16 weeks after laying. In contrast, most eggs from unmated females took longer to hatch (21–23 weeks), and most offspring were female. It appears that all C. hookeri females are capable of parthenogenetic reproduction, and thus could benefit from the numerical advantage this yields. Nevertheless, our phylogeographic evidence shows that the majority of all‐female populations over a wide geographic area originate from a single loss of sexual reproduction.     

The role of leaf wounding and an epigeal predator on caterpillar damage to tomato plants

The effects of leaf wounding and the presence of a New Zealand carabid predator, Megadromus antarcticus, on the mortality of, and leaf damage caused by, Spodoptera litura on tomatoes were examined in glass houses. The presence of the non-climbing carabid increased S. litura mortality with a subsequent decrease in leaf damage. Leaf wounding produced a possible decrease in herbivory but did not affect S. litura mortality. Neither leaf wounding or the presence of carabids affected the vertical distribution of leaf damage on the tomato plants. The role of M. antarcticus as a biocontrol agent for tomato pests in New Zealand is briefly discussed.     

A field trial to assess the effects of rabbit grazing on spring barley

Spring barley is widely grown throughout the UK and significant yield loss can occur as a result of rabbit grazing. In a 3-yr trial, spring barley was grown in six enclosures following current agronomic procedures and was subjected to grazing by different population densities of rabbits. The annual yield loss at the end of the trial was 0.5% rabbit⁻¹ ha⁻¹. The yield loss per rabbit was calculated to be around 25 kg and the financial loss was calculated as £2.00 per rabbit at 1998 prices (approx. £80 tonne⁻¹). Models allowing farmers to predict the levels and costs of damage by rabbits to winter wheat and for silage have already been developed. The results from this trial enable farmers to extend their predictions to include spring barley. The implications for this are discussed.     

Statistical power analysis of a 2-year field study and design of experiments to evaluate non-target effects of genetically modified Bacillius thuringiensis corn

Abstract 1. A 2‐year field study was conducted in 2000 and 2001 at a farm in Monmouth, Illinois to evaluate the effect of MON 863, a transgenic corn event that expresses the Cry3Bb1 protein for control of corn rootworms, on diverse groups of arthropod populations in a corn ecosystem. 2. The field study employed a split‐plot design with MON 863 and conventional corn as the main plots and several insecticide treatments as subplots; each main plot was replicated four times (i.e. n = 4 block replications for each corn variety). A large number of arthropod taxa were trapped, taxonomically characterised, and counted in all plots. A mixed linear repeated‐measures model was used for analysis of each taxon collected to determine if there was an effect of MON 863 or insecticide regime on that taxonomic group. 3. This report describes the results of a power analysis to determine the ability of the study design to detect an effect of MON 863 corn on the abundance of different groups of arthropods. A 50% difference in average taxon abundance between MON 863 and conventional corn plots was the criterion used in assessing the power. 4. A statistical power analysis of the taxonomic group comparisons made in the 2‐year field study (with independent assignment of treatments each year) showed that only about 28% (22 of 56) of the statistical comparisons made with single years of data achieved ≥80% power to detect a 50% difference in population density. When data from both years of the study were analysed jointly, this level of power was obtained for 86% (24 of 28) the comparisons made. 5. Graphical examination of the mean abundance and coefficient of variation (CV) for different taxa indicated that high abundance (> 5 trap captures per plot per sampling period) and low CV (< 100%) contributed to high statistical power (> 80%). Taxa with extremely low abundance (mean trap captures < 1 individual per plot per sampling period) generally had high CV (> 100%), and statistical comparisons for those taxa had lower power (< 80%). 6. The relevance of these findings for designing field studies on the effects of genetically modified crops on non‐target arthropods with desired levels of power is discussed.     

Molecular Epidemiology of Cryptosporidiosis in Children in Malawi

ABSTRACT: Few studies have examined the molecular epidemiology of cryptosporidiosis in developing countries. In this study, DNA of 69 microscopy-positive human fecal samples collected from Malawi were examined by multilocus genetic analyses. From 43, 27 and 28 of the samples, the SSU rRNA, 70 kDa heat shock protein (HSP70) and 60 kDa glycoprotein (GP60) genes, respectively, were successfully PCR-amplified. Restriction analysis of the SSU PCR products showed that 41 of the 43 PCR-positive samples had C. hominis and 2 had C. parvum. Sequence analysis of the HSP70 and GP60 gene contirmed the species identification by SSU rRNA PCR-RFLP analysis, but also revealed high intraspecific variations. Altogether, six HSP70 subtypes and six GP60 subtypes (belonging to lour subtype alleles) of C. hominis were found. Linkage diseyuilibrum analysis of the two genetic loci showed possible intraspecitic recombination. Thus, cryptosporidiosis in the study area was largely caused by anthroponotic transmission. The high intraspecitic variation and existence of genetic recombination were probably results of high transmission of cryptosporidiosis in this area.