Bionomics of Alloxysta pleuralis, a cynipoid hyperparasitoid of an aphidiid parasitoid Trioxys indicus

Alloxysta pleuralis parasitizes the larvae of Trioxys indicus, a parasitoid of Aphis craccivora. Either of the sexes of this hyperparasitoid (A. pleuralis) was ready to mate shortly after emergence. During courtship the females carried the males on the top of her back for 2–3 min. Although the hyperparasitoid is obligatory, a similar, typical oviposition exploration pattern takes place on healthy aphids, however, then the eggs are laid only in parasitized aphids in the haemocoel of the larvae of the parasitoid. The life-cycle takes about a month. Superhyperparasitism was commonly observed. Adults survived for 4–13 days.

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Résumé Alloxysta pleuralis, est un endohyperparasitoïde des larves de Trioxys indicus, parasite du puceron Aphis craccivora. Les deux sexes d'A. pleuralis sont aptes à l'accouplement peu après l'émergence (10–30 min). La femelle est passive pendant la pariade. Elle porte le mâle sur son dos pendant 2 à 3 min. La copulation dure 30 sec. Bien que l'espèce soit hyperparasite obligatoire, le comportement exploratoire de ponte s'observe sur les pucerons non-parasités. Cependant les oeufs ne sont pondus qu'à l'intérieur des pucerons parasités, dans l'haemocoele des larves de troisième stade de T. indicus. Les adultes ne s'alimentent pas sur l'hôte, mais sur le miellat des pucerons. Le cycle dure environ un mois. On observe souvent du superhyperparasitisme. Les adultes vivent de 4 à 13 jours.

     

Response ofChelonus blackburni [Hym.: Braconidae] to different ages and densities of potato tuber moth eggs

The response of an efficient egg-larval parasitoidChelonus blackburni Cameron to different ages and densities of potato tuber mothPhthorimaea operculella (Zeller) eggs was studied in a laboratory system. The parasitoid accepted 0–1, 1–2 and 2–3 day old eggs for parasitization. However, the eggs belonging to the first two age groups were significantly more acceptable when compared to the last age group. At low host density levels of 2 and 5 eggs per parasitoid, parasitoid emergence was zero. On increasing the host density, percent progeny production increased till a plateau was reached at a parasitoid-host ratio of 1∶50. This ratio thus proves to be ideal for obtaining maximum percent progeny production in the case of 0–1 and 1–2 day old eggs. Further increase in host density did not result in any significant increase in percent progeny production.      

Aspects of life-table studies and functional response of Lysiphlebia mirzai

The fecundity, reproductive rate, and survival of Lysiphlebia mirzai parasitising third instar nymphs of the cereal aphid Rhopalosiphum maidis were measured at six different host densities under constant laboratory conditions. The survival rate (l_x) of the female parasitoids was unaffected by host density, with an average adult life-span of 5–6 days at all densities. The age-specific fecundity rate (m_x) was host density-dependent. The value of m_x decreased rapidly from the first day of parasitisation. The number of hosts available determined the maximum possible number of mummies. At 200 hosts available per day, the average fecundity was 184.6 mummies/female; the maximum number of mummies yielded by any female was 200. The relationship between host density and the number of aphids parasitised per female was linear at 50 aphids/cage/day, but at higher host densities (100 aphids/cage/day) a significant curvilinear regression was observed. The intrinsic rate of natural increase (r_m) increased with increasing host density. Maximum value of r_m (0.262) was obtained at a host density of 200. The response of r_m to changes in host density and parasitoid sex ratio is shown. A typical type II functional response was observed for L. mirzai. The curve was described by a logistic curve, N_p=200/[1+exp(5.65–1.60 ln N_o)]. The search rate of the parasitoid was inverse host density-dependent. No significant variation in the sex ratio of F₁ offspring was observed at different initial host densities. Sex ratio values exceeded 0.5 at all host densities. The results evaluated the reproductive potential of L. mirzai as a promising biological control agent.     

Whitefly control in cut gerbera: is it possible to control Trialeurodes vaporariorum with Encarsia formosa?

