宛氏拟青霉与球孢白僵菌对柑橘木虱的致病力分析

【目的】比较宛氏拟青霉WS-11和球孢白僵菌QB-28对柑橘木虱成虫的致病力,为生防制剂的田间应用提供理论支持。【方法】采用孢子悬浮液浸没法比较研究了2种真菌对柑橘木虱的致病力,并利用时间-剂量-死亡率模型估计了2种真菌对柑橘木虱的致死剂量与致死时间。【结果】宛氏拟青霉WS-11在孢子悬浮液浓度为1×108 spores/m L时,累计死亡率达到90.67%,球孢白僵菌QB-28则达到97.33%。时间-剂量-死亡率模型中Hosmer-Lemeshow方法拟合异质性检验表明模型拟合良好,在接种后9 d,宛氏拟青霉WS-11和球孢白僵菌QB-28对柑橘木虱的LC50分别为7.57×10~6 spores/m L和8.39×105 spores/m L;当孢子悬浮液浓度为1×108 spores/m L时,2种真菌对柑橘木虱的LT50分别为2.50 d和1.93 d。【结论】宛氏拟青霉WS-11和球孢白僵菌QB-28对柑橘木虱均有较好的致病力,具有较好的生防潜质,其中球孢白僵菌对柑橘木虱的致病力高于宛氏拟青霉,致死效率更高。     

球孢白僵菌HFW-05对烟粉虱的致病力及组织病理影响

环境温湿度是影响白僵菌菌株致病力的关键因素,本文测定了不同温、湿度下白僵菌Beauveria bassiana HFW-05对烟粉虱Bemisia tabaci若虫及卵的致病力,同时观察了烟粉虱感病若虫的组织病理变化。结果表明,各浓度下烟粉虱若虫的校正死亡率随时间变化曲线基本一致,接种3-4 d时出现死亡高峰,白僵菌HFW-05对烟粉虱1龄、2龄、3龄若虫的LC_(50)分别为5.94×10~4、1.06×10~5、5.08×10~5孢子/mL,LT50分别为2.54 d、2.68 d、3.18 d;白僵菌HFW-05对卵的致病力很低,1×108孢子/mL接种浓度下,卵的6 d感染率仅为24.9%。在25℃、30℃下,HFW-05对烟粉虱若虫表现出最强的致病力,高于或低于此温度时,烟粉虱若虫死亡速度减慢,死亡率降低。相对湿度发生变化时,烟粉虱若虫死亡速度和死亡率明显不同,相对湿度高于90%时,烟粉虱若虫死亡速度最快,死亡率最高,相对湿度介于70%-90%时,白僵菌HFW-05对烟粉虱若虫的致病力无明显差异,但校正死亡率显著低于环境湿度大于90%的处理,相对湿度低于70%时,烟粉虱死亡率也达到60%左右。组织病理学观察显示尾部舌状突是HFW-05侵染烟粉虱若虫的关键部位。研究结果表明白僵菌HFW-05在烟粉虱的生物防治中有较大的潜力。     

