|Bumblebee male on Queen Anne's Lace, |
an introduced species in North America.
The paper in question is:
Small scale additions of native plants fail to increase beneficial insect richness in urban gardens. by KEVIN C. MATTESON and GAIL A. LANGELLOTTO. Insect Conservation and Diversity (2011) 4, 89–98.
Here are their conclusions:
1. Despite increasing interest in gardening for wildlife, experiments testing the conservation value of garden alterations are scarce, particularly in heavily urbanised landscapes.
2. In this paper, we assess the ability of discrete additions of native wildflowers (70 plants of seven plant species added and subsequently monitored for 2 years) to augment species richness of beneficial insects including bees, butterflies and predatory wasps in New York City community gardens. We also evaluate the overall use of native and introduced flowers by these insect groups in the urban garden study sites.
3. Bayesian analyses failed to find a strong influence of the native plant additions on beneficial insect richness, after correcting for prior floral abundance.
4. In addition, butterflies and megachilid (leaf-cutter) bees were found to heavily utilise introduced ornamental and crop flowers in these gardens, even when native flowers were present.
5. Our results suggest that exotic garden plants are utilised by, and important in maintaining richness of, beneficial insects in urbanised landscapes. Furthermore, garden manipulations need to be more substantial than often recommended, if they are to significantly influence the richness of beneficial insects in urban gardens.
There is no question but that fostering the growth of native wildflowers provides for a more diverse habitat. And the study cited above does not demonstrate that there are no long term negative effects of foraging on introduced plants for beneficial insect diversity.
But in the short term, as most pollinator observers have noted, introduced and invasive flowering plants seem to be just as good for pollinators as the native species.