We investigated the impact of inundative releases of the parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae), for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), on cut gerbera (Gerbera jamesonii L.) under controlled greenhouse conditions. Experimental units consisted of ten plants covered and separated from other units by gauze tents. We assessed three release rates of the aphelinid parasitoid: a 7-week experiment with a standard release rate (10 m⁻²/14 days), and a subsequent 3-month trial with high (100 m⁻²/week) and very high (1,000 m⁻²/week) release rates. Experimental units without release of parasitoids served as control treatment. Gerbera plants were infested initially with 50–100 juvenile and 50–70 adult whiteflies in the first experiment, and in the second experiment with less than 50 juveniles per plant and 50–70 adults. Whitefly and parasitoid population density were assessed in weekly intervals using infestation and activity categories. Results show that parasitized whiteflies were present in all treatments within 2 weeks after initial release. Unfortunately, it was not possible to control whiteflies with standard release rates of E. formosa. Although parasitism rates slightly increased, the effect on whitefly populations was negligible. Large amounts of honeydew and growth of sooty mold fungi caused the termination of the first experiment. In a second experiment, E. formosa was tested at 10–100 times higher release densities. In contrast to the first experiment, whitefly densities increased steadily during the first 8 weeks, but remained constant until the end of the experiment in both treatments. Parasitism by E. formosa reached its maximum after 8 weeks. We discuss possible reasons for the low efficiency of E. formosa as a whitefly antagonist in greenhouse production of gerbera.     

Host–parasitoid interaction as affected by interkingdom competition

Although still underrepresented in ecological research, competitive interactions between distantly related organisms (so-called “interkingdom competition”) are expected to be widespread in various ecosystems, with yet unknown consequences for, e.g. trophic interactions. In the model host–parasitoid system Drosophila melanogaster–Asobara tabida, toxic filamentous fungi have been shown to be serious competitors that critically affect the density-dependent survival of host Drosophila larvae. This study investigates the extent to which the competing mould Aspergillus niger affects key properties of the well-studied Drosophila–parasitoid system and how the host–parasitoid interaction influences the microbial competitor. In contrast to slightly positive density-dependent host mortality under mould-free conditions, competing A. niger mediated a strong Allee effect for parasitised larvae, i.e. mortality decreased with increasing larval density. It was found that the common toxic fungal metabolite kojic acid is not responsible for higher death rates in parasitised larvae. Single parasitised Drosophila larvae were less harmful to fungal reproduction than unparasitised larvae, but this effect vanished with an increase in larval density. As predicted from the negative effect of fungi on host survival and thus on parasitoid fitness at low larval densities, A. tabida females spent less time foraging in fungus-infested patches. Interestingly, even though high host larval densities increased host survival, parasitoids still reduced their search efforts in fungus-infested patches, indicating a benefit for host larvae from feeding in the presence of noxious mould. Thus, this experimental study provides evidence of the potentially important role of interkingdom competition in determining trophic interactions in saprophagous animal communities and the dynamics of both host–parasitoid and microbial populations.     

Effect of high temperature on photosynthesis and transpiration of sweet corn (<Emphasis Type="Italic">Zea mays</Emphasis> L. var. <Emphasis Type="Italic">rugosa</Emphasis>)

Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25, 35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate (P _N) of sweet corn was found for the lowest temperature of 28–34 μmol m⁻² s⁻¹ while the P _N for the highest temperature treatment was 50–60 % lower. We detected a gradual decline of about 1 P _N unit per 1 °C increase in temperature. Maximum transpiration rate (E) fluctuated between 0.36 and 0.54 mm h⁻¹ (≈5.0–6.5 mm d⁻¹) for the high temperature treatment and the minimum E fluctuated between 0.25 and 0.36 mm h⁻¹ (≈3.5–5.0 mm d⁻¹) for the low temperature treatment. Cumulative CO₂ fixation of the 40/35 °C treatment was 33.7 g m⁻² d⁻¹ and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to 5 g(CO₂) kg⁻¹(H₂O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, P _N, and E of Zea: the high temperature which reduced P _N, vapor pressure deficit (VPD) that was directly related to E but did not affect P _N, and quasi stem conductance (QC) that was directly related to P _N but did not affect E. As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment.     

Bionomics ofTrioxys indicus [Hym.: Aphidiidae], a parasitoid ofAphis craccivora [Hem.: Aphididae]: 31. Effect of host haemolymph on the numerical response of the parasitoid

The influence of kairomones on the numerical response of the parasitoidTrioxys indicus against its hostAphis craccivora at its varying density was studied. The kairomones (applied as aqueous extract of the host) significantly enhanced the rate of parasitisation and multiplication and the area of discovery of the parasitoid and also the K-values of mortality of the host at all parasitoid densities introduced (1, 2, 4, 8, 12 and 16 parasitoids) into troughs having about 200 hosts. The sex-ratio of F₁ offspring decreased at lower parasitoid densities and remained more or less unchanged at higher parasitoid densities after the application of kairomones. The present findings indicate that if kairomones are applied properly, the number of hosts destroyed by a stimulated parasitoid will be about 200, twice the number reported earlier, thus fewer parasitoids will be needed to regulate an estimated population of the hosts.      

