埃玛菌素对小菜蛾幼虫的毒力及其对子代种群增长的影响

研究了不同温度下埃玛菌素（emamectin）对小菜蛾Plutella xylostella幼虫的毒力,并用生命表法研究了25℃下埃玛菌素亚致死剂量LC₃₀）处理小菜蛾3龄初期幼虫后对其子代的影响。结果表明,埃玛菌素为典型的正温度系数药剂,对小菜蛾幼虫的触杀毒力在温度16～31℃间提高了10倍左右,口服毒力在相同温度范围内提高1 000倍左右,显示了埃玛菌素对该虫极高的口服毒力。25℃下埃玛菌素亚致死剂量处理当代幼虫后,对其子代的存活和繁殖均有明显影响,处理组和对照组子代的世代存活率分别为3.7%和35.5%,平均产卵量分别为92.4和148.3,种群趋势指数分别为1.8和27.4,净增殖率（R₀）分别为3.66和33.81,内禀增长力（r_m）分别为0.0665和0.0978。     

茚虫威和六伏隆对小菜蛾卵、幼虫和成虫的药效（英文）

化学防治是世界各地防治小菜蛾Plutella xylostella (L.)的主要方法。选择对小菜蛾各发育阶段高效的杀虫剂有助于很好地控制这一害虫。本研究用浸叶法测定了茚虫威和六伏隆对小菜蛾卵、幼虫和成虫的毒性。茚虫威和六伏隆对小菜蛾卵的LC₅₀值分别为201.40 和 37.32 mg/L。茚虫威和六伏隆对3龄幼虫也有很好的毒性（茚虫威的LC₅₀ 为 4.82 mg/L; 六伏隆的LC₅₀ 为1.48 mg/L)。对成虫的毒性结果表明, 这两种杀虫剂对成虫均没有理想的毒性（茚虫威的LC₅₀ 为845.20 mg/L; 六伏隆的LC₅₀ 为3 438 mg/L)。根据计算的LC₅₀值, 六伏隆对小菜蛾卵和幼虫的毒性比茚虫威高, 但是茚虫威对成虫的毒性更高。     

球形芽孢杆菌对致倦库蚊的后致死作用

研究了球形芽孢杆菌Bacillus sphaericus C3-41菌株对致倦库蚊Culex quinquefasciatus幼虫的毒力及其后致死作用。生物测定表明,该菌株对目标蚊幼虫具有很高的毒力,其丙酮粉剂对3～4龄幼虫48 h的半致死浓度(LC₅₀)为(6.92±0.22) μg/L。用不同亚致死浓度处理2～3龄致倦库蚊幼虫,存活幼虫在后期发育中存在明显的延续死亡和损伤现象,经LC₃₀、LC₅₀、LC₇₀、LC₉₀和LC₉₈剂量的C3.41粉剂处理的致倦库蚊羽化前的总死亡率分别为84%、91%、95%、97%和100%,同时存活的幼虫、蛹和成蚊的发育和行为也受到一定的影响。这种后致死作用随处理浓度的升高而增强,可能同球形芽孢杆菌毒素蛋白对处理期间蚊幼虫中肠上皮细胞造成的损伤相关。     

