Egg laying and development of Neotropical trichogrammatid species in artificial eggs

The goal of this work was to assess the suitability of two artificial diets for egg laying and development of Trichogramma atopovirilia Oatman & Platner, Trichogrammatoidea annulata De Santis, and Trichogramma bruni Nagaraja (all Hymenoptera: Trichogrammatidae). Additionally, the quality of wasps reared in vitro was compared with those reared in vivo. The ‘standard’ diet consisted of Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae) pupal holotissues (65%), chicken egg yolk (18%), fetal bovine serum (8.5%), lactalbumin hydrolysate (8.5%), and anticontaminants (0.3%). The ‘modified’ diet differed from the standard one only in the D. saccharalis pupal holotissues, that were replaced with Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae) ones. Females of the three trichogrammatid species laid eggs in artificial eggs containing any artificial medium, but the modified one received more eggs. Although the standard diet was accepted for oviposition by the three wasp species, no development occurred. On the modified diet, only T. atopovirilia was able to develop to adult emergence. Adult F1 were of a quality that was similar to insects reared in vivo.     

Karyotypes of some species of Hyacinthaceae from Ethiopia and Kenya

Karyotypes for 8 different species of Hyacinthaceae from Ethiopia and Kenya are presented. Five represent new chromosome information: Drimia macrocarpa (2n = 20 + 4 B), Ledebouria revoluta (2n = 28), L. somaliensis (2n = 30), L. urceolatu (2n = 20), Ornithogalum grucillimum (2n = 24). A table summing up the present chromosome information from tropical East and North East-Africa are given.     

Competitive exclusion of a worldwide invasive pest by a native. Quantifying competition between two phytophagous insects on two host plant species

1. High competitive ability is believed to be an important characteristic of invasive species. Many animal studies have compared the competitive ability of invasive species with a native species that is being displaced, but few have looked at systems where an invasive species has failed to establish itself. These types of studies are important to determine if competition is relevant not only to invading species but also to the biotic resistance of a community. 2. The thrips species F. occidentalis is a highly invasive pest that has spread from its original range (the western states of the USA) to a worldwide distribution. Despite this, F. occidentalis is largely absent or occurs in low numbers in the eastern states of the USA, where the native F. tritici dominates. It is possible that F. tritici is competitively excluding F. occidentalis from this region. 3. Larval competition between these two thrips species was tested on two known plant hosts, Capsicum annuum (a crop plant), and Raphanus raphanistrum (an invasive weed), using a response surface design with number of larvae surviving as the response variable. The response surface design allowed competition models to be fit to data using maximum likelihood estimation, thus generating quantitative values for interspecific competition. 4. On both plant hosts, the native F. tritici did not experience significant interspecific competition from the invasive F. occidentalis. In contrast, F. occidentalis did experience significant interspecific competition from F. tritici. Competition from F. tritici larvae on F. occidentalis larvae was estimated to be 1.72 times (on C. annuum) and 1.76 times (on R. raphanistrum) the effect of intraspecific competition. The invasive F. occidentalis appears to be competitively excluded by the native F. tritici. 5. This study confirms the importance of competition in the biotic resistance of a community and is one of the few animal studies to not only test for competition in an apparently resistant ecosystem but also to quantify the level of interspecific competition between two animal species.     

The relative toxicity and persistence of insecticides applied as water-dispersible powders against stored-product beetles

Twelve insecticides, formulated as water-dispersible powders, were applied to strips of filter paper and their toxicities to eight species of stored-product beetles were determined. The insecticides were DDT, methoxychlor, lindane, aldrin, dieldrin, synergized pyrethrins, malathion, fenthion, Chlorthion, diazinon, trichlorphon and carbaryl. The insects were adults of Sitophilus granarius (L.), S. zeamais Mots., Tribolium castaneum (Herbst), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.), Stegobium paniceum (L.), Lasioderma serricorne (F.), and Ptinus tectus Boield. Tables of LD 50 values are presented in terms of deposits of active ingredient between the limits investigated, namely 0.625 and 80 mg./sq.ft., for 2-day and 3-day periods of continuous exposure at 25d? C. and 70% R.H. The data give a broad view of the susceptibility of each insect species to the different insecticides, the effectiveness of each insecticide against the range of insect species, and the speed of action of the insecticides. Trichlorphon had a very low toxicity to all species except O. surinamensis and was omitted from further testing. Deposits of the remaining eleven water-dispersible powders on filter paper were stored and tested at intervals up to 16 months. This yielded information on the persistence of the formulations after application to a chemically inert substrate. Five of the insecticides-malathion, fenthion, Chlorthion, diazinon and carbaryl were then investigated for their persistence on cement, tile, whitewash on tile, wood, and sacking. This test revealed loss of effectiveness of some of the organophosphorus insecticides because of volatility or of alkalinity of the substrate, although some of the results obtained with tiles were difficult to explain. Factors such as surface activity, porosity and real surface area may have played a role, as well as the physical state of the insecticide in the formulation.     

