Post introductory risk assessment studies on Zygogramma bicolorata (Coleoptera: Chrysomelidae), a classical biological control agent of Parthenium hysterophorus (Asteraceae) in India

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), a biological control agent of Parthenium hysterophorus L. (Asteraceae), was feeding on leaves of Helianthus annuus in India, raising concerns of its host range. Based on the age grading technique, it was shown that the majority of Z. bicolorata on sunflower plants at any time were reproductively immature. This establishes that Z. bicolorata does not pose any risk to sunflower in India.     

Rearing the Mexican beetle Zygogramma bicolorata (Chrysomelidae: Coleoptera) on a semi-synthetic diet

A semi-synthetic diet utilising parthenium leaf powder was evaluated for rearing the Mexican beetle Zygogramma bicolorata Pallister under in vitro conditions at 26±1°C, 65% RH. Significant differences were observed in the biological parameters of the beetle viz., the grub survival (54.3%), pupation (47.2%), fecundity (54.6/day) and total developmental period (37.7 days), when reared on the semi-synthetic diet compared to those when reared on natural parthenium leaves (91.5, 85.5, 74.8 and 29.8, respectively). The feasibility of utilising the semi-synthetic diet for mass production of the beetle is discussed.     

Age-related Feeding by the Parthenium Beetle Zygogramma bicolorata on Sunflower and its Effect on Survival and Reproduction

Freshly emerged adults of Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), introduced for biological control trials against the noxious weed Parthenium hysterophorus , were seen to feed and lay eggs on sunflower leaves under confined conditions in the laboratory. The time taken for initiation of feeding was found to be positively correlated with adult age, while survival after feeding on the crop was negatively correlated. However, adults that had fed on sunflower even for 1 day on P. hysterophorus were incapable of ovipositing, and young larvae could not feed on the crop. Under field conditions, newly emerged adults were only attracted to feed on plants that were treated either with a crude aqueous extract of leaves or pollen grains of P. hysterophorus , indicating that the chances of Z. bicolorata becoming a pest of sunflower are negligible. Age-related Feeding by the Parthenium Beetle Zygogramma bicolorata on Sunflower and its EVect on Survival and Reproduction     

银胶菊(Parthenium hysterophorus)中抗TMV活性成分的分离及活性测定

采用活性跟踪法从银胶菊中分离获得抗病毒活性物质,经质谱和核磁共振分析,确定该物质为小白菊内酯.采用半叶枯斑法和叶圆盘法测定了其对烟草花叶病毒(Tobacco mosaic virus,TMV)的抑制效果,结果表明:0.2 mg/mL的小白菊内酯在混合接种和药液浸泡两种处理中均表现出较好的体外抑制TMV活性,其抑制率分别为69.0%和72.1%;在离体条件下对烟草叶圆盘中的烟草花叶病毒复制也具有良好的抑制效果,抑制率为72.3%.     

Larval parasitism by native insects on the introduced stem-galling moth Epiblema strenuana Walker (Lepidoptera: Tortricidae) and its implications for biological control of Parthenium hysterophorus (Asteraceae)

Abstract  The significance of natural enemies in the failure or reduced effectiveness of weed biological control agents remains largely unknown. Larval and pupal parasitism by native insects in the stem-galling moth Epiblema strenuana was studied in north Queensland, 4 (1986–87) and 16 (1998–99) years after its introduction as a biological-control agent for Parthenium hysterophorus . Specific questions answered in this study are: (i) Has parasitism increased over the years?; (ii) Are the levels of parasitism influenced by the host plant phenology?; and (iii) What are the potential implications of current parasitism levels for the effectiveness of E. strenuana ? There was no increase in the parasitoid species assemblage over the years. In 1986–87, Antrocephalus sp. and Bracon sp. were the most predominant species. The combined larval and pupal parasitism was low (2.6%) and there was no seasonal difference in the parasitism levels. In 1998–99 Bracon sp. was the most prevalent species. Parasitism by Bracon sp. in 1998–99 was several times higher (22.9%) than the combined larval and pupal parasitism in 1986–87. However, parasitism by Bracon sp. remained low (6.5–8.2%) at the beginning of the parthenium-growing season, and reached peak levels (49–53%) only at the end of the season. Parasitism by Bracon sp. was also significantly lower in rosettes (7.2%) than in flowering plants (22.8%). Galling can have a negative impact on the weed only when initiated at the rosette stage. In 1998–99 lower levels of parasitism early in the season when most plants are in the rosette stage suggest that the impact of parasitism on the effectiveness of the gall insect may not be significant.     