The effect of host nutrition on growth and development of the parasitoid waspVenturia canescens

We investigated the effect of host (Plodia interpunctella; Lepidoptera: Pyralidae) nutritional status on development of the solitary endoparasitoid,Venturia canescens (Hymenoptera: Ichneumonidae). Parasitoids from 3rd (L3) instars reared on a deficient diet during early parasitism took longer to develop and suffered higher mortality than those reared from hosts fedad libitum although there was not a significant difference in the size of eclosing wasps from the two groups. L5 hosts reared at high density produced smaller parasitoids, which developed more rapidly than those reared from hosts from low density containers, although mortality was higher in the latter. In a separate experiment we starved groups of 10–20 hosts (parasitized as L3) daily beginning on the 4th day after parasitism, to determine the host developmental stage required for successful parasitoid development to eclosion. Parasitoid survivorship increased with length of host access to food, while the egg-to-adult parasitoid development time increased throughout the experiment. Parasitoid size decreased with increasing periods of host starvation. The successful emergence ofVenturia depends uponPlodia reaching the size normally attained in the mid-5th instar, or 50–70% of the mass of healthy late 5th instars. Our results show that when earlier instars are parasitized, host growth is essential for successful parasitoid development to eclosion. Furthermore, they suggest that, for many koinobionts, host suitability may be greatly influenced by feeding rate and food quality.     

Parasitism by Pteromalus cerealellae (Hymenoptera: Pteromalidae) on the Cowpea weevil, Callosbruchus maculatus (Coleoptera: Bruchidae): Host density, temperature effects, and host finding ability

Studies on interactions between a larval parasitoid, Pteromalus cerealellae (Boucek) and one of its hosts, Callosobruchus maculatus (F.) were carried out in the laboratory. The number of host larvae parasitized by P. cerealellae increased with host larvae at low densities and tended to a plateau at a density of 25 larvae per female parasitoid. Each parasitoid was able to parasitize more hosts and produced more offspring at 20 and 25 °C than at 30 °C. The number of non-infested seeds mixed with seeds infested with the last instar of C. maculatus did not preclude P. cerealellae from identifying infested seeds and attacking larvae inside them. When infested seeds were tightly packed, several host larvae escaped parasitism. P. cerealellae may be a useful biological control agent in newly harvested cowpea with low C. maculatus infestation, and lowering the temperature of the storage system may enhance the effectiveness of this parasitoid.     

Chlorophyll fluorescence imaging of photosynthetic activity in sun and shade leaves of trees

The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R _Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P _N on a leaf area basis (mean of 9.1–10.1 μmol CO₂ m⁻² s⁻¹) and Chl basis, which correlated well with the higher values of stomatal conductance G _s (range 105–180 mmol m⁻² s⁻¹), as compared to shade leaves (G _s range 25–77 mmol m⁻² s⁻¹; P _N: 3.2–3.7 μmol CO₂ m⁻² s⁻¹). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R _Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R _Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the leaf area, and in general to a higher extent in sun leaves than in shade leaves.     

European field collections and Canadian releases ofCeranthia samarensis (Dipt.: Tachinidae), a parasitoid of the gypsy moth

A programme to collect, import and release into Canada the gypsy moth parasitoid,Ceranthia samarensis (Diptera: Tachinidae) is described. The parasitoid's potential for biological control in Canada is also discussed. The parasitoid was collected in Europe by exposing experimental gypsy moth larvae in areas where local gypsy moth populations were at low densities. Following field exposure, the host larvae were returned to the laboratory and parasitoids reared from them. This technique has shown thatC. samarensis is the suffers 7–16% hyperparasitism. From 83–90% of theC. samarensis typically enter diapause as pharate adults within the puparia. Laboratory tests of post-exposure host rearing conditions indicate that constant temperatures disrupt the normal parasitoid diapause and that this effect can not be offset by use of either static long or short photoperiods or natural daylengths. Shipping and cold-storage procedures for puparia are described. Post-storage time to emergence of adultC. samarensis decreased with longer cold storage periods and with higher post-storage incubation temperatures. Emergence requires 112 degree-days above a threshold of 8°C after a period of at least 8 months cold storage. Releases of adultC. samarensis into field cages at four locations in southern Ontario are documented. While dissection of host larvae from the field cages has failed so far to demonstrate evidence of parasitism, we remain hopeful that some establishment of the parasitoid has occurred.      

