Ultrastructural Characterisation and Molecular Taxonomic Identification of Nosema granulosis n. sp., a Transovarially Transmitted Feminising (TTF) Microsporidium

A novel microsporidian parasite is described, which infects the crustacean host Gammarus duebeni. The parasite was transovarially transmitted and feminised host offspring. The life cycle was monomorphic with three stages. Meronts were found in host embryos, juveniles, and in the gonadal tissue of adults. Sporoblasts and spores were restricted to the gonad. Sporogony was disporoblastic giving rise to paired sporoblasts, which then differentiated to form spores. Spores were not found in regular groupings and there was no interfacial envelope. Spores were approximately 3.78 x 1.22 microns and had a thin exospore wall, a short polar filament, and an unusual granular polaroplast. All life cycle stages were diplokaryotic. A region from the parasite small subunit ribosomal RNA gene was amplified and sequenced. Phylogenetic analysis based on these data places the parasite within the genus Nosema. We have named the species Nosema granulosis based on the structure of the polaroplast.     

Cuticular Proteins in Insects and Crustaceans

Comparisons between crustacean and insect cuticles are hamperedby the paucity of cuticular protein sequences for the former.Sufficient complete sequences are available for insect cuticularproteins to allow recognition of conserved motifs and relationshipsamong proteins that reflect the type of cuticle from which theyhave been extracted. All five sequences from an arachnid andtwo of 14 from crustaceans have a motif found in the largestgroup of insect cuticular proteins. Numerous insights have beengained from studying insect cuticular proteins and their genes.These insights have been summarized in hopes of encouraginginterest in building on the foundations laid by Dorothy Skinnerwith the exoskeleton of Gecarcinus.     

Life‐history consequences and disease resistance of western tent caterpillars in response to localised,herbivore‐induced changes in alder leaf quality

1. Plants can respond to herbivore damage with phenotypically plastic changes in quality that negatively affect herbivores and prevent subsequent attack – induced defences. 2. The present study tested whether trees respond to herbivory with localised induction, and whether life‐history traits and disease resistance of an insect herbivore are altered on induced branches of the trees. 3. The influences of localised, within‐branch, herbivore‐induced changes in red alder trees (Alnus rubra Bong.) on fitness characteristics of western tent caterpillars (Malacosoma californicum pluviale Dyar) were evaluated. In the field, randomly selected branches of trees were infested with tent caterpillar larvae and the adjacent branches were maintained as non‐infested controls. In the laboratory, larvae were fed leaves from either induced or non‐induced branches through to adult emergence. A second cohort of larvae was challenged with a viral pathogen to compare their disease susceptibility on induced versus non‐induced foliage. 4. Herbivore‐induced, localised responses of damaged branches reduced leaf quality for growth and the fecundity of female western tent caterpillars, but not that of males. Larvae fed induced leaves had a higher survival overall and a reduced mortality due to unidentified non‐viral pathogens than did their counterparts on non‐induced leaves. However, there was no influence of leaf quality on baculovirus‐induced mortality. 5. These findings suggest that localised induced changes in leaf quality could potentially influence populations of tent caterpillars in contradictory ways by reducing their growth rate and fecundity to a modest degree, while improving their survival and resistance to unidentified non‐viral pathogens to a larger extent.     

Chilling Sensitivity of Photosynthetic Oil-Seedlings: I COTTON SUNFLOWER

Despite the high probability that sensitive post-emergent seedlingswill be exposed to suboptimal temperatures which significantlyaffect subsequent development and yield, growers of long-season,indeterminate crops must rely upon empirically determined ‘earliestplanting dates’ Most ‘chilling-stress’ studieshave dealt, not with photosynthetic seedlings, but rather withthe effect of low, non-freezing temperatures (< 10 ?) upongerminating seeds and pre-emergent seedlings. A photosyntheticseedling growth system was used to monitor the effects of temperaturesfrom 10 to 35? upon the roots and aerial portions of chilling-sensitivecotton and relatively chilling-resistant sunflower oil-seedlings.Length measurements of cotton seedlings were too variable tobe reliable indicators of temperature treatment effects, butroot and shoot fresh weights could be used as non-destructivemeasurements of differences in root and shoot temperature responsesin both cotton and sunflower seedlings. The fresh weights wereindicative of the relative water status of seedling roots andshoots, including that of seedlings returned to 30? after exposureto other temperatures. Growth of both cotton and sunflower seedlingswas inhibited to some degree at non-optimal temperatures andthe capacities of the roots and shoots to return to normal waterstatus, as indicated by fresh weights and relative water contents,was correlated with sensitivity to suboptimal temperatures Key words: Cotton, sunflower, temperature, water status     

Phylloplane bacteria increase the negative impact of food limitation on insect fitness

1. When populations of herbivorous insects increase in density, they can alter the quantity or quality of their food. The impacts of diet‐related stressors on insect fitness have been investigated singly, but not simultaneously. 2. Foliage quantity and quality of red alder, Alnus rubra, were manipulated together with the presence of non‐entomopathogenic phylloplane bacteria to investigate their impacts, singly and in combination, on survival, pupal mass, growth rate, fecundity and egg quality of a cyclic forest insect, the western tent caterpillar, Malacosoma californicum pluviale. 3. Food limitation (half food) had strong negative impacts on all life‐history traits. When the larvae were fed continuously, however, neither ingesting phylloplane bacteria nor eating leaves from damaged branches (induced foliage) affected survival. In the half‐food treatment, ingesting bacteria further increased mortality, while feeding on induced foliage improved survival. 4. Growth rate and pupal mass of both sexes were reduced for larvae with food limitation compared with continuously fed insects and this was exacerbated when the larvae also ate bacteria‐treated leaves. A combination of bacteria and induced foliage also reduced larval growth rate by 5% in the full‐food treatment. 5. Fecundity (eggs per egg mass) was 2.7 times greater in full‐food than in food‐limited treatments but neither phylloplane bacteria nor plant induction had an effect. Insects fed induced foliage produced smaller eggs. Overall, there was no evidence of a three‐way interaction between the three stressors, although there were negative synergistic effects, primarily between food limitation and the ingestion of phylloplane bacteria.