Population growth and predation interference between two species of predatory phytoseiid mites (Acarina: Phytoseiidae) in interactive systems

Summary Populations of two species of phytoseiid mite predators, Phytoseiulus persimilis Athias-Henriot and Amblyseius degenerans (Berlese), feeding on a tetranychid prey, Tetranychus pacificus McGregor, were allowed to grow separately as well as together on bush lima bean (Phaseolus lunatus Var.) arenas in the laboratory. The population plateau attained by P. persimilis was nearly 5 times higher than that for A. degenerans when each species was on separate leaf arenas. When they were on the same arena, P. persimilis was outcompeted by A. degenerans after about 70 days of population growth. When dispersal to other arenas was necessary for the predators to find prey in another experiment, P. persimilis survived well but not A. degenerans. The mechanisms underlying species displacement were explored further. The differential mortality of immature predators at different developmental stages due to interspecific predation was concluded to be responsible for the population decline of P. persimilis, and the decline of A. degenerans in another experiment was attributed to its sedentary tendency regardless of prey distribution and to the lack of alternative food sources in the system. The implications to biological control of mutual predation between predator species is discussed briefly.     

The occurrence of HT-2 toxin and other trichothecenes in Norwegian cereals

A total of 449 grain samples, 102 barley, 169 wheat and 178 oat samples were collected from different regions of Norway from 1996–1998 crops, mainly from grain loads and silos. The samples were analysed for type A and B trichothecenes, the largest groups of mycotoxins produced by the Fusarium species, by gas chromatography with mass spectrometric detection (GC-MS). Factors affecting the presence of the different trichothecenes are discussed. Deoxynivalenol (DON) and HT-2 toxin were the trichothecenes most frequently detected, followed by T-2 toxin, nivalenol, and scirpentriol, scirpentriol being detected only in seven samples (>20 g/kg).Oats were the grain species most heavily contaminated with an incidence(% >20 g/kg) and mean concentration of positive samples of 70%(115 g/kg) for HT-2 toxin, 30% (60 g/kg) for T-2 toxin, 57%(104 g/kg) for DON, and 10% (56 g/kg) for nivalenol. The corresponding values for barley were 22% (73 g/kg), 5% (85 g/kg),17% (155 g/kg) and 6% (30 g/kg), and for wheat 1.2% (20 g/kg),0.6% (20 g/kg), 14% (53 g/kg) and 0% for HT-2, T-2, DON and nivalenol, respectively. Norwegian oats were found to contain HT-2 and T-2 toxin in concentrations that might be at threat to human health for high consumers of oats. The amount of DON was significantly lower than in the crop from previous years.This revised version was published online in October 2005 with corrections to the Cover Date.     

Metabolic rate and life stage of the mites Tetranychus cinnabarinus boisd. (Prostigmata) and Phytoseiulus persimilis A-H. (Mesostigmata)

Summary Respiration rates (oxygen uptake per individual) of the herbivorous mite Tetranychus cinnabarinus Boisd. and of the predatory mite Phytoseiulus persimilis A-H. were measured at 25°C for all life stages, including eggs, using a Cartesian Diver micro-respirometer.Metabolic rates (oxygen uptake per unit weight) ranged between 0.27 and 2.32 nl O₂ g^-1 live weight h^-1 in T. cinnabarinus, and between 0.99 and 3.69 nl O₂ g^-1 live weight h^-1 in P. persimilis. The difference in metabolic rate ranges is attributed to different modes of life. The metabolic rates of both species are higher than those of comparable mite species, which is attributed to their small size, rapid development and limited sclerotization.Respiration-body weight regression gave the single equation log₁₀ R=-0.091+1.213 log₁₀ W for all post-embryonic stages of T. cinnabarinus but two equations for P. persimilis of log₁₀ R=0.394+1.116 log₁₀ W for gravid females and log₁₀ R=0.880+0.348 log₁₀ W for all non-reproducing post-embryonic stages. The single respiration-body weight relationship for T. cinnabarinus reflects the continuous growth pattern of this species, and the two relationships for P. persimilis reflect the accelerated growth following fertilization. The significance of these results for invertebrate population metabolism studies is discussed.     

Callus induction and plant regeneration from excised zygotic embryos of the seed-propagated yams Dioscorea composita Hemsl. and D. cayenensis Lam.

