繁育寄主对稻螟赤眼蜂寄生行为及寄生能力的影响

【目的】繁育寄主影响赤眼蜂的生物学特性,为明确米蛾Corcyra cephalonica(Stainton)卵繁育的稻螟赤眼蜂Trichogramma japonicum Ashmead是否和二化螟Chilo suppressalis(Walker)卵繁育稻螟赤眼蜂在防治二化螟上有差别,及田间用米蛾卵作为稻螟赤眼蜂续代寄主的可行性,本实验观察了羽化自不同寄主的稻螟赤眼蜂的寄主选择和寄生行为,研究了两种繁育寄主对稻螟赤眼蜂寄生能力的影响,为田间防治水稻螟虫提供参考信息。【方法】室内利用选择试验观察了由米蛾卵和二化螟卵繁育出的稻螟赤眼蜂对两种寄主的选择趋性及在两种寄主上的寄生行为和寄生能力,统计了羽化子代蜂的寿命。【结果】由二化螟卵繁育的稻螟赤眼蜂表现出了对二化螟卵的选择偏好,而米蛾卵繁育的稻螟赤眼蜂在米蛾卵和二化螟卵间没有表现出寄主选择偏好。寄主搜寻时间不受繁育寄主及供试寄主的影响,卵表探测时间和穿刺及产卵时间不受繁育寄主的影响,但同一寄主繁育的稻螟赤眼蜂在米蛾卵上的卵表探测时间显著长于在二化螟卵上的卵表检测时间。除二化螟卵繁育蜂寄生二化螟卵时的寄生率(36.95%)和羽化率(45.68%)较低外,米蛾卵繁育蜂寄生米蛾卵或二化螟卵以及二化螟卵繁育蜂寄生米蛾卵等3组处理间的寄生率、羽化率均无显著差异,各处理组间子代蜂寿命也无显著差异。【结论】繁育寄主影响稻螟赤眼蜂的寄主选择和寄生能力,但不影响寄生蜂搜寻寄主的能力和寄生行为。     

冷藏米蛾卵对稻螟赤眼蜂和玉米螟赤眼蜂子代质量的影响

【目的】以稻螟赤眼蜂Trichogramma japonicum Ashmead和玉米螟赤眼蜂T.ostriniae为试验对象,研究低温冷藏米蛾卵对赤眼蜂子代质量的影响,为米蛾卵的合理利用,赤眼蜂的工厂化生产和应用提供理论依据。【方法】将米蛾卵在不同温度(1、4、7、10℃)下冷藏不同时间(3、5、7、10、15、20、25、30、40d),研究米蛾卵冷藏后作为寄主卵对两种赤眼蜂子代寄生卵量、F_2代羽化出蜂率和雌蜂率的影响,利用赤眼蜂子代寄生卵量、F_2代羽化出蜂率和雌蜂率三者乘积表示赤眼蜂子代质量(Q),根据赤眼蜂子代质量判断冷藏米蛾卵对子代质量的影响。【结果】米蛾卵冷藏温度和时间对赤眼蜂子代寄生卵量影响显著,但不同赤眼蜂种类和不同冷藏温度间表现不同。繁殖稻螟赤眼蜂时,米蛾卵在4℃下冷藏赤眼蜂寄生卵量下降最缓,米蛾卵冷藏20d内赤眼蜂寄生卵量与对照之间差异不显著,在其他温度下米蛾卵冷藏3 d稻螟赤眼蜂寄生卵量与对照之间差异达到显著水平;繁殖玉米螟赤眼蜂时,米蛾卵在4℃下冷藏赤眼蜂寄生卵量下降最缓,米蛾卵冷藏20d赤眼蜂寄生卵量与对照之间差异达到显著水平,1℃下冷藏赤眼蜂寄生卵量下降最快,米蛾卵冷藏5 d赤眼蜂寄生卵量与对照之间达到显著水平。米蛾卵冷藏对稻螟赤眼蜂和玉米螟赤眼蜂F_2代的羽化率和雌蜂率产生的不利影响相对较小,米蛾卵冷藏30 d赤眼蜂F_2代的羽化率仍在70%以上,雌蜂率仍在75%以上。【结论】米蛾卵冷藏超过一定的时间以后会对稻螟赤眼蜂和玉米螟赤眼蜂子代的寄生卵量,F_2代的羽化出蜂率和雌蜂率产生不利影响,从而降低子代稻螟赤眼蜂和玉米螟赤眼蜂的质量,但在适宜的温度下冷藏一定时间内对其子代质量影响不显著,其中4℃下冷藏米蛾卵繁殖的赤眼蜂子代质量最佳,冷藏30 d赤眼蜂子代质量降低不到50%。     

