Activity patterns and egg production in Coccophagus bartletti, an aphelinid parasitoid of scale insects

ABSTRACT.

• 1 Daily patterns of oviposition and host-feeding were examined in Coccophagus bartletti Annecke & Insley. Females began to host-feed and oviposit during the second or third day after emergence. Thereafter, both activities occurred regularly.
• 2 During long observation periods (5 h) most oviposition (93%) and host-feeding (90%) occurred within the first 3.5 h of wasps first encountering hosts. Experiments demonstrated that levels of activity were low for the rest of the day, and nocturnal oviposition occurred only if wasps had no alternative.
• 3 Dissection of female wasps that had been exposed to hosts, or withheld from them, for given periods of time, revealed that activity levels are governed by egg availability. Dispersal activity may also be influenced by the physiological state of the ovaries.
• 4 Production of a full complement of eggs (at 24±1°C (12 h L) and 18±1°C (12 h D)) took 48h or longer after host-feeding, and if wasps were withheld from hosts and provided with honey, the effects of egg resorption could be detected after about 10 days. Trends in oögenesis and oösorption in C. bartletti females seem not to conform with interpretations of oögenesis-oösorption cycles in other parasitoids.
• 5 The pattern of activity exhibited by C. bartletti females is not inflexible, but the major aspects mentioned above are species-specific. In general, information is needed about daily and hourly patterns of parasitoid oviposition and host-feeding before experiments are designed to test theories of parasitoid behaviour. Interpretation may otherwise rest on assumptions about their physiological condition.

     

Phosphorus sorption and extractability in Andic soil incubated with plant residues of variable P content

Sodium acetate extractable P and P sorption were measured in a high P-sorbing Andept soil (Mission series) following incubation with Winter wheat (Triticum aestivum (L.)Nugaines) and red clover (Trifolium pratense (L.)Florex) plant residue. The effects of plant residue P content, moisture regime, and quantity added were evaluated over a twelve week incubation period. Increased extractable P and decreased P sorption occured when the P content of residue exceeded 0.1% P for both winter wheat and red clover. The extractable P decreased and the P sorbed increased for all treatments and the check as the incubation time progressed. Extractable P increased and P sorption decreased more under air dry moisture conditions than at –0.03 MPa or saturation. Extractable P levels increased and P sorption decreased with increasing amounts of added residue. The effects of the residue additions decreased with increasing incubation time.     

Phosphate sorption isotherms for evaluating phosphorus requirement of wetland rice soils

Summary Phosphate sorption isotherms were developed for five Philippine wetland rice soils using the conventional technique and a modified one. In the conventional method, P requirements of soils varied between 280 and 810 g P/g soil. In the modified method, they varied from 160 to 540 g P/g soil at 0.2 ppm P in solution. Soils with high P-sorption capacities had vermiculite and halloysite as the dominant clay minerals. Soil reduction by flooding decreased P-sorption by 28–70 percent at 0.2 ppm P in solution. The decrease in P-sorption due to soil reduction was greatest in a crystalline soil with vermiculite and halloysite as the dominant clay minerals and least in a soil with dominant X-ray amorphous silicates in the clay fraction.Desorption of freshly adsorbed P under reduction was greater in HCO ₃ ^– solution than in CaCl₂ and it increased with level of applied P. Desorption patterns of freshly adsorbed P were similar to adsorption patterns but values of P in solution were lower at desorption. Soils varied with respect to desorption of freshly sorbed P. Desorption studies indicate that soils vary in intensity factor with respect to P and thus influence P availability to plants. Use of P-sorption and P-desorption data obtained under reduced soil condition was proposed for detecting P needs of submerged rice soils.Results of a pot study with IR36 at different levels of solution P (reduced) in one soil indicated a high degree of correlation between adjusted P levels and the measured growth parameters. About 0.12 ppm P in the soil solution or 0.46 ppm P desorbed in HCO ₃ ^– solution (equivalent to 100 mg P/kg soil) was adequate for near-maximum plant height, tiller production, total dry matter yield, plant P content, and total P uptake.     

Zn buffering capacity and Zn accumulation in Swiss chard for some sludge-amended soils