The RustPuccinia abruptavar.partheniicola,a Potential Biocontrol Agent of Parthenium Weed: Environmental Requirements for Disease Progress

The rust fungusPuccinia abruptavar.partheniicola,a potential biological control agent of parthenium weed (Parthenium hysterophorus), was evaluated under controlled environmental conditions. A range of spore germination temperatures as well as dew period durations and temperatures were investigated to determine some of the environmental requirements for disease establishment and disease progress. Plants were inoculated with urediniospores and exposed to dew periods between 3 to 12 h at temperatures of 10, 15, or 20°C. For disease expression, the inoculated plants were then grown in a glasshouse at one of two temperature regimes (30/26°C or 18/13°C; day/night). Urediniospores germinated best at 12 ± 1°C, with lower germination rates at 5°C or above 20°C. No infection occurred when the plants were exposed to dew periods of ≤3 h, regardless of the incubation temperature. The disease progressed most rapidly when plants were inoculated and incubated for a dew period of at least 12 h at a temperature of 15 ± 1°C. The disease progressed most slowly following inoculation at dew periods of 6 h or less. Disease progress was more rapid when the plants were exposed to a cool-temperature regime (18/13°C) than when exposed to a warm-temperature regime (30/26°C). This suggests that good infection of parthenium weed could be obtained when the urediniospores arrive on the plants during the afternoon in the cooler months of the central Queensland autumn when relatively long dew periods are expected.     

Biology and Host Specificity of the Stem Galling Weevil Conotrachelus albocinereus Fiedler (Col.: Curculionidae), a Biocontrol Agent for Parthenium Weed Parthenium hysterophorus L. (Asteraceae) in Queensland, Australia

The stem-galling weevil Conotrachelus albocinereus Fiedler has been investigated as a potential biological control agent against parthenium weed ( Parthenium hysterophorus L.) in Australia. Adults were tested in multiple-choice feeding and oviposition tests on 56 plant species in 51 genera. No feeding or oviposition was recorded on any non-target plant except annual ragweed ( Ambrosia artemisiifolia L.), a closely related weed. Field releases of the weevil in Queensland, Australia, commenced in 1995 and establishment has been recorded at several sites.     

Seasonal biology and abundance of Psyllaephagus pistaciae,a biocontrol agent of the common pistachio psylla Agonoscena pistaciae

The solitary endoparasitoid Psyllaephagus pistaciae Ferrière (Hymenoptera: Encyrtidae), is the most widely distributed biological control agent of the common pistachio psyllid, Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Psylloidea), in Iran. The pupation and overwintering sites of diapausing parasitoids and the psyllid were studied for 2 years using emergence traps in pistachio orchards in Rafsanjan, Iran. The psyllid mummies containing the overwintering parasitoid adhered to pistachio leaves and were carried on these leaves away from the tree when they latter senesced. The present results verified that plant litter which included dried grasses and old pistachio leaves tended to support a greater population of adult winter-form psyllid and psyllid mummies during the winter through early spring than other options examined. Adult parasitoids appeared in the field in early April, about 30 days after the emergence of adult psyllids, but almost at the same time as the hatching of the first generation psyllid nymphs in early April. Rates of parasitism of CPP were generally low throughout most of the year, ranging from 1 to 5%, but rose in late autumn to about 11%. Results suggest that the density of P. pistaciae is not great enough to keep pace with the psyllid populations in these orchards. They explain why growers consider it necessary to apply pesticides for this pest. However, this parasitoid undoubtedly does play an important role in the natural control of A. pistaciae late in the growing season, particularly in non-sprayed orchards. Conservation of these natural enemies should be one of the objectives in the development of sustainable pest management programs.     