亚致死剂量阿维菌素和氟虫睛处理小菜蛾对寄生蜂菜蛾绒茧蜂生长发育的影响

分别在小菜蛾体内的菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾2龄幼虫亚致死剂量（＝LC₁₀）的阿维菌素和氟虫睛,研究上述杀虫剂处理对寄主体内菜蛾绒茧蜂结茧率和羽化率的影响。结果表明： 在菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾LC₁₀剂量阿维菌素处理的菜叶后,菜蛾绒茧蜂的结茧率分别下降26.6%,22.8%和5.8%,饲喂小菜蛾LC₁₀剂量氟虫睛处理的菜叶后,菜蛾绒茧蜂的结茧率分别下降76.9%,42.5%和18.5%。上述阿维菌素处理对菜蛾绒茧蜂成虫羽化率影响不显著,但上述氟虫睛处理可显著抑制菜蛾绒茧蜂成虫羽化率,在菜蛾绒茧蜂处于卵期、早期幼虫和中期幼虫时,饲喂小菜蛾LC₁₀ 剂量氟虫睛处理的菜叶可导致菜蛾绒茧蜂成虫羽化率分别下降53.1%,36.1%和47.8%。结果显示,即便是对寄主小菜蛾幼虫很低的剂量（LC₁₀剂量）也会显著危害小菜蛾幼虫体内的菜蛾绒茧蜂的生长发育。此外,饲喂小菜蛾幼虫亚致死剂量杀虫剂对菜蛾绒茧蜂生长发育的影响与杀虫剂种类及蛾绒茧蜂发育阶段有关。     

根虫瘟霉原始菌株及转寄主菌株在不同培养条件下胞外蛋白酶的诱导表达特性

通过比较根虫瘟霉Zoophthora radicans 3个菌株（原始菌株R₀、转寄主菌株R₁和R₅）在不同培养条件下诱导胞外蛋白酶的差异,发现在含昆虫表皮和明胶的培养基中,均能诱导表达高水平的胞外蛋白酶,而在营养缺乏的MS培养基和营养丰富的萨氏培养基中则胞外蛋白酶的表达水平均很低。37 kD的丝氨酸蛋白酶在任何条件下都能被诱导表达,是各菌株中的保守序列所编码的胞外蛋白酶。46 kD的金属蛋白酶仅能在含明胶的培养基中被诱导表达,而葡萄糖可抑制其表达。在萨氏培养基中,67 kD 的蛋白酶条带在转寄主过程中消失了,而46 kD的金属蛋白酶条带和117 kD的条带随着转寄主传代数增加而明显,表明菌株在转染过程中选择表达了对新寄主具有较高基质特异性的胞外蛋白酶。     

根虫瘟霉不同菌株对小菜蛾幼虫血淋巴酚氧化酶原的激活作用

在对小菜蛾Plutella xylostella幼虫血淋巴酚氧化酶原的存在部位及免疫激活作用特点研究的基础上,比较了根虫瘟霉Zoophthora radicans不同菌株对酚氧化酶原激活系统的免疫激化及防御作用的差异。研究发现, 酚氧化酶原主要位于小菜蛾幼虫血细胞膜及血细胞裂解液中,极少存在于血浆中。在免疫激活剂昆布多糖存在下,分别测得小菜蛾幼虫血细胞碎片、血细胞裂解液和血浆的酚氧化酶活性为26.80 U,16.68 U和2.53 U。酚氧化酶原显著地受血浆和昆布多糖同时存在的激活,但两者单独存在时对酚氧化酶原的激活作用较弱。根虫瘟霉菌丝裂解液对酚氧化酶原有不同程度的激活作用,其激活作用在有血浆存在时显著增强,其酚氧化酶活性可提高2.9～3.4倍。各菌株间对酚氧化酶原的激活作用则以ARSEF1342菌株最强,ARSEF2699和F99101菌株次之,ARSEF1100菌株最弱。被激活的酚氧化酶可粘附于根虫瘟霉菌丝上并能产生黑化反应,各菌株间酚氧化酶粘附于ARSEF1342菌株的能力最强,粘附于ARSEF2699和F99101菌株的次之,粘附于ARSEF1100菌株的最弱。但酚氧化酶粘附于昆布多糖的能力显著强于各虫霉菌株,表明各菌株在一定程度上能逃避寄主的免疫识别;各菌株激活酚氧化酶原及酚氧化酶粘附于菌株强弱,与对小菜蛾毒力呈负相关性,表明高毒力菌株具有易逃避寄主免疫识别的趋向。     

