Geographic range, impact, and parasitism of lepidopteran species associated with the invasive weed Lantana camara in South Africa

Six isolates of Trichoderma were screened for antagonism to Armillaria in tea stem sections buried in the soil. The inability of Armillaria to invade Trichoderma-colonized stem sections and the reduction of its viability in the plant materials following invasion of these by Trichoderma were used as indicators of antagonism. Four isolates of the species Trichoderma harzianum significantly (P<0.001) reduced the incidence of the pathogen in the plant materials. Isolate T4 completely eliminated the pathogen from plant materials in sterile soil and also antagonized two different isolates of the pathogen in nonsterile soil. Application of this T. harzianum isolate to the soil as a wheat bran culture significantly (P<0.001) reduced viability of Armillaria in woody blocks of inoculum. Soil amendment with coffee pulp also reduced the inoculum viability but did not affect the incidence of Trichoderma in the blocks of inoculum. We conclude that the direct application of wheat bran-formulated T. harzianum into soil surrounding woody Armillaria inoculum sources can suppress the pathogen. Further, no organic amendment is needed to enhance development of the antagonist in the soil as a pre-requisite to suppressing the pathogen.     

Biology, host range, and risk assessment supporting release in Africa of Falconia intermedia (Heteroptera: Miridae), a new biocontrol agent for Lantana camara

The ornamental hybrid shrub, Lantana camara L. (lantana), is a serious environmental weed and has been targeted for biological control in South Africa since 1961. The established biocontrol agents cause insufficient levels of damage and additional natural enemies are required to reduce the invasiveness of this weed. The lantana mirid, Falconia intermedia (Distant), is a promising new agent that was imported from the Caribbean for life history and host-range studies. The nymphs and adults are leaf-suckers that cause chlorotic speckling, which reduces the photosynthetic capacity of the plant. Biological studies indicate that F. intermedia has considerable biocontrol potential, in that it has a high intrinsic rate of increase, the potential for multiple generations a year, highly mobile adults, and a high level of damage per individual. Host-specificity trials indicated that the lantana mirid has a narrow host range, with L. camara being the most suitable host, but several indigenous African species in the closely related genus Lippia are suitable alternative host plants. Under multiple-choice conditions, adults showed a significant and strong oviposition preference for L. camara over the Lippia species. A risk assessment of potential nontarget effects indicated that three Lippia species could sustain damage levels in the field. The relatively low probability of damage to indigenous species was considered a justified trade-off for the potentially marked impact on L. camara. The regulatory authorities accepted the results of this study and F. intermedia was released against L. camara in South Africa in April 1999.     

Biology of Polypedilum n. sp. (Diptera: Chironomidae), a promising candidate agent for the biological control of the aquatic weed Lagarosiphon major (Hydrocharitaceae) in Ireland

Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae), an aquatic macrophyte native to Southern Africa that has become invasive in several countries worldwide, is a potential target for biological control. Biology studies were conducted on Polypedilum (Pentapedilum) n. sp. near reei Oyewo & Sæther (Diptera: Chironomidae), a midge whose larvae were discovered mining the plant's shoot tips in its native range. Field surveys indicated that the midge occurred only at a small number of sites but attained high densities (up to 370 shoots damaged/m²) that prevented further growth from the shoot tips. A population of the midge was imported into quarantine in Ireland to evaluate its potential as a candidate biological control agent. The adult stage is terrestrial and short-lived (4–5 d), with females depositing one–two egg packets into the water bodies. First-instar larvae fed externally on the stems and leaflets. Later instars fed on the apical meristems and burrowed into the shoot tips, with resultant damage stunting the apical growth. Larvae moved readily between shoots to complete their development and pupated within the tunnels excavated by the late instar larvae. Developmental time to adulthood ranged from 31 to 49 days at 20.7°C and a 15 L:9-D cycle. This is the first time that a chironomid has been imported and successfully cultured for consideration as a classical biological control agent. Several aspects of the midge's biology suggest that host specificity testing is warranted to determine its potential as a biocontrol agent of L. major.     

Refining a kick sampling strategy for the bioassessment of benthic macroinvertebrates in headwater streams

Small headwater streams constitute a large proportion of the river channel network in many parts of the world. In this study, two multihabitat kick sampling methods (60-second and 20-second) were compared across 10 small headwater streams in the southwest and east of Ireland in spring and summer 2009 to determine the influence of sampling on various benthic macroinvertebrates in headwater streams. The performance of each method, over time and replication, was examined using a range of benthic macroinvertebrate metrics, as well as the community composition and structure recorded by both methods. The ability to recruit taxa, as well as the field sampling and laboratory processing effort required for each method, was also assessed. Results indicated that both kick sampling methods generally recorded similar metric scores with the exception of taxonomic richness (t = 180 s and n = 9 replicates test) where the 20-second kicks consistently out preformed those calculated for the 60-second kicks. All other metrics compared generally performed equally as well regardless of the method used. Multivariate analysis of macroinvertebrate community assemblage, using SIMPROF, RELATE and CS-SMC analyses, further highlighted the high similarity in the macroinvertebrate assemblage recorded between both methods. Finally, the 20-second kicks recruited taxa as efficiently as 60-second kicks samples so long as replication was equal but required less sampling effort (NSE) and processing time. Therefore, the shorter 20-second kicks can be used to assess the ecological health of headwater streams, provided that adequate replication is adopted, resulting in significant effort, cost and time savings.     

