Michael Brownbridge

Characterization of Beauveria bassiana and Metarhizium anisopliae isolates for management of tarnished plant bug, Lygus lineolaris (Hemiptera: Miridae)

Selected morphological and physiological characteristics of four Beauveria bassiana (Balsamo) Vuillemin isolates and one Metarhizium anisopliae (Metschnikoff) Sorokin isolate, which are highly pathogenic to Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), were determined. There were significant differences in conidial size, viability, spore production, speed of germination, relative hyphal growth, and temperature sensitivity. Spore viability after incubation for 24h at 20 degrees C ranged from 91.4 to 98.6% for the five isolates tested. Spore production on quarter-strength Sabouraud dextrose agar plus 0.25% (w/v) yeast extract after 10 days incubation at 20 degrees C ranged from 1.6x10(6) to 15.5x10(6)conidia/cm(2). One B. bassiana isolate (ARSEF 1394) produced significantly more conidia than the others. Spore germination was temperature-dependant for both B. bassiana and M. anisopliae. The time required for 50% germination (TG(50)) ranged from 25.0 to 30.9, 14.0 to 16.6, and 14.8 to 18.0h at 15, 22, and 28 degrees C, respectively. Only the M. anisopliae isolate (ARSEF 3540) had significant spore germination at 35 degrees C with a TG(50) of 11.8h. A destructive sampling method was used to measure the relative hyphal growth rate among isolates. Exposure to high temperature (40-50 degrees C) for 10min had a negative effect on conidial viability. The importance of these characteristics in selecting fungal isolates for management of L. lineolaris is discussed.

Pathogenicity of Beauveria bassiana, Metarhizium anisopliae (Deuteromycotina: Hyphomycetes), and other Entomopathogenic Fungi Against Lygus lineolaris (Hemiptera: Miridae)

Abstract The pathogenicity of 32 fungal isolates from the genera of Beauveria, Verticillium, Paecilomyces, Metarhizium, Mariannaea, and Hirsutella to second-instar tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), was tested under laboratory conditions. These isolates originated from various insect hosts and substrates from France, Denmark, Austria, Italy, Turkey, Syria, and the United States. A single exposure concentration (1 × 107 conidia/ml) assay for each isolate was first conducted by immersing the insects in 10 ml of a fungal suspension for 5 s. These were followed by concentration-mortality assays on five of the most pathogenic isolates using four test concentrations ranging from 2 × 104 to 2 × 107 conidia/ml. B. bassiana 726 (Bemisia-passaged GHA strain) was used as a standard for comparison in all of the assays. Among the test isolates, three produced mortality not significantly different from the water control. Mortality ranged from 35 to 98% among the other 29 isolates. The LC50 values of the five most pathogenic isolates ranged from 0.8 to 5.0 × 105 conidia/ml. The LT50 values for these isolates ranged from 6.0 to 6.9, 3.1 to 5.1, and 2.5 to 4.0 d for concentrations of 2 × 105, 2 × 106, and 2 × 107 conidia/ml, respectively. Two strains of B. bassiana (ARSEF 1394, 5665) and one M. anisopliae (ARSEF 3540) were more pathogenic to the nymphs than the standard, having significantly lower LC50 and LT50 values. Our results demonstrated that several genera of entomopathogenic fungi have promise as microbial control agents against L. lineolaris.

Field trials to evaluate effects of Bt-transgenic silage corn expressing the Cry1Ab insecticidal toxin on non-target soil arthropods in northern New England, USA

Traditionally, control of European corn borer (Ostrinia nubilalis) Hübner has been achieved through the use of chemical insecticides. With increasing emphasis on reducing pesticide inputs in agricultural production, alternative management technologies are now being used including transgenic silage corn modified to express Cry1Ab protein toxins derived from Bacillus thuringiensis (Bt) Berliner. The Cry1Ab toxin is expressed by all plant cells and throughout the growing season. Furthermore, the toxins are exuded from corn plant roots into the rhizosphere, raising concerns over possible side-effects on non-target beneficial organisms in the same habitat. In addition, detrivores are exposed to crop residues containing the toxin when incorporated into the soil. The current 2-year study (2003, 2004) evaluated effects of two silage-corn varieties: Pioneer var. 38A25 (Bt-corn expressing the Cry1Ab toxin) and Pioneer var. 38A24 (parent isoline) on species diversity and evenness of carabid beetles and Collembola. Pitfall traps were used to collect surface-dwelling species on a bimonthly schedule from April to October. Soil cores were taken once a month from April to October to sample subterranean species, which were extracted using Berlese funnels. All individuals were recorded and identified where possible to species level for analysis in the Simpson’s D and Shannon–Wiener H’ diversity indices. Evenness was measured using Simpson’s E’, after which dominant species were analyzed in a multivariate ordination analysis. Results showed Bt-corn had no negative effects on any of the organisms analyzed. There was a significant year effect on the abundance of surface-dwelling Collembola and on species diversity of soil-dwelling Collembola. Our findings suggest that crop management practices and/or environmental conditions (e.g., heavy rainfall during the 2004 growing season) had the greatest impact on species diversity and evenness, rather than the crop itself (Bt or isoline).