不同寄主来源的根虫瘟霉菌株对小菜蛾幼虫的毒力比较

在不同寄主来源的4株根虫瘟霉Zoophthora radicans对小菜蛾 Plutella xylostella 2龄幼虫的生物测定中,发现源于小菜蛾的菌株ARSEF1100毒力最强,在0.53～319.32/mm²的孢子剂量下,接种后第8 天累计死亡率为2.38%～97.44%,虫尸全部表现典型的虫瘟霉症状;源于叶蝉的ARSEF2699和F99101菌株的同日累计死亡率分别为2.38%～50.00% (剂量为1.56～314.84/mm²孢子)和2.38%～57.89% (剂量为1.84～484.08/mm²的孢子);而源于菜粉蝶的ARSEF1342菌株在3.54～633.0/mm²的孢子剂量下只引发6.52%～13.63%的累计死亡率,后3个菌株致死的小菜蛾幼虫仅部分表现典型症状。所获数据经时间剂量-死亡率模型模拟分析,剂量效应参数依次为ARSEF1100 (1.89) > F99101 (1.48) > ARSEF2699 (1.23) > ARSEF1342 (0.37),相互间差异均达极显著水平。接种后4～8 天内,ARSEF1100的LD₅₀值分别为231.68、113.08、71.41、40.87和35.30/mm²的孢子,其毒力远高于其余3个菌株;ARSEF2699的相应LD₅₀值为1344.43、922.39、555.58、410.06和397.07/mm²的孢子;F99101的LD₅₀值为666.86、451.64、413.82、350.65和332.57/mm²的孢子,而ARSEF1342的毒力太弱难以估计。这些结果表明,ARSEF1100菌株最有希望用于小菜蛾的微生物防治。     

Wolbachia感染对拟澳洲赤眼蜂寿命、生殖力和嗅觉反应的影响

研究了通过共享同一寄主卵,短管赤眼蜂Trichogramma pretiosum体内共生的Wolbachia被水平传递到拟澳洲赤眼蜂T. confusum体内后,Wolbachia对新宿主拟澳洲赤眼蜂的影响。结果表明： Wolbachia的侵染能使拟澳洲赤眼蜂进行不完全的产雌孤雌生殖,增加拟澳洲赤眼蜂子代雌性比例,但却导致了雌蜂寿命缩短和繁殖力降低的生理损失。Wolbachia感染的当代处女蜂及其建立的种群连续5代(F₁～F₅),其子代雌蜂百分率分别为79.17%、76.60%、68.66%、72.58%、68.15%和64.06%,基本上呈现出逐代降低的趋势,并越来越接近对照的63.85%。处女蜂及F₁～F₅代雌蜂的平均寿命分别为4.33、5.50、5.60、6.68、7.32和7.50天,而未感染交配雌蜂寿命为7.59 天;处女蜂及F₁～F₅代雌蜂平均产卵量分别为11.33、70.00、86.41、93.90、102.92和124.38粒/雌,除F₅代外,均显著低于未感染交配雌蜂的产卵量134.81粒/雌。用四臂嗅觉仪测定了Wolbachia新宿主拟澳洲赤眼蜂对寄主小菜蛾的嗅觉反应,结果表明Wolbachia的侵染具轻微干扰拟澳洲赤眼蜂嗅觉反应的负面影响。未感染Wolbachia的拟澳洲赤眼蜂及Wolbachia供体短管赤眼蜂对寄主小菜蛾具较强的嗅觉反应,其雌蜂在小菜蛾腹部鳞片正己烷提取液和小菜蛾卵表正己烷提取液处理区内滞留时间显著或极显著长于对照区。而感染Wolbachia的拟澳洲赤眼蜂F₂代和F₃代雌蜂,尽管在小菜蛾腹部鳞片正己烷提取液处理区内滞留时间比对照区长,但没有达到显著水平;其F₂代雌蜂在小菜蛾卵表正己烷提取液处理区内滞留时间与对照区相比,也没有达到显著水平。随Wolbachia在拟澳洲赤眼蜂种群中垂直感染代数的增加,拟澳洲赤眼蜂对寄主小菜蛾的嗅觉反应恢复正常,在Wolbachia感染后的 F₄～F₆代,雌蜂在两种提取液处理区内的滞留时间均显著或极显著长于对照区。     