繁育寄主对三种赤眼蜂个体大小及抱卵量的影响

【目的】繁育寄主及成蜂日龄均会影响赤眼蜂体内的抱卵量,为了解繁育寄主及育出赤眼蜂个体大小与赤眼蜂抱卵量的关系,我们在室内研究了米蛾Corcyra cephalonica(Stainton)卵和亚洲玉米螟Ostrinia furnacalis(Güenée)卵作为繁育寄主对3种赤眼蜂雌蜂大小、抱卵量的影响。【方法】在光周期14L∶10D、温度25±1℃的室内条件下,以米蛾卵、亚洲玉米螟卵作为繁育寄主,解剖不同日龄(羽化后12-72 h)松毛虫赤眼蜂Trichogramma dendrolimi Matsumura、玉米螟赤眼蜂Trichogramma ostriniae Pang et Chen以及稻螟赤眼蜂Trichogramma japonicum Ashmead,观察雌蜂抱卵量,测量成蜂的大小,分析雌蜂抱卵量与其日龄、个体大小以及繁育寄主的关系。【结果】在羽化后48 h以内,3种蜂的抱卵量随雌蜂日龄的增长而增加。羽化后72 h,除米蛾卵繁育的玉米螟赤眼蜂及玉米螟卵繁育的松毛虫赤眼蜂的抱卵量比羽化后48 h时略高外,其他组合均出现下降。以亚洲玉米螟卵为繁育寄主时的玉米螟赤眼蜂的抱卵量显著高于对应日龄的以米蛾卵为繁育寄主时的抱卵量,而松毛虫赤眼蜂(除羽化后12和24 h外)和稻螟赤眼蜂则相反;以米蛾卵为繁育寄主时,相同日龄的赤眼蜂中,松毛虫赤眼蜂抱卵量最高,稻螟赤眼蜂的抱卵量最低;以亚洲玉米螟卵为繁育寄主时,玉米螟赤眼蜂抱卵量最高,稻螟赤眼蜂抱卵量最低。雌蜂抱卵量与雌蜂个体大小呈线性正相关,相关程度随雌蜂日龄增加而更加明显。【结论】后足胫节长度可以作为评价松毛虫赤眼蜂、玉米螟赤眼蜂和稻螟赤眼蜂质量的指标。赤眼蜂抱卵量受繁育寄主、赤眼蜂蜂种及雌蜂日龄的显著影响,寄主的适合性也会影响育出赤眼蜂的大小,筛选合适的繁育寄主有助于提高赤眼蜂的质量。     

松毛虫赤眼蜂滞育诱导及解除条件研究

【目的】以柞蚕Antheraea pernyi卵为繁殖寄主,对松毛虫赤眼蜂Trichogramma dendrolim滞育诱导及解除条件进行研究,以解决赤眼蜂工厂化生产和大面积应用中面临的的中、长期储存问题。【方法】通过观测不同发育阶段(寄生柞蚕卵在26℃培养40、96和144 h)、滞育诱导温度(10、13和16℃)和诱导时间对松毛虫赤眼蜂滞育的影响,确定松毛虫赤眼蜂滞育诱导条件;通过观测滞育诱导温度和滞育后的贮藏温度对滞育解除的影响,确定松毛虫赤眼蜂滞育解除条件。【结果】在松毛虫赤眼蜂的不同发育阶段对其进行持续的低温刺激均能使其导入滞育,但以小幼阶段(26℃培养40 h)开始效果最佳,寄生卵在26℃培养40 h后,转入10℃和13℃下连续诱导31 d,滞育率可达100%和99.12%。滞育诱导温度和滞育后的贮藏温度对松毛虫赤眼蜂解除滞育所需时间和解除滞育后的羽化出蜂率有较大影响,10℃诱导滞育后置于1℃冷藏的赤眼蜂解除滞育所需时间最短,解除滞育后的羽化出蜂率和单卵出蜂数更高,更耐储存。此条件下冷藏约30 d开始打破滞育,在正常发育下温度下羽化出蜂,60 d羽化出蜂率达到95.24%,冷藏4个月后羽化出蜂率仍在60%以上,单卵出蜂数高于50头。【结论】松毛虫赤眼蜂最佳滞育诱导条件为26℃培养40 h后,转入10℃连续低温诱导31 d;最佳滞育解除条件为1℃低温储存,但储存期不能超过4个月。     

