UVM Theses and Dissertations
Format:
Print
Author:
El Damir, Mohammed
Dept./Program:
Plant and Soil Science
Year:
2005
Degree:
PhD
Abstract:
Sunn Pest, Eurygaster integriceps Puton, is an important insect pest of wheat and barley in the Near and Middle East. Entomopathogenic fungi are being studied as an alternative to widespread application of synthetic pesticides for Sunn Pest management. The objectives of this study were to 1) test the use of a forewing of the house fly (Musca domestica L.), 1/4 strength sabauroud dextrose agar (SDA Y/4), and dry agar-agar as substrates to assess the effect of relative humidity (RH) (91,95,98 and 100 ± 1%) and temperature (15,20, and 30 ± 1°C) on spore germination of Beauveria bassiana 5672 and Metarhizium anisopliae 1080 isolates at 24, 48 and 72 h post exposure; 2) evaluate spore germination, virulence against a surrogate host [the western flower thrips, Frankliniella occidentalis (Pergande)] and spore production capabilities at different temperature and RH combinations on 6 single spore isolates newly obtained from each 5672 and 1080; and 3) evaluate conidial production of two isolates of B. bassiana (5672 and CA-44) and one M. anisopliae (500B) using corn, wheat, and millet and three water volumes (substrate: water) (1:0.5), (1:1) and (1:1.5). In this study, we found that similar influences of temperature and RH were observed when conidial germination of 5672 and 1080 was tested on SDAY/4 and fly forewing, whereas little or no germination occurred with agar- agar as a substrate. Conidial germination occurred at temperatures of 15 -30°C and >̲95% RH and temperatures of 20-30°C and >95% RH for B. bassiana 5672 and M. anisoplia 1080, respectively. We conclude that the SDAY/4 medium triggered the conidial germination of these fungi similar to the house fly forewing cuticle and that SDAY/4 is a substitute substute of cuticle when examining the influence of temperature and RH on conidial germination.
At all RH and temperatures tested, some single spore isolates from 5672 and 1080 germinated higher than their corresponding multi spore isolate. At 95% RH, the conidial germination was poor and only occurred at 20°C for two single spore isolates (5672-4 and 5672-5) as well as for the multispore isolates 5672 and 1080. Metarhizium anisoplia isolates were more virulent against western flower thrips than B. bassiana isolates tested. At 100% RH, mortality of western flower thrips was higher than the mortality at other %RH levels tested. No conidial production was found at <95% RH. In the mass production study, we found that M. anisopliae tended to produce more conidia than the B. bassiana isolates. Conidial production of M. anisopliae increased up to 8.6 and 2.9 times between the lowest and highest water volume ratio on corn and millet, respectively. Wheat tended to produce more conidia depending on the water volume used, while only slight increases were observed for 5672. Although there were exceptions, in general, we found that conidial production was positively influenced by increased water ratio, particularly for M. anisopliae (500B). Depending on the combination of isolate growing media and water volume, differences up to 240 times were observed. These differences can have a dramatic effect on the economical production of entomopathogenic fungi for field application. Our results provide useful information for the selection, prediction, development and mass production of entomopathogenic fungi for targeting Sunn Pest in their overwintering sites.
At all RH and temperatures tested, some single spore isolates from 5672 and 1080 germinated higher than their corresponding multi spore isolate. At 95% RH, the conidial germination was poor and only occurred at 20°C for two single spore isolates (5672-4 and 5672-5) as well as for the multispore isolates 5672 and 1080. Metarhizium anisoplia isolates were more virulent against western flower thrips than B. bassiana isolates tested. At 100% RH, mortality of western flower thrips was higher than the mortality at other %RH levels tested. No conidial production was found at <95% RH. In the mass production study, we found that M. anisopliae tended to produce more conidia than the B. bassiana isolates. Conidial production of M. anisopliae increased up to 8.6 and 2.9 times between the lowest and highest water volume ratio on corn and millet, respectively. Wheat tended to produce more conidia depending on the water volume used, while only slight increases were observed for 5672. Although there were exceptions, in general, we found that conidial production was positively influenced by increased water ratio, particularly for M. anisopliae (500B). Depending on the combination of isolate growing media and water volume, differences up to 240 times were observed. These differences can have a dramatic effect on the economical production of entomopathogenic fungi for field application. Our results provide useful information for the selection, prediction, development and mass production of entomopathogenic fungi for targeting Sunn Pest in their overwintering sites.