绿僵菌素的分离制备及其对蛴螬的毒力

以金龟子绿僵菌金龟子变种Metarhizium anisopliae var. anisopliae菌株MaQ10发酵液为材料,采用萃取、浓缩、制备色谱及重结晶技术,分离纯化出5种绿僵菌素的晶体,经与标准样品以及参考文献相对照,此5种晶体与绿僵菌素A、A2、B、C和E相吻合。进而,采用浸渍法测定了绿僵菌素A和B对大等鳃金龟Exolontha serrulata (Gyllenhall) 和卵圆齿爪鳃金龟Holotrichia ovata Chang 1龄幼虫的触杀毒力。结果表明： 绿僵菌素A和B对大等鳃金龟的触杀活性,在处理后96～120 h内最高,LC₅₀分别为78.1571 mg/L和88.7562 mg/L; 处理浓度为300 mg/L时,LT₅₀分别为13.4159 h和10.5331 h。绿僵菌素A和B对卵圆齿爪鳃金龟的触杀活性,在处理后96 h时最高,LC₅₀分别为66.5308 mg/L和79.4309 mg/L;处理浓度为300 mg/L时,LT₅₀分别是13.6399 h和9.9451 h。     

双翅目昆虫复眼性特化光感受器的比较研究

雄性双翅目昆虫,包括家蝇Musca domestica、丽蝇Calliphora erythrocephala、华虻Tabanus mandarinus和憎黄虻Atylotus miser Szilady,其复眼性特化光感受器中央小网膜细胞R₇的分布从背区扩展到腹区。在雄性家蝇、华虻和憎黄虻复眼中,性特化光感受器中央小网膜细胞R₇的感杆延伸到基底膜,并同中央小网膜细胞R₈的感杆并列排列。但在雄性丽蝇复眼中,性特化光感受器中央小网膜细胞R₇的感杆不延伸到基底膜。在雌性双翅目昆虫复眼中,性特化光感受器中央小网膜细胞R₇仅仅分布在复眼的腹区,其数量比中央小网膜细胞R₈少得多。     

Pathogenicity of Paecilomyces fumosoroseus isolates to diamondback moth, Plutella xylostella: correlation with spore size, germination speed, and attachment to cuticle

Infectivity to larvae of the diamondback moth, Plutella xylostella, was compared among eight Paecilomyces fumosoroseus isolates. Isolate infectivity was assessed for correlation with spore length and germination speed. Four isolates applied to P. xylostella cuticle were also compared for number of spores remaining on the cuticle after washing and for percentage germination after 36 h. Infection of larvae inoculated with the different isolates at an average dosage of 4000 conidia/cm2 ranged from 2 to 47%. The correlation of infectivity with spore length and germination speed in broth was highly significant. Fewer spores of the least infective isolate, ARSEF 1576, attached to larval cuticle compared to spores of the more infective isolates ARSEF 3682, 4461, and 4482 (P < 0.05). After 36 h on larval cuticle, the percentage of spores germinated for isolates 1576 and 3682 was 3 and 95%, respectively. Spores of isolate 1576 were smaller, germinated more slowly, and attached to cuticle in smaller numbers than spores of the more infective isolates. Further research will expand our understanding of the mechanisms of virulence among isolates of P. fumosoroseus.     

Factors influencing the infectivity of isolates of Paecilomyces fumosoroseus against diamondback moth, Plutella xylostella

Paecilomyces fumosoroseus isolate 1576 was isolated from an insect, but is avirulent against larvae of diamondback moth, Plutella xylostella, and several other species. Isolate 1576 grew faster and produced more conidia than isolate 4461 on potato dextrose agar. Pregermination of conidia failed to increase the infectivity of isolate 1576, but the procedure did increase the infectivity of isolates 3682, 4461, and 4482. Isolates 1576 and 4461 were both more infective when moisture was high during incubation of inoculated larvae. Starved Pl. xylostella larvae were more susceptible than fed larvae to isolate 1576 (40 and 10% mortality, respectively), but starved and fed larvae were similar in susceptibility to isolate 4461. These results show that isolate 1576 grows vigorously in aerial culture and is capable of infecting stressed Pl. xylostella larvae. Further tests are needed to characterize its pathogenicity toward its original host or closely related species.     

