Showing papers by "CABI published in 2002"

Herbivory in global climate change research: direct effects of rising temperature on insect herbivores

Abstract: This review examines the direct effects of climate change on insect herbivores. Temperature is identified as the dominant abiotic factor directly affecting herbivorous insects. There is little evidence of any direct effects of CO2 or UVB. Direct impacts of precipitation have been largely neglected in current research on climate change. Temperature directly affects development, survival, range and abundance. Species with a large geographical range will tend to be less affected. The main effect of temperature in temperate regions is to influence winter survival; at more northerly latitudes, higher temperatures extend the summer season, increasing the available thermal budget for growth and reproduction. Photoperiod is the dominant cue for the seasonal synchrony of temperate insects, but their thermal requirements may differ at different times of year. Interactions between photoperiod and temperature determine phenology; the two factors do not necessarily operate in tandem. Insect herbivores show a number of distinct life-history strategies to exploit plants with different growth forms and strategies, which will be differentially affected by climate warming. There are still many challenges facing biologists in predicting and monitoring the impacts of climate change. Future research needs to consider insect herbivore phenotypic and genotypic flexibility, their responses to global change parameters operating in concert, and awareness that some patterns may only become apparent in the longer term.

Coping with crowds: density-dependent disease resistance in desert locusts.

Abstract: Parasite transmission generally exhibits some form of positive density dependence. Thus, as population density increases, so too does the per capita risk of becoming infected. Under such circumstances, natural selection should favor individuals that use cues associated with population density to determine the optimal allocation of resources to disease resistance mechanisms. As a consequence, individuals experiencing crowded conditions are predicted to be more resistant to parasites and pathogens than those experiencing low-density conditions. This phenomenon (termed "density-dependent prophylaxis") [Wilson, K. & Reeson, A. F. (1998) Ecol. Entomol. 23, 100-101] is predicted to be particularly prevalent in outbreak pest species and in species exhibiting density-dependent phase polyphenism, such as the desert locust, Schistocerca gregaria. Here we show that, as predicted, desert locusts reared under crowded conditions are significantly more resistant than solitary locusts to the entomopathogenic fungus, Metarhizium anisopliae var. acridum, a key natural disease of acridids and an important agent in locust and grasshopper biocontrol. Moreover, enhanced pathogen resistance in crowded locusts is associated with elevated antimicrobial activity, but not with any difference in thermal preferences or behavioral fever response. These results have implications for understanding the development and biocontrol of locust plagues.

Natural enemy diversity and pest control: patterns of pest emergence with agricultural intensification.

Abstract: Concern over declining biodiversity and the implications for continued provision of ecosystem services has led, recently, to intense research effort to describe relationships between biodiversity and ecosystem functioning. Here we extend this effort to the relationship between natural enemy species diversity and natural pest control. From simple modelled food-webs and simulations of natural enemy species loss we derive specific predictions concerning the effect of herbivore life-history traits, such as life-cycle type and concealment, on the shape (reflecting diversity effects) and variance (reflecting species composition effects) of the relationship between natural enemy diversity and pest-control. We show that these predictions are consistent with the emergence of different pest types following intensification of rice production in Asia. We suggest that basic biological insights can help define the structure of ecological processes and allow more accurate predictions of the effect of species loss on the delivery of ecosystem services.

Diversity and host preference of leaf endophytic fungi in the Iwokrama Forest Reserve, Guyana

Abstract: Endophytic fungi were isolated from living symptomless leaves of 12 tree species from two locations in the Iwokrama Forest Reserve, Guyana. Sixty-four fungal morphotaxa were characterized from 2492 cultures, which were derived from a total of 2520 sample units. Species of Colletotrichum, Nodulisporium, Pestalotiopsis and Phomopsis were most frequently isolated. Colonization was greater in samples from the midrib than in those from laminar tissue, and slightly greater at the tip of the lamina compared with the base of the leaf. In contrast to studies in temperate ecosystems, no distinct fungal communities were identified for individual plant species, suggesting that the degree of host preference is low. The implications for estimation of fungal diversity in tropical systems are explored.

Benchmarking in tourism and hospitality industries : the selection of benchmarking partners

Abstract: A general review of benchmarking benchmarking in the hotel industry measuring business performance a mixture regression model data envelopment analysis evolutionary data envelopment analysis (EDEA).