孢悬液浓度和宿主体型大小对球孢白僵菌对松墨天牛幼虫的致病力的影响

【目的】球孢白僵菌Beauveria bassiana是一种被广泛用于害虫生物防治的生防菌。本研究探讨了孢悬液浓度和宿主体型大小对球孢白僵菌对松墨天牛Monochamus alternatus幼虫的致病力的影响,旨在为松墨天牛的生物防治提供科学基础。【方法】分别用0.5%吐温-80(CK)以及1×10~5, 1×10~6, 1×10~7, 1×10~8和1×10~9孢子/mL的球孢白僵菌孢悬液接种松墨天牛4龄幼虫,统计接种后15 d内幼虫死亡率和染菌率。同时用最佳浓度(1×10~9孢子/mL)的球孢白僵菌孢悬液接种体型大小分别为100～150, 200～220, 300～320, 400～420, 500～520和600～650 mg/头的松墨天牛幼虫,测定接种后20 d内幼虫的死亡率和染菌率。【结果】接种1×10~5～1×10~9孢子/mL的球孢白僵菌后,松墨天牛4龄幼虫起初活动自如,后在头部出现烧灼状伤并且体色逐渐变红,最后周身长满菌丝。不同浓度下,随球孢白僵菌孢子浓度升高,松墨天牛4龄幼虫校正死亡率和校正染菌率增加。接种1×10~6～1×10~9孢子/mL球孢白僵菌孢悬液15 d的松墨天牛4龄幼虫累计校正死亡率均可达到100%,1×10~7, 1×10~8和1×10~9孢子/mL浓度下,松墨天牛达到100%校正死亡率所需时间最少。接种0 (CK), 1×10~5, 1×10~6, 1×10~7, 1×10~8和1×10~9孢子/mL球孢白僵菌孢悬液的松墨天牛4龄幼虫校正染菌率在第15天分别为0, 20.00%, 86.67%, 90.00%, 96.67%和100.00%,表现为白僵菌孢子浓度越高,染菌率越高。1×10~9孢子/mL的接种浓度下,松墨天牛幼虫个体越大,天牛幼虫死亡率和染菌率越高。表现在第20天时,体型大小为100～150, 200～220, 300～320, 400～420, 500～520和600～650 mg/头的幼虫的死亡率分别为76.67%, 76.67%, 66.67%, 93.33%, 100.00%和100.00%,染菌率分别为60.00%, 63.33%, 60.00%, 86.67%, 96.67%和100.00%。【结论】球孢白僵菌悬浮液浓度对松墨天牛幼虫的死亡和侵染有显著影响,表现为随孢子浓度的增加而增加;同时,松墨天牛幼虫个体越大,死亡率和染菌率越高。研究结果对开展利用球孢白僵菌防治松墨天牛具重要借鉴和指导意义。     

孢悬液浓度和宿主体型大小对球孢白僵菌对松墨天牛幼虫的致病力的影响

【目的】球孢白僵菌Beauveria bassiana是一种被广泛用于害虫生物防治的生防菌。本研究探讨了孢悬液浓度和宿主体型大小对球孢白僵菌对松墨天牛Monochamus alternatus 幼虫的致病力的影响,旨在为松墨天牛的生物防治提供科学基础。【方法】分别用0.5% 吐温-80(CK)以及1×10⁵, 1×10⁶, 1×10⁷, 1×10⁸和1×10⁹孢子/mL的球孢白僵菌孢悬液接种松墨天牛4龄幼虫,统计接种后15 d内幼虫死亡率和染菌率。同时用最佳浓度(1×10⁹孢子/mL)的球孢白僵菌孢悬液接种体型大小分别为100~150, 200~220, 300~320, 400~420, 500~520和600~650 mg/头的松墨天牛幼虫,测定接种后20 d内幼虫的死亡率和染菌率。【结果】接种1×10⁵~1×10⁹孢子/mL的球孢白僵菌后,松墨天牛4龄幼虫起初活动自如,后在头部出现烧灼状伤并且体色逐渐变红,最后周身长满菌丝。不同浓度下,随球孢白僵菌孢子浓度升高,松墨天牛4龄幼虫校正死亡率和校正染菌率增加。接种1×10⁶~1×10⁹孢子/mL球孢白僵菌孢悬液15 d的松墨天牛4龄幼虫累计校正死亡率均可达到100%,1×10⁷, 1×10⁸和1×10⁹孢子/mL浓度下,松墨天牛达到100%校正死亡率所需时间最少。接种0 (CK), 1×10⁵, 1×10⁶, 1×10⁷, 1×10⁸和1×10⁹孢子/mL球孢白僵菌孢悬液的松墨天牛4龄幼虫校正染菌率在第15天分别为0, 20.00%, 86.67%, 90.00%, 96.67%和100.00%,表现为白僵菌孢子浓度越高,染菌率越高。1×10⁹孢子/mL的接种浓度下,松墨天牛幼虫个体越大,天牛幼虫死亡率和染菌率越高。表现在第20天时,体型大小为100~150, 200~220, 300~320, 400~420, 500~520和600~650 mg/头的幼虫的死亡率分别为76.67%, 76.67%, 66.67%, 93.33%, 100.00%和100.00%,染菌率分别为60.00%, 63.33%, 60.00%, 86.67%, 96.67%和100.00%。【结论】球孢白僵菌悬浮液浓度对松墨天牛幼虫的死亡和侵染有显著影响,表现为随孢子浓度的增加而增加;同时,松墨天牛幼虫个体越大,死亡率和染菌率越高。研究结果对开展利用球孢白僵菌防治松墨天牛具重要借鉴和指导意义。     

