Location: Emerging Pests and Pathogens Research2013 Annual Report
1a. Objectives (from AD-416):
Develop the potential of entomopathogenic fungi to manage pear thrips, western flower thrips and other major insect pests with soil-dwelling stages, and to encourage the implementation of fungus-based biocontrol methods as part of total IPM approaches for use greenhouse and forest environments against these pests.
1b. Approach (from AD-416):
Utilize entomopathogenic fungi from the University of Vermont (UVM) collection, the ARS Collection of Entomopathogenic Fungal Cultures (ARSEF; Ithaca, NY), and newly isolated strains from greenhouse and field studies to develop improved methods for the use of these fungi in practical programs for the integrated pesticidal and biological control of soil-dwelling stages of western flower thrips and other major insect pests in greenhouses as well as of pear thrips affecting sugar maple trees. The isolation and preservation of new fungal germplasm and co-deposition of old and new UVM isolates in ARSEF remain a major activity. Development of new or improved means and formulations to deliver fungal entomopathogens to control soil-dwelling stages of thrips and other insects in greenhouses is a major concern. Improving the ability of fungal control agents to resist drought and high temperatures with a balanced set of modified formulations and applications approaches is critically important.
3. Progress Report:
Pear Thrips Population Assessment. During the summer of 2012, moderate to heavy damage from pear thrips (75 – 80% defoliation) was observed on sugar maple trees in some areas. This correlated with the relatively high thrips populations based on emergence from soil samples (an average of 4 thrips per sample) taken in November 2011. High temperatures in the spring of 2012 resulted in early thrips emergence from the soil. This allowed the thrips to enter the buds and provided an extended period of time in which damage occurred. This pattern has been observed in past years. Pear thrips population levels in sample sites in Vermont, western New Hampshire, and eastern New York taken in November 2012 were low to moderate, averaging less than 1 thrips per sample. This is likely a result of the unusually hot and dry conditions in the fall of 2012. Pear thrips overwinter in the upper layers of forest soil and survival may be reduced as a result of these conditions. In addition, temperatures in the spring of 2013 encouraged rapid leaf expansion so thrips feeding in the unopened buds was minimized and damage was limited. These results demonstrate that soil sampling is an effective means of forecasting pear thrips damage when coupled with spring temperatures and tree/leaf phenology. Preservation of Fungal Natural Resources. A total of 73 fungal isolates were sent to the USDA ARS National Collection of Entomopathogenic Fungi for permanent storage. The fungi were isolated from European fruit lecanium, Parthenolecanium corni; hemlock woolly adelgid, Adelges tsugae; and ants from Vermont, Rhode Island, New Mexico, Arizona, and Texas. This adds to the existing collection of potentially potent insect-killing fungi ready for further assessment and development into biopesticides. The following species, all of which appeared to have insecticidal capabilities were transferred into the national collection (numbers in parentheses indicate number of different isolates transferred): Beauveria sp. (4); Lecanicillium sp. (21); Aspergillus sp. (3); Penicillium sp. (3); Fusarium sp. (18); Alternaria sp. (2); Cladosporium sp. (1); Colletotrichum sp. (1); Rhinocladiella sp. (1); Epicoccum sp. (1); Yeast cells (4); Not identified, but appears to be entomopathogenic (14). Advancing the Potential of Fungi for Crop Protection. Two strains of Beauveria bassiana from the UVM Worldwide Collection of Entomopathogenic Fungi were selected for combination to create isolates with superior mycoinsecticidal qualities through nuclear hybridization. One strain, ERL-1744 (#9587 ARS USDA), was isolated from western flower thrips (Frankliniella occidentalis, WFT) and demonstrates a high level of virulence and the capacity to grow rapidly. The second strain, ERL-1578 (#9297 ARS USDA), was isolated from western corn rootworm, Diabrotica virgifera, and has good thermoresistance but comparatively low insecticidal activity against thrips. Wall lysis of blastospores to isolate the protoplasts was carried out using a complex of commercially available enzymes from Trichoderma harzianum at two concentrations, 0.5 and 1% with 1M of sucrose. Conjugation, i.e., transfer of genetic material between cells of the two selected isolates, was achieved by mixing blastospores of both isolates in polyethylene glycol (PEG) and centrifuging at 3000 rev/min for 15 min at 15°C. The solution was plated from which 20 new isolates were created, 10 per enzyme concentration. Replicated tests of these new isolates and the original two strains were conducted to compare conidial productivity, insecticidal activity to WFT and thermoresistance. All of these are critical characteristics for a mycopesticide. Four of the 20 new strains (GA-11, GA-16, GA-19 and GA-21) produced significantly more conidia than the original isolates when grown on millet. Insecticidal activity of the 20 strains was tested against second instar WFT. It was determined that WFT mortality 6 d after treatment was around 50% or more for six of the new isolates, which was as good or better than ERL-1744. The faster a fungus kills its host, the less plant damage occurs. After 9 d, mortality rates of 80-90% were observed for these six isolates, which was comparable to ERL-1744. Three of the new isolates (GA-11, GA-13, and GA-19) exhibited greater thermoresistance to exposure to 45°C for 2 hr than either of the original strains. This enhances its tolerance to adverse storage conditions and improves its efficacy in field or greenhouse crops under a range of environmental conditions.