Phenotypic degeneration occurs during sector formation in Metarhizium anisopliae

Abstract: Aims: The formation of sectors was observed during subculturing of an isolate of the entomopathogenic fungus Metarhizium anisopliae, a fungus used for biological control of insect pests. The aim of the investigation was to establish whether sector formation was accompanied by changes in physiological characters. Methods and Results: Four degenerative morphological states, with reduced sporulation capacity, were characterized. Subcultures were taken from each sector and four new culture lines established. The new lines were further subcultured every 21 d. A physiological assessment of each line was undertaken after 42 d using TLC of secondary metabolites and fluorogenic enzyme tests. Full sporulation capacity was not regained on subculture, although some cultures recovered partially. Changes in secondary metabolite profiles and the loss in detection of activity of specific enzymes were observed. Conclusions: Sector formation was frequently accompanied by changes in the ability to produce secondary metabolites and enzymes. Significance and Impact of Study: The results illustrate the importance of maintaining the stability of important cultures during routine subculture. The consequences could have significant implications if degenerate cultures are used as inocula for liquid fermentation cultures or industrial scale production.

Ecosystem engineering : a trivialized concept?

Abstract: In a recent review in TREE [1xThe role of pocket gophers as subterranean ecosystem engineers. Reichman, O. and Seabloom, W. Trends Ecol. Evol. 2002; 17: 44–49Abstract | Full Text | Full Text PDF | Scopus (173)See all References][1], Reichman and Seabloom discuss the important impacts of burrowing mammals as keystone ecosystem engineers. The article eloquently explains the importance of one group of ecosystem engineers, but, in restricting the term ‘ecosystem engineer’ to keystone species, I believe that it seriously understates the value of the concept.Reichman and Seabloom's definition requires that the ‘change to the physical environment should be distinctive from processes that are strictly abiotic…and large relative to purely physical processes operating in the system’. They also state that ‘discussions of ecosystem engineering have become trivialized by characterizing any influence on the environment as engineering because all plants and animals affect the physical environment in some way’. I have strong reservations about these two statements.I do not believe that the definition of ecosystem engineering should be based purely on the physical effect. As explicitly stated in the original definitions of ecosystem engineering, the physical effects caused by engineers should ‘modulate the availability of resources to other organisms’ [2xOrganisms as ecosystem engineers. Jones, C.G. et al. Oikos. 1994; 69: 373–386CrossrefSee all References][2]. The key point is that the changes in resource flow caused by ecosystem engineering affect other organisms. Thus, the value of the ecosystem-engineering concept lies in its formalization of interactions among organisms that are mediated by the physical environment, and that were hitherto not included in ecological theory. It is an additional class of interactions that should be integrated with trophic ecology to give us a more complete understanding of interspecific interactions [3.xIntegration of ecosystem engineering and trophic effects of herbivores. Wilby, A. et al. Oikos. 2001; 92: 436–444CrossrefSee all References, 4.xPositive and negative effects of organisms as physical ecosystem engineers. Jones, C.G. et al. Ecology. 1997; 78: 1946–1957CrossrefSee all References].Far from trivializing the concept, the fact that all organisms affect the physical environment in some way emphasizes the possible ubiquity of ecosystem engineering. All organisms also have trophic interactions, but does this trivialize trophic ecology? Should we restrict discussions of trophic interactions to those interactions involving keystone species? If most species do turn out to have ecosystem engineering interactions with other species, then the label ‘ecosystem engineer’ will be trivial, but the engineering processes definitely are not. Indeed, in concentrating on the identification of keystone engineers, rather than on the engineering processes that they control and their generality, we risk an ‘accumulation of ‘‘just-so’’ stories’ that was warned against when the concept was introduced [2xOrganisms as ecosystem engineers. Jones, C.G. et al. Oikos. 1994; 69: 373–386CrossrefSee all References][2].In Box 1 of their article, Reichman and Seabloom explain how soil excavation and herbivory by pocket gophers Thomomys bottae interact with competitive interactions among plant species to govern vegetation composition and spatial pattern. Thus, the authors summarize a considerable body of work that describes pocket gophers in terms of the impact of their herbivory and soil disturbance on plant community structure. From this process perspective, ecosystem-engineering effects, alongside trophic effects, are described in such a way that allows comparison of species in similar or dissimilar ecosystems. I suggest that such an integrative approach is the way forward for the study of ecosystem engineering. Our goal should be to elucidate how widespread and important ecosystem engineering interactions are, rather than restricting ourselves to the most apparent examples from the outset.

