Electrohydrodynamic effects on two species of insects with economic importance to stored food products

An electrohydrodynamic (EHD) system which generated air ions within a strong electric field was used to study responses of stored-product insectsTribolium confusum (du Val) andPlodia interpunctella (Hübner). Larval mortality of both species generally increased with increased exposure time to ions of either polarity. The larvae and pupae ofT. confusum suffered a higher mortality rate than the adults. The insects initially exhibited distinct avoiding motions away from regions of high towards low fluxes of air ions of both polarity. Insects moved vigorously, tumbled, flipped, curled up, and aggregated when the EHD system was turned on. The control insects not exposed to air ions survived and showed a total absence of such behaviour. For bipolar exposures, the insects occupied the neutral zone where the effects were minimal due to cancellation of the fields. Prolonged exposures of more than 20 min produced a quiescent state. EHD-enhanced mass transfer of the liquid component from physical objects established in fluid mechanics was invoked as a possible cause for insect mortality and avoiding behaviour to ions. Body fluid losses increased linearly with time of exposure (R ²0.97) for all biological stages of insect growth. The larvae and pupae ofT. confusum lost 12 and 15% of their body fluids, respectively, after 80 min of exposure to negative air ions. Fluid losses of such a magnitude are likely to have contributed to insect fatality.     

Enhancement of evaporation rates from thin layers of liquids exposed to air ions

A beta-ray gauge system was used to study evaporation rates and drying times of liquids exposed to relatively high fluxes of air ions of either polarity produced by a corona discharge. Evaporation rates from thin layers of water, ethyl alcohol, and carbon tetrachloride increased considerably when exposed to air ions, compared to untreated liquids under constant environmental conditions. Drying times of liquid layers exposed to air ions were shortened by a factor of at least two over liquids that had not been exposed to ions. The drying time of a liquid layer was found to increase with the decrease of ion fluxes at the liquid surface. Threshold values of 1.9×10¹¹ positive ions and 2.7×10¹¹ negative ions cm^–2 s^–1 were established below which no increase in the evaporation rates were observed for ethyl alcohol and carbon tetrachloride. The evaporation rate of water at these same ion fluxes was significantly higher than that of the control. The present experiments indicate that a stream of air ions could play a major role in the observed enhancement of evaporation rates.     

The relationship between the amount of insect-repelling phenolic compounds in pennywort tea and the number of infesting cigarette beetles in the tea bag during one-year storage

Cigarette beetle, Lasioderma serricorne (F.), is a common food-product pest widely found in homes. This paper investigated the relationship between the number of infesting cigarette beetles and the phenolic content of pennywort tea made from young and mature leaves during one-year storage. It was found that cigarette beetles started to appear in tea bags after six months of storage. More adults were found than larvae and pupae. In addition, the number of cigarette beetles infesting pennywort tea made from mature leaves was higher than when it was made from young leaves. The amount of phenolic compounds in pennywort tea was analyzed by Folin–Ciocalteau assay. The results of a regression analysis indicated that the number of adult cigarette beetles correlated negatively with the amount of phenolic compounds in pennywort tea made from young leaves – when the total phenolic content decreased, the number of infesting cigarette beetles increased (r² = 0.80). The number of larvae and pupae showed a weak negative correlation with the amount of phenolic compounds (r² = 0.40 and r² = 0.56, respectively). Similar correlations were found in pennywort tea made from mature leaves, but the number of infesting beetles was higher due to the lower phenolic content of the mature leaves.     

Susceptibility of Megalurothrips sjostedti developmental stages to Metarhizium anisopliae and the effects of infection on feeding, adult fecundity, egg fertility and longevity

The susceptibility of immature stages of the legume flower thrips, Megalurothrips sjostedti, to the entomopathogenic fungus Metarhizium anisopliae, was investigated under laboratory conditions. The adult stage was found to be more susceptible to infection than the larval and pupal stages. Mortality at all stages was dose-dependent, with the highest concentration of 1×10⁸ conidia ml^–1 producing the highest mortality (26, 46 and 100% for larvae, pupae and adults, respectively) at 8 days post-inoculation. At the same concentration, daily pollen consumption was significantly reduced at 2 days after treatment in infected adults but more slowly in infected larvae. Fecundity, egg fertility and longevity in adults surviving infection as larvae were significantly reduced compared to the control.     

The spatial distribution of the wheat-bulb fly,Leptohylemyia coarctata (fall.) (Diptera: Anthomyiidae)

The spatial distribution of the eggs, larvae, pupae and adults of the wheat-bulb fly was investigated by fitting 42 sets of data comprising 1334 samples to the Poisson and negative binomial distributions, and by using the power law (S²=am^b). In general, the tests indicated that all stages were aggregated and fitted the negative binomial model.     