A tissue culture method for regeneration of plantlets from calluses of Dioscorea composita Hemsl. and Dioscorea cayenensis L. is described. Zygotic embryos were used as initial explants. Calluses were obtained on Murashige & Skoog basal medium supplemented with 18 M 2,4-D and plantlets were regenerated on media containing 0.1 M zeatin and 3.3 mM glutamine according to previously described protocols [3]. Inclusion of 0.3% (w/v) activated charcoal in media did not increase callusing. Regeneration of plantlets from D. cayenensis calluses occurred only at low levels of 2,4-D (2.25 M) contained in the media tested. The results indicated that there were genotype-dependent differences between the yam species in their ability to regenerate plantlets in vitro.     

Lack of carcinogenicity of agaritine by subcutaneous administration in mice

Agaritine (A), an ingredient of the cultivated mushroom of commerce Agaricus bisporus, was administered by subcutaneous injection to two groups of randomly bred Swiss mice. In the first group the animals of both sexes were treated at a 100 g/g body weight basis five times at weekly intervals, while in the second group the mice received a single A treatment of 100 g/g body weight for females and 50 g/g body weight for males. The administration of the compound resulted in no detectable carcinogenic effect in the animals. Since some of the breakdown products of A were shown to be carcinogenic in mice and the mushroom itself was found to be mutagenic, the field is discussed in the light of the obtained results.     

Trapping efficiency of three carnivorous Pinguicula species

Summary In situ trapping efficiencies of Pinguicula alpina L., P. villosa L., and P. vulgaris L. were compared with each other and with those of artificial traps at a subarctic site in northern Sweden. P. vulgaris had the highest trapping efficiency i.e., 21–37 g prey trapped cm^-2 day^-1 and apparently has some means of attracting prey. The other two species trapped about 14–18 g cm^-2 day^-1, a value similar to that of paper traps mimicing plant leaves. By weight, Nematocera and Collembola were the dominant groups trapped by P. alpina. P. villosa trapped mainly Collembola, while small Nematocera dominated the prey caught by P. vulgaris. Mites (Acarina) were caught in high numbers but contributed only a small part of the total captured biomass owing to their low weight.     

Effects of cadmium on foraging behaviour of lake charr, Salvelinus namaycush

Synopsis Foraging behaviour of lake charr, Salvelinus namaycush, exposed to 0.5 and 5.0 g l^–1 cadmium concentrations for 106–112 d, was examined in a flow-through stream channel using fathead minnows, Pimephales promelas, as prey. Five modes of foraging behaviour were observed and quantified (ending at fixate-orient; ending at approach and/or chase; ending at failed attack; ending at capture and loss; successful consumption). Each mode represented an increasingly progressive end-point from initial sighting of the prey to final consumption. Compared to controls., 0.5 g l^–1 Cd-exposed predators captured significantly fewer prey, while 5 g l^–1 Cd-exposed predators made fewer attacks. Both Cd-exposed groups consumed fewer prey than controls.     

Functional responses of Iphiseius degenerans and Neoseiulus teke (Acari: Phytoseiidae) to changes in the density of the cassava green mite, Mononychellus tanajoa (Acari: Tetranychidae)

The functional responses of protonymph and adult female Iphiseius degenerans and Neoseiulus teke to increasing density of three stages of their prey, the cassava green mite (CGM), Mononychellus tanajoa, were studied on excised cassava leaf discs under laboratory conditions. The responses obtained were predominantly sigmoid type III curves with the highest plateau when both stages of I. degenerans and N. teke were preying on CGM eggs. In all cases, the predation rate of the former species exceeded that of the latter. The empirical data were fitted by four different models. From the models, the attack coefficient (a) and handling time (T _h) were estimated. For a given predator stage (protonymph or adult female), the predator's attack coefficient declines and handling time increases as the prey gets larger. For a given prey stage, the predator's attack coefficient increases and handling time decreases as the predator stage becomes larger.     