Zinc sorption by soils can greatly affect its availability to plants. This study was conducted to determine the relationship between the Zn sorption capacity and plant Zn accumulation in five sludge-amended soils using Swiss chard (Beta vulgaris L.) as an indicator plant. Zinc sorption as a function of Zn concentration and pH was determined for the soils which received no sludge amendment; also DTPA (diethylenetriaminepentaacetic acid) extractable Zn was determined in all soils. Whereas the responses of DTPA-Zn and plant Zn to pH and the quantities of Zn sorbed were similar, the logarithm of DTPA-Zn accounted for only 82% of the variability in the logarithm of Zn accumulation by the plants. The variability was better explained when pH was included with DTPA-Zn in stepwise multiple regressions. The Zn buffering capacity, defined as the ratio of the change in quantity of Zn sorbed ( Zn_s) to the change in Zn solution concentration (Zn₁) (or Zn_s/Zn₁), and the estimated quantity of Zn sorbed were used as a basis to measure Zn intensity. Zinc intensity, which reflects Zn solution concentration, was the predominant factor controlling Zn accumulation by Swiss chard, judging from the good fit of the values of both parameters to the Michaelis-Menten equation. The maximum Zn accumulation was approximately 9 mmol kg^–1.Scientific paper no. 8901-29, Department of Agronomy and Soils, College of Agriculture and Home Economics Research Center. Washington State University, Pullman, WA 99164, USA.Scientific paper no. 8901-29, Department of Agronomy and Soils, College of Agriculture and Home Economics Research Center. Washington State University, Pullman, WA 99164, USA.     

COPPER SORPTION AND RELEASE BY CYCLOTELLA MENEGHINIANA (BACILLARIOPHYCEAE) AND CHLAMYDOMONAS REINHARDTII (CHLOROPHYCEAE)1

Initial Cu⁺⁺ sorption by Cyclotella meneghiniana Kütz. (Cu⁺⁺-sensitive) and Chlamydomonas reinhardtii Dangeard (Cu⁺⁺-resistant) was rapid in the first 5 min of Cu⁺⁺ incubation with little sorption after 2 h. On a cell to cell basis, Cyclotella sorbed ca. five times more Cu⁺⁺ from the medium than Chlamydomonas. In MBL medium with EDTA Cyclotella and Chlamydomonas cells sorbed 21.0 and 4.41 nM Cu⁺⁺/10⁶ cells respectively in 6 h with 0.3 mg Cu⁺⁺/l in the medium. Proportionally similar quantities of Cu⁺⁺ were sorbed when the cells were Cu⁺⁺ incubated in MBL + citrate or filtered lake water. Cleaned cell walls of Cyclotella sorbed little Cu⁺⁺ (1.7 nM/10⁶ cells) as compared to living cells (17.5 nM Cu⁺⁺/10⁶ cells) in 3 h. Therefore, in living Cyclotella most of the Cu⁺⁺ taken up must be absorbed by the protoplasm or perhaps by the organic layer surrounding the silica wall. Cleaned cell walls of Chlamydomonas sorbed 3.5 nM Cu⁺⁺/10⁶ cells and living Chlamydomonas cells sorbed 2.6 nM Cu⁺⁺/10⁶ cells. This indicates that most of the Cu⁺⁺ sorbed by Chlamydomonas cells remained bound to the cell wall and probably did not readily enter into the protoplasm: When placed in Cu⁺⁺ free medium after Cu⁺⁺ incubation, Cyclotella and Chlamydomonas cells released 46 and 59% respectively of the Cu⁺⁺ sorbed.     

Development and physiology of follicular atresia during ovarian growth in the house fly, Musca domestica

Atretic follicles regularly occur in the ovary of the house fly, Musca domestica. The frequency of ovarian follicular atresia and the proportion of atretic follicles per ovary are related to the stage of oögenesis and to the age of the females. Only vitellogenic follicles may become atretic. The atresia may occur at any stage of vitellogenesis, though most follicles become atretic in mid-vitellogenesis. Atretic follicles are completely resorbed within 24–36 hr. The follicle cells may play a synthesizing role during growth and disintegrating one during follicle resorption. The induction of glycogen synthesis by the cessation of RNA and protein synthesis and by vitellogenesis in normal follicles is discussed. The same processes occur prematurely in the atretic follicle which can be thus distinguished by a high content of glycogen.     

Phosphorus Limitation in Boreal Forests: Effects of Aluminum and Iron Accumulation in the Humus Layer

Plant growth in boreal forests is generally considered to be predominantly nitrogen (N) limited, but forested groundwater discharge areas may be exceptions. In this study, we conducted tests to determine whether highly productive forested groundwater discharge areas generally differ from adjacent groundwater recharge areas in terms of humus chemistry and the availability of phosphorus (P) and N to plants. We investigated six forested sites, divided into groundwater discharge and adjacent groundwater recharge areas, in northern Sweden. The humus layers of the forested groundwater discharge areas were clearly distinguished from the adjacent groundwater recharge areas by having higher acid-digestible calcium (Ca) and/or aluminium (Al) and iron (Fe) content and higher organic P and N content. Soil solution inorganic N (NH₄ ⁺ and NO₃ ⁻) and pH were higher in the groundwater discharge areas than in the groundwater recharge areas. The organic P content showed a positive linear relationship to the Al and Fe content in the humus layer, indicating that organic P is associated with Al and Fe compounds in the humus. A plant bioassay using humus substrate from one groundwater discharge area and the adjacent groundwater recharge area found that plants grown in groundwater discharge area humus (with a high P-fixation capacity) increased their biomass upon P fertilization, whereas no growth response was found for N additions. By contrast, plants grown in humus from the groundwater recharge area did not respond to added P unless N was added too. This study suggests that groundwater discharge can affect the nutrient availability of N and P both directly, via increased P fixation due to the redistribution of Al and Fe, and indirectly, via the inflow of groundwater high in Ca and alkalinity, maintaining a high pH in the humus layer that favors in situ N turnover processes. Received 2 March 2001; Accepted 9 November 2001.     

