氮肥和寄主龄期对斑痣悬茧蜂生长发育特征的影响

[目的]为揭示寄生蜂发育表现是否与土壤施氮量有关，以及该关系是否依赖于寄生时的寄主龄期，对斑痣悬茧蜂（Meteorus pulchricornis）在该因素处理下的生长发育特征进行了研究。[方法]用不同施氮水平（20、50、100、200、300 mg？L-1）的盆栽大豆饲喂斜纹夜蛾（Spodoptera litura）幼虫，分别以2龄和4龄幼虫为寄主供斑痣悬茧蜂寄生，观察子代蜂发育指标。[结果]施氮量、寄主龄期及其互作均显著影响子代蜂存活、历期、成虫体型大小和寿命，但影响的程度和格局不同：施氮量对子代蜂存活和发育历期的影响明显大于寄主龄期，而对子代蜂成虫体型大小和寿命的影响明显小于寄主龄期。子代蜂发育参数与施氮量之间存在非线性关系，但该关系取决于寄生时的寄主龄期：子代蜂存活与施氮量在寄生4龄幼虫时表现出非线性关系，但在寄生2龄幼虫时无显著关系；子代蜂发育历期与施氮量之间存在二次函数曲线关系，但在寄生2龄幼虫时中等水平施氮量的发育历期较长，而寄生4龄幼虫时在较高水平施氮量处理下的发育历期较长；子代蜂成虫体型大小与施氮量之间在寄生2龄幼虫时，表现出正相关直线关系；但寄生4龄幼虫时没有变化；子代成虫寿命在寄生2龄幼虫时与施氮量之间表现出三次函数曲线关系，但在寄生4龄幼虫时没有变化。[结论]土壤施氮可通过寄主龄期大小而影响寄生蜂子代发育表现，而且该影响与施氮量多存在非线性关系。
[Objectives] This study examined the combined effect of nitrogen fertilizer application to soils with host instars at parasitism on developmental performances of the parasitoid Meteorus pulchricornis attacking Spodoptera litura larval hosts feeding on soybean plants on the treated soils. [Methods] Nitrogen fertilizer was assigned to potted soybean seedlings with five-level treatments,the Hoagland’s solution containing nitrogen of 20,50,100,200 and 300 mg？L-1,respectively. The leaves excised from these plants were used to feed S.litura larvae from neonate to either 2nd or 4th instar,which were then exposed to M.pulchricornis for parasitism. Developmental performances of offspring parasitoids were observed. [Results] The N application,host instar at parasitism,and their interactions influenced developmental performances of offspring parasitoids,with variable effects in pattern and magnitude. The N treatment had stronger effects on developmental survival and duration,but weaker effects on offspring adult size and longevity,than the host instar did. Parasitoid developmental parameters changed in a non-linear relationship with the levels of N application,but such relationship varied depending on the host instar at parasitism. Offspring developmental survival increased with N application levels in a parabolic curve from parasitizing the 4th instar larvae,but did not change from parasitizing the 2nd instar larvae. Offspring developmental duration changed as a quadratic function of N application levels,in different shapes between attacking the 2nd and 4th instar larvae. Offspring adult body size increased slightly with N application levels in a linear way from attacking the 2nd,but did not change from parasitizing the 4th instar larvae. Offspring adult longevity changed in as a cubic function of N fertilizer levels from attacking the 2nd instar larvae,but did not change from attacking the 4th instar hosts. [Conclusions] The results of this study suggest that N