Laws A N, Joern A
Division of Biology, Kansas State University, Manhattan, KS 66506, USA.
Bull Entomol Res. 2012 Apr;102(2):123-30. doi: 10.1017/S0007485311000472. Epub 2011 Sep 27.
Grasshoppers host a number of parasitoids, but little is known about their impact on grasshopper life history attributes or how those impacts may vary with land use. Here, we report on a three-year survey of nine grasshopper species in a tallgrass prairie managed with fire and bison grazing treatments. We measured parasitoid prevalence and the impact of parasitoid infection on grasshopper fecundity to determine if grasshopper-parasitoid interactions varied with management treatment. Adult female grasshoppers were collected every three weeks from eight watersheds managed with different prescribed burning and grazing treatments. Grasshopper fecundity with and without parasitoids was estimated through dissections of reproductive tracts. Dipteran parasitoids from two families (Nemestrinidae and Tachinidae) were observed infecting grasshoppers. We found significant effects of grazing treatment, but not burn interval, on grasshopper-parasitoid interactions. Parasitoids were three times more abundant in watersheds with bison grazing than in ungrazed watersheds, and the relative abundance of nemestrinid and tachinid flies varied with grazing treatment. Parasitoid prevalence varied among grasshopper species from <0.01% infected (Mermiria bivittata) to 17% infected (Hypochlora alba). Parasitoid infection reduced individual grasshopper fecundity, with stronger effects on current reproduction than on past reproduction. Furthermore, current fecundity in parasitized grasshoppers was lower in grazed watersheds compared to ungrazed watersheds. Nemestrinid parasitoids generally had stronger impacts on grasshopper fecundity than tachinid parasitoids, the effects of which were more variable.
蝗虫体内寄生着多种寄生性昆虫，但人们对它们如何影响蝗虫的生活史特征，以及这些影响如何随土地利用方式而变化却知之甚少。在此，我们报告了一项针对高草草原中9种蝗虫进行的为期三年的调查，该草原采用了火烧和野牛放牧处理措施。我们测量了寄生性昆虫的感染率以及寄生感染对蝗虫繁殖力的影响，以确定蝗虫与寄生性昆虫之间的相互作用是否会因管理措施的不同而有所变化。每隔三周，从八个采用不同规定火烧和放牧处理措施的流域收集成年雌性蝗虫。通过解剖生殖道来估计有无寄生情况下蝗虫的繁殖力。观察到来自两个科（长足虻科和寄蝇科）的双翅目寄生性昆虫会感染蝗虫。我们发现放牧处理措施对蝗虫与寄生性昆虫之间的相互作用有显著影响，但火烧间隔时间则没有，在有野牛放牧的流域中，寄生性昆虫的数量是未放牧流域中的三倍，而且长足虻科和寄蝇科苍蝇的相对丰度会随放牧处理措施而变化。寄生性昆虫的感染率在不同蝗虫种类中有所不同，从感染率小于0.01%（双线瘤虻）到17%（白纹异痂蝗）不等。寄生感染降低了蝗虫个体的繁殖力，对当前繁殖的影响比对过去繁殖的影响更大。此外，与未放牧流域相比，放牧流域中被寄生蝗虫的当前繁殖力更低。一般来说，长足虻科寄生性昆虫对蝗虫繁殖力的影响比寄蝇科寄生性昆虫更强，而寄蝇科寄生性昆虫的影响则更具变异性。
