Biological control of the diamondback moth, Plutella xylostella: A review

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is one of the most destructive cosmopolitan insect pests of brassicaceous crops. It was the first crop insect reported to be resistant to DDT and now, in many crucifer producing regions, it has shown significant resistance to almost every synthetic insecticide applied in the field. In certain parts of the world, economical production of crucifers has become almost impossible due to insecticidal control failures. Consequently, increased efforts worldwide have been undertaken to develop integrated pest management (IPM) programs, principally based on manipulation of its natural enemies. Although over 130 parasitoid species are known to attack various life stages of DBM, most control worldwide is achieved by relatively few hymenopteran species belonging to the ichneumonid genera Diadegma and Diadromus, the braconid genera Microplitis and Cotesia, and the eulophid genus Oomyzus. DBM populations native to different regions have genetic and biological differences, and specific parasitoid strains may be associated with the specific DBM strains. Therefore, accurate identification based on genetic studies of both host and parasitoid is of crucial importance to attaining successful control of DBM through inoculative or inundative releases. Although parasitoids of DBM larvae and pupae are currently its principal regulators, bacteria-derived products (e.g., crystal toxins from Bacillus thuringiensis) and myco-insecticides principally based on Zoophthora radicans and Beauveria bassiana are increasingly being applied or investigated for biological control. Viruses, nematodes and microsporidia also have potential as biopesticides for DBM. When an insect pest is exposed to more than one mortality factor, there is the possibility of interactions that can enhance, limit, or limit and enhance the various aspects of effectiveness of a particular control tactic. This paper reviews the effectiveness of various parasitoids and entomopathogens against DBM, interactions among them, and their possible integration into modern IPM programs.     

Potentially pathogenic and biocontrol Ascomycota associated with green wall structures of basket willow (<Emphasis Type="Italic">Salix viminalis</Emphasis> L.) revealed by phenotypic characters and ITS phylogeny

Ascomycota are among the fungi that cause serious willow diseases in all natural habitats worldwide. This study was conducted to determine if basket willow used in green wall structures (GWS) built of willow stems were infected by potentially important fungal diseases or their antagonists in urban areas of eastern Canada. In total, 13 different phenotypic genera belonging to eight families of ascomycetous fungi were isolated and identified according to their sexual and/or asexual forms. Venturia pathogenic species complex were represented by three different anamorphs: Fusicladium, Fusicladium-Cladosporium, and Pollaccia as anamorph. They were responsible for the highest incidence value on leaves (IF > 15%). Cryptodiaporthe, Drepanopeziza, and Glomerella dominated on bark (IF > 5%). A significantly higher incidence value of fungal communities was found on first year than on second year GWS. The correspondence analysis using χ² distance showed that communities of potentially pathogenic species are closely related to diseased plants, while healthy plants often contain biocontrol species such as Cladobotryum mycoparasite on healthy bark and Alternaria sp. antagonist on healthy leaves. The phylogenetic positions of the different fungal taxa and their relationship have been revealed by use of PCR amplified internal transcriber spacer (ITS) region of rDNA.     

Management of soil microbial communities to enhance populations of Fusarium graminearum-antagonists in soil

Fusarium head blight (FHB), incited by Fusarium graminearum Schwabe is one of the most devastating diseases of wheat. Primary inoculum generated on crop residue is the driving force of FHB epidemics. Fusarium survival on crop residues is affected by soil microbial antagonists. The incorporation of green manures has been shown to increase the density and diversity of microbes in soils, particularly the density and the pathogen-inhibitory activity of specific bacteria and fungi. Evidence of increased streptomycete populations in soil as a response to green manure incorporation, and their negative effect on the survival of Fusarium oxysporum Schlechtendahl in soil, suggests their potential use to reduce the survival of related pathogens. There is, however, no precedent for the use of green manures to promote indigenous streptomycete populations to control FHB. This study investigated the use of green manures (sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench–S. bicolor (L.) Moench var. sudanense (Piper)] and common buckwheat [Fagopyrum esculentum (Moench)]) for reducing F. graminearum survival in association with wheat residues. Soil bacterial density, streptomycete density and the density and inhibitory activity of F. graminearum-antagonists were monitored from planting until 3 and 6 months following the incorporation of green manures in greenhouse and field experiments, respectively. The decomposition of wheat residues and survival of Fusarium in residues was also assessed. The use of green manures did not statistically impact the survival of F. graminearum in wheat residue. However, green manures promoted the development of higher densities and antagonistic abilities of F. graminearum-antagonists in soils. Additionally, streptomycete densities and F. graminearum-antagonist densities were significantly and positively correlated with reduced survival of Fusarium. The results of our study suggest that the use of green manures can enhance populations of indigenous soil microorganisms antagonistic to the survival of F. graminearum in wheat residue.     