低剂量~(60)Co-γ射线辐照对梨小食心虫羽化、繁殖和成虫寿命的影响

【目的】本研究采用低剂量的⁽⁶⁰⁾Co-γ射线辐照梨小食心虫Grapholitamolesta雄蛹,分析辐照对梨小食心虫繁殖的影响,为利用(60)Co-γ射线辐照梨小食心虫Grapholitamolesta雄蛹,分析辐照对梨小食心虫繁殖的影响,为利用⁽⁶⁰⁾Co-γ射线防治梨小食心虫提供理论依据。【方法】设置辐照剂量为0、25、50和75 Gy的(60)Co-γ射线防治梨小食心虫提供理论依据。【方法】设置辐照剂量为0、25、50和75 Gy的⁽⁶⁰⁾Co-γ射线对梨小食心虫羽化前1 d的雄蛹进行辐照处理,分析辐照对其羽化率、繁殖能力及寿命的影响。【结果】不同辐照剂量处理的梨小食心虫羽化率均有下降,但与对照组相比无显著性差异,说明辐照对其羽化率影响较小。辐照组雄蛾与正常雌蛾的交配率与对照组无显著性差异。与对照组相比,经25、50和75 Gy辐照处理羽化的雄蛾与正常雌蛾交配后,其单雌产卵量无显著性差异。随着辐照剂量的升高,梨小食心虫的孵化率逐渐下降。与对照组孵化率74.38%±6.15%相比,75Gy处理组的孵化率明显降低,仅为22.68%±7.20%。与对照组相比,随着辐照剂量的升高,辐照组雄虫的平均寿命均有不同程度的下降。【结论】利用低剂量的(60)Co-γ射线对梨小食心虫羽化前1 d的雄蛹进行辐照处理,分析辐照对其羽化率、繁殖能力及寿命的影响。【结果】不同辐照剂量处理的梨小食心虫羽化率均有下降,但与对照组相比无显著性差异,说明辐照对其羽化率影响较小。辐照组雄蛾与正常雌蛾的交配率与对照组无显著性差异。与对照组相比,经25、50和75 Gy辐照处理羽化的雄蛾与正常雌蛾交配后,其单雌产卵量无显著性差异。随着辐照剂量的升高,梨小食心虫的孵化率逐渐下降。与对照组孵化率74.38%±6.15%相比,75Gy处理组的孵化率明显降低,仅为22.68%±7.20%。与对照组相比,随着辐照剂量的升高,辐照组雄虫的平均寿命均有不同程度的下降。【结论】利用低剂量的⁽⁶⁰⁾Co-γ射线辐照可影响梨小食心虫繁殖,为进一步优化辐照条件和利用(60)Co-γ射线辐照可影响梨小食心虫繁殖,为进一步优化辐照条件和利用⁽⁶⁰⁾Co-γ射线防治梨小食心虫提供理论指导。     