Ecology of a cyanobacterial mat community in a Korean thermal wastewater stream

Cyanobacterial mats along a small stream receiving thermal wastewater from an artificial hot spring in the mid-upper part of the Mankyeong River system, Korea, were studied during the winter of 1995-1996. In the cyanobacterium, Oscillatoria terebriformiscomprised >95% of total biomass. Ash-free dry-weight (AFDW) and chlorophyll a in the cyanobacterial mats decreased significantly (r²= 0.78 and 0.83, respectively) with distance downstream from the thermal water outlet, while primary productivity increased slightly. The concentrations of the majority of ions sharply decreased with distance downstream, although they were not markedly related with spatial changes in AFDW, Chl a and primary productivity. O. terebriformis appeared to have a tremendous potential in wastewater treatment because of its marked ability to glean ions.     

Natural mortality factors acting on citrus leafminer, Phyllocnistis citrella, in lime orchards in South Florida

Seasonal mortality of the citrusleafminer, Phyllocnistis citrellaStainton, was studied from 1994 through 1998 in`Tahiti' lime, Citrus aurantifolia (Christm.) Swingle,in Homestead, Florida. Survival of eachdevelopmental host stage and the proportionattacked by indigenous and introduced naturalenemies were determined. Before the recovery ofthe introduced parasitoid, Ageniaspiscitricola Logvinovskaya, in 1995, thethird-instar host had the highest averageproportion of parasitized individuals (0.14)followed by the prepupa (0.11) while the firstinstar had the lowest proportion parasitized(0.02). After the first recovery andestablishment of A. citricola, theproportion of pupae parasitized increased to0.56 followed by the prepupa (0.14) and thethird instar (0.11). Before the introduction ofA. citricola, the highest proportion ofhosts killed by predation was observed insecond instar (0.17) and third instar (0.15).After the establishment of the introducedspecies, the proportion of dead individuals dueto predation was greater for second instar(0.31) and third instar (0.21) larvae.Mortality caused by indigenous natural enemieswas significantly correlated with increases ofP. citrella density. Parasitism ofP. citrella by the exotic parasitoid,A. citricola, correlated less well to hostdensity over the season (r² = 0.12) thandid mortality caused by indigenous naturalenemies (r² = 0.76). Moreover, a higherpercent mortality in population of P. citrellawas obtained from predation by theindigenous natural enemies than the introducedparasitoid as shown in the mortality estimatesfrom 1995 to 1998.     

Light- and Clock-Controlled Leaflet Movements in Samanea saman*: A Physiological,Biophysical and Biochemical Analysis**

Leaflet movements in the legume Samanea saman are under joint control by light and a circadian oscillator. The movements are driven by massive fluxes of K⁺, Cl^?, and H⁺ through pulvinar motor cell membranes. Light and the oscillator affect leaflet movements by altering the activity of ion transport systems. Some effects of light on ion transport may be mediated by the phosphatidylinositol (PI) cycle, since brief irradiation of the pulvinus with white light accelerates PI turnover.     

Potato slab dehydration by air ions from corona discharge

Space charge (air ions) produced by single corona electrodes was used to enhance drying rates from fresh slabs of potato. The drying path was traced by a beta-ray gauge which provided both sensitivity and reproducibility to the measurements of drying time. The rate of evaporation was increased 2.2 to 3.0 times when subjected to fluxes of 3.02×10¹² positive ions alone or in combination with 7.31×10¹² negative air ions/cm² per s compared to that from an air-drying control slab. Electric wind caused by an ionic drag force seems to be the principal driving force for the observed enhancement in drying rates.     

Interaction between the tachinid parasite,Sturmiopsis inferens and granulosis virus in the sugarcane shoot borer,Chilo infuscatellus [Lep.: Crambidae]

Competition between granulosis virus (GV) and the larval parasite,Sturmiopsis inferens Tns. (Tachinidae: Diptera), was studied in 3^rd — and 4^th — instar larvae of the sugarcane shoot borer,Chilo infuscatellus Snellen (Crambidae: Lepidoptera), under laboratory conditions. Mortality due to GV infection and parasitization was 76.8 and 47.6 per cent, respectively, when they were tested separately. But when hosts were infected simultaneously with microfeeding of GV and larval parasite, a significantly low parasitism (5.5%) was obtained compared to 74.8 per cent mortality by GV infection. When the larvae were microfed with the GV 6 days after inoculation with parasitic maggots, mortality due to the virus was reduced significantly to 20.5 per cent, but when the maggot inoculation was preceded by virus microfeeding 6 days before, parasitization was unsuccessful, while 75% of larvae died of virus. Results obtained from field — collected larvae also showed that significantly more parasite puparia were recovered from healthy larvae than from virus — infected larvae. Similar differences in parasitization were not obtained in the case of healthy or virus — infected pupae.      

