Host gall size and oviposition success by the parasitoid Eurytoma gigantea

Abstract. 1. Eurytoma gigantea Walsh is a specialist parasitoid of the tephritid gallmaker Eurosta solidaginis (Fitch).
2. In the natural environment the incidence of parasitism by Eurytoma is greater in small galls than in large ones.
3. Laboratory experiments demonstrated that small galls are not more frequently discovered; however, oviposition attempts on small galls were more likely to be successful.
4. Eurytoma spends much time probing galls too big to penetrate; this leads to a decrease in foraging efficiency when many large galls are present.
5. The chance of successfully penetrating a gall depends on the thickness of the gall wall and the length of the parasitoid's ovipositor.
6. A simulation model was constructed which shows that a gallmak-er's chance of being parasitized depends on gall size, the number of parasitoids that discover the gall, and their ovipositor lengths.     

ELISA absorbance cut-off method affects malaria sporozoite rate determination in wild Afrotropical Anopheles

ABSTRACT. Malaria sporozoite infection rates in a mixed species group of 244 Anopheles gambiae Giles sensu lato and 115 An. funestus Giles wild female mosquitoes were compared using three methods to determine cutoff absorbance values for positivity of a Plasmodium falciparum Welch enzyme-linked immunosorbent assay (ELISA). Positive controls were based on P. falciparum circumsporozoite protein. As negative controls, four wild male Anopheles were included on each microtitre plate; tests were repeated on four consecutive days for each plate.
Infection rates were estimated at 13.1–22.8% using the mean absorbance value of negative controls plus three standard deviations, 11.7–12.8% using double the mean and 12.5–13.6% using the fixed cut-off value of 0.20 (allowing for 20% variation in negative control absorbance values).
Observed agreement for positivity or negativity among samples tested four times was 98.6% for the 2× mean method, 97.2% for the fixed cut-off 0.20 value, but only 82.7% for the mean +3 SD method. It was concluded that the 2× mean cut-off method is most reliable for field studies. P. falciparum sporozoite rates of 12.2% in An. funestus and 11.9% in An. gambiae s. l . were thus determined on the basis of the 2× mean cut-off method.
This comparative evaluation demonstrates that vector infectivity rates can be seriously over-estimated from sporozoite ELISA tests, by as much as 87% in one case considered here, depending on the absorbance cut-off method applied for negative controls.     

A Multi-Unit Sampling System and Its Use in the Characterization of Ultradian and Infradian Growth in Tetrahymena*

SYNOPSIS. A multi-unit automatic sampling device for investigation of microbial growth under a wide variety of conditions is described. The kinetics of asynchronous population growth for batch cultures of Tetrahymena pyriformis (W) at several temperatures show that there are 2 distinct growth phases: an exponential ultradian growth phase that is strongly temperature dependent and a non-stationary growth phase, the infradian phase, that shows little or no temperature dependence over the range from 15–27 C.     

Phylogenetic Position of Amblyospora Hazard & Oldacre (Microspora: Amblyosporidae) Based on Small Subunit rRNA Data and Its Implication for the Evolution of the Microsporidia

ABSTRACT. Sequences of the small subunit rRNA genes of Amblyospora californica and an Amblyospora sp. from Culex salinarius were determined. These sequences were compared phylogenetically with 16 other microsporidia. The results suggest Amblyospora forms a sister taxon to the rest of the microsporidia examined. The basal position of Amblyospora is discussed with respect to the evolution of microsporidian life cycles. These sequences represent the longest microsporidian small subunit rRNA genes sequenced to date, 1,359 and 1,358 bp, respectively. Structural features and GC content (49% for both) are comparable to those of other microsporidia which have been sequenced.     