Suitability of different mite prey for the development of the predatory mite,Phytoseiulus persimilis

Development of the phytoseiid mitePhytoseiulus persimilis Athias-Henriot was studied when fed on three mite species as prey. The tenuipalpid mite,Brevipalpus pulcher (Canestrini & Fanzago), is an unsuitable prey forP. persimilis as predatory larvae reared on any stages developed to the protonymphal stage only. WhenP. persimilis larvae were reared on the eriophyid mite,Eriophyes dioscoridis Soliman & Abou-Awad, only a few developed to adulthood, but failed to oviposit. On the contrary, predatory larvae fed on the tetranychid mite,Tetranychus urticae Koch, matured in a significantly shorter period and resulting females exhibited a high rate of reproduction.     

Okadaic acid causes breakdown of self-incompatibility in Brassica oleracea: evidence for the involvement of protein phosphatases in the incompatible response

Summary Detached pistils from inbred lines of Brassica oleracea L. var alboglabra were fed with okadaic acid (OA), an inhibitor of serine/threonine protein phosphatases, via the transpiration stream. Following self-pollination, pollen tubes were observed to have grown into or through the styles of pistils treated with OA, but not those of untreated controls. Treatment with 1 M OA was sufficient to completely overcome self-incompatibility (SI) in an inbred line homozygous for the S63 allele, though an OA concentration of 5 M was required to cause breakdown of SI in an inbred line homozygous for the S29 allele. At the higher concentration used, pollen tube growth was arrested before the pollen tubes reached the ovary, but this effect was also noted in cross-pollinated styles treated in the same manner. These data provide evidence for the involvement of type 1 and/or type 2A protein phosphatases in the Brassica SI signal transduction mechanism. Present address after November 1993: Department of Biology, Colorado State University, Fort Collins, Colorado, USA     

Prey capture by three Pinguicula species in a subarctic environment

The number and biomass of prey captured were estimated for Pinguicula alpina, P. villosa and P. vulgaris in a subarctic environment. Seasonal captures were estimated for one site per species for 4–5 years. Captures were related to reproductive status (reproductive/non-reproductive) and to leaf area. For one species (P. vulgaris) the catch was also compared across a range of habitats. Of the seasonal catch, 50–75% was obtained during June and less than 5% during August. For P. alpina and P. villosa the seasonal catch varied threefold or more between years (means of 89–329 g dry matter plant^–1 season^–1 for P. alpina, and 11–91 g dry matter plant^–1 season^–1 for P. villosa), whereas the between-year variation for P. vulgaris was small (mean c. 600 g plant^–1 season^–1). Large variations were, however, observed among habitats for P. vulgaris. Captured prey may contribute a substantial amount of nutrients to the most successful individuals (up to 85% of the mean seasonal turnover), but prey capture varied greatly and during any given season many individuals obtained only marginal amounts of nutrients through carnivory. P. vulgaris trapped almost twice as much per unit leaf area and season as the other two species (224 for P. vulgaris versus 127 g cm^–2 season^–1 for the other two species). Reproductive individuals of P. vulgaris trapped almost twice as much as non-reproductive individuals (after taking differences in leaf area into account). For the other two species no differences were observed between reproductive and non-reproductive individuals.     

Biological differences in reproductive strategy between the mosquito sibling species Anopheles gambiae sensu stricto and An. quadriannulatus

Females of the afrotropical mosquito species Anopheles gambiae Giles sensu stricto and An. quadriannulatus (Theobald) (Diptera: Culicidae) were studied for the effect of blood meal size and the frequency of blood feeding on reproductive development during the first gonotrophic cycle. To standardize the blood meals, meals were administered by enema in some experiments. The effects of insemination, mosquito size, and metabolic reserves at emergence on egg development were also investigated. Maximum insemination was reached after seven days, varying from 62% in An. quadriannulatus to 95% in An. gambiae and was significantly different (P<0.05) between the two species. Insemination had no effect on feeding success. Females of An. quadriannulatus were significantly larger than An. gambiae females (mean wing size 2.90 ±0.01 mm versus 2.82 ±0.01 mm), but the protein, glycogen, and lipid content of newly emerged females of the two species were not significantly different. Without a blood meal, larger females of both species were significantly more likely to develop oocytes up to Christopher's stage II. With one blood meal, 27% of An. gambiae became pre-gravid and 73% matured eggs. In contrast, all An. quadriannulatus females remained in the pre-gravid stage following ingestion of one blood meal. Vitellogenesis was significantly reduced in smaller-sized pre-gravid An. quadriannulatus compared to larger individuals. When given the opportunity to feed up to three times on three successive days, all females of An. gambiae matured eggs but only 85% of An. quadriannulatus did so. When 1 l of human blood was administered by enema, none of the females of either species developed eggs. With a single enema of 1.5 l of human blood, only An. gambiae developed eggs. A similar result was observed with 1 l and 1.5 l enemas of bovine blood although some An. gambiae also developed eggs with 1 l of blood. Anopheles quadriannulatus developed eggs only when given two 1 l enemas on successive days. However, the percentage of females developing eggs was significantly lower than that of An. gambiae. The implications of these differences in reproductive strategy are discussed in the light of behavioural traits in the field.     