黄瓜苗根围拮抗细菌X3的分子鉴定

采用生理生化、Biolog和16S rDNA分子鉴定3种不同方法,对抑制黄瓜苗期猝倒病病原真菌的细菌菌株X3进行了鉴定．生理生化鉴定显示该菌株为Pseudomonas aeruginosa;而Biolog鉴定显示其为P．spinosa;进一步对该菌株作16S rDNA基因的测定与分析,表明其与已报道的P．aeruginosa 16S rDNA具有93．7％的同源性,二者在所建系统发育树中处于同一分枝,据此确定该菌株为P．aeruginosa。     

Predicting the Impact of the Biocontrol Agent Aulacidea subterminalis (Cynipidae) on Growth of Hieracium pilosella (Asteraceae) under Differing Environmental Conditions in New Zealand

A gall wasp, Aulacidea subterminalis, was released into the field in New Zealand in 1999 for biocontrol of the grassland weed Hieracium pilosella. To predict its likely impact in the field, the effect of the gall wasp on plant growth was measured under stress-free conditions in a shade house trial with potted plants. Plants with galls showed a reduction in stolon length of 75%. They had slightly lower total dry matter and reduced root weight. In a glasshouse experiment to measure the impact of water stress, nutrient stress, and plant competition on growth of H. pilosella and performance of the gall wasp, the number and mean diameter of gall clusters were not significantly different between treatment and control plants. However, galled plants produced more, but shorter, stolons in all stress treatments, and stolons that were more branched in nutrient- and water-stressed plants, than ungalled plants. Under the plant competition treatment, total stolon length relative to biomass was greater with, than without, wasps, indicating that stolons were thinner. Galling by A. subterminalis is likely to reduce vegetative reproduction of H. pilosella whether or not the plants are stressed, indicating that the wasp may be a successful biocontrol agent.     

Characterization of <Emphasis Type="Italic">Penicillium</Emphasis> Species by Ribosomal DNA Sequencing and BOX,ERIC and REP-PCR Analysis

The genus Penicillium is one of the largest and widely distributed fungal genera described to date. As a result, its taxonomic classification and species discrimination within this genus has become complicated. In this study, 52 isolates that belonged to the Penicillum genus and other related genera were characterized using two DNA-based methods: (i) analysis of the nucleotide sequences of internal transcribed spacers in ribosomal DNA and (ii) analysis of DNA fingerprints that were generated by polymerase chain reactions with specific primers for enterobacterial repetitive intergenic consensus (ERIC) and repetitive extragenic palindromic (REP) sequences, and BOX elements. Using both methods, Penicillium species were discriminated from other fungal genera. Furthermore, Penicillium species that include strains which are used as biocontrol agents, such as P. glabrum, P. purpurogenum, and P. oxalicum, could be distinguished from other Penicillium species using these techniques. Based on our findings, we propose that a polyphasic approach that includes analysis of the nucleotide sequences of ribosomal DNA and detecting the presence of highly conserved, repeated nucleotide sequences can be used to determine the genetic relationships between different Penicillium species. Furthermore, we propose that our results can be used as a start point to develop a strategy to monitor the environmental presence of particular strains of Penicillium species when they are used as biocontrol agents.     

Selection of Trichoderma stromaticum isolates for efficient biological control of witches’ broom disease in cacao

Witches’ broom is the most devastating disease of cacao in Brazil, and losses to it entail serious socio-economical and environmental problems. Biological control of the causal agent Moniliophthora perniciosa (Mp) using the antagonistic fungus Trichoderma stromaticum (Ts) is promising, although the identification of superior isolates is necessary. Here, we report a study on the selection of more effective Ts isolates based on field experiments. Sixty-three Ts isolates from a local collection were applied on brooms and placed under typical conditions of shaded-cacao plantations in southeastern Bahia State (Brazil), during two periods of three months each. The percentages of Ts sporulation and incidence and severity of Mp were the parameters used for biocontrol assessments. The results from both experiments were very distinct, indicating a high phenotypic variation in this collection and suggesting a significant effect of the environment in the Ts–Mp interaction. Ts-sporulation rates were negatively correlated with the presence of Mp in the brooms and a number of isolates reduced Mp incidence more efficiently than the reference isolate. Contrasting isolates in their efficiency of reducing Mp incidence were selected and further tested in four subsequent field trials for validation purposes. The results partially confirmed their biocontrol phenotypes but also suggested isolate-specific responses to environmental variations. Inhibition of Mp-basidiospore germination by total protein secreted in culture supernatants of Ts isolates correlated well with field results and revealed a potentially useful procedure for pre-screening of large collections towards selection of better biological control isolates. The characteristics and efficiency of the method as a reliable protocol for identification of superior BCAs in the witches’ broom—cacao pathosystem is discussed.     