Pollen morphology in relation to the taxonomy and phylogeny of some native Greek Aegilops species

The pollen morphology of some native Greek Aegilops species is investigated in LM (quantitative pollen characters) and SEM (exine sculpture) using acetolysed material. Furthermore, quantitative data are subjected to a multivariate analysis. The tetraploid Ae. cylindrica and its diploid parent Ae. caudata show a distinct morphological affinity as regards their quantitative pollen profile and the features of the exine sculpture. The tetraploid Ae. triuncialis is morphologically divergent from both its parents Ae. caudata and Ae. umbellulata due to the very large values of its quantitative pollen characters. However, the SEM survey of the exine sculpture indicates a rather high degree of similarity between Ae. triuncialis and Ae. umbellulata. No significant differences have been found between the two varieties of Ae. caudata (caudata and polyathera) concerning the quantitative pollen characters as a total or the morphology of the exine sculpture. The resultant clustering of the taxa on the basis of the quantitative pollen characters as well as the recorded similarities of their exine pattern are related to their sectional classification based on cytogenetical and morphological data.     

Physiological responses to flooding and light in two tree species native to the Amazonian floodplains

In Amazonian floodplains, plant survival is determined by adaptations and growth strategies to effectively capture sunlight and endure extended periods of waterlogging. By measuring gas exchange, quantum efficiency of photosystem 2 (PSII), and growth parameters, we investigated the combined effects of flooding gradients and light on two common evergreen floodplain tree species, the light-tolerant Cecropia latiloba and the shade-tolerant Pouteria glomerata. Individual plants were subjected to different combinations of light and flooding intensity in short-term and long-term experiments. Plants of C. latiloba lost all their leaves under total submersion treatments (plants flooded to apex and with reduced irradiance) and showed highest maximum assimilation rates (A_max) in not flooded, high light treatments (6.1 μmol CO₂ m⁻² s⁻¹). Individuals of P. glomerata showed similar patterns, with A_max increasing from 1.9 μmol CO₂ m⁻² s⁻¹ under total flooding to 7.1 μmol CO₂ m⁻² s⁻¹ in not flooded, high light treatments. During the long-term flooding experiment, quantum efficiency of PSII (F_v/F_m) of C. latiloba was not affected by partial flooding. In contrast, in P. glomerata F_v/F_m decreased to values below 0.73 after 120 days of total flooding. Moreover, total submergence led P. glomerata to reduce significantly light saturation point (LSP), as compared to C. latiloba. For both species morphological adjustments to long-term flooding, such as the production of adventitious roots, resulted in reduced total biomass, relative growth rate (RGR) and leaf mass ratio (LMR). Growth increase in C. latiloba seemed to be more limited by low-light than by flooding. Therefore, the predominant occurrence of this species is in open areas with high light intensities and high levels of inundation. In P. glomerata flooding induced high reductions of growth and photosynthesis, whereas light was not limiting. This species is more abundant in positions where irradiance is reduced and periods of submergence are slightly modest. We could show that the physiological requirements are directly responsible for the flooding (C. latiloba) and shade (P. glomerata) tolerance of the two species, which explains their local distribution in Amazonian floodplain forests.     

Relative toxicity of three wheat herbicides to two species of Coccinellidae

Abstract On the High Plains of the USA, herbicides specific for broad-leaf weeds are regularly applied to winter wheat in the early spring, sometimes late enough to coincide with the colonization of fields by cereal aphids and their natural enemies. We tested the toxicity of three such herbicides, Ally (Dupont), Rave (Syngenta) and 2,4-D ester (generic), to neonate larvae of two coccinellid species important in cereal aphid biocontrol, Coleomegilla maculata DeGeer and Hippodamia convergens Guérin-Méneville. Topical treatment of larvae with 2,4-D resulted in 25% and 60% mortality in the two species, respectively, with surviving C. maculata larvae experiencing a 5% increase in developmental time. No significant effects were noted for the other two materials, save for a 2.5% increase in developmental time for C. maculata larvae exposed to Rave. No material caused significant mortality in either species when larvae were fed on prey (Schizaphis graminum Rondani) treated with herbicide 24 h earlier, although 2,4-D reduced developmental time slightly in C. maculata. When herbicide applications are delayed enough in spring to coincide with aphid activity in wheat, farmers can reduce the risk of disrupting biological control by selecting an alternative to 2,4-D.     