Susceptibility of the taro beetle, Papuana uninodis (Coleoptera, Scarabaeidae) to two new Bacillus popilliae isolates from Papuana spp

Two morphological types of Bacillus popilliae, causal agent of the milky disease, have been isolated from taro beetles (Papuana spp, Coleoptera: Scarabaeidae). B. popilliae from P. woodlarkiana woodlarkiana (Papua New Guinea) was a type A1 with a small sporangium (4.1 x 1.6 microm) and a large spore (2.1 x 1.4 microm) and parasporal body (1.8 x 1.2 microm) that sometimes overlap. B. popilliae from P. uninodis and P. woodlarkiana laevipennis (Solomon Islands) was a type B2 with a small sporangium (2.8 x 1.3 microm), a small eccentric spore (1.1 x 0.7 microm), and no parasporal body. The infectivity of these B. popilliae to Papuana uninodis larvae was compared with two B. popilliae samples from Popillia japonica in injection tests. The hemolymph of P. uninodis supported the germination and growth of isolates from Papuana and P. japonica. Results were similar in third instars and adults. Highest infection (spores present) and mortality was caused by the isolates from Papuana: mortality reached almost 100% 4 weeks after injection of the B2 type B. popilliae with 40% of larvae and 52% of adults infected. Injection of type A1 caused lower mortality but a similar percentage infected. Of two A1 B. popilliae from P. japonica, one caused a mortality comparable to type A1 from Papuana but lower infection; an older isolate resulted in low mortality and only one infected larva. B. popilliae type A1 from P. woodlarkiana was produced in the Solomon Islands by injection of spores in P. uninodis. Thirty four percent of the injected larvae and 31% of the adults produced spores with an average yield of 3.2 and 0.8 x 10(9) spores/insect, respectively. Oral application of a single dose of 10(7) spores of the B. popilliae isolates from P. uninodis or P. japonica did not cause infection and similarly inoculation of the food with spores of B. popilliae type B2 did not result in infections. However, when different rates were applied to the food of second- and third-instar P. uninodis, the B. popilliae type A1 from P. woodlarkiana caused up to 15% infection and concentration-related mortality.     

Genetic variation in a host-parasite association: potential for coevolution and frequency-dependent selection

Abstract.— Models of host‐parasite coevolution assume the presence of genetic variation for host resistance and parasite infectivity, as well as genotype‐specific interactions. We used the freshwater crustacean Daphnia magna and its bacterial microparasite Pasteuria ramosa to study genetic variation for host susceptibility and parasite infectivity within each of two populations. We sought to answer the following questions: Do host clones differ in their susceptibility to parasite isolates? Do parasite isolates differ in their ability to infect different host clones? Are there host clone‐parasite isolate interactions? The analysis revealed considerable variation in both host resistance and parasite infectivity. There were significant host clone‐parasite isolate interactions, such that there was no single host clone that was superior to all other clones in the resistance to every parasite isolate. Likewise, there was no parasite isolate that was superior to all other isolates in infectivity to every host clone. This form of host clone‐parasite isolate interaction indicates the potential for coevolution based on frequency‐dependent selection. Infection success of original host clone‐parasite isolate combinations (i.e., those combinations that were isolated together) was significantly higher than infection success of novel host clone‐parasite isolate combinations (i.e., those combinations that were created in the laboratory). This finding is consistent with the idea that parasites track specific host genotypes under natural conditions. In addition, correspondence analysis revealed that some host clones, although distinguishable with neutral genetic markers, were susceptible to the same set of parasite isolates and thus probably shared resistance genes.     