球孢白僵菌侵染对管氏肿腿蜂雌成蜂的不利影响

【目的】本研究旨在探究球孢白僵菌Beauveria bassiana对管氏肿腿蜂Scleroderma guani雌成蜂的不利影响,为今后利用管氏肿腿蜂携带球孢白僵菌联合防控松墨天牛Monochamus alternatus等蛀干害虫的技术研发奠定基础。【方法】本实验测定了5种不同浓度的球孢白僵菌孢悬液(1.0×10~4~1.0×10~8孢子/m L)和孢子粉(1.0×107孢子/雌)(以无菌水为对照)对雌成蜂的侵染力和致死力的影响。【结果】球孢白僵菌的孢悬液和孢子粉均会感染雌成蜂,不同浓度孢悬液接种于雌成蜂体表时,孢悬液对雌成蜂的感染率和致死率均与孢悬液浓度呈正相关性。接菌第2和4天,仅最高浓度孢悬液对雌成蜂有致死和感染现象;第5天,1.0×10~8,1.0×10~6和1.0×10~4孢子/m L孢悬液对雌成蜂的感染率分别为56.0%,8.0%和4.0%,致死率分别为88.0%,44.0%和16.0%;第6天,1.0×10~8孢子/m L孢悬液对雌成蜂的致死率高达100%,是最低浓度孢悬液对雌成蜂致死率的6.25倍。同时,孢悬液和孢子粉(含相同孢子数)相比,前者对雌成蜂的致死率更高;接菌第7天,孢悬液(1.0×10~7孢子/m L)对雌成蜂的致死率为100%,是孢子粉的3.12倍。这可能与雌成蜂对孢子粉有一定的清理或抖落行为有关。【结论】今后在利用管氏肿腿蜂携菌防控天牛等蛀干害虫时,可优先选用球孢白僵菌孢悬液,并控制雌成蜂携菌后及时释放,以便在其感染潜伏期4~5 d以内,有效传至天牛蛹室。     

美国白蛾高毒力球孢白僵菌菌株筛选

【目的】美国白蛾Hyphantria cunea(Drury)是世界性检疫害虫,目前已经入侵到我国长江下游地区(从辽宁丹东至安徽芜湖)。作者在前期研究中,在芜湖地区成功获得了被球孢白僵菌Beauveria bassiana侵染的美国白蛾僵虫。本研究拟在前期已获取菌株的基础上,筛选生物学性状良好且对美国白蛾幼虫具有高致病力的球孢白僵菌菌株,以期为我国长江下游地区利用昆虫病原真菌防治美国白蛾奠定基础。【方法】对采集自美国白蛾僵虫的7株球孢白僵菌菌株(Bb01-1,Bb08-5,Bb08-6,Bb08-11,Bb22-2,Bb22-3和Bb22-5)进行生物学特性研究,以候选菌株菌落形态、生长速率、产孢量、萌发率和抗紫外能力等参数确定优良菌株;并将生物学性状良好的球孢白僵菌菌株配制成5个浓度(5×10~6,1×10~7,5×10~7,1×10~8和5×10~8孢子/m L)的孢悬液,采用浸渍法处理美国白蛾4龄幼虫,以幼虫死亡率、侵染率等指标评价菌株的致病力。【结果】供试菌株Bb22-2,Bb22-3和Bb22-5为粉状菌落,其菌落直径大,产孢早且孢子层厚;同时,这3个菌株在菌落生长速率和产孢量以及孢子萌发率、紫外照射处理后的萌发率也均显著优于其他4个菌株。毒力测定结果表明,这3个菌株对美国白蛾4龄幼虫表现出很强的致病力,各菌株处理11 d后美国白蛾幼虫校正死亡率为80%~90%。这3个菌株对美国白蛾幼虫的侵染率均高(侵染率53%~87%),并且呈现随浓度升高侵染率上升的趋势。其中,菌株Bb22-2侵染率均要高于其他2个菌株。【结论】本研究成功筛选获得了生物学性状良好且对美国白蛾高毒力的球孢白僵菌菌株。鉴于中国长江下游地区气候特点与美国白蛾生物学习性,可以预期采用昆虫病原真菌防治美国白蛾在该地区将具有很好的应用前景,但其实际应用价值尚需进一步的田间试验进行确认。     