Production of Trichoderma micropropagules as a biocontrol agent in static liquid culture conditions by using an integrated bioreactor system

ABSTRACT

In this study, we optimised the conditions for the production of micropropagules of Trichoderma harzianum EGE-K38 in static liquid culture in Modified Czapec Medium (MCM) containing 8?g/L glucose in an integrated tray bioreactor system designed by our research group. Incubation temperature, air flow rate, inoculum spore concentration, inoculation size, medium volume and the use of spores or agar plugs containing mycelia as inoculum were individually studied as one factor at a time. The maximum micropropagule count was 5.2?±?0.2?×?10^9?cfu/mL and dry cell weight was 17?±?2?g/L. For the subsequent drying processes, the maximum drying yield percentage ((viable micropropagule counts after drying/viable cells before drying)*100) after drying of micropropagules was 23.30% (cfu/cfu). Results obtained from our integrated tray bioreactor system showed that static liquid culture fermentation offers potential for industrial scale fungal BCAs production.     

Colonization of Sclerotinia sclerotiorum sclerotia by a biocontrol isolate of Trichoderma harzianum,and effects on myceliogenic germination

Sclerotia of Sclerotinia sclerotiorum were incubated on cultures of Trichoderma harzianum. Myceliogenic germination decreased by 50% within 1 day and continued to decrease over time. Quantitative PCR showed a decrease in Sclerotinia DNA for older sclerotia, but not fresh sclerotia. Trichoderma DNA increased and persisted inside older sclerotia but not fresh sclerotia.     

Increasing survival and efficacy of a bacterial biocontrol agent of fire blight of rosaceous plants by means of osmoadaptation

The efficacy of Pseudomonas fluorescens EPS62e in the biocontrol of Erwinia amylovora, the causal agent of fire blight of apple and pear, depends on the colonization of plant surfaces after spray application. A procedure to increase cell survival in the phyllosphere was developed consisting of saline stress and osmolyte amendment to the growth medium during inoculum preparation. Hyperosmotic stress induced the synthesis of the osmolytes trehalose, N-acetylglutaminylglutamine amide and glucosyl-glycerol, but decreasing growth rate. Amendment of the growth medium with glycine betaine increased growth rate and cell yield and promoted its intracellular accumulation. Under controlled environment conditions, osmoadaptation increased by 10- to 100-fold cell survival to desiccation and to low relative humidity conditions on plant surfaces, in comparison with the nonosmoadapted controls. In the field, cell survival increased 100-1000 times in immature fruit upon osmoadaptation but was not significantly affected in flowers where active colonization occurs. The efficacy in the control of fire blight infections was increased 30-50% upon osmoadaptation on immature fruits but was not affected in blossoms. The method of osmoadaptation may be useful for improving the fitness and efficacy of biological control agents of phyllosphere pathogens under limiting humidity conditions.     

Evaluation of fungal culture filtrate containing chitinase as a biocontrol agent against Helicoverpa armigera

AIMS: To evaluate the biocontrol efficacy of culture filtrate containing chitinase from Trichoderma harzianum against Heliothis. METHODS AND RESULTS: T. harzianum was cultured by submerged fermentation using colloidal chitin as sole carbon source. The ability of the culture filtrate to hydrolyse colloidal chitin indicated the presence of chitinase as one of its components. Biocontrol assay on Heliothis showed that the culture filtrate is a potent antifeedant as it reduced the feeding rate and body weight of the larvae. It reduced the successful pupation and increased larval and pupal mortality in a dosage-dependent manner when applied topically. The highest mortalities (70%) were recorded for groups treated with 2000 U ml(-1) chitinase activity. The percentage of adult emergence was zero for the highest chitinase concentration (2000 U ml(-1)) tried. CONCLUSIONS: The studies showed that the culture filtrate containing chitinase from T. harzianum is capable of negatively affecting the growth and metamorphosis of Heliothis larvae. SIGNIFICANCE AND IMPACT OF THE STUDY: In view of the need for safer and environmentally friendly pest management tools, the present study could help in the development of enzyme-based biopesticides against Heliothis.     