The effects of Chilomonas on the life history traits of [-2pt] Daphnia longispina under semi-natural conditions and the implications for competition in the plankton

Assuming that heterotrophic flagellates (H.F.) can sustain cladoceran life cycles, particularly at periods of low food and high detritus conditions, the growth, reproduction and life span of Daphnia longispinawere studied under conditions of summer food limitation. They were fed both natural resources and natural food enriched with a culture of the colourless Chilomonas (ovoid cell, 8 × 25 m). Four H.F. morphotypes occurred in the natural water and the first experiments with Daphnia, showed that the cladoceran would most easily ingest those of 5 m–10 m, while the addition of Chilomonas severely depressed the H.F. of 2 m. The capability of this flagellate to ingest small H.F. was confirmed using fluorescent particles ranging from 0.94 to 3.95 m. As a consequence, Daphnia could control the abundance of H.F., but also compete with the largest morphotypes. To study the influence of the H.F. on the life span of Daphnia, the cladoceran was acclimated for two generations, before the start of the experiments. In semi-natural conditions, constant temperature, without predators and fed natural water, the summer daphnids achieved smaller sizes, produced fewer offspring and lived for a shorter time than when Chilomonas was added to their diet. Despite the addition of 560 g C l^-1, this was not sufficient to enhance the Daphnia reproduction to the level of the spring population fed natural water. These results clearly illustrate that the heterotrophic flagellates contributed significantly to improving the reproduction and survival of the daphnids. They emphasise the importance of the microbial loop as a link to larger consumers, particularly when unpalatable or nutritionally inadequate algae are dominant, which is often so in lakes during summer.     

A continuous flow-chamber to study prey preferences of Golden Perch (Macquaria ambigua Richardson) larvae

This paper describes the use of a continuous-flow chamber for maintaining small and fragile fish larvae and their prey in a healthy state and under suitable conditions over a 24 h period for studies on prey preferences. Survival of golden perch (Macquaria ambigua Richardson) larvae and prey was high and ten replicates on food preferences were carried out simultaneously. The larvae preferred small Daphnia carinata King (780–860 m) over larger ones (2000–3120 and 3680–5440 m) and preferred cladocerans (Daphnia carinata King and Moina micrura Kurz) over calanoids (Boeckella de Guerne & Richard). The chamber is also suitable for studies on feeding behaviour and diet requirements of fish larvae.     

Use of a bioassay to evaluate the toxicity of beauvericin to bacteria

An agar diffusion bioassay was used to compare the sensitivities of bacteria to the mycotoxin beauvericin. Bacillus pumilus LACB101 was inhibited by filter-paper disks containing 0.1 g of beauvericin; B. cereus, B. mycoides, B. sphaericus, Paenibacillus alvei, P. azotofixans, P. macquariensis, and P. pulvifaciens by 1 g; and P. validus by 25 g. The anaerobes Eubacterium biforme, Peptostreptococcus anaerobius, P. productus, Bifidobacterium adolescentis, and Clostridium perfringens were also inhibited by beauvericin.     