球孢白僵菌不同分离株对西花蓟马的毒力测定

【背景】西花蓟马是我国重要的一种入侵性害虫,已对多种化学农药产生了抗性。【方法】采用孢子悬浮液喷雾处理生测法,研究了8个球孢白僵菌菌株BbKM030716、BbCG051229、BbJS080625、BbQJ031121、BbXW060615、BbSM090521、BbYY090613和BbMZ051230对西花蓟马成虫的毒力,并用＂时间—剂量—死亡率＂模型进行了分析。【结果】供试球孢白僵菌各菌株对西花蓟马成虫侵染致病的剂量效应参数值分别为1.43、0.87、0.93、0.98、1.23、0.92、1.07和0.86。用1.25×104～1.25×108个·mL-1孢子悬浮液接种后,连续10d内西花蓟马的校正死亡率分别为44.13%～98.49%、12.63%～78.90%、30.36%～96.92%、51.36%～98.74%、26.14%～98.59%、7.27%～78.71%、49.06%～98.74%和27.67%～87.36%。球孢白僵菌对西花蓟马成虫的致死剂量是时间的函数,各菌株对西花蓟马成虫的致死中时随孢子浓度的增大而逐渐减小。【结论与意义】球孢白僵菌菌株BbKM030716、BbJS080625、BbQJ031121和BbXW060615对西花蓟马成虫具有较强毒力,可作为西花蓟马生防制剂开发的潜力菌株。     

卵孢白僵菌及添加杀虫助剂对两种地老虎的生物活性测定

【目的】确定卵孢白僵菌Beauveria brongniartii菌株NEAU30503对八字地老虎Xestia c-nigrum(Linnaeus)和小地老虎Agrotis ypsilon(Rottemberg)的杀虫活性。【方法】采用浸叶法测定NEAU30503对地老虎低龄幼虫的生物活性,土壤处理法测定对高龄幼虫的杀虫活性。【结果】NEAU30503对5日龄八字地老虎幼虫第15天毒力回归方程为y=0.6568x-0.1636(r=0.9846),其LC_(50)、LC_(80)分别为7.28×10~7孢子/m L、139.14×10~7孢子/m L;对5龄八字地老虎幼虫毒力回归方程为y=1.0929x-3.2893(r=0.9801),其LC_(50)、LC_(80)分别为3.85×10~7孢子/L、22.65×10~7孢子/L。未死幼虫化蛹后仍有部分蛹死于白僵菌感染,并能明显降低成虫羽化率。白僵菌与Bt、茶皂素、以及亚致死剂量的高效氯氢菊酯和阿维菌素混用能明显提高其杀虫活性和杀虫速度。【结论】NEAU30503对地老虎具有较高的杀虫活性,土壤处理防治高龄幼虫效果好,喷雾处理防治低龄幼虫加入少量的高效氯氢菊酯或茶皂素效果明显。本研究为开展白僵菌田间防治地老虎提供了科学依据。     