The risks of biocontrol: transient impacts and minimum nontarget densities

Abstract: The biocontrol of insect pests may pose a risk to native insects if the bio- control agent attacks nontarget species. Potential biocontrol agents are screened before release to determine their acceptance of nontarget species and the suitability of nontarget species for their development. Here we show that, even though a biocontrol agent has very low acceptance of a nontarget species, it may nonetheless have a large impact on the nontarget population. This impact does not require the nontarget species to be a suitable prey capable of supporting the biocontrol agent population, but instead may be a transient impact that occurs soon after the agent is released. Because the population of biocontrol agents is likely to increase rapidly in response to the high density of its target pest, the resulting high density of the agent population may dominate its low acceptance of the nontarget species, causing a strong decline or even local extirpation of the nontarget. We demonstrate this possibility using models of host-parasitoid dynamics that incorporate a broad range of assumptions about the life histories of hosts and parasitoids, and that dem- onstrate how various common aspects of host-parasitoid biology are likely to reduce this risk considerably. The predictions of the models are reasonably approximated with a simple formula, which potentially provides a simple method for assessing the risk of transient impacts, but which should only be applied loosely (in a qualitative manner) and in the context of a fuller understanding of other factors affecting risk in the system in question.

Evolutionary relationships within Aspergillus section Flavi based on sequences of the intergenic transcribed spacer regions and the 5.8S rRNA gene.

Abstract: Sequences of the intergenic transcribed spacer regions and the 5.8S rRNA gene (455 nucleotides) of type strains or representative isolates of 23 species and subspecies either currently assigned to Aspergillus subgenus Circumdati section Flavi or other closely related sections, were analyzed. Parsimony analysis of sequence data indicated that species of Aspergillus section Flavi form distinct clades. The three main clades identified based on sequence data could also be distinguished based on colony color, and their ubiquinone systems. The ‘A. flavus’ clade includes species characterized with Q-10(H2) as their main ubiquinone, conidial colors in shades of green, and dark sclerotia. The ‘A. tamarii’ clade involves species with ubiquinone system Q-10(H2), and conidia in shades of olive to brown, while the ‘A. alliaceus’ clade consists of species with Q-10 ubiquinone system, and conidia in shades of ocher. The synnematous species A. coremiiformis was found to be closely related to species in the ‘A. tamarii’ clade. A. thomii and A. terricola var. americana were found to be related to the ‘A. flavus’ clade in spite of producing brownish colonies. Three species, A. nomius, A. avenaceus, and A. leporis were found to form separate lineages not closely related to any of the main clades identified. It is suggested that A. clavatoflavus and A. zonatus be excluded from Aspergillus section Flavi. Phylogenetic analysis of partial 26S rRNA gene sequences (564 nucleotides) supported our findings.

Parasitism of the horse chestnut leaf miner, Cameraria ohridella Deschka and Dimic (Lep., Gracillariidae), in Serbia and Macedonia

Abstract: A study concerning the parasitism of Cameraria ohridella, a pest of Aesculus hippocastanum invading Europe, has been carried out in Serbia and Macedonia in 1998 and 1999. From C. ohridella 14 species of parasitoids were reared, which are polyphagous and occur in the whole of Europe. Twelve of the species found belong to the Chalcidoidean family Eulophidae. The rates of parasitism at different sampling dates did not exceed 25 %. The results, when compared with data from central Europe, showed that C. ohridella most certainly does not originate from Serbia or Macedonia – the regions in which C. ohridella was observed for the first time – as an indigenous leaf miner on A. hippocastanum.