Mathematical model of the distribution of small negative ions in air conditioned rooms

The distribution of small negative ions with mobility k_r=0.5+ (cm²/Vs) in an air conditioned room is presented. The air was ionized by an ion generator, which was placed at the outlet of the air duct. The measurements were made at 100 different locations in the room. It was established, that the main factors in the distribution of ions were the coordinates of points in the room space. Regression analysis method was applied to determine optimal estimate of identified static characteristics of ions distribution. The main purpose of this research was to obtain data for the correct placement of ion generators in air conditioned or ventilated rooms.     

Stress and physiological,behavioral and performance patterns of children under varied air ion levels

The possibility that individual differences in reactivity to stressors are a major factor underlying discordant results reported for air ion studies prompted an investigation of response patterns in school children under both normal indoor air ion levels and moderately increased negative air ion levels (4000±500/cm³). It was hypothesized that the impact of stressors is reduced with high negative air ionization, and that resultant changes in stress effects would be differentially exhibited according to the children's normal degree of stimulus reactivity. A counter-balanced, replicative, withinssubject design was selected, and the subjects were 12 environmentally sensitive, 1st–4th grade school children. In addition to monitoring stress effects on activity level, attention span, concentration to task and conceptual performance, measures were also made of urinary 5-hydroxyindole acetic acid levels and skin resistance response (SRR) to determine if changes extended to the physiological state. The cold water test was used to add physical stress and enable calculations of Lacey's autonomic lability scores (ALS) as indicators of individual reactivity. The results show main effects for air ions on both physiological parameters, with 48% less change in %SRR (P<0.01) and 46% less change in urinary 5-HIAA levels (P<0.055) during negative air ions, indicating increased stress tolerance. Strong interactive effects for ALS x air ion condition appeared, with high and low ALS children reacting oppositely to negative air ions in measures of skin resistance level (P<0.01), wrist activity (P<0.01) and digit span backwards (P<0.004). Thus individual differences in autonomic reactivity and the presence or absence of stressors appear as critical elements for internal validity, and in preventing consequent skewed results from obscuring progress in air ion research.     

Cd2+和Pb2+对花翅摇蚊(Chironomus kiiensis)幼虫生长发育的影响及富集效应

河流、湖泊等水生环境中普遍存在的重金属污染破坏水生生态系统并间接威胁人类健康。为探究重金属胁迫下水生昆虫花翅摇蚊（Chironomus kiiensis）生态毒理,测定了重金属Cd²⁺和Pb²⁺胁迫对花翅摇蚊化蛹率和羽化率的影响,检测了摇蚊的口器致畸与富集效应。研究结果表明,Cd²⁺和Pb²⁺影响摇蚊幼虫化蛹和羽化过程,单一重金属离子处理14 d Pb²⁺处理组的化蛹率和羽化率分别为22.22%和8.89%,低于Cd²⁺的化蛹率（25.56%）和羽化率（11.11%）,表现出更强的抑制效应。混合离子1：2和2：1配比处理组化蛹率和羽化率均为11.11%和4.44%,显著低于单一重金属离子胁迫下的化蛹率和羽化率。单一重金属离子及混合离子处理均能导致花翅摇蚊幼虫口器致畸,表现为上颚前齿断裂,中齿和基齿磨损、缺失,下唇板齿部不规则,下唇板边缘齿与中央齿磨损、断裂、增生、缺失。不同重金属离子处理下幼虫口器致畸率不同,并与暴露时间呈正相关,其中1：2配比处理14 d致畸率达到40.61%。重金属离子在摇蚊幼虫体内产生生物富集效应,单一重金属离子处理下的Pb²⁺富集含量7 d至14 d由11.46 mg/kg上升至31.32 mg/kg,不同配比混合离子处理下Pb²⁺富集含量均呈增加趋势,其中1：2配比处理组由15.48 mg/kg上升至42.50 mg/kg,而Cd²⁺在单一重金属与1：1混合离子处理组7 d至14 d的富集含量无显著性变化,2：1配比处理组由14.20 mg/kg下降至9.52 mg/kg,1：2配比由5.85 mg/kg上升至20.99 mg/kg。这些研究结果表明Cd²⁺和Pb²⁺胁迫影响花翅摇蚊幼虫生长发育且口器出现畸型,与重金属在幼虫体内的富集密切相关,为研究重金属对水生生态系统多重效应提供了理论依据。     