柑桔全爪螨高致病力菌株芽枝状枝孢霉的生物学特性研究

【目的】明确柑桔全爪螨Panonychus citri(Mc Gregor)高致病力菌株芽枝状枝孢霉Cladosporium cladosporioides(CQBBW3)的生物学特性。【方法】通过单因素试验,测试了不同培养基、碳源、氮源、温度及pH对CQBBW3菌株生长和产孢的影响。【结果】CQBBW3菌株的LC50为4.66×108个孢子/m L,LT50为6.2353 d。最佳生长培养基是淀粉琼脂培养基,最适产孢培养基为察氏培养基;菌丝生长最适碳源和氮源为甘露醇和甘氨酸,产孢最适碳源和氮源为乳糖和赖氨酸;最适生长温度为25℃,最适产孢温度为15℃和30℃;最适生长pH值为6.0~8.0,最适产孢pH值7.0。【结论】CQBBW3菌株对柑桔全爪螨有较好的杀虫活性,喜好25℃、中性、富含有机营养的环境。本研究为菌株快速培养及其真菌杀虫制剂的开发与田间应用奠定基础。     

球孢白僵菌对小猿叶甲的致病力测定

在室内研究了分离自小猿叶甲的一株球孢白僵菌(SCAU-BB 01D)对小猿叶甲的致病力。结果表明,该菌株能感染小猿叶甲的成虫和各龄幼虫,但对不同虫期的致病力存在差异。在105~108孢子/m l的浓度范围内,随着处理浓度的升高,各虫期小猿叶甲的感病死亡率增加,在最高浓度1×108孢子/m l,处理后成虫第14天及1~3龄幼虫第10天的累计死亡率分别为84.7%、94.0%、96.0%和81.0%。用TDM模型对成虫和各龄幼虫的致病力数据进行模拟,所建模型均顺利通过Hosm er-L em eshow拟合异质性检验,表明模型拟合良好,并由模型估计出了该菌株对小猿叶甲各虫期的致死剂量与致死时间。在处理后第10天,成虫和1~3龄幼虫的致死中浓度(LC50)分别为2.68×107、1.07×106、1.63×105孢子/m l和8.31×106孢子/m l,而第14天成虫的LC50为2.38×106孢子/m l。随着浓度的增加,各虫期所需的感病死亡时间缩短,在最高浓度1×108孢子/m l,球孢白僵菌对小猿叶甲成虫及1~3龄幼虫的致死中时(LT50)分别为9.28、4.29、4.40d和5.06 d。综合分析白僵菌对各虫期的致死剂量及致死时间可以看出,不同虫期的小猿叶甲对球孢白僵菌敏感性不同。结果表明该菌株在小猿叶甲生物防治中具有一定的潜力。     

一株球孢白僵菌转基因工程菌在继代培养中的变异

基因工程是解决昆虫病原真菌致死慢、致死率低的有效途径,但在传代培养过程中,被转入的基因是否会丢失以及转基因工程株是否会像野生型菌株那样频繁地发生变异,引起产孢减少和毒力减退等生产性状的退化？针对这些问题,研究一株球孢白僵菌Beauveria bassiana转外源蝎毒基因工程菌株在继代培养过程中的的变异现象,发现工程株也和野生型菌种一样会发生菌落局变,但所插入的蝎毒基因并未丢失。与野生型出发菌株及其单孢分离株相比,工程株的角变率居高不下而产孢量及对松毛虫的毒力显著降低。然而,从该工程株筛选出的一株单孢分离     

Use of chitin to improve a Beauveria bassiana alginate-pellet formulation

A study was undertaken to evaluate optimum concentrations of chitin in sodium alginate pellet formulations to enhance conidia production. Chitin concentrations tested were 0, 0.5, 1, 2, 3 and 4% (w/v), with (2%, w/v) or without wheat bran. The different chitin-wheat bran pellet combinations were prepared with Beauveria bassiana isolate Qu-B306 at 10⁸ conidia mL^-1. After 21 days of incubation in a humid chamber at 28°C, conidia production was assessed. Improvements up to three times the initial conidia number were achieved using 2% chitin and 2% wheat bran. Higher levels of chitin decreased the number of conidia per pellet. For all chitin concentrations, conidia number increased with the addition of wheat bran (P≤0.05). Contamination by saprophytic fungi was reduced by the incorporation of chitin in the pellet formulation.     

