Plants can retain either physiologically active green leaves or inactive brown leaves over winter. Research has suggested that leaf retention incurs a cost due to higher herbivore load in the following year; however, no distinction has, thus, far been made between retention of green and brown leaves. We surveyed the over-winter retention of physiologically active green and inactive brown leaves of valley oaks (Quercus lobata) and examined their relationship with the diversity and density of 15 gall-making cynipid wasp species. Cynipid diversity in the spring was 8.2-fold greater on larger trees with more green leaf retention. Brown leaf retention was not associated with spring cynipid diversity, but was related to a substantial 20-fold reduction in spring cynipid densities on large trees. Retention of either leaf type was generally a poor predictor of summer cynipid diversity and density. Overall, green leaf retention better explained cynipid diversity, but brown leaf retention better explained cynipid densities. These differing effects may be explained by the fact that green leaves provide a common cue used by herbivores to find a suitable host. Retained brown leaves, however, may be an ecological trap for over-winter gall wasps that normally drop to the ground.

在冬季，植物可以保留生理活性的绿叶或不活动的棕叶。研究表明，由于第二年的食草动物负载增加，叶片滞留会产生成本。然而，迄今在保留绿叶和棕叶之间没有任何区别。我们调查了橡树栎（Quercus lobata）的生理活性绿色和非活性棕色叶子在冬季的滞留情况），并研究了它们与15种制gall柏黄蜂物种的多样性和密度的关系。春季的Cynipid多样性在较大的树木上具有更大的绿叶保留率，是后者的8.2倍。棕色叶片的保留与春季cynipid的多样性无关，但是与大树上春季cynipid的密度显着降低20倍有关。保留任何一种叶子类型通常都不能很好地预测夏季cynipid的多样性和密度。总体而言，绿叶保留能更好地说明cynipid的多样性，而棕叶保留能更好地说明cynipid的密度。这些不同的影响可以通过以下事实来解释：绿叶提供了食草动物用来寻找合适寄主的共同线索。但是，保留的棕叶可能是通常落在地面上的越冬gall的生态陷阱。