果实种类及发育阶段对梨小食心虫幼虫钻蛀率和蛹重的影响

【目的】明确梨小食心虫Grapholitha molesta在寄主果实上的钻蛀率和蛹重与寄主种类和果实发育阶段的关系,为其田间预测预报和综合防控提供技术依据。【方法】在室内条件下测定了接卵后72 h梨小食心虫初孵幼虫在不同发育阶段的3个种共6个品种水果［苹果Malus pumila (嘎啦苹果), 桃Amygdalus persica (大久保毛桃、丰白毛桃和霞光油桃), 梨Pyrus bretschneideri (砀山酥梨和玉露香梨)］果实上的钻蛀率以及在不同果实状态的4个水果品种(大久保毛桃、丰白毛桃、砀山酥梨和玉露香梨)果实上72 h的钻蛀率;比较了接卵后24 h和72 h初孵幼虫在不同发育阶段的3个苹果品种(嘎啦苹果、富士苹果和金冠苹果)果实上的钻蛀率;并测定了不同发育阶段的金冠苹果、富士苹果、嘎啦苹果、砀山酥梨和丰白毛桃上的梨小食心虫蛹重。【结果】接卵后72 h梨小食心虫初孵幼虫在6个不同水果品种果实上的钻蛀率从高到低依次为：霞光油桃＞嘎啦苹果＞砀山酥梨＞玉露香梨＞大久保毛桃＞丰白毛桃;除霞光油桃外,其他5个水果品种果实的发育阶段显著影响初孵幼虫钻蛀率。对于嘎啦苹果,接卵后72 h初孵幼虫在其幼果上的钻蛀率最高(73.69%),在其着色期果实上钻蛀率最低(32.51%);在大久保毛桃、丰白毛桃、砀山酥梨和玉露香梨上,接卵后72 h初孵幼虫的钻蛀率均随果实生长发育而增加。初孵幼虫在3 个苹果品种着色期和成熟期果实上的钻蛀率随处理时间的增加而显著下降,而在其幼果上变化不显著。寄主种类及其发育阶段也显著影响梨小食心虫蛹重,成熟毛桃和梨饲养的雌、雄蛹重显著高于未成熟果实饲养的蛹重,着色期苹果不利于蛹重的增加。【结论】果实种类及发育阶段显著影响梨小食心虫初孵幼虫钻蛀率和蛹重,取食成熟期梨和桃的梨小食心虫初孵幼虫钻蛀率和蛹重显著高于取食未成熟果实的个体。     

施药后不同时间玉米田中常用农药残留对玉米螟赤眼蜂的影响

【目的】为明确玉米田中常用杀菌剂和杀虫剂对玉米螟赤眼蜂Trichogramma ostriniae的安全性。【方法】室内用田间推荐剂量在玉米叶片上施用4种杀菌剂(甲基硫菌灵、戊唑醇、叶枯唑和吡唑醚菌酯)以及4种杀虫剂(阿维菌素、氯虫苯甲酰胺、高效氯氰菊酯和吡虫啉),施药后1, 3, 5和7 d调查玉米螟赤眼蜂成虫接触玉米叶片24 h时的死亡率、寄生能力(寄生的麦蛾Sitotroga cerealella卵量)及子代羽化率。【结果】施药后不同时间,不同杀菌剂和杀虫剂对玉米螟赤眼蜂成虫的死亡率、寄生能力和羽化率产生显著影响。4种杀菌剂中,叶枯唑和吡唑醚菌酯对玉米螟赤眼蜂寄生能力持续影响时间长,在施药7 d后,玉米螟赤眼蜂成虫接触含叶枯唑和吡唑醚菌酯残留的玉米叶片24 h时其寄生的麦蛾卵量分别为20.25和20.80粒;戊唑醇对玉米螟赤眼蜂的影响最大,施药7 d后玉米螟赤眼蜂成虫接触含戊唑醇残留的 玉米叶片24 h时子代羽化率为18.48%,施药3 d后接触时死亡率高达37.03%。4种杀虫剂中,阿维菌素和吡虫啉对玉米螟赤眼蜂寄生能力持续影响时间长并且毒性较大,在施药7 d后,玉米螟赤眼蜂成虫接触含阿维菌素和吡虫啉残留的玉米叶片24 h时的寄生的麦蛾卵量为3.43和9.19粒,施药后1-3 d时死亡率分别高达96.21%和74.00%;高效氯氰菊酯对玉米螟赤眼蜂子代羽化的持续伤害时间长,施药7 d后玉米螟赤眼蜂成虫接触含高效氯氰菊酯残留的玉米叶片24 h时的子代羽化率为27.92%。总体来说,4种杀虫剂对玉米螟赤眼蜂的影响较4种杀菌剂大。【结论】田间释放玉米螟赤眼蜂防治玉米螟Ostrinia nubilalis前7 d不建议喷施戊唑醇、叶枯唑和吡唑醚菌酯3种杀菌剂以及阿维菌素和吡虫啉两种杀虫剂,前5 d不建议喷施甲基硫菌灵和高效氯氰菊酯,氯虫苯甲酰胺使用时应该根据该药的田间推荐浓度合理喷施。     