Nutrient resorption from senescing leaves in two Stipa species native to central Argentina

Abstract Nutrient resorption from senescing leaves enables plants to conserve and reuse nutrients. As such, it could be expected that plant species adapted to infertile soils have a higher nutrient resorption efficiency (percentage reduction of nutrients between green and senesced leaves) and/or higher nutrient resorption proficiency (absolute reduction of nutrients in senesced leaves) than those adapted to fertile soils. Our objective was to compare nitrogen (N) and phosphorous (P) resorption of two congener grasses that successfully occupy uplands of relatively low fertility (Stipa gynerioides) or lowlands of relatively high fertility (Stipa brachychaeta) in natural grasslands of central Argentina. The two Stipa species did not differ in N and P resorption efficiency, but S. gynerioides had a higher N and P resorption proficiency than S. brachychaeta. As a consequence, leaf‐level N and P use efficiency were higher in the species adapted to low fertility conditions than in the species adapted to high fertility conditions. The higher nutrient resorption proficiency of S. gynerioides was also associated with relatively low leaf‐litter decomposition and nutrient release rates found in a previous study.     

Modeling population dynamics of two cockroach species: effects of the circadian clock, interspecific competition and pest control

The German cockroach Blattella germanica is obviously one of the most spread household pests in the world, and is now virtually impossible to sustain outside human constructions. The double-striped cockroach B. bisignata, on the other hand, is limited to Southeast Asia and mostly living in the open space, yet is able to establish in cockroach-free households, too. In this article, we develop a stage-structured population model of these two species to explore (i) whether their circadian clocks impact their long-term population dynamics, (ii) which of these species is a superior competitor, and (iii) how stringent potential pest control strategies have to be to significantly impact established populations of the German cockroach. The results of the model are as follows. Firstly, phase shifts in the light-to-dark cycle did not affect cockroach population dynamics unless males and females were out of phase and their mate finding abilities rather limited. In addition, for the hypothesized circadian clock genotypes, the shorter is the inactivity period relative to the activity one or the less arrhythmic is the population, the more viable the population is and the quicker it grows to large numbers. Secondly, the German cockroach was the superior competitor: it was able to invade and drive out established populations of the double-striped cockroach and prevent any invasion of the latter. Finally, only a significant and simultaneous reduction in a number of most sensitive German cockroach parameters resulted in species extirpation. Only carefully designed and data-based models of German (and double-striped) cockroach population dynamics can be helpful in our quest to win the fight over this unwelcome but very sturdy species.     

Evaluation of some coccinellid species for the biological control of aphids in protected cropping

Four species of Coccinellidae, Adalia bipunctata (L.), Coccinella septem-punctata L., Coelomegilla maculata de G. and Cycloneda sanguinea L., were compared as predators of aphids on cucumbers and chrysanthemums. In laboratory feeding tests C. maculata and C. sanguinea proved the most voracious but the former could not remain on cucumber foliage long enough to be effective. The fecundity of C. sanguinea was the highest of those studied and a satisfactory laboratory rearing technique has been developed for this species.     

Acute toxicity and anti acetylcholinesterase potential of some biphenyl derivatives to non target species

Five newly synthesised biphenyl derivatives were evaluated for their acute contact toxicity (LC50) against rice weevil and honey bee and anti acetylcholinesterase potential (I50) against honey bee, fish, pigeon and rat. Amongst, O,O-dimethyl-O, p-Nitro-biphenyl phosphate was most potent against rice weevil, whereas p-(4-Nitrophenyl) phenyl-N-methyl carbamate against honey bee. Based on I50 values the biphenyl derivatives of phosphoric acid esters were more potent anti acetylcholinesterase (AChE) agents against rat and fish brain AChE while derivative of carbamic esters towards pigeon brain AChE. The anti AChE potency of both groups appear to be of the same order towards bee head AChE.     

两种入侵植物与三种本地植物根系特征的比较研究

以菊科2种入侵植物飞机草(Chromolaena odorata (L.)R. M. King & H. Rob)和紫茎泽兰( Eupatorium adenophorum Speng)以及生活型相似的3种本地植物异叶泽兰(Eupatorium heterophyllum DC.)、佩兰(Eupa-torium for...     

Competitive interactions and persistence of two nematode species that parasitize Drosophila recens

Drosophila recens is parasitized in the wild by two nematodes, Howardula aoronymphium , a host generalist, and Parasitylenchus nearcticus , a host specialist known only from D .  recens . In order to understand how these two parasite species coexist, we compared their ability to infect and grow in D .  recens , their effects on host fecundity and survival, and whether one parasite species was competitively superior in double infections. The specialist nematode P. nearcticus had greater rates of infection and reproduction than the generalist H. aoronymphium , and completely sterilized females in single and mixed infections. The specialist was competitively superior in mixed infections, as generalist motherworms were significantly smaller than in single infections. These results suggest that P. nearcticus might competitively exclude H. aoronymphium if D. recens were the only host available. It is likely that H. aoronymphium persists in D. recens by transmission from other, more suitable host species.     

