Morphological and Biochemical Correlates in the Characterization of Sarcocystis spp.1

ABSTRACT. Isoenzyme electrophoretic techniques were applied to the characterization of seven Sarcocystis spp. that had been identified by conventional morphological studies. Cystozoites were harvested from macroscopic cysts from sheep, cattle, and mice and from microscopic cysts from sheep, cattle, and goats. Soluble cystozoite extracts were subjected to cellulose acetate gel electrophoresis and characterized at 15 of the 39 enzyme loci examined. Genetic relationships among isolates were examined by simple phenetic clustering. Two different morphological types of macroscopic cysts from sheep, identified as S. gigantea (syn. S. ovifelis) and S. medusiformis, consistently differed at 40% of the loci examined. Such genetic divergence confirms their separate morphotypic classification. Both differed from microscopic cyst isolates from sheep at 87% of the loci examined; however, two different morphotypes of microscopic cysts were found in the sheep sampled (thick-walled and thin-walled cysts). Until sufficient numbers of each type can be isolated and examined separately, both were regarded as belonging to the species S. tenella (syn. S. ovicanis). Macroscopic and microscopic cysts from cattle consistently differed at 80% of the loci thereby supporting their separate classification as S. hirsuta (syn. S. bovifelis) and S. cruzi (syn. S. bovicanis), respectively. Isolates from goats (microscopic cysts identified as S. capracanis) differed from S. tenella and S. cruzi at 20% and 47% of the loci, respectively. All macroscopic cyst isolates from the various host animal species (including S. muris from mice) differed from each other at nearly all loci. Isoenzyme electrophoretic techniques therefore provided genetic evidence supporting the classification of these various Sarcocystis spp. by their morphological characteristics.     

Detecting seasonal variation in composition of adult Coccinellidae communities

1. Following its recent global spread, Harmonia axyridis (Coleoptera: Coccinellidae), an aphid predator of East Palearctic origin, dominated local coccinellid communities. While long‐term trends in this change are well documented, little is known about seasonal changes. 2. Seasonal changes in communities of adult Coccinellidae were investigated in central Europe (Prague), from April to November in 2010–2014. The beetles were collected at 2‐weekly intervals by net‐sweeping particular stands of trees (Tilia spp., Acer spp. and Betula sp.). The numbers of beetles caught were recalculated per unit effort, and average species abundance and community richness, dominance and diversity were calculated for each 2‐week period. 3. Frequencies of 21 established species varied throughout the vegetative season and general trends in this variation were similar in each of the 5 years of this study. In May–June the abundant species was Adalia decempunctata, which was later replaced by Harmonia axyridis as the most abundant species in late summer. Coccinella septempunctata colonized trees occasionally in summer. This sequence of species substitution occurred every year and was reset during winter. Species richness decreased and dominance increased during the course of each vegetative season. The diversity of the coccinellid community (Shannon index H′) significantly decreased during the course of the vegetative season. This was caused by a gradual increase in the dominance of H. axyridis, the abundance of which explained 88% of variation in H′. 4. The existence of a significant seasonal difference indicates that it is important to take this into consideration when comparing coccinellid communities.     

Secondary host preferences and reproductive activity of the bird cherry-oat aphid, Rhopalosiphum padi

Of 15 species of grass, including cereals, alate exules and emigrants of Rhopalosiphum padi preferred to colonise Lolium perenne. Emigrants colonised cereals twice as readily as alate exules. Apterous exules also preferred L. perenne to cereals. Although small when reared on L. perenne, R. padi was more fecund per unit weight than on any of the other grasses tested. On the later growth stages of Dactylis glomerata and L. perenne, R. padi developed faster and were more fecund than on Phleum pratense at the same growth stages. At low temperatures R. padi were more fecund on P. pratense than on L. perenne and D. glomerata and vice versa at high temperatures. The secondary host preferences and reproductive activity of R. padi are discussed in relation to possible suitable hosts for viviparous overwintering and the pest status of this aphid in Britain.     

Short-term forecasting of wheat yield loss caused by the grain aphid (Sitobion avenae) in summer

A damage model was used to take into account the effect on winter wheat yield of the size, duration and timing of Sitobion avenae infestation in summer, and the influence of insecticide applications. It was validated as far as possible using available data, and appeared to be sufficiently accurate to be useful. The model was applied to a total of 32 winter wheat fields over the period 1975 to 1983 in eastern England and the Netherlands, to obtain estimates of yield losses associated with not applying insecticides at the end of ear emergence (G.S. 59), mid-anthesis (G.S. 65) or the end of anthesis (G.S. 69). These estimates of future yield losses were related in multiple regressions to the number of S. avenae per tiller at the time the insecticide was applied, and the rate of population increase over the previous few days. Basing the decision about whether to apply insecticide on forecasts from the multiple regression equations appeared to be slightly more profitable than prophylactic spraying when the chemical cost alone was considered, but substantially more profitable when the application cost and wheeling loss were also taken into account. The strategy minimising losses involved forecasts at all three crop growth stages. It was validated using a further 21 fields studied in 1984 and 1985, and gave better results than the EPIPRE system, which over-estimated the number of fields requiring spraying, and the economic threshold of George & Gair (1979), which under-estimated the number requiring spraying. However, the accuracy of the damage model needs to be checked against measured yield losses in order to establish the success of the multiple regression strategy conclusively.     

Water uptake by some chamber materials

Abstract. The characteristics of water uptake by several materials have been studied. Nitrile rubber, silicone rubber and perspex retained substantial quantities of water. Metals took up smaller, but still significant, amounts of water, and glass was the least water-retentive material used in the tests. The surface structure of the material, revealed by scanning electron microscopy, does not necessarily account for its water uptake characteristics. The results are discussed in relation to the design and construction of psychrometer and porometer chambers.     

Boundary layer conductance of the leaves of some tropical timber trees

Abstract The boundary layer conductance of brass models of leaves exposed in a wind tunnel was determined from their cooling characteristics. Conductances were generally very low, as expected from large leaves. Nusselt numbers were calculated from the rates of heat loss, so that the results could be compared with established theory. There was generally good agreement between observed and calculated values. Leaves with veins displayed an apparent transition from a laminar to a turbulent boundary layer, and so did leaves inclined at an angle from the horizontal. In still air the observed rates of heat loss by natural convection were substantially higher than those calculated.