Screening and bioassay of entomopathogenic fungi for the control of silverleaf whitefly, Bemisia argentifolli

Isolates of Beauveria bassiana (Balsamo) Vuillemin, Paecilomyces farinosus (Holm ex SF Gray) Brown and Smith and Verticillium lecanii (Zimmermann) Viegas were evaluated for their pathogenicity to adults, eggs, first and third instars of silverleaf whitefly, Bemisia argentifolli (Bellows and Perring) (Homoptera: Aleyrodidae). Conidial dilutions were prepared in 0.05% Tween® and leaves treated by immersion in these suspensions. Assessments of nymphal infection were made 2, 3, 5, 7, and 10 days post-treatment. Infection rates in adults and eggs were made 14 days post-treatment. All isolates were pathogenic to nymphs and adults. None of the isolates were pathogenic to eggs. Isolates L3444 (P. farinosus) and L3009 (B. bassiana) were the most pathogenic to first instars and adults with LC50 and LC90 values of 7.3 × 104 and 3.1 × 106 conidia/ml, and 1.3 × 106 and 1.0 × 107 conidia/ml, respectively. Isolate FR20 (V. lecanii) was the most pathogenic to third instars with LC50 and LC90 values of 4.8 × 103 and 7.4 × 105 conidia/ml, respectively. Results imply that L3444 and L3009 are the most efficient isolates, based on their pathogenicity to first instars and adults. Results are discussed in relation to using fungi for management of silverleaf whitefly in greenhouses.RésuméDes isolats de Beauveria bassiana ( Balsamo) Vuillemin, Paecillomyces farinosus (Holm ex SF) Brown et Smith, et Verticillium lecanii (Zimmerman) Viegas ont été évalués quant à leur pathogénicité pour les adultes, les oeufs et les larves du premier et troisième stades de développement de l’aleurode du peuplier, Bemisia argentifolli (Bellows et Perring) (Homoptera: Aleyrodidae). Les dilutions de conidies étaient préparées dans une solution du Tween 0,05%® et les feuilles traitées par immersion dans ces suspensions. La recherche des nymphes infectées fut effectuée 2,3,5, 7 et 10 jours après le traitement. Le taux d’infection chez les adultes et les oeufs était évalué 14 jours après le traitement. Tous les isolats ont montré un pouvoir pathogène vis-à-vis des nymphes et les adultes mais aucun d’entre eux n’a manifesté de pathogénicité à l’égard des oeufs. Les isolats L3444 (P. farinosus) et L3009 (B. bassiana) étaient les plus pathogènes vis-à-vis des premiers stades de développement et des adultes. A la CL50 et CL90, les concentrations respectives étaient de 7,3 × 104 et de 3,1 × 106 conidies / ml pour les premiers stades, et de 1,3 × 106 et de 1,0 × 107 conidies / ml pour les adultes. L’isolat FR20 (V. lecanii) fut le plus effectif pour nymphes du 3ème stade de développement avec des valeurs respectives de la CL50 et CL90 équivalentes à 4,8 × 103 et 7,4 × 105 conidies / ml. Les résultats suggèrent que, compte tenu de leur pathogénicité vis-à-vis des premiers stades et des adultes, les isolats L3444 et L3009 sont les plus efficaces. Les résultats discutent aussi de l’utilisation des produits fongiques pour le contrôle de l’aleurode du peuplier argenté dans les serres.

Prospects for Mycopathogens in Thrips Management

With the need to reduce reliance on chemical pesticides, there is increasing interest in the exploitation of biological control agents for use in integrated pest management strategies. Of the biocontrol options considered for thrips, entomopathogenic fungi are particularly attractive candidates. The incidence of entomogenous fungi in thrips populations, and the efficacy of certain species against thrips in laboratory and greenhouse trials is documented. These data indicate the great potential Hyphomycete fungi have for use as mycoinsecticides in thrips suppression programs but highlight the lack of experimental work specifically directed toward their proper use. Steps necessary to develop fungal agents for thrips management are addressed in light of investigations on thrips and other insect pests, and recent advances in fungal technologies. Future research should aim to develop a better understanding of the complex interrelationships between the pest, pathogen and the environment. The role of molecular biology in the advancement of mycopathogens as practical control agents is briefly discussed.

Effect of Temperature and Host Life Stage on Efficacy of Soil Entomopathogens Against the Swede Midge (Diptera: Cecidomyiidae)

ABSTRACT The Swede midge, Contarinia nasturtii Kieffer, is an economically significant pest of cruciferous crops in Canada and the northeastern United States. The effect of temperature on the virulence of three entomopathogenic nematode species, Heterorhabditis bacteriophora, Steinernema carpocapsae, and Steinernema feltiae, the entomopathogenic fungus Metarhizium brunneum, and a H. bacteriophora+M. brunneum combination treatment to C. nasturtii larvae, pupae, and cocoons was investigated. In the laboratory, all three nematode species successfully reproduced inside C. nasturtii larvae: H. bacteriophora produced the highest number of infective juveniles per larva, followed by S. carpocapsae and S. feltiae. H. bacteriophora and the H. bacteriophora+M. brunneum combination treatment generally caused the highest mortality levels to all C. nasturtii life stages at 20°C and 25°C, whereas S. feltiae caused the highest mortality to larvae and pupae at 16°C. No nematode species caused significant mortality when applied in foliar treatments to the infested host plant meristem and, in spite of high mortality, an antagonistic interaction was observed in the H. bacteriophora+M. brunneum combination treatment when compared with expected mortality. In trials conducted in broccoli fields in Elora, Ontario, M. brunneum suppressed adult emergence of C. nasturtii from infested soil in 2012 and all nematode treatments successfully suppressed adult emergence in 2013; however, no significant effects were observed in field trials conducted in Baden, Ontario.