Effects of different formulations on viability and medium-term storage of Metarhizium anisopliae conidia

Abstract: The aim of this work was to evaluate the effects of different formulations on the viability of Metarhizium anisopliae conidia. In a first experiment, the viability of conidia mixed with eight emulsifiable adjuvant oils (EAO), seven wetter/spreaders, three vegetable oils and four mineral oils was evaluated 24h and 48h after spreading over SDA medium surface. Some formulations, which did not present any adverse effect on conidial viability in the first 24h of incubation, were recommended for the medium-term storage experiment. In a second experiment, the effects of different formulations on medium-term storage (40 weeks) of M. anisopliae var. acridum conidia were evaluated at 10oC and 27oC. Five EAO, one vegetable oil, a mixture of mineral oils and pure dry conidia were tested. In the experiment 1, the oil formulations did not cause any negative effect on conidial germination. The treatments with the adjuvant oils Actipronâ, Ashladeâ and Codacideâ gave germination levels equal to mineral and vegetable oils after 24h of incubation. The wetter/spreader Ethokenâ C12 was lethal to conidia. All tested emulsifiable adjuvant oil-based formulations were compatible to the conidia as the oil-based formulations after 48h of incubation. In the experiment 2, conidial viability within the same formulation declined over time. Conidial viability was maintained above 90% at 10oC in all tested formulants. The conidial suspension with Ashladeâ gave equal germination levels to Shellsol plus Ondina, when stored at 10oC and 27oC for 40 weeks. Thus EAO can be used to formulate M. anisopliae conidia without adverse effects on viability.

Strategies for the isolation of cellulolytic fungi for composting of wheat straw

Abstract: It was shown that inoculation of straw with cellulolytic fungi offers potential for manipulating and improving the composting of cellulose waste, where the C:N ratio is not optimal for composting. In this paper we report on a screening strategy used to isolate novel cellulolytic fungi from field samples. The screen comprised of two phases. In phase I, 300 cellulolytic fungi were isolated to pure culture from field samples collected from Hawaii, China and the UK. Isolates were selected on the basis of high cellulolytic activities and growth rates on cellulose agar. A total of 137 lead isolates progressed to an unreplicated phase II screen to rapidly identify strains that improved quality of the resulting compost over and above that of the uninoculated control. Compost quality was assessed by measuring C:N ratio, water holding capacity, water content and potential and polysaccharide content of the resulting compost. Effect on the aggregate stability of soil and the growth of wheat seedlings was assessed when compost was added to a sandy loam soil. Performance of each isolate was quantified by allocating a utility score for each compost analysed. Utility scores were based on the sum of the logged ranked score in each assay. The 10 highest scoring isolates were subsequently processed through a replicated phase II screen and the best performing isolates identified by calculating utility scores as before. Significantly lower C:N ratios, higher water-holding capacities and improved aggregate stabilities were obtained with some inoculated treatments compared to the uninoculated control, whilst the results obtained for polysaccharide content and plant growth showed no significant differences. Isolate 304, isolated from decomposing vegetation obtained from Egham, Surrey, UK, and identifed as a Trichurus sp., appeared the most effective inoculant, significantly decreasing the C:N ratio by 36% and increasing the aggregate stability of soil by 54% compared to the uninoculated control. As a result of adopting this screening strategy, it has been possible to identify cellulolytic fungi that can, under non-sterile (laboratory) conditions, significantly improve the quality of compost. This screening approach therefore offers real possibilities for selecting microbial inoculants in low-tech agricultural practices.

Biological Control of Weeds

Abstract: As technology advances and agricultural practices are ever changing, weeds are having an increasing rather than a decreasing impact on man’s affairs It has been estimated that crop losses due to weeds vary from 10–20%, which, in the USA alone, would amount to over US $15 billion per annum (Bridges 1994) However, a more recent and probably more accurate calculation puts the annual cost of non-indigenous weeds to US agriculture at US $27 billion (Pimentel et al 2000) In such agricultural ecosystems, there has been a significant increase in the use of chemical herbicides since the 1950s, when these comprised less than 20% of all pesticides sold By the 1980s, herbicides accounted for over 50% of the pesticide market (Jutsum 1988), and this is still rising due mainly to radical changes in cultivation practices

Host specificity of the cassava green mite pathogen Neozygites floridana

Abstract: Tests were conducted on the hostspecificity of a Brazilian isolate of thefungus Neozygites floridana, a potentialbiological control agent for the cassava greenmite, Mononychellus tanajoa, in Africa.Five insect and two mite species, mostly fromthe cassava agroecosystem, were evaluated forsusceptibility to N. floridana, namelyEuseius concordis, E. citrifolius, Phenacoccus herreni, Stethorus sp., Aleurothrixus aepim, Apoanagyrusdiversicornis, and Bombyx mori.Individuals of each species were exposed tocapilliconidia (the infective stage of thefungus). None of the tested individuals wasfound with hyphal bodies (the vegetative stageof the fungus), whereas 73 to 94% of thecassava green mites in the controls becameinfected. Non-germinated capilliconidia were,however, found attached to several individualsin most species. N. floridana appears tobe safe for exportation. Further evaluation ofits performance against M. tanajoa inAfrica is therefore desirable.