Identification of a Penicillium urticae metabolite which inhibits Beauveria bassiana

A metabolite of a common soil fungus, Penicillium urticae, which inhibits conidia germination and growth of Beauveria bassiana, was identified. The production, extraction from the culture, and purification of the metabolite is described. Two-dimension thin-layer chromatography, reverse-phase chromatography, mass spectrophotometer and bioassay data indicate that the metabolite is patulin. The implication of patulin inhibition of B. bassiana and its subsequent effect on the potential role of B. bassiana as a control agent of soil-inhabiting insects is discussed.     

Properties of a lipase produced by Beauveria bassiana: purification and biochemical studies

Lipases are some of the crucial enzymes during the fungal penetrating process of the insect integument. Due to the importance and lack of information on the microbial lipases of Beauveria bassiana, investigations were carried out to purify and biochemically characterize these enzymes. The results obtained on growth medium demonstrated the highest activity of lipase 6 days after inoculation while the pH of the medium was 7.1. After three purification steps, the purified enzyme was 9.91-fold with specific activity of 20816 U/mg protein, recovery of 25% and molecular weight of 25 kDa. The purified lipase had the optimal pH and temperature at 7 and 35°C and was stable for 36–72 h under those conditions. Ca^{2 +} significantly increased the enzyme activity and NaCl decreased it at all the tested concentrations. In addition, Mn^{2 +} had no effect on enzyme activity but Mg^{2 +} and Zn^{2 +} increased it only at the highest concentration used. Three out of the four inhibitors used, significantly decreased the purified lipase activity so that most inhibition and changes in the enzyme kinetic parameters were obtained by using different concentrations of EDTA. Knowledge of enzymology provides important information for the development of fungi as microbial pest control agents opening new avenues for study of the role of enzymes in virulence.     

蜡蚧轮枝菌和球孢白僵菌的共发酵

【目的】球孢白僵菌(Beauveria bassiana)和蜡蚧轮枝菌(Verticillium lecanii)是国内外目前研究应用最广泛的杀虫生防真菌,欲扩大其防治范围、增强防治效果、降低生防成本。【方法】采用共发酵技术,通过组合菌株产孢能力和杀虫毒力比较试验,确定蜡蚧轮枝菌和球孢白僵菌共发酵的可行性。【结果】蜡蚧轮枝菌L-31和球孢白僵菌Q-55共发酵的最佳配比为1:1时,按10%总量接种于发酵培养液中(培养液按酵母膏5.0 g/L、葡萄糖20.0 g/L、麦芽糖提取物5.0 g/L、KH2PO43.0 g/L、黄小米200.0 g/L,pH 6.5配制),23.0°C±0.1°C恒温静置发酵12 d,共发酵液的含孢量可达1×109CFU/mL以上,杀虫毒力比较强,其对温室白粉虱和菜青虫可同时显效,处理9 d后的致死中浓度LC50分别为2.09×104±0.12 CFU/mL和3.17×105±0.11 CFU/mL,发酵液浓度为1×108CFU/mL时的致死中时间LT50分别为2.11±0.14 d和4.27±0.43 d,温室小区试验校正防效在80%以上,与其各单一菌株发酵液的防效之间存在显著性差异。【结论】通过两株生防真菌的共发酵研究,为杀虫真菌的扩谱增效以及植物害虫的有效防治提供科学依据和有效途径。     

Transformations of steroids by Beauveria bassiana

The course of transformations of testosterone and its derivatives, including compounds with an additional C1,C2 double bond and/or a 17alpha-methyl group, a 17beta-acetyl group or without a 19-methyl group, by a Beauveria bassiana culture was investigated. The fungi promoted hydroxylation of these compounds at position 11alpha, oxidation of the 17beta-hydroxyl group, reduction of the C1,C2 or C4,C5 double bonds and degradation of the progesterone side-chain, leading to testosterone. The structure of 4-ene-3-oxo-steroids had no influence on regio- and stereochemistry of hydroxylation. In a similar manner, dehydroepiandrosterone was hydroxylated by Beauveria bassiana at position 11alpha, however, a small amount of 7alpha-hydroxylation product was also formed.     