Conflicts between a fungal entomopathogen, Zoophthora radicans, and two larval parasitoids of the diamondback moth

Zoophthora radicans (Zygomycetes: Entomophthorales), Diadegma semiclausum (Hymenoptera: Ichneumonidae), and Cotesia plutellae (Hymenoptera: Braconidae) are all natural enemies of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae). Adult C. plutellae are not susceptible to Z. radicans infection but the pathogen can infect and kill adult D. semiclausum. Infection of adult D. semiclausum prior to exposure to P. xylostella host larvae significantly reduced the number of parasitoid cocoons subsequently developing from the host larvae. Although Z. radicans infection of P. xylostella larvae prior to parasitism by D. semiclausum or C. plutellae always resulted in the death of the immature parasitoids, neither species discriminated between healthy and Z. radicans-infected host larvae in an oviposition choice experiment. However, host larvae recently killed by Z. radicans were always rejected by D. semiclausum but sometimes accepted by C. plutellae. At 20 degrees C, egg to pupa development took 6.7 and 7.8 days for D. semiclausum and C. plutellae, respectively. C. plutellae parasitism significantly increased host instar duration but D. semiclausum parasitism did not. Cadavers of P. xylostella larvae parasitized 1 day prior to fungal infection showed no reduction in Z. radicans conidia yield. However, cadavers of larvae parasitized 3 days prior to fungal infection demonstrated a marked decrease in Z. radicans conidia yield. Z. radicans infection of P. xylostella larvae < or = 4 days after parasitism resulted in 100% parasitoid mortality; thereafter, the reduction in parasitoid cocoon yield decreased as the time between parasitism and initiation of fungal infection increased. The extended duration of the host larval stage induced by C. plutellae parasitism increased the availability of the parasitoid to the pathogen. Estimates of interspecific competition indicated a similar pattern for the interaction between Z. radicans and each species of parasitoid.     

Consequences of Interspecific Competition on the Virulence and Genetic Composition of a Nucleopolyhedrovirus in Spodoptera frugiperda Larvae Parasitized by Chelonus insularis

Nucleopolyhedroviruses ( Baculoviridae ) are virulent insect pathogens that generally show a high degree of host specificity and have recognized potential as biological insecticides. Whenever viruses are applied for pest control, a proportion of the infected insects will also be parasitized by hymenopteran or dipteran parasitoids and interspecific competition for host resources will occur; the severity of such competition is likely to be modulated to a large degree by the virulence of each type of parasite. We examined the impact of parasitism by the solitary egg-larval endoparasitoid Chelonus insularis (Hymenoptera: Braconidae) on the speed of kill of nucleopolyhedrovirus-infected Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae and the pattern of host growth and virus production in infected and/or parasitized hosts. We also examined the effect of parasitism on the virulence, infectivity and genetic composition of serially passaged virus. Both parasitism and viral infection resulted in a marked reduction in host growth. When third instar larvae were dually parasitized and virus-infected, the growth rate was even more severely affected compared to parasitized larvae. There was a significant increase in virus production in larvae infected at later instars. Interspecific competition resulted in a substantial decrease in pathogen production in parasitized larvae infected at the fourth instar, but not in parasitized larvae infected at earlier instars. The serial passage experiment resulted in the appearance of four distinct genetic isolates of the virus detected by restriction endonuclease analysis. Of the three isolates that appeared in nonparasitized larvae, two showed increased virulence, expressed by mean time to death, and for one of these the infectivity, expressed as LC 50 , was reduced. One isolate that appeared in parasitized larvae (isolate D) had increased virulence and infectivity. Southern blot analysis indicated that virus isolate D was most likely generated by point mutation of a restriction site or by alterations such as duplications, deletions or by recombination of two or more genotypic variants present in the wild-type nucleopolyhedrovirus isolate. Our study provides clear evidence of interspecific competition within the host, since, depending on the timing of inoculation, adverse effects were observed upon both the parasitoid and the virus.     