Influence of initial egg density and host size on the development of the gregarious parasitoid <Emphasis Type="Italic">Bracon hebetor</Emphasis> on three different host species

Bracon hebetor (Say) (Hymenoptera : Braconidae) is a gregarious parasitoid that attacks a variety of important lepidopterous pests of stored product and in the field. In this study the effect of host species, size and larval competition on parasitoid size, survival and development were investigated. In laboratory studies, wasp eggs at a range of densities, were placed on larvae of different weight of three Lepidoptera host species namely Adoxophyes orana (Fischer von Röslerstamm, Tortricidae), Plodia interpunctella (Hubner, Pyralidae) and, Lobesia botrana(Dennis & Schiffermueller, Tortricidae). On A. orana survival of immature parasitoids was very low at all densities and different host weights. On L. botrana survival progressively reduced as egg density increased at both host weights examined for this host. Survival on P. interpunctella was significantly affected by egg density but not by host weight. Initial egg density had a significant effect on the size of emerging adults from each rearing host. Smaller adult parasitoids emerged as egg density per larva increased. Larval host weight of P. interpunctella and A. orana had a significant effect on the size of emerging adult parasitoids mainly at the higher egg densities used in these experiments. The above results of host quality on fitness of parasitoid are discussed.     

Effect of temperature on the development, fecundity, progeny sex ratio and life-table of Campoletis chlorideae, an endolarval parasitoid of the pod borer, Helicoverpa armigera

Development, survival, fecundity, progeny sex ratio (PSR) and age-specific life-table parameters of the parasitoid Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) were examined at six different constant temperatures (12, 17, 22, 27, 32 and 37°C) in the laboratory [70 ± 10% RH and 10:14 h (light:dark) photoperiod]. Second instar larvae of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were reared on chickpea (Cicer arietinum L.) and used as the host. Development times shortened as the temperature increased from 12 to 37°C. The estimated lower developmental threshold (tL) was 3.4°C. The thermal summation for total immature stages was 379.97 degree-days. A reciprocal relationship between temperature and longevity was observed in the range of 12–17°C. The maximum mortality of pupae (71.8%) occurred at 37°C. At 22°C, the yield of a female parasitoid averaged 137.3 ± 14.7 (mean ± SD) progeny, of which 89.6 ± 7.6 were daughters. The number of daughters produced decreased when the females were kept either above or below 22°C, although the PSR was female biased in the range of 17–27°C. The analyses of life-table parameters, developmental rates, reproduction, mortality and PSR suggest that maximum population growth (r _m ) is near 27°C. There was little variation observed in most of the desired qualities of C. chlorideae in the range of 17–27°C, and it appears that the parasitoid is adapted to a wide range of temperatures. We suggest that for maximum production the parasitoid should be reared at 22 ± 4°C and be released in areas where the temperature ranges between 17° and 27°C, as in the plains of northern India.     

Influence of host distribution on foraging behaviour in the hyperparasitoid wasp, Dendrocerus carpenteri

The foraging behaviour of Dendrocerus carpenteriCurtis (Hymenoptera: Megaspilidae), an ectophagous hyperparasitoid of aphidiine wasps inside mummified aphids, was examined in the laboratory with an experimental system consisting of broad bean, Vicia fabaL, the pea aphid, Acyrthosiphon pisumHarris, and a primary parasitoid, Ephedrus californicusBaker. Pea aphids parasitised by E. californicusoften disperse from their feeding sites (or off host plants) before dying and mummifying. Response of female hyperparasitoids to host distribution was evaluated at two spatial scales. At the first scale, behaviour of hyperparasitoids was examined on individual plants with different densities of hosts. At the second scale, habitat complexity and host location were manipulated in large foraging cages containing several plants. I show that patterns of density-dependent hyperparasitism can result from the foraging behaviour of D. carpenteri. However, dispersal of parasitised aphids may not reduce the incidence of hyperparasitism if hyperparasitoids systematically search the habitat.     

