| In the present study, non-woven fabric bands impregnated with Beauveria bassiana, an important entomogenous fungus, was used in different ways in Maanshan Forest Farm, Southern Anhui, to better control the pine sawyer, Monochamus alternates, an important vector of the pine wood nematode, Bursaphelenchus zylophilus.Through UV mutation, comparison of extracellular proteases production and sporulation, and Bioassay of virulence on the sawyer, RCEF16, a highly virulent and resistant to UV, was obtained. The conidia of B. bassiana on the bands made from the strain survived longer in forests.Field trail included 3 application ways: successive one release for 3 years, once release in one year and 2 releases of half dose in one year. As compared to either population size or mortality of pines in the control pine plantation, those of the 3 treatments decreased significantly, and among them, successive one releases for 3 years resulted in the lowest sawyer population and lowest tree mortality, although the differences between the treatments were not significant. In addition, the B. bassiana inoculum in soil in this treatment survived the longest.An trapping test in a pine plantation with some attractants showed that all trapped adult sawyers from the treated areas died more than from the control area, with infection at around 20%, suggesting that the release of the fungus increased significantly the chance of the infection. In a cage test, mortality and the infection rates of the sawyers in the cages of all the treated areas were significantly higher than in the control area. In addition, the sawyer cadavers infected by B. bassiana were found and collected in all the treated areas. The cadaver numbers of the treatments were not significantly different although they were all significantly higher than that of the control. All these indicated the band application in the pine plantations did suppressed the pine sawyers substantially.Esterase isozyme profiles were tested for the released isolate and the isolates resulted from the collected cadavers were compared. They could be divided into 3 groups. Group 1 included No. 16, the released isolate and those isolates from cadaver No 1-6, group 2 included the isolate from cadaver 7, and Group 3 included those from cadaver 8 and 9. In group 1, the isolates had very close isozyme profiles, and they accounted for 66.7% of allthe isolates from the cadavers collected, indicating that the infection of the sawyers were caused mostly by the isolate released in the same year.At the end of the experiment, the rates of dead trees, numbers of oviposition scar, invasion holes and larvae in pine trees were investigated finally. The result showed that all these estimates were not significantly different between the treatments, but significantly lower than those of the control. Among the treatments, the estimates of the treatment of successive one release for 3 years were the lowest, followed by those of 2 releases of half dose in one year. The ratio of oviposition scars to invasion holes of the treatment of successive one release for 3 years was the highest, suggesting the poorest invasion success and successful suppression of the sawyer by the fungus. The ratios of invasion holes to larvae of all the treatments were higher than that of the control, suggesting higher mortality of the larvae after entrance into the trees by mortality factors including the fungus. In consideration of ail the previous results, the release of lower dose and higher frequency contributed to survival of the fungus and sustainable control of the pine sawyer.Among the larvae of the sawyers treated with different isolates of B. bassiana, more deaths, lower pupation rate, poorer emergence and shortened emergence time occurred. Many did not complete their life cycle.Different exposure sites onto the fungal bands on the sawyers were tested for infection. The infection rose and medium lethal time declined in an order of antenna, mouth part, leg and abdomen.Virulence of different entomogenous fungi... |
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