短时高温对桃小食心虫生长发育与繁殖的影响

【目的】桃小食心虫Carposina sasakii是我国北方落叶果树的重要害虫。本研究旨在探索短时高温对桃小食心虫生长发育和繁殖的影响。【方法】在室内23±1℃、 相对湿度80%±7%和15L∶9D条件下, 测定了桃小食心虫卵、 幼虫、 蛹、 成虫在经历35, 38和41℃高温处理1～4 h后各阶段的发育历期、 存活率和产卵量。【结果】 短时高温对卵的孵化率无明显影响; 经41℃处理后, 初蛀果幼虫(1日龄)的发育历期明显延长, 且存活率显著降低, 3日龄以上的幼虫受到的影响不明显; 11日龄蛹的羽化率在38℃和41℃处理中明显降低, 畸形率也显著升高; 经38℃和41℃处理的成虫存活率降低, 寿命缩短, 产卵量也减少。【结论】短时高温处理对桃小食心虫卵的影响较小, 而对成虫的影响较大。这些结果有助于深入了解该虫在高温季节种群数量变动机制。     

不同寄主对梨小食心虫产卵选择的影响

【目的】为了明确不同世代的梨小食心虫Grapholita molesta(Busck)如何应对不同寄主进行产卵地点的选择。【方法】本文以受孕雌虫为研究对象,在室内进行受孕雌虫产卵对不同种类(桃、梨和苹果)的寄主嫩捎和果实的选择性试验。【结果】结果表明:(1)不同世代的受孕雌虫的产卵地点受到不同寄主种类的显著影响。越冬代、第2代和第3代受孕雌虫偏爱在梨果、桃梢上产卵,而第1代受孕雌虫偏爱在桃果和梨果上产卵。苹果梢和果实的引诱率最低。(2)卵的孵化率的变化趋势与受孕雌虫的落卵率一致。除了不同世代受孕雌虫在梨果上产的卵的孵化率存在差异以外,卵孵化率在同一世代的不同寄主果实、不同寄主嫩梢以及同一寄主的不同世代间差异不显著。【结论】因此,桃梢稳定吸引梨小食心虫产更多的可育卵,而桃果仅吸引第1代成虫产较多的可育卵,梨果吸引其余3代成虫产较多的可育卵。可见,梨小食心虫的产卵选择行为具有试探性,为后代占据优势生态位提供保障。     

湿度对梨小食心虫存活和繁殖的影响

【目的】本研究旨在明确湿度变化对梨小食心虫Grapholitha molesta(Busck)在果实外各阶段存活率和蛀果率的影响及湿度对害虫最终存活率产生影响的关键阶段。【方法】在室内相对湿度25%,40%,55%,70%和85%条件下,记录和分析梨小食心虫的产卵量、卵孵化率、幼虫蛀果率、老熟幼虫化蛹率、蛹羽化率以及产卵、化蛹和羽化时间。【结果】湿度高低对化蛹率没有影响,供试的5种相对湿度下,化蛹率均为100%;但湿度对产卵量、卵孵化率、幼虫蛀果率、蛹羽化率和世代存活率均有显著影响,湿度越高,各阶段存活率、幼虫蛀果率和世代存活率也越高。不同虫态存活对湿度要求从高到低依次为:幼虫蛀果期成虫期卵期蛹期老熟幼虫期。湿度对害虫世代存活率产生显著影响主要发生在幼虫蛀果期、成虫期和卵孵化期。同时,湿度提高利于成虫产卵、化蛹和羽化,反之发育延缓。【结论】湿度会显著影响梨小食心虫各阶段的存活率、幼虫蛀果率和繁殖,成虫盛发期、卵期和蛀果期的湿度影响害虫种群数量和蛀果率的关键阶段。     

Influence of Diaphania hyalinata (L.) (Lepidoptera: Crambidae) egg density on the parasitization capacity of Trichogramma exiguum Pinto & Platner and Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

The effects of the egg density of Diaphania hyalinata (L.) on several biological parameters of Trichogramma exiguum Pinto & Platner and T. pretiosum Riley were investigated. For that, 24h-old egg masses were isolated in glass tubes (15 replicates; 1 egg mass = 1 replicate), and offered to parasitization by a newly-emerged female of T. pretiosum or T. exiguum 24h at the proportion of one female to 5, 10, 15, 20, 25, 30, 35 and 40 eggs of D. hyalinata. The following parameters were evaluated: number of parasitized eggs, number of individuals per egg, viability and sex ratio. Trichogramma exiguum parasitized more eggs than T. pretiosum when more than 25 eggs were available per female. The percentage of emergence was satisfactory to T. pretiosum in densities up to 15 eggs/female and up to 20 eggs/female for T. exiguum. The number of individuals per egg was not statistically different in both species except in the density of 25 eggs/female. It can be concluded that T. exiguum performed better than T. pretiosum at larger clutch sizes, as T. exiguum parasitization capacity increased as a result of the size of the host clutch size.     

