Assessments of the microbial biocontrol potential of novel strains of Beauveria bassiana s.l. against greenhouse shore fly, Scatella tenuicosta: virulence, mass production capacity, and effects on shore fly reproduction

Authors: UGINE, TODD - Cornell University; Wraight, Stephen; SANDERSON, JOHN - Cornell University

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2013
Publication Date: 4/1/2013
Citation: Ugine, T.A., Wraight, S.P., Sanderson, J.P. 2013. Assessments of the microbial biocontrol potential of novel strains of Beauveria bassiana s.l. against greenhouse shore fly, Scatella tenuicosta: virulence, mass production capacity, and effects on shore fly reproduction. Biological Control. 65:348-356.

Interpretive Summary: The shore fly Scatella tenuicosta is viewed primarily as a nuisance pest in greenhouses. Larvae and adults feed on algae that grow on wet greenhouse surfaces. Because these insects do not directly damage plants, their control by means other than broad-spectrum chemical insecticides has not been extensively investigated. Recent studies have indicated, however, that these insects are potentially important mechanical (contact) vectors of many plant pathogens, and there is increasing demand for additional control methods. Objectives of the current research were to assess the biological control potential of new strains of the insect pathogenic fungus Beauveria bassiana recently isolated from shore flies and partially characterized in a previous study. A series of laboratory tests revealed that the new strains are substantially more virulent than currently registered strains of this fungus and have excellent mass-production potential; however, reproductive capacity of infected flies (number and viability of eggs) was not affected until the fourth day after treatment (the day before death due to infection). As shore flies begin laying eggs 24 hours after emergence, these results indicate less potential for these agents to control this pest than initially believed, and underscore the need to integrate these fungal pathogens into IPM systems, especially in combination with agents effective against the immature stages (larvae and/or pupae) of shore flies.

Technical Abstract: The biological control potential of three strains of Beauveria bassiana s.l. originally isolated from the shore fly Scatella ternuicosta was assessed in a series of laboratory bioassays. Comparisons were made to two commercially available strains of B. bassiana. Two of the new strains proved 27–67 times more virulent than the commercial strains in terms of LC50 and were more rapidly lethal. B. bassiana s.l. strain ST1 exhibited a mass production capacity comparable to commercial stain GHA of B. bassiana, producing 2.8 x 10**12 conidia/kg barley-based solid substrate in ventilated mushroom spawn bags. The shore fly strains of Beauveria sporulated on a higher percentage of killed adult flies and produced substantially greater numbers of conidia per cadaver than the commercial strains, indicating that these pathogens are well adapted to this host. Female flies treated with strain ST1 survived for only 5 days, with longevity being reduced by 8-10 days compared to control insects. This reduction in survival had a large impact on total lifetime egg production, reducing it by 78–88 percent. However, fungal growth within infected female shore flies had no effect on egg production or egg viability until the day before the flies succumbed to mycosis (day 4 post inoculation). As a consequence, the intrinsic rate of shore fly population increase and population doubling time were little affected by fungal infection. These findings underscore the challenges involved with use of slow-acting pathogens for control of highly fecund greenhouse pests and the fundamental necessity of integrating these agents into integrated pest management systems.