Changes in phosphorus concentrations and pH in the rhizosphere of some agroforestry and crop species

The aim of this work was to assess whether agroforestry species have the ability to acquire P from pools unavailable to maize. Tithonia diversifolia(Hemsley) A. Gray, Tephrosia vogelii Hook f., Zea mays and Lupinus albusL. were grown in rhizopots and pH change and depletion of inorganic and organic P pools measured in the rhizosphere. Plants were harvested at the same growth stage, after 56 days for maize and white lupin and 70 days for tithonia and tephrosia, and the rhizosphere sampled. The rhizosphere was acidified by tithonia (pH change –0.3 units to pH 4.8) and lupins (–0.2 units to 4.9), alkalinised by tephrosia (+0.4 units to pH 5.4), and remained unchanged with maize growth. Concurrent with acidification in the rhizosphere of tithonia there was a decline in resin-P (0.8 g P g^–1). However, there was also a decline in NaOH extractable inorganic P (NaOH-P_i) (5.6 g P g^–1 at the root surface) and organic P pools (NaOH-P_o) (15.4 g P g^–1 at 1.5 mm from the root), which would not be expected without specific P acquisition mechanisms. Alkalinisation of tephrosia rhizosphere was accompanied by changes in all measured pools, although the large depletion of organic P (21.6 g P g^–1 at 5 mm from the root) suggests that mineralisation, as well as desorption of organic P, was stimulated. The size of changes of both pH and P pools varied with distance away from the rhizoplane. Decline of more recalcitrant P pools with the growth of the agroforestry species contrasted with the effect of maize growth, which was negligible on resin-P and NaOH-P_i, but led to an accumulation of P as NaOH-P_o (14.2 g P g^–1 at 5 mm from the root). Overall the depletion of recalcitrant P pools, particularly P_o, suggests that the growth of tithonia and tephrosia enhance desorption and dissolution of P, while also enhancing organic P mineralisation. Both species appear to have potential for agroforestry technologies designed to enhance the availability of P to crops, at least in the short term.     

Silicon amelioration of aluminium toxicity in teosinte (Zea mays L. ssp. mexicana)

The influence of different Al concentrations, (0, 60 and 120 M Al) on growth and internal concentrations of Al, Si and selected organic acids was analysed in plants of teosinte (Zea mays L. ssp. mexicana), a wild form of maize from acid soils from Mexico. The plants were grown in nutrient solutions (pH 4.0) with or without 4 M silicon. Analysis with the GEOCHEM speciation program did not reveal differences between free activities of Al³⁺ in solutions with and without 4 M Si, but solutions with Si yielded lower concentrations of monomeric Al species, [Al]_mono, when analysed by a modified aluminon method. Plants grown on solutions with similar [Al]_mono, but differing in silicon, showed highly significant differences in growth and tissue concentrations of Al and organic acids. Silicon prevented growth inhibition at [Al]_mono concentrations as high as 35 M, while plants grown without Si suffered severe growth reductions with 33 M [Al]_mono. In solutions with similar [Al]_mono concentrations plants with Si had lower tissue Al concentrations and higher concentrations of malic acid than plants without Si. In view of both the significant influence of Si on the response of plants to Al toxicity and the fact that some soluble Si is always present in soil solutions, the addition of low Si concentrations to nutrient solutions used for Al-tolerance screening is recommended.     

In vitro regeneration of silktree (Albizzia julibrissin) from excised roots

Root segments (1 cm long) were excised from 15–20 day old seedlings of silktree (Albizzia julibrissin) grown on B5 medium. About 50% of the control (no growth regulators added) root explants formed shoot buds within 15 days after placement on the culture medium. After 30 days, there were about 4 shoots per control explant. Addition of low levels of various auxins (0.5 M) did not influence the formation of shoot buds from the explants. Higher concentrations (5M), however, decreased shoot regeneration. Kinetin and 2iP did not influence shoot regeneration at the concentrations tested (1 & 10 M). Addition of benzyladenine, Zeatin, or thidiazuron to the culture medium increased both the percentage of explants that formed shoots and the number of shoots per explant. Thidiazuron was highly effective in stimulating shoot formation at low concentrations (<1 M). At 0.05 M thidiazuron, 95% of the explants produced shoots and about 10 shoots were formed per explant. Compared to TDZ, higher concentrations (10 M) of benzyladenine and Zeatin were required to enhance shoot formation. Upon excision and transfer to B5 medium, regenerated shoots developed into normal rooted plantlets.Abbreviations BA Benzyladenine - IAA Indoleacetic acid - IBA Indolebutyric acid - NAA Naphthaleneacetic acid - TDZ Thidiazuron - 2ip Isopentenyladenine     

The influence of temperature on glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and the regulation of these enzymes in a mesophilic and a thermophilic cyanobacterium