Behavior of Trichogramma atopovirilia Oatman & Platner and T. pretiosum Riley (Hymenoptera: Trichogrammatidae) on Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) egg masses.

In this study we analyzed the impact of physical barriers of Spodoptera frugiperda (J. E. Smith) egg-masses on the behavior of Trichogramma atopovirilia Oatman & Platner and Trichogramma pretiosum Riley. The duration of drumming, drilling, oviposition, period spent over the egg-mass, and interval between parasitized eggs were timed, and the number of parasitized eggs were recorded. The presence of scales on the egg-masses caused a significant increase in the time spent by both parasitoids on each process and a decrease in the residence time over the egg-mass and in the number of parasitized eggs, with an increase in the number of egg layers. There was a significant decrease in the number of parasitized eggs in relation to egg-masses with one layer and no scales. We observed that the physical barriers in fall armyworm egg-masses changed the behavior of T. atopovirilia and T. pretiosum, affecting their parasitization capacity.     

松毛虫卵期几种寄生蜂的共寄生现象及其对寄生率的影响

松毛虫赤跟蜂 Trichogramma dendrolimi Matsumura 白跗平腹Pseudanastatusalbitarsis Ashmead松毛虫宽缘金小蜂Pachyneuron olitarium(Harig), 松毛虫黑卵蜂 Telenomus dendrolimusi Chu和大蛾卵跳小蜂Ooenvyrtus Kuwanae(Howard)是松毛虫卵期几种主要寄生蜂。通过对上述几种寄生蜂寄生习性的研究表明：赤眼蜂和平腹小蜂不但能寄生新鲜害虫卵,还可以寄生对方已寄生并巳发育1-3天的寄生卵,但羽化串均不高;松毛虫宽缘金小蜂不寄生新鲜害虫卵,专门寄生赤眼蜂寄生后巳发育1-7,天的寄生卵,其中又以赤眼蜂发育3-5天的卵寄生串和羽化率为最高。除赤眼蜂和平腹小蜂可以混合使用外,其它蜂种混用都不同程度地存在相互排挤的现象。如果先让平腹小蜂寄生尔后再让赤眼蜂寄生或先让赤眼蜂寄生,尔后再让跳小蜂或黑卵蜂寄生,能够提高卵块寄生串和充分发挥各自天敌的作用。     

Impact of peach extrafloral nectar on key biological characteristics of Trichogramma minutum (Hymenoptera: Trichogrammatidae)

This study investigated the longevity, fecundity, and host feeding of a wild and a commercially reared strain of Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae) when presented with peach extrafloral nectar. Both the wild and commercial T. minutum strains lived longer and parasitized more Grapholita molesta (Busck) eggs when provided peach extrafloral nectar and water than when provided only water. Nectar-fed wild and commercially reared females lived 11.6 and 9.9 d and produced 105.2 and 61.0 offspring, respectively. When provided only water, wild females lived 3.3 d and produced 52.8 offspring, whereas commercially reared females lived 2.0 d and produced 24.4 offspring. Nectar feeding significantly increased the number of G. molesta eggs destroyed by host feeding by both wild and commercial strains.     

Pattern of Egg Management by Trichogramma cacoeciae and T. dendrolimi (Hymenoptera: Trichogrammatidae)

The effect of temporary host deprivation on parasitization rates of Trichogramma cacoeciae Marchal and T. dendrolimi Matsumura was investigated. The study was conducted with females that we allowed to engage in 3 days of oviposition after various periods of host deprivation. It seems that the production and management of eggs by the two species is completely different. During the first day of oviposition, parasitization by T. cacoeciae was almost unaffected after 1 to 5 days of host deprivation. As deprivation time increased, however, the number of parasitized hosts decreased from an average of 28.6 ±2.0 hosts provided at emergence to an average of 12.5 ±2.3 hosts when the waiting time was 10 days. The number of hosts parasitized on the first day of parasitization by T. dendrolimi were not affected whatever the waiting test period. During the second or third days of oviposition, the lack of suitable hosts for T. cacoeciae did not depress egg-laying potentiality, whereas a strong reduction in parasitization rates by T. dendrolimi occurred in the next 2 days of oviposition whatever was the waiting period. This leads to ca. 50% reduction in total activity of 3 days of oviposition. Only in T. cacoeciae was it possible to distinguish between ageing and host deprivation. The data suggest that T. dendrolimi is a typical proovigenic species, while T. cacoeciae is neither definitely proovigenic nor synovigenic. A slight decrease in rate of emergence of offspring of T. cacoeciae females that had waited 8 to 10 days for their hosts was observed. As far as biological control is concerned, the efficiency of T. dendrolimi females may be more sensitive to host deprivation than T. cacoeciae.     