Effects of dissolved organic matter from sewage sludge on the atrazine sorption by soils

The effects of dissolved organic matter (DOM), water soluble organic matter derived from sewage sludge, on the sorption of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-trazine) by soils were studied using a batch equilibrium technique. Six paddy soils, chosen so as to have different organic carbon contents, were experimented in this investigation. Atrazine sorption isotherms on soils were described by the linear equation, and the distribution coefficients without DOM (Kd) or with DOM (Kd*) were obtained. Generally, the values of Kd*/Kd initially insoil-solution system form. Critical concentrations of DOM (DOMnp) were obtained where the value of Kd* was equal to Kd. The presence of DOM with concentrations lower than DOMnp promoted atrazine sorption on soils (Kd* ＞ Kd), whereas the presence of DOM with concentrations higher than DOMnp tended to inhibit atrazine sorption (Kd* ＜ Kd). Interestingly, DOMnp for tested soils was negatively correlated to the soil organic carbon content, and the maximum of Kd*/Kd (i.e.Kmax) correlated positively with the maximum of DOM sorption on soil (Xmax). Further investigations showed that the presence of hydrophobic fraction of DOM evidently promoted the atrazine sorption on soils, whereas the presence of hydrophilic DOM fraction obviously tended to inhibit the atrazine sorption. Interactions of soil surfaces with DOM and its fractions were suggested to be the major processes determining atrazine sorption on soils. The results of this work provide a reference to the agricultural use of organic amendment such as sewage sludge for improving the availability of atrazine in soils.     

Biodegradation of atrazine in surface soils and subsurface sediments collected from an agricultural research farm

The purpose of the present study was to assess atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) mineralization by indigenous microbial communities and to investigate constraints associated with atrazine biodegradation in environmental samples collected from surface soil and subsurface zones at an agricultural site in Ohio. Atrazine mineralization in soil and sediment samples was monitored as ¹⁴CO₂ evolution in biometers which were amended with ¹⁴C-labeled atrazine. Variables of interest were the position of the label ([U-¹⁴C-ring]-atrazine and [2-¹⁴C-ethyl]-atrazine), incubation temperature (25°C and 10°C), inoculation with a previously characterized atrazine-mineralizing bacterial isolate (M91-3), and the effect of sterilization prior to inoculation. In uninoculated biometers, mineralization rate constants declined with increasing sample depth. First-order mineralization rate constants were somewhat lower for [2-¹⁴C-ethyl]-atrazine when compared to those of [U-¹⁴C-ring]-atrazine. Moreover, the total amount of ¹⁴CO₂ released was less with [2-¹⁴C-ethyl]-atrazine. Mineralization at 10°C was slow and linear. In inoculated biometers, less ¹⁴CO₂ was released in [2-¹⁴C-ethyl]-atrazine experiments as compared with [U-¹⁴C-ring]-atrazine probably as a result of assimilatory incorporation of ¹⁴C into biomass. The mineralization rate constants (k) and overall extents of mineralization (P _max ) were higher in biometers that were not sterilized prior to inoculation, suggesting that the native microbial populations in the sediments were contributing to the overall release of ¹⁴CO₂ from [U-¹⁴C-ring]-atrazine and [2-¹⁴C-ethyl]-atrazine. A positive correlation between k and aqueous phase atrazine concentrations (C _eq ) in the biometers was observed at 25°C, suggesting that sorption of atrazine influenced mineralization rates. The sorption effect on atrazine mineralization was greatly diminished at 10°C. It was concluded that sorption can limit biodegradation rates of weakly-sorbing solutes at high solid-to-solution ratios and at ambient surface temperatures if an active degrading population is present. Under vadose zone and subsurface aquifer conditions, however, low temperatures and the lack of degrading organisms are likely to be primary factors limiting the biodegradation of atrazine.Abbreviations C _eq solution phase atrazine concentration at equilibrium - C _s amount of atrazine sorbed - CLA [2-¹⁴C-ethyl]-atrazine - k first-order mineralization rate constant - K _d sorption coefficient - m slope - P _max maximum amount of CO₂ released - RLA [U-¹⁴C-ring]-atrazine