三株球孢白僵菌侵染烟粉虱的比较生长动力学及其毒力

同一种虫生真菌的不同菌株对于特定昆虫宿主的毒力可存在显著差异,真菌在昆虫体内的生长能力不同可能是引起这种差异的原因之一。为了探讨真菌在宿主体内的生长动力学与其毒力的关系,本研究用生测法测定了3株球孢白僵菌（GZGY-1-3、SCWJ-2、WLMQ-20）在高剂量（1×108孢子/mL）和低剂量（1×106孢子/mL）下对烟粉虱4龄若虫的毒力,用实时荧光定量PCR技术对真菌在宿主体内的拷贝数进行了定量,用荧光显微方法观察了白僵菌侵染烟粉虱的过程。生物测定实验结果显示：不论在高剂量还是低剂量下,菌株GZGY-1-3杀死烟粉虱所需的时间最短（在高剂量和低剂量下LT50分别为2.29d和6.10d）,其次是菌株SCWJ-2（LT50分别为3.03d和7.38d）,菌株WLMQ-20所需时间最长（LT50分别为4.13d和9.39d）。对于同一菌株,其高剂量下的毒力显著高于低剂量下的毒力。实时荧光定量PCR实验显示,接触高剂量孢子后烟粉虱获得的孢子数远远高于接触低剂量时的孢子数。接种后,每一菌株和每一剂量下的真菌生长都表现出一个相似的模式。在接种24h后,真菌细胞数量显著下降,在接种后24–48h之间是一个简短的恢复阶段,接种48–72h后是真菌的细胞数略有净增长的稳定时期,在宿主死亡前后的阶段,真菌数量急剧增加,与接种后最初24h相比高了近1 000倍。然而,尽管它们的生长模式相似,但是却存在着量上的差异,由致病性强、剂量高的菌株侵染的昆虫体内的最终真菌菌体数高。荧光显微技术观察到的白僵菌对烟粉虱的侵染过程证实了定量PCR的结果。这些结果说明菌株间毒力的差异在一定程度上是由真菌生长动力学的量化差异所决定的。     

莱氏绿僵菌对斜纹夜蛾的致病力及生理效应

【目的】测定莱氏绿僵菌Metarhizium rileyi Nr5772菌株对斜纹夜蛾Spodoptera litura幼虫及蛹的致病能力,研究莱氏绿僵菌侵染后在寄主体内的发育及对寄主的生理效应,探讨莱氏绿僵菌的致病机制。【方法】采用浸渍法测定莱氏绿僵菌孢子对斜纹夜蛾3-6龄幼虫及蛹的致死中浓度(LC_(50))和致死中时(LT_(50))。采用微量注射法接种莱氏绿僵菌虫菌体,在不同时间后采集斜纹夜蛾幼虫血淋巴,在显微镜下检查虫菌体的数量、形态及寄主血细胞数量,并用酶标仪测定寄主血淋巴酚氧化酶(Phenoloxidase,PO)的活性。【结果】M.rileyi孢子对3龄斜纹夜蛾幼虫毒力最强,10 d后LC_(50)=3.12×10~6个孢子/mL,龄期越大,致病力越低;孢子浓度为5×10~9个/mL时,对3龄幼虫的致死速度最快,LT_(50)=4.55 d,致死速度随龄期的增大和浓度的降低逐渐减缓;M.rileyi孢子对蛹的致病力远低于对幼虫的致病力。注射接种虫菌体后,64 h内,虫菌体数量在寄主血腔中以幂函数的形式增长,寄主的血细胞数量没有明显的变化;在侵染初期(接种后44 h内),血淋巴PO活性正常;在侵染后期,虫菌体数量不再增加(55-64 h后),逐渐转化为菌丝体,并快速杀死寄主,PO活性受到抑制。【结论】莱氏绿僵菌Nr5772菌株对斜纹夜蛾幼虫有较强的致病力,应在害虫低龄期应用;莱氏绿僵菌在侵染初期对寄主血细胞和血淋巴PO无影响,后期则完全抑制PO活性。