Ecological Studies on the Larger Grain Borer, Prostephanus truncatus (Horn) (Col.: Bostrichidae) and their Implications for Integrated Pest Management

Abstract: In this article, we review studies of the ecology of the larger grain borer, Protephanustruncatus, both outside and within the maize storage systems. Laboratory studies have shown that P. truncatus can breed on a wide range of woody substrates (branches, roots, and seeds). Pheromone trap catches in different habitats strongly suggest that P. truncatus is well-established in certain non-agricultural environments, presumably breeding in dead or dying wood. In Meso-America, West and East Africa, P. truncatus reproduction in the field has been documented in branches ring-barked by cerambycid beetles. Within a maize store, P. truncatus densities can increase from very small initial colonies of probably less than 200 individuals to densities in excess of 1000 beetles per kg after about 4–6 months of storage. Insect parasitoids are very often found in smallholders' grain stores attacked by P. truncatus, but they do not contribute significantly to population regulation. Declines in maize store population levels in Benin from 1993 to 1996, and in adult abundance in pheromone traps in the natural environment in Kenya, have been attributed to predation by the introduced predator, Teretriusnigrescens, but in recent years pheromone trap catches in West Africa suggest that the situation may be complex. Several environmental factors, notably temperature, humidity, and daylength, and their interactions, have been correlated with P. truncatus flight activity, as well as, in West Africa, the emptying of maize stores. Laboratory experiments have shown food quality also affects flight activity. Factors terminating dispersal and flight are most likely attraction to the male-released aggregation pheromone. Short range attraction to plant volatiles has also been recorded. In Africa the highest densities of P. truncatus tend to occur in humid lowlands, which contrasts with the situation in meso-America where P. truncatus tend to occur in greatest numbers in cooler upland regions. Pheromone trap catches can be significant predictors of the risk of stores becoming infested. Coupled with the development of a rule-based model of flight activity, these studies may offer the prospect of predicting the risk of store infestation based upon temperature and humidity measurements.

Sarcoptic Mange in Free-Ranging Pampas Foxes in the Gran Chaco, Bolivia

Abstract: Sarcoptes scabiei infestation was diagnosed in two freshly dead free-ranging pampas foxes (Pseudalopex gymnocercus) in the Gran Chaco, Bolivia. Diagnosis was made based on histologic evaluation of skin biopsies and identification of the parasite from skin scrapings. Characteristic gross lesions consistent with mange were noted in 19 of 94 observations of free-ranging pampas foxes in the region from December 1998 to January 2000. None of 16 crab-eating foxes (Cerdocyon thous) observed during the same time period had visible lesions consistent with scabies. These are the first case reports of S. scabiei in pampas foxes.

Potential hosts of Prostephanus truncatus (Coleoptera: Bostrichidae) among native and agroforestry trees in Kenya.

Abstract: This study was carried out to establish the extent to which an invasive stored products pest, Prostephanus truncatus Horn exploits wood as a feeding and breeding resource in Kenya. Twenty seven out of 84 native and agroforestry trees and shrubs supported the breeding of P. truncatus under laboratory conditions. Adult survival (<1% to 18%) for 8 weeks was recorded on 51 tree species that did not support breeding. The breeding success of this beetle varied widely between host tree species and showed no obvious trends based on tree systematics or wood hardness. Studies of P. truncatus survival on two host tree species found that the greatest increase in the P. truncatus population occurred on stem sapwood, whilst the smallest population increase was on twigs. Breeding also varied greatly from season to season; studies on ten selected host species showed that reproduction was often greatest in wood samples collected and tested during the dry season in September. The implications of these findings for the management of P. truncatus infestations in farm stored maize are discussed.