Nitrogen and fungicide applications against Erysiphe cruciferarum affect quality components of oilseed rape

Oilseed rape (Brassica napus L.) is one of the most important oilseed crops in temperate climates. Erysiphe cruciferarum is an important disease of oilseed rape and causes crop loss in warmer areas of Europe. The research investigated the effect of nitrogen fertilizer and fungicidal treatment against powdery mildew infection caused by E. cruciferarum of oilseed rape on seed components, including protein, oil, oleic acid, linolenic acid and undesirable substances such as sinapic acid esters (SAE) and glucosinolates (GSL), using near infrared spectroscopy (NIRS). Five susceptible oilseed rape varieties were employed in this research using four treatment groups: no nitrogen fertilization and no fungicidal treatment (N₀–F₀); no nitrogen fertilization but fungicidal treatment (N₀–F₁); and nitrogen fertilization but no fungicidal treatment (N₁–F₀); nitrogen fertilization and fungicidal treatment (N₁–F₁). Nitrogen fertilization increased the protein, but lowered the oil content, of the seeds. Fungicidal treatments significantly increased oil contents in all varieties tested, however reduced protein levels in fertilized and non-fertilized plots. The level of linolenic acid did not change significantly in any plots of any treatment combinations; a similar result was observed in the level of oleic acid in most of the genotypes. Nitrogen fertilization increased GSL and SAE levels, whereas fungicidal treatment had no effect. Our findings demonstrated that nitrogen fertilization can markedly influence some quality parameters in oilseed rape; however, the application of fungicides reduced side effects of nitrogen fertilizer and resulted a reduction on GSL, SAE and protein contents but an increase on total oil and oleic acid contents.     

Host-acceptance behaviour of Alloxysta pleuralis, a cynipoid hyperparasitoid of an aphidiid parasitoid Trioxys indicus on aphids

Alloxysta pleuralis parasitizes the larvae of Trioxys indicus, a parasitoid of Aphis craccivora. The pattern of host-searching of A. pleuralis was random regarding the host-stage. Earlier second instar to early fourth instar larvae of T. indicus within the haemocoel of the living aphid were found susceptible for attack, however, the third instar larvae were more parasitized. The rate of oviposition was very low (8.5 eggs/h). The number of pricks into the aphid was significantly more for the aphids that contained susceptible stages of the potential host. The occurrence of superhyperparasitism was lower when the hyperparasitoids were offered a choice of all host stages than were offered no-choice.

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Résumé A. pleuralis est un hyperparasitoïde endophage de Trioxys indicus, parasitoïde d'Aphis craccivora, puceron de Cajanus cajan. Bien que les larves de T. indicus soient susceptibles d'être attaquées du début du second stade au début du quatrième stade, celles du troisième stade sont nettement préférées. L'absence de fifférence entre les fréquences de visites et de contacts avec les hôtes de différents stades a montré que le comportement de prospection de A. pleuralis s'effectue au hasard. Cependant, la fréquence des piqûres/hôte est significativement supérieure chez lez hôtes préférés, ce qui donne une indication sur le fait que A. pleuralis pique un puceron pour rechercher un hôte potentiel. Il est possible que la femelle perçoive la présence de l'hôte dans le puceron en décelant avec les récepteurs sensoiriels de sa tarière les changements physiologiques caractéristiques du puceron parasité, et qu'elle les utilise pour piquer à répétition le puceron jusqu'à ce qu'elle trouve l'hôte potentiel. Le superhyperparasitisme était relativement faible et plus fréquent dans les expériences où l'hyperparasite n'avait pas de choix.

     

Variation of acharan sulfate and monosaccharide composition and analysis of neutral <Emphasis Type="Italic">N</Emphasis>-glycans in African giant snail (<Emphasis Type="Italic">Achatina fulica</Emphasis>)

Acharan sulfate content from African giant snail (Achatina fulica) was compared in eggs and snails of different ages. Acharan sulfate was not found in egg. Acharan sulfate disaccharide →4)-α-d-GlcNpAc (1→4)-α-l-IdoAp2S(1→, analyzed by SAX (strong-anion exchange)–HPLC was observed soon after hatching and increases as the snails grow. Monosaccharide compositional analysis showed that mole % of glucosamine, a major monosaccharide of acharan sulfate, increased with age while mole % of galactose decreased with age. These results suggest that galactans represent a major energy source during development, while acharan sulfate appearing immediately after hatching, is essential for the snail growth. The structures of neutral N-glycans released from eggs by peptide N-glycosidase F (PNGase F), were next elucidated using ESI-MS/MS, MALDI-MS/MS, enzyme digestion, and monosaccharide composition analysis. Three types of neutral N-glycan structures were observed, truncated (Hex_2–4-HexNAc₂), high mannose (Hex_5–9-HexNAc₂), and complex (Hex₃-HexNAc_2–10) types. None showed core fucosylation.     