Untersuchungen zur Veränderung der Unkrautflora bei mehrmaligem Getreidenachbau auf einer Tonschwarzerde des Thüringer Beckens

The latent effects of precocenes I and II (PI and PH) and juvenile hormone I (JHI) when topically applied to the last three instars of Spodoptera littoralis (Boisd.) larvae have been studied. Application of both PI or PII resulted in morphogenetic abnormalities resemble some effects induced by administration of JHI, e.g., larval‐pupal intermediate, partial or severe cases of untanned pupae and imperfect moths. In PII‐treatments, the effect was instar‐dose‐dependent. The intermediate dose (55 μg) was more effective on S. littoralis larvae than other doses. The effectiveness of both doses of 40 or 70 μg in production of deformed larvae and pupae decreased when applied as repeated doses instead of single ones. In Pi‐treatments, the lower dose (25 μg) was more harmful to Spodoptera larvae than the higher dose (70 μg). Repeated application by either lower or higher doses did not enhance the production of imperfect insects. Application of JHI induced symptoms ranging from supernumerary instars, larval‐pupal intermediate, untanned pupae and deformed adults. The effect was dose‐dependent. In all tested compounds, there apparently was a latent or delayed effects. Although the insects were treated while they were larvae the complete effects were not apparent until after the insect had become a pupa or an adult. More efforts will be needed to understand how does precocene interferes with the process of tanning or sclerotization?     

Local measurements of nitrate and potassium fluxes along roots of maritime pine. Effects of ectomycorrhizal symbiosis

In order to assess the actual role of ectomycorrhizae in ion uptake by the ectomycorrhizal root system, we used a microelectrode ion flux estimation methodology that provided access to local values of net fluxes. This made it possible to investigate the heterogeneity of ion fluxes along the different types of roots of Pinus pinaster associated or not with ectomycorrhizal species. We compared two fungi able to grow with nitrate in pure culture, Rhizopogon roseolus and Hebeloma cylindrosporum, the former having a positive effect on host tree shoot growth (c. +30%) and the latter a negative effect (c.? 30%). In non‐mycorrhizal plants (control), NO₃^– was taken up at higher rates by the short roots than by the long ones, whereas K⁺ uptake occurred mainly in growing apices of long roots. In mycorrhizal plants, H. cylindrosporum did not modify K⁺ uptake and even decreased NO₃^– uptake at the level of ectomycorrhizal short roots, whereas R. roseolus strongly increased K⁺ and NO₃^– fluxes at the level of ectomycorrhizal short roots without any modification of the fluxes measured along the fungus‐free long roots. The measurement of ion influxes at the surface of the ectomycorrhizal roots can provide a way to reveal actual effects of mycorrhizal association on ion transport in relation to mycorrhizal efficiency in natural conditions.     

Branchial and renal ion fluxes and transepithelial electrical potential differences in rainbow trout,Oncorhynchus mykiss: effects of aluminium at low pH

Synopsis Adult rainbow trout, Oncorhynchus mykiss, were acutely exposed for 4 hours to low pH (4.4) and elevated Al-concentrations (300 µgI^–1) in soft water (Ca²⁺ + Mg²⁺ = 25 µmolI^–1). Comparison of branchial and renal ion fluxes (Na⁺, Cl^–, Mg²⁺, Ca²⁺ and NH₄ ⁺) gave evidence that pH and Al effects were primarily localized at the gill site. The negative whole body ion balance seemed to be caused by stimulatory effects on Na and Cl efflux especially under Al stress and to a lesser extent by inhibition of influx. Measurements of gill potentials indicated positive shifts, which were similar in response to increasing levels of H⁺ ions and Al. It is suggested that Al-induced changes of branchial potentials causes high diffusable loss of ions through interference with membrane-bound Ca²⁺ at the gill site.     

Relationship between predation by Podisus nigrispinus and developmental phase and density of its prey,Plutella xylostella

This study evaluated the predation by Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae) at various densities of larvae and pupae of the pest Plutella xylostella (L.) (Lepidoptera: Plutellidae). We tested predator behavior of female P. nigrispinus at six experimental densities (1, 5, 10, 15, 20, or 25 prey items in a 1‐l transparent plastic container, replicated 15 times for each density) of both the fourth instar and pupae of P. xylostella. The number of prey consumed was monitored every 15 min for 12 h and was subsequently monitored at 24 h. Podisus nigrispinus females were weighed before and after the experiments to determine the effect of different densities of prey on their weight gain. Female predators had a Type‐II functional response, with attack rate estimated at 1.387 and 0.260 and a handling time of 0.091 and 0.183 h^?1 for larvae and pupae, respectively. Podisus nigrispinus consumed on average 10.9 larvae or 5.5 pupae in 24 h. Despite the similarity of the response type, P. nigrispinus preferred to feed on larvae, rather than on pupae.     

