槲栎超寄生橡子内象甲幼虫的适应对策

栎属植物的橡子常常受到象甲的侵害， 对橡子存活产生影响， 但有关橡子对象甲幼虫适合度影响的研究尚未见报道。本研究旨在通过对槲栎Quercus aliena种子雨进程以及象甲幼虫逃逸过程的调查， 研究二者之间的进化适应关系。结果表明： 当年槲栎的种子产量为51.92±29.26粒/m²， 虫蛀率达到42.4%。虫蛀的橡子中65%以上被象甲超寄生， 且显著大于完好的橡子。在种子下落过程中， 早期从橡子中逃逸的象甲幼虫要比后期逃逸的大。对某一超寄生的橡子而言， 首先逃逸出的象甲幼虫要比随后逃逸的幼虫大。另外， 从早期脱落的橡子中逃逸的幼虫明显小于后期脱落的橡子。象甲幼虫的干重随着橡子内象甲幼虫数量的增加而显著下降。象甲幼虫寄生数量与橡子的长径和短径呈现明显的正相关关系。尽管超寄生降低了象甲虫的适合度， 但雌性成体象甲产卵过程中偏好选择大橡子在一定程度上可以减少这种不利影响。因此， 小橡子可能更容易逃脱象甲的超寄生而获得较大的存活机会。

Adaptive strategies of weevil larvae in the superparasitized acorns of the Oriental white oak, Quercus aliena (Fagaceae)

Acorns of oaks are usually attacked by weevils. Although the interaction between acorns and weevils has been well studied, how acorns affect the fitness of weevil larvae remains unclear. In this study, we attempted to investigate the evolutionary adaptation of weevils to the development of acorns through carefully investigating the seed fall processes and the characteristics of larval emergence from the trapped acorns of the Oriental white oak, Quercus aliena. Our results indicated that seed crop of Q. aliena was 51.92 ± 29.26 nuts/m² with an infestation rate estimated of 42.4% in 2009. The infested acorns were much larger than the sound ones. About 65% of the infested acorns were superparasitized by weevil larvae. Weevil larvae emerged earlier were much larger than those exited later from infested acorns after seed fall. Early emerged weevil larvae were much larger than those coming out later from the same individual superparasitized acorn. Weevil larvae parasitized in the early abscised acorns were smaller than those in later abscised ones. Our results demonstrated that dry weight per weevil larva was decreased significantly with the increase in the number of weevil larvae in single acorn. The number of weevil larvae was closely and positively correlated with length and maximum width of acorns, respectively. Although the fitness of weevil larvae was reduced in the superparasitized acorns, a preference of female weevil for larger acorns to oviposition may counter this disadvantage. Our results may suggest that smaller acorns may benefit from superparasitization because large acorns attract female weevils to oviposit more eggs.