Genetic analyses of the functions of [NiFe]-hydrogenase maturation endopeptidases in the hyperthermophilic archaeon Thermococcus kodakarensis

The maturation of [NiFe]-hydrogenases requires a number of accessory proteins, which include hydrogenase-specific endopeptidases. The endopeptidases carry out the final cleavage reaction of the C-terminal regions of [NiFe]-hydrogenase large subunit precursors. The hyperthermophilic archaeon Thermococcus kodakarensis harbors two [NiFe]-hydrogenases, a cytoplasmic Hyh and a membrane-bound Mbh, along with two putative hydrogenase-specific endopeptidase genes. In this study, we carried out a genetic examination on the two endopeptidase genes, TK2004 and TK2066. Disruption of TK2004 resulted in a strain that could not grow under conditions requiring hydrogen evolution. The Mbh large subunit precursor (pre-MbhL) in this strain was not processed at all whereas Hyh cleavage was not affected. On the other hand, disruption of TK2066 did not affect the growth of T. kodakarensis under the conditions examined. Cleavage of the Hyh large subunit precursor (pre-HyhL) was impaired, but could be observed to some extent. In a strain lacking both TK2004 and TK2066, cleavage of pre-HyhL could not be observed. Our results indicate that pre-MbhL cleavage is carried out solely by the endopeptidase encoded by TK2004. Pre-HyhL cleavage is mainly carried out by TK2066, but TK2004 can also play a minor role in this cleavage.

     

Critical influence of seasonal sampling on the ecological quality assessment of small headwater streams

Variability in the ecological quality assessment of reference sites was tested on small headwater streams in Ireland. Although headwater streams constitute a large portion of the river channel network, they are not routinely monitored for water quality. Various metrics were used including the Irish Q-value and the newly developed Small Streams Risk Score (SSRS), and metrics applied elsewhere in the Atlantic biogeographic region in Europe, including the Biological Monitoring Working Party score (BMWP), the Average Score per Taxon (ASPT), the Ephemeroptera, Plecoptera and Trichoptera taxa (EPT), the Belgium Biotic Index (BBI) and the Danish Stream Fauna Index (DSFI). The AQEM (version 2.5a) assessment software was used to apply some of these metrics. The spring and summer datasets are used to test the performance of biotic metrics with respect to season, and the applicability of their use to assess the ecological quality of wadeable streams. The quality status of most sites assigned by the various metrics was high using the spring invertebrate data, and an apparent considerable deviation in quality status occurred when the summer data was applied. Seasonal differences were noted using all the biotic indices and are attributed to the absence of pollution-sensitive groups in summer. Seasonal variability in the water quality status was particularly evident in acidic streams draining non-calcareous geologies with peaty soils that had relatively lower numbers of taxa. Some indices applied reflect a greater seasonal difference in the quality category assigned. The least amount of variability between seasons was obtained using the ASPT and the SSRS risk assessment system. Results suggest that reference status is reliably reflected in spring when more pollution-sensitive taxa were present, and that a new ecological quality assessment tool is required for application in summer when impacts may be most severe. This highly heterogeneous freshwater habitat seems to have too few taxa present in the summer to reliably determine the ecological quality of the stream using the available indices. Handling editor: R. Bailey     

Use of life table statistics and degree day values to predict the colonisation success of Hydrellia lagarosiphon Deeming (Diptera: Ephydridae), a leaf mining fly of Lagarosiphon major (Ridley) Moss (Hydrocharitaceae), in Ireland and the rest of Europe

Hydrellia lagarosiphon is a leaf mining fly of the submerged aquatic plant Lagarosiphon major and native to South Africa. With many favorable attributes this fly has the potential to be a valuable biological control agent of L. major, which has become a problematic weed in many parts of the world. Reproductive and developmental biology of H. lagarosiphon was determined at four constant temperatures (10, 13.5, 16.5, 20 °C) to evaluate the rate of increase and predicted colonisation success in areas where L. major occurs and areas where its continued spread is probable. Development rates increased with decreasing temperatures and were greatest at 10 °C taking 157.9 days. Linear regression of developmental rate data for temperatures 10–20 °C indicated that 517 degree days were required above a minimum of 7.5 °C to complete development. Between two and eight generations per year were estimated across the climatic regions of Europe using the degree day model. The fitted quadratic model for the net reproductive rate (R_o) indicated that R_o falls below 1.0 at 9.9 °C, suggesting a decline in population growth when fly populations are subjected to prolonged periods of temperatures below 10 °C. The values of R_o for selected sites range from 0 to 13, with all but a few sites in northern Europe being suitable for the establishment of H. lagarosiphon. A minimum of two generations were required each year to sustain population growth and most biogeographical regions in Europe appeared suitable for the establishment of permanent populations of H. lagarosiphon. The implications for the release strategy of the fly are discussed.