The Effect of Ration on Acclimation to Environmental Acidity in Rainbow Trout

Freshwater salmonids exposed to low environmental pH typically suffer a net loss of ions, primarily Na⁺ and Cl^–, across the gills, resulting in reduced plasma and tissue ion concentrations. However, in recent experiments in our laboratory, juvenile rainbow trout, Oncorhynchus mykiss, fed a ration of 1% body weight d^–1 or greater showed no ionoregulatory disturbance during chronic, sublethal acidification. This raised the possibility that these fish had acclimated to low pH in that they would be better able to withstand further, more severe acidification than fish that had no prior experience of acid conditions: previous studies had concluded that such acclimation does not occur. This hypothesis was tested by measuring unidirectional ion fluxes during a 24h acute acid challenge (pH 4.2) in juvenile rainbow trout that had previously been exposed to either ambient pH 6.2 (naive fish) or sublethal low pH 5.2 (acid pre-exposed fish) for 90 days, and fed a ration of either 1.0 or 0.25% d^–1 (wet basis). No mortalities were observed during the acute acid challenge in the fish fed the higher ration and no differences between the two groups in the response of Na⁺ fluxes were observed. Sodium influx in both groups was significantly inhibited throughout the challenge and Na⁺ net flux was significantly stimulated over the first 6h. Prior to the acute acid challenge, the fish fed the lower ration that had previously been exposed to pH 5.2 had significantly lower plasma ion concentrations than those fish previously exposed to pH 6.2. Both groups suffered mortalities; those of the naive fish (22% by 24h) being markedly lower than those of the acid pre-exposed fish (68% by 24h). However, there were no significant differences in either Na⁺ or Cl^– fluxes between the two groups of fish during the acid challenge: both showed significant inhibition of ion influxes and significantly greater net ion losses, resulting in reduced plasma ion concentrations. These results indicate that rainbow trout are unable to acclimate to environmental acidification irrespective of the availability of dietary salts.     

Evaporation rate enhancement of water with air ions from a corona discharge

Space charges (air ions) produced by a single point-to-plane corona electrode system were used to study the enhancement in the evaporation rates of water at three ion current levels. The maximum evaporation rates of 0.019 and 0.017 g·min^?1 were observed at a 1 cm electrode gap for negative and positive air ions, respectively. The cumulative evaporation rates were linear with time and an ion-enhanced rate was about 4 times greater than the control. The current density distribution measurements agreed fairly well with those predicted from the Warburg law. The principal driving force for the observed evaporation enhancement was an ion drag phenomenon which created vortex motions in water when air ions were subjected to an externally applied electric field. Theoretical considerations from derived relationships in fluid mechanics demonstrate that the mass transfer coefficient is higher for positive than negative ions of the same current strength because of the mobility difference between the charges in the medium.     

Design and construction of cage environments for air ion and electric field research

This report describes the design and construction of cage environments suitable for chronic exposures of large groups of mice to air ions and electric fields. These environments provide defined and reproducible ion densities, ion flux, DC electric fields, sound levels, air temperature and air quality. When used during a 2 year study, these cage environments served as a durable and reliable continuous exposure system. Three environmental chambers (cubicles) housed a total of 12 cages and provided control of air temperature, air purity and lighting. Exposure cages had grounded metal exterior walls, a plexiglass door and interior walls lined with formica. An internal isolated field plate supplemented with guard wires, energized with ca 1000 VDC, created about a 2 kV/m electric field at the grounded cage floor. Air ions resulted from the beta emission of sealed tritium foils mounted on the field plate. Cages provided high ion (1.3×10⁵ ions/cc), low ion (1.6×10³ ions/cc) and field only (ion depleted < 50 ions/cc) conditions for both polarities with similar electric fields in ionized and field only cages. Detailed mapping of the floor level ion flux using 100 cm² flat probes gave average fluxes of 880 fA cm^–2 in high ion cages and 10 fA cm^–2 in low ion cages. Whole body currents measured using live anesthethized mice in high ion cages averaged 104±63 pA. Both ion flux and whole body currents remained constant over time, indicating no charge accumulation on body fur or cage wall surfaces in this exposure system.