Do sympatric Trichogramma species parasitize the pest insect Helicoverpa armigera and the beneficial insect Chrysoperla carnea in different proportions?

Parasitism of two host species by five Trichogramma species (Hymenoptera, Trichogrammatidae) was studied in the laboratory. The host species were: i) the bollworm Helicoverpa armigera Hübner (Lepidoptera, Noctuidae), an important pest of many crops in the tropics and subtropics, and ii) one of its natural enemies, the lacewing Chrysoperla carnea Stephens (Neuroptera, Chrysopidae), a predator often used as a biological control agent. The proportion of H. armigera eggs parasitized from the total number of parasitized hosts differed between Trichogramma species. The average number of parasitized eggs per female in 24 h by Trichogramma pintoi and T. bourarachae was 10 of H. armigera and about 0.5 of C. carnea. For the other three Trichogramma species (T. cordubensis, T. evanescens and T. turkestanica) these averages varied from 6 to 11 H. armigera eggs and from 3 to 4 C. carnea eggs. Total adult offspring production, contacts with hosts, secondary clutch size and sex-ratio of each Trichogramma species were determined as well. The results show that sympatric Trichogramma may parasitize target and non-target species in different proportions. If this difference corresponds to the field situation, simple laboratory tests could be performed to select not only efficient biogical control agents, but also species which are the least detrimental to non-target hosts.     

Comparison Between the Control Efficacy of Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) and Two Trichogramma cacoeciae Marchal Strains Against Grapevine Moth ( Lobesia botrana Den. & Schiff.), Depending on Their Release Density

In the first generation of the grape moth Lobesia botrana, Trichogramma evanescens spread to a greater extent than Trichogramma cacoeciae and parasitized most of the grape moth eggs. Reduction of damage to grapes was improved by doubling the number of T. evanescens release points in the first and second generations. In the second generation of the grape moth, T. cacoeciae was more efficient than T. evanescens . The highest proportion of individuals belonging to the reared and natural T. cacoeciae strains were found in the plot in which they were initially released. The total number of individuals emerging from parasitized eggs eggs was the same for each strain, which would suggest that neither predominated. Whichever T. cacoeciae strain considered, a density of 800 release points ha -1 did not induce greater parasitization than a density of 400 release points ha -1 .     

Factors influencing parasitism of Trichogramma dendrolimi on eggs of the Asian corn borer, Ostrinia furnacalis

Laboratory studies were made to determine the capacity of Trichogramma dendrolimi to parasitize eggs of Ostrinia furnacalis, as affected by the rearing host species, substrate of host eggs, host age, original locality of host populations, and cold storage of host eggs. Wasps reared from eggs of Antheraea pernyi showed parasitic capacity on eggs of O. furnacalis on average twice as high as that of the wasps reared from eggs of Corcyra cephalonica. When the age of O. furnacalis eggs at 26 °C increased from 0–6 h to 18–24 h, the proportion of wasps that successfully parasitized host eggs, the number of host eggs parasitized, and the rate of parasitization all decreased by >50%. The number of O. furnacalis eggs parasitized per female T. dendrolimi increased with the number of host eggs available, and reached 22.9 in a 24 h period. However, the parasitic capacity of female T. dendrolimi on eggs of O. furnacalis laid on plant leaves was similar to that of O. furnacalis eggs laid on wax paper. Levels of parasitism of O. furnacalis eggs from two widely separated localities, i.e. Changchun (43.50° N, 125.20° E) and Hangzhou (30.18° N, 120.07° E), were similar. Cold storage of O. furnacalis eggs at 4 °C for 5 days did not affect parasitization. Results obtained in this study indicate that although O. furnacalis is a less preferred and less suitable host than many other hosts, such as Dendrolimus punctatus, Actias selene ningpoane, Philosamia cynthia, A. pernyi, C. cephalonica, within the host-species range of T. dendrolimi, the parasitoid has the potential to achieve 50–60% or even higher rates of parasitization of O. furnacalis eggs in corn fields under suitable conditions, and could be used in the biological control of the pest.