Germination-Arrest Factor (GAF): 3. Determination that the herbicidal activity of GAF is associated with a ninhydrin-reactive compound and counteracted by selected amino acids

A novel, naturally-occurring herbicide (Germination-Arrest Factor, GAF), produced by Pseudomonas fluorescens WH6 and several related isolates of rhizosphere bacteria, irreversibly arrests germination of the seeds of a wide range of graminaceous species, including a number of important grassy weed species. GAF activity has been shown previously to be associated with a hydrophilic, low molecular weight compound that contains an acid group. In the present study, thin-layer chromatography (TLC) of extracts of WH6 culture filtrate demonstrated that GAF activity migrates on TLC plates with a particular ninhydrin-reactive compound. This compound was found to be present in GAF-producing P. fluorescens isolates and absent in P. fluorescens strains that lack the ability to produce GAF. Treatments, including mutagenesis, which resulted in the loss of GAF activity in culture filtrates from P. fluorescens WH6 were shown to result in the disappearance of this ninhydrin-reactive compound from extracts of WH6 culture filtrates or in alteration of its appearance on TLC chromatograms. The ninhydrin-reactivity of GAF indicates that it probably contains an amino group, as well as the acid group previously demonstrated, and suggests that GAF may be a small peptide or amino acid analog. Biological investigations motivated by this conclusion demonstrated that the effects of GAF in inhibiting the germination of seeds of annual bluegrass (Poa annua L.) could be counteracted by treatment with alanine or glutamine and, to lesser extent, by several other amino acids, suggesting that this compound may act by interfering with some aspect of amino acid metabolism or function.     

In vitro evaluation of combination of Trichoderma harzianum and chitosan for the control of sapstain fungi

In vitro assays were undertaken to evaluate the control of two sapstain fungi, Leptographium procerum and Sphaeropsis sapinea by a combination of chitosan or chitosan oligomer and an albino strain of Trichoderma harzianum. Spore germination and hyphal growth of the test fungi were assessed on media amended with chitosan or chitosan oligomer with and without T. harzianum using either simultaneous inoculation with test fungus or inoculation 1, 2, or 3 days after pre-infection with test fungus.There was no mycelial growth of the test fungi regardless of chitosan concentrations used when either L. procerum or S. sapinea was simultaneously inoculated with T. harzianum. However, the dose–response of chitosan or chitosan oligomer on the test fungi was apparent when T. harzianum was not simultaneously inoculated with test fungus but introduced later. There was a greater growth reduction at higher concentrations (0.075–0.1% v/v) of chitosan, and overall chitosan oligomer was more effective than chitosan aqueous solution.Chitosan alone was able to restrict or delay the germination of spores but the combination of chitosan and T. harzianum inhibited spore germination and hence colony formation of test fungi regardless of time delay.     

<Emphasis Type="Italic">Apis mellifera</Emphasis> and <Emphasis Type="Italic">Osmia cornuta</Emphasis> as carriers for the secondary spread of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> on apple flowers

The efficiency of two pollinators, Apis mellifera L. (Hymenoptera: Apidae) and the mason bee Osmia cornuta (Latreille) (Hymenoptera: Megachilidae), as carriers of biocontrol agents (BCA) from flower to flower (secondary colonisation) was investigated on apple cv ‘Golden Delicious’. The BCA tested was Bacillus subtilis, strain BD170 (Biopro®) developed for the control of the ‘fire blight’ caused by Erwinia amylovora (Burril) Winslow et al. The two insect species were studied as secondary BCA carriers on apple plants in pots under net screened tunnels. Their behaviour and capacity to deposit the BCA in the most receptive flower parts were compared both by washing, diluting and plating the flower organs on a recovery medium and by means of PCR analyses based on a molecular marker. O. cornuta showed better performances with respect to A. mellifera. For the field trials, pollinators were introduced in four apple orchards. During apple’s flowering, the BD170 (100 g hl^?l) was sprayed once in two fields, and twice in the others. The pollinators’ efficacy in carrying the BCA from sprayed flowers to the stigmas of newly opened ones at different times after the spray treatment was evaluated. The detection of the BCA was performed by PCR analysis. The percentages of positive PCR flower samples were higher in the internal treated areas of the fields with respect to the external untreated ones, but the high colonisation level found in the latter and in the flowers opened in both areas several days after the treatment(s) demonstrated that pollinators can play an important role as secondary carriers.