Effects of Destruxin A on Hemocytes Morphology of Bombyx mori

Destruxin A （DA）, a kind of cyclo-hexadepsipeptide isolated from entomopathogenic fungus, Metarhizium anisopliae, is an inhibitor of insect＇s immunity. But its mechanism has not been clarified yet. In this study, the effects of DA on morphologic changes of in vivo and in vitro hemocytes of silkworm, Bombyx mori, were investigated by means of inverted phase contrast microscopy （IPCM）, fluorescence microscopy （FCM） and environmental scanning electron microscopy （ESEM）. The results indicated that DA was cytotoxic to granulohemocytes （GR） and plasmatocytes （PL）. The LC 50 values of DA against in vitro GR and PL of silkworm were 68.77 and 84.11 μg mL-1, respectively. However, the hemocytes in vivo were more susceptible to DA, although at the extremely low dose of 10 μL of 12.5 μg mL-1 for each insect （i.e., 0.036 μg g-1 body weight, or approximately 0.25 μg mL-1 hemolymph）, DA could induce obviously morphologic alterations of hemocytes in vivo. The results imply that there might be some factors in silkworm＇s hemolymph, which influence the interaction of DA and hemocytes.

The production relationship of destruxins and blastospores of Metarhizium anisopliae with virulence against Plutella xylostella

Metarhizium anisopliae as an essential entomopathogenic fungus has been known to produce destruxins （a kind of cyclo-peptidic mycotoxins） and blastospores in submerged culture. Blastospores and destruxins are candidates for in- secticides, but the relations of both productions and the impact factors are unclear yet. In this study, we investigated the effects of inoculums, rotation, dissolved oxygen （DO） on the productions of blastospores and destruxins A and B （DA and DB） in submerged culture of M. anisopliae strain MaQ01. The results indicated that DO levels were regulated by inoculum amounts and rotation speeds, meanwhile, the productions of DA, DB and blastospores were also closely influenced by those factors. Totally, when DO value was more than 40%, the higher productions of destruxins and blastospores were achieved, by contrast, lower than 40% of DO values resulted in lower productions. The regression analysis suggested that the productions of DA, DB and blastospores were positively correlated with the DO levels. Meanwhile, the positive correlations between the productions of DA or DB and blastospores were also found. Briefly, when the rotation is 150 r min-1 and the inoculum is 1.0xl06 spore mL-1, the DA, DB and blastospores achieved the best production of 61.81 mg mL-1, 24.74 mg mL-1 and 5.73x 108 spore mL-1, respectively. In addition, the pathogenicities of blastospores and conidia against Plutella xylostella were bioassayed. The higher mortalities of P. xylostella were totally recorded in blastospore treatments than in conidia treatments, especially in lower dosages and earlier periods. Our research will give some new insights to production of destruxins and blastospores by using M. anisopliae.

4种种子处理剂对菜心安全性及保护作用评价

为评价4种种子处理剂对菜心种子的安全性以及对黄曲条跳甲Phyllotreta striolata(Fabricius)的防治效果和保苗作用,本研究开展了室内、田间安全性试验以及田间保护试验。室内安全性试验结果显示,40%溴酰·噻虫嗪种子处理悬浮剂、600 g/L吡虫啉悬浮种衣剂、18%噻虫胺种子处理悬浮剂、54%吡虫·氟虫腈悬浮种衣剂用量分别低于5120、9600、2880、7040 g(a.i.)/100 kg种子时,对菜心种子发芽和生长无影响。田间安全性及保护作用结果显示,40%溴酰·噻虫嗪种子处理悬浮剂和54%吡虫·氟虫腈悬浮种衣剂保护作用显著,菜心出苗后25 d的株高和鲜重与对照组相比均有增加,且差异显著。结果表明40%溴酰·噻虫嗪种子处理悬浮剂和54%吡虫·氟虫腈悬浮种衣剂对菜心种子具有较好的安全性,且对菜心苗期有良好的保护作用。