Allocation of searching time within the soybean canopy by parasitoids attacking the green cloverworm

We examined the searching behavior of a guild of primary parasitoids which attack the green cloverworm,Plathypena scabra (Fabricius), as well as that of an associated hyperparasitoid. We hypothesized that self-superparasitism is an important constraint on the foraging behavior of primary parasitoids, and therefore these parasitoids should avoid portions of the soybean canopy where parasitized caterpillars accumulate. Conversely, we hypothesized that the hyperparasitoid preferentially searches parts of the canopy where parasitized caterpillars accumulate. In a greenhouse experiment, we found that exposure to parasitoids [eitherCotesia marginiventris (Cresson) orDiolcogaster facetosa Ashmead] resulted in the accumulation of caterpillars lower in the canopy. In a field experiment, we measured the amount of time parasitoids spent searching in each of three strata (upper, middle, bottom) of the soybean canopy. Leaf area in each stratum was used to calculate expected values for search effort. The time spent searching each of the strata was proportional to leaf area for all primary parasitoids, exceptD. facetosa, which spent significantly more time searching the top stratum of plants than predicted by leaf area in that stratum. The hyperparasitoidMesochorus discitergus (Say) tended to search the bottom stratum of the canopy. Thus only one of the three primary parasitoids appears to search in a manner that would reduce its rate of encounter with previously parasitized green cloverworms. The hyperparasitoid searching pattern may increase its probability of encountering parasitized caterpillars, thereby increasing its foraging success.     

Oviposition pattern byCotesia ayerzai [Hym.: Braconidae] onAscia monuste [Lep.: Pieridae] under laboratory conditions

Various aspects of the parasitims of caterpillars ofAscia monuste orseis byCotesia ayerzai, were studied in laboratory choice tests. Individual ♂♂ were found to be extremely variable in ovipositional duration, as well as in the number of eggs oviposited. To simulate parasitoid dispersal, or low host density, we isolated ♂♂ for 60 min following initial exposure and compared our tests with ♂♂ which had not been isolated. No differences in (1) the number of eggs oviposited per host instar; (2) the conditional probability of host encounter; (3) host acceptance; and (4) the conditional probability of instar specific parasitism were found between these groups. Held ♂♂ did, however, reject hosts after ovipositor insertions in a higher proportion.      

Bioremoval of hexavalent chromium from water by a salt tolerant bacterium, Exiguobacterium sp. GS1

Pollution of terrestrial surfaces and aquatic systems by hexavalent chromium, Cr(VI), is a worldwide public health problem. A chromium resistant bacterial isolate identified as Exiguobacterium sp. GS1 by 16S rRNA gene sequencing displayed high rate of removal of Cr(VI) from water. Exiguobacterium sp. GS1 is 99% identical to Exiguobacterium acetylicum. The isolate significantly removed Cr(VI) at both high and low concentrations (1–200 μg mL⁻¹) within 12 h. The Michaelis–Menten K _m and V _max for Cr(VI) bioremoval were calculated to be 141.92 μg mL⁻¹ and 13.22 μg mL⁻¹ h⁻¹, respectively. Growth of Exiguobacterium sp. GS1 was indifferent at 1–75 μg mL⁻¹ Cr(VI) in 12 h. At initial concentration of 8,000 μg L⁻¹, Exiguobacterium sp. GS1 displayed rapid bioremoval of Cr(VI) with over 50% bioremoval in 3 h and 91% bioremoval in 8 h. Kinetic analysis of Cr(VI) bioremoval rate revealed zero-order in 8 h. Exiguobacterium sp. GS1 grew and significantly reduced Cr(VI) in cultures containing 1–9% salt indicating high salt tolerance. Similarly the isolate substantially reduced Cr(VI) over a wide range of temperature (18–45  °C) and initial pH (6.0–9.0). The T _opt and initial pH_opt were 35–40  °C and 7–8, respectively. Exiguobacterium sp. GS1 displayed a great potential for bioremediation of Cr(VI) in diverse complex environments.