The transition from invasive species control to native species promotion and its dependence on seed density thresholds

Question: Does the seed density of invasive species affect establishment by native species in a bare ground context (following invasive species control efforts), and is it possible to promote transition to a native species dominated state by manipulating sowing density of the native community? Location: Experimental wetland basin in Chanhassen, Minnesota, USA. Methods: A mesocosm experiment investigated the influence of Phalaris arundinacea (invasive species) propagule pressure on establishment of native wet meadow species in the context of a newly restored wetland. Mesocosms were sown with P. arundinacea (0, 10, 50, 100, or 500 seeds/m²) and a mix of native species (3000 or 15000 seeds/m²). Results: When planted at densities > 100 seeds/m², P. arundinacea increased suppression of native species. Also, high native seed density suppressed P. arundinacea biomass production. This effect was more pronounced when P. arundinacea seed density was high (> 100 seeds/m²), but high native seed density (15000 seeds/m²) did not suppress recruitment of P. arundinacea from seed. Conclusions: The transition from post‐control bare ground (a common result of efforts to control invasive species) to native species establishment depends on both native species and invader seed density. These results suggest that a threshold of P. arundinacea propagule pressure exists, beyond which transition to a native community is less likely without management intervention. P. arundinacea can establish in the presence of a newly developing native plant community, even at very low densities of P. arundinacea seed. Invader control (following initial site clearing efforts) is essential to native species establishment.     

Surface ciliation of anuran amphibian larvae: persistence to late stages in some species but not others

Scanning electron microscopy was used to examine the surfaces of 21 species of tadpoles from six families, from Gosner Stage 25/26 until close to metamorphosis. Contrary to most previous reports, ciliated epidermal cells persisted until late stages in many but not all species and not at all locations examined. The commonest location for ciliated cells was around the nostrils, suggesting a role in chemosensation. Ciliated cells also occurred around the circumference of the eye, suggesting a cleaning role. Several species had ciliated cells on the tail. The densest, most regular arrays of ciliated cells occurred in species that tend to hang motionless in still-water pools, suggesting a respiratory function for these cells.     

Effects of temperature on persistence times of native and invasive gammarid species in the stomachs of Cottus gobio

Gastric lavage was used to investigate the effects of temperature on persistence time of two amphipod species, one native Gammarus pulex and one invasive Gammarus roeseli , in the stomachs of bullhead Cottus gobio . Persistence time was strongly influenced by temperature and prey type, such that G. pulex species degraded faster than G. roeseli .     

Using artificial neural networks to determine the relative contribution of abiotic factors influencing the establishment of insect pest species

The use of multi-layer perceptrons (MLP) to determine the relative significance of climatic variables to the establishment of insect pest species is described. Results show that the MLP are able to learn to accurately predict the establishment of a pest species within a specific geographic region. Analysis of the MLP yielded insights into the contribution of the individual input variables and allowed for the identification of those variables that were most significant in either encouraging or inhibiting establishment.     

Allocation to reproduction and relative reproductive costs in two species of dioecious Anacardiaceae with contrasting phenology

Background and Aims

The cost of reproduction in dioecious plants is often female-biased. However, several studies have reported no difference in costs of reproduction between the sexes. In this study, the relative reproductive allocation and costs at the shoot and whole-plant levels were examined in woody dioecious Rhus javanica and R. trichocarpa, in order to examine differences between types of phenophase (i.e. physiological stage of development).

Methods

Male and female Rhus javanica and R. trichocarpa were sampled and the reproductive and vegetative allocation of the shoot were estimated by harvesting reproductive current-year shoots during flowering and fruiting. Measurements were made of the number of reproductive and total current-year shoots per whole plant, and of the basal area increment (BAI). The numbers of reproductive and total current-year shoots per 1-year-old shoot were counted in order to examine the costs in the following year at the shoot level.

Key Results

A female-biased annual reproductive allocation was found; however, the ratio of reproductive current-year shoots per tree and the BAI did not differ between sexes in Rhus javanica and R. trichocarpa. The percentage of 1-year-old shoots with at least one reproductive current-year shoot was significantly male-biased in R. trichocarpa, but not in R. javanica, indicating that there was a relative cost at the shoot level only in R. trichocarpa. The female-biased leaf mass per shoot, an indicator of compensation for costs, was only found in R. javanica.

Conclusions

Relative reproductive costs at the shoot level were detected in Rhus trichocarpa, which has simultaneous leafing and flowering, but not in R. javanica, which has leafing followed by flowering. However, the costs for the whole-plant level were diminished in both species. The results suggest that the phenophase type may produce the different costs for R. javanica and R. trichocarpa through the development of a compensation mechanism.Key words: Modularity, phenology, reproductive allocation, reproductive cost, Rhus javanica, Rhus trichocarpa