The activities and kinetics of the enzymes G6PDH (glucose-6-phosphate dehydrogenase) and 6PGDH (6-phosphogluconate dehydrogenase) from the mesophilic cyanobacterium Synechococcus 6307 and the thermophilic cyanobacterium Synechococcus 6716 are studied in relation to temperature. In Synechococcus 6307 the apparent K _m's are for G6PDH: 80M (substrate) and 20M (NADP⁺); for 6PGDH: 90M (substrate) and 25M (NADP⁺). In Synechococcus 6716 the apparent K _m's are for G6PDH: 550M (substrate) and 30M (NADP⁺); for 6PGDH: 40M (substrate) and 10M (NADP⁺). None of the K _m's is influenced by the growth temperature and only the K _m's of G6PDH for G6P are influenced by the assay temperature in both organisms. The idea that, in general, thermophilic enzymes possess a lower affinity for their substrates and co-enzymes than mesophilic enzymes is challenged.Although ATP, ribulose-1,5-bisphosphate, NADPH and pH can all influence the activities of G6PDH and 6PGDH to a certain extent (without any difference between the mesophilic and the thermophilic strain), they cannot be responsible for the total deactivation of the enzyme activities observed in the light, thus blocking the pentose phosphate pathway.Abbreviations G6PDH glucose-6-phosphate, dehydrogenase - 6PGDH 6-phosphogluconate dehydrogenase - G6P glucose-6-phosphate - 6PG 6-phosphogluconate - RUDP ribulose-1,5-bisphosphate - Tricine N-Tris (hydroxymethyl)-methylglycine     

Effect of aldosterone on incorporation of amino acids into renal medullary proteins

Summary Studies on the effects of pretreatment with aldosterone on the incorporation of³H leucine or³H methionine into proteins in renal slices were carried out in Joklik-modified minimal essential medium. Administration of aldosterone (2 g/100 g body wt) to adrenalectomized rats increased³H leucine incorporation into trichloroacetic acid insoluble fractions of crude homogenates of cortical slices by 15.5±0.4% and of medullary slices by 53.5±1.3%. No increase in isotope incorporation was observed in slices of renal papilla or spleen prepared from the same rats. Aldosterone had no effect on the³H-leucine content of the trichloroacetic acid-soluble fractions of all three renal zones and the spleen. The dose of aldosterone that elicited a half-maximal increase in³H-methionine incorporation into proteins of renal medullary slices (0.45 g of aldosterone/100 g body wt) was indistinguishable from that needed to elicit a halfmaximal increase in the urinary K⁺/Na⁺ ratio (0.35 g of aldosterone/100 g body wt). Dexamethasone, a potent glucocorticoid, at a dose of 0.8 g/100 g body wt did not augment³H-leucine incorporation into renal medullary proteins but was effective at 8 g/100 g body wt. Spirolactone (SC-26304), a potent anti-mineralocorticoid, abolished the effect of aldosterone on amino acid incorporation into medullary proteins when administered at a 100-fold higher dosage [i.e., 80 gvs. 0.8 g (per 100 g body wt)]. These results imply that the action of aldosterone on amino acid incorporation is mediated by the mineralocorticoid rather than the glucocorticoid pathway, presumably the mineralocorticoid receptors. Moreover, pretreatment of the rats with actinomycin D (70–80 g/100 g body wt) erased the effect of aldosterone (0.8 g/100 g body wt) on amino acid incorporation into medullary proteins.In paired experiments with³H and³⁵S methionine, aldosterone (0.8 g/100 g body wt) increased methionine incorporation into trichloroacetic acid precipitable proteins of subcellular fractions of the renal medulla. The effect of aldosterone on incorporation of methionine into medullary cytosol proteins was analyzed further by polyacrylamide gel electrophoresis at pH 8.3 in tris-glycine buffer. The gel profiles indicate that aldosterone significantly increased methionine incorporation into at least one protein (independent of the isotope) with a molecular weight of 31,000. This increase was inhibited by either pretreatment of the rat with actinomycin D (70–80 g/100 g body wt or SC-26304 (80 g/100 g body wt). Dexamethasone (0.8 g/100 g body wt) did not increase incorporation of methionine into the medullary cytosol proteins resolved by polyacrylamide gel electrophoresis.