Tropical zooplankton: phenotypic and spatial analyses of polymorphic Ceriodaphnia cornuta (Crustacea: Cladocera)

SUMMARY. 1. The predation-balanced polymorphism of Ceriodaphnia cornuta (a small-eyed horned form and a large-eyed unhorned form) in Lake Gatun, Panama, is re-examined approximately 12 years after the original study (Zaret, 1972a). We consider morphological variability, distribution and fecundity of the population inhabiting Laboratory Bay.
2. The two morphological characters emphasized by Zaret, eye size and horn length, are studied in detail. The C. cornuta population exhibits wide, yet continuous variation; coefficients of variation are 28% or eye diameter and range from 114% to 136% for horn and spine lengths. Phenotypic variation in the population is characterized by: (1) negative correlations between spine lengths and eye size; (2) positive correlations among spines from different body regions (anterior horn, lateral spines, and tail spine); and (3) weak correlations between body length and spine lengths.
3. While the horned and unhorned forms continue to coexist in Laboratory Bay. the frequencies of horned forms have increased in the open water areas since the time of the original study. The increase in horned form frequencies may be due to changes in fish predation intensity. Did vertical distribution patterns of the forms remain very similar to each other.
4. In contrast to previous laboratory findings, egg ratio calculations from field samples revealed similar clutch sizes for the horned and unhorned forms. The egg development time of the horned form, however, was found to be approximately 30% longer than that of the unhorned form, perhaps because of increased moulting difficulties produced by the presence of spines.     

Integrated Analysis of Growth and Light Interception in Winter Lettuce II. Differences between Cultivars

‘Integrated growth analysis’ (emphasizing aspectsof crop and plant structure) and ‘light conversion analysis’(stressing the efficiency of interception and photosyntheticconversion of light) have been used to investigate the wintergrowth of different cultivars of butterhead and crisphead typesof glasshouse lettuce. Measurements from ‘Ambassador’ (large-framed butterhead),‘Renate’ (medium-sized butterhead) and ‘Cristallo’(crisphead) were made, statistical progressions were fittedto the primary data and hence estimates of all the analyticalcomponents were derived. Curves for crop growth rate, like those for most other components,followed a generally similar pattern for all three cultivars.In integrated growth analysis, the biomass curve for Ambassadorlay above the curves for the other cultivars. The weight advantagewas initially 60 per cent and it persisted with only a smallreduction (to 40 per cent) until the final harvest. Relativegrowth rate varied little between cultivars because differencesobserved in leaf area ratio were complementary to those seenin net assimilation rate. In light conversion analysis, differences in light interceptingefficiency between cultivars were not statistically significant,though Ambassador attained full interception 4 days earlierthan Renate and 6 days earlier than Cristallo. Differences inlight utilizing efficiency were small and non-significant exceptduring the post-rosette stage when the value for Renate waslower than that of either Ambassador or Cristallo. Deviationsaround the fitted curves were correlated with fluctuations inthe light regime. An assessment is made of the utility and limitations of thetwo procedures. It is concluded that both approaches can assistin analyzing the rate of dry matter production in crops or plantstands. Integrated growth analysis is advantageous when theneed arises to treat individual and population-based attributessimultaneously, while light conversion analysis provides a meansof explicitly incorporating the primary environmental variableinfluencing growth. Lactuca sativa L., lettuce cultivars, growth analysis, crop growth rate, relative growth rate, light interception, light utilization     

Potassium-Ammonium Uptake Interactions in Tobacco Seedlings

Short-term (< 12 h) uptake experiments were conducted with6–7-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K⁺ andNH₄⁺. At equal solution concentrations (0.5 mol m^–3) netK⁺ uptake was inhibited 30–35% by NH₄⁺ and NH₄⁺ uptakewas decreased 9–24%. Removal of NH₄⁺ resulted in completerecovery in K⁺ uptake rate, but NH⁴⁺ uptake rate did not recoverwhen K⁺ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m^–3. The relative effectof K⁺-NH₄⁺ interactions was not altered when Cl- was replacedwith SO₄^2–, but the magnitudes of the uptake rates wereless in the absence of Cl-. The V_max for NH₄⁺ uptake was reducedfrom 128 to 105 µmol g^–1 dry wt. h^–1 in thepresence of 0.5 mol m^–3 K⁺ and the K_m for NH₄⁺ doubledfrom 12 to 27 mmol m^–3 in the presence of K⁺. The resultsof these K⁺-NH₄⁺ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K⁺ coupled to NH₄⁺influx via an antiporter cannot be ruled out as contributingto the decrease in net K⁺ uptake. Key words: Nicotiana tabacum, K⁺, NH₄⁺, Uptake interactions