Transformation of cinoxacin by Beauveria bassiana

The ability of the fungus Beauveria bassiana ATCC 7159 to transform the antibacterial agent cinoxacin was investigated. Cultures in sucrose-peptone broth were dosed with cinoxacin, grown for 20 days, and then extracted with ethyl acetate. Two metabolites were detected and purified by high-performance liquid chromatography. The major metabolite was identified by mass and proton nuclear magnetic resonance spectra as 1-ethyl-1,4-dihydro-3-(hydroxymethyl)[1,3]dioxolo[4,5-g]cinnolin-4-one and the minor metabolite was identified as 1-ethyl-1,4-dihydro-6,7-dihydroxy-3-(hydroxymethyl)cinnolin-4-one. B. bassiana also reduced quinoline-3-carboxylic acid to 3-(hydroxymethyl)quinoline.     

Modelling Beauveria bassiana horizontal transmission

1 We modelled horizontal transmission of Beauveria bassiana in Colorado potato beetle (CPB) between larval cadavers and soil inhabiting prepupae. 2 The rate of disease transmission, based on the probability of a prepupa contacting sporulating cadavers on the soil surface, is a non‐linear function of cadaver density and also dependent upon temperature. 3 The spatial pattern of cadavers is needed to estimate prepupal contacts with cadavers. Observational field studies determined Johnson distributions to model the spatial pattern of cadavers and prepupae in the field. The model also implicitly incorporates within‐field larval spatial pattern into estimates of field‐level horizontal transmission. 4 Potential for horizontal transmission is higher in simulations using weather data from the warmer year of 1995, than in simulations of the cooler growing season of 1993. 5 Simulations of CPB populations under northern Maine climatic conditions recorded in 1993 and 1995 suggest that horizontal transmission can range from 3 to 24% depending upon the timing of primary infection of larvae in the field. 6 Two simulated sequential applications of B. bassiana targeted at peak first instars resulted in maximum horizontal infection in both years. 7 Sensitivity analysis suggests that horizontal transmission is most sensitive to changes in the proportion of cadavers that sporulate and least sensitive to changes in the time between larval death and the onset of cadaver sporulation. 8 Field validation of the model indicates good prediction of one measure of horizontal infection, the proportion of prepupae which eventually sporulated after being released in controlled field experiments.     

Beauveria bassiana protoplast regeneration and transformation using electroporation

Summary Regeneration of Beauveria bassiana GK2016 protoplasts demonstrated three phases: (1) enlargement, (2) formation of a chain of budding cells, and (3) development of a true germ tube from the original protoplast. Regeneration frequencies of up to 80% were obtained when using the stabilizer ammonium sulphate. Using electroporation, protoplasts were transformed to methyl 1,2-benzimidazole carbamate (MBC) resistance with the Neurospora crassa MBC-resistant -tubulin gene. A transformation efficiency of one of three transformants per 5 g vector DNA was obtained. The MBC phenotype was stable and transformants grew in the presence of 5 g MBC/ml. Southern DNA-DNA hybridization analysis demonstrated that integration of the vector into the chromosomal DNA had occurred. Correspondence to: G. G. Khachatourians     

Cloning of a cuticle-degrading protease from the entomopathogenic fungus, Beauveria bassiana

Abstract A Beauveria bassiana extracellular subtilisin-like serine endoprotease is a potential virulence factor by virtue of its activity against insect cuticles. A cDNA clone of the protease was isolated from mycelia of B. bassiana grown on cuticle/chitin cultures. The amino acid sequence of this gene was compared to that of Metarhizium anisopliae Pr1, the only pathogenicity determinant so far described from an entomopathogenic fungus, and proteinase K, isolated from Tritirachium album , a saprophytic fungus. The cDNA sequence revealed that B. bassiana Prl is synthesized as a large precursor ( M _r 37 460) containing a signal peptide, a propeptide and the mature protein predicted to have an M _r of 26 832.