Improving low water activity and desiccation tolerance of the biocontrol agent Pantoea agglomerans CPA-2 by osmotic treatments

AIMS: To study the improvement of tolerance to low water activity (aw) and desiccation during spray drying in Pantoea agglomerans cells subjected to mild osmotic stress during growth. METHODS AND RESULTS: The micro-organism was cultured in an unmodified liquid (control) or in aw-modified media, and viability of these cells was evaluated on unstressed (0.995) and 0.96 aw stressed solid media, in order to check total viability and aw stress tolerance respectively. Significant improvements in viability on unmodified medium were observed with cells grown for 24 h in NaCl 0.98 aw, glycerol 0.98 aw and 0.97 aw and for 48 h in NaCl 0.98 aw and 0.97 aw modified media. Both yield improvements and water stress tolerance were achieved with low aw media. Cells grown for 24 h in NaCl 0.98 aw or for 48 h in NaCl 0.98 aw, 0.97 aw and 0.96 aw, glucose 0.97 aw and glycerol 0.97 aw showed improved aw stress tolerance in comparison with control cells. The best results were obtained with NaCl treatments (0.98 aw and 0.97 aw) which also exhibited better survival rates than control cells during spray-drying process and maintained their efficacy against postharvest fungal pathogens in apples and oranges. CONCLUSIONS: NaCl treatments are very appropriate for improving P. agglomerans low aw tolerance obtaining high production levels and maintaining biocontrol efficacy. SIGNIFICANCE AND IMPACT OF THE STUDY: Improving stress tolerance of biocontrol agents could be an efficient way to obtain consistency and maintain efficacy of biological control under practical conditions.     

Snail predation by larvae of Sepedon scapularis Adams (Diptera: Sciomyzidae), a potential biocontrol agent of snail intermediate hosts of schistosomiasis in South Africa

Malacophagous larvae of the fly Sepedon scapularis Adams were shown experimentally to be effective predators of three species of aquatic pulmonate snails tested as prey: Bulinus africanus (Krauss) an important intermediate host of Schistosoma haematobium (Bilharz), Bulinus tropicus (Krauss) and the invasive species Physa acuta Draparnaud. Survival of S. scapularis larvae from instar to instar was negatively affected by the size of prey snails, since larvae tended to be asphyxiated by the mucous secretions of the snails, or by the larval hydrofuge hairs becoming entangled in snail faeces. In experiments to test the choice of S.scapularis larvae for different species and sizes of snails, B.africanus was significantly disfavoured compared with the other two snail species. Small snails (< 3 mm) were more frequently killed by all three larval instars of S.scapularis. First instars killed few, if any, large snails (> 7 mm), whereas second and third instars preyed effectively on all sizes of snails. Third instars killed significantly more snails than younger instars. For larvae offered only one species of snail as prey, the mean total number of snails killed per larva during its entire development was 49 B.africanus, 45 B.tropicus or 34 P.acuta. It is concluded that S.scapularis is potentially useful as a biological control agent for use against indigenous Bulinus and exotic Physa snails.     

Survival of Beauveria brongniartii in the soil after application as a biocontrol agent against the European cockchafer Melolontha melolontha

The survival of the entomopathogenic fungusBeauveria brongniartii and its efficacyagainst the European cockchafer, Melolontha melolontha, was examined over 16months after application as a biologicalcontrol agent in different soil types inSwitzerland. In the absence of M. melolontha,the reduction of the number of the CFU in thesoil was nearly 90%. In soils with highorganic content and increased catalase activitythe decline in the CFU density of B.brongniartii was more pronounced. At siteswhere M. melolontha was present, thesurvival was significantly longer. Theapplication of B. brongniartii resultedin a maximal infection rate of 75% in the M. melolontha population. The number of CFU ofB. brongniartii in the soil started todecrease only when the M. melolonthapopulation was reduced during the epizootic(reduction of 46% on average). The rapiddecrease of the fungus in the absence of thehost gives further evidence of the highspecificity of the fungus and that asaprophytic multiplication without the host isunlikely. The fungus was isolated on aselective medium as well as by baiting withGalleria mellonella. The latter methoddid not reveal the significant differencesmentioned above, which leads to the assumptionthat the two methods may select for differentfungal strains.     

Isolation and characterization of microsatellite loci from Lochmaea suturalis, the heather beetle (Coleoptera: Chrysomelidae), a pest in Europe and a biocontrol agent in New Zealand

The heather beetle Lochmaea suturalis which is native to northwest Europe has been released as a biocontrol agent for heather in New Zealand. We have isolated and optimized eight microsatellite loci from New Zealand beetles. These loci provide markers with high polymorphism ranging from four to 20 alleles per locus. Observed heterozygosity averaged 0.631 per locus. These results suggest the markers are useful for population studies that will contribute to assessment of L. suturalis as a biocontrol agent.