SeEtta et al, This is very interesting. I collecting some of these, or something very similar, from Plains Cottonwood about a week ago at Roselawn Cemetery in Fort Collins. The makers of these pale circles are emerging in a container in my "lab" (aka kitchen). Yes, they are leafminers. Many different groups of insects, from flies to beetles to moths, have representatives with the leafmining habit. The causal organisms in the case you documented are tiny moths, very likely in the genus Phyllonorycter, family Gracillariidae. The larvae tunnel around between the top and lower layers of the leaf, with the fed-upon area usually appearing as a discolored blotch or meandering trail (depending on the species of miner and its particular style). When the larvae are done feeding, they pupate (in this case within the mine), and emerge (in this species, at this time of year). Tiny, pale moths emerged today in my container from mined leaves picked 4 days ago. I suspect you are correct in your guess the birds are after pupae (which would be detectable to them as a dark area within the pale mines). If you go back and look at these trees, my guess is for mines from which the causal moth has emerged and flown away, you will see a slender, dark pupal skin protruding from each mine, or at least a tiny hole.
Thanks for sharing this observation with the group. Dave Leatherman Fort Collins Date: Tue, 25 Sep 2012 00:46:45 -0600 Subject: [cobirds] Insect infestation and migrating warblers From: [email protected] To: [email protected] I posted on Saturday about a feeding frenzy of warblers (Yellow-rumps and a few Orange-crowned and Wilson's and a Townsend's) that day. I noticed that leaves on the cottonwood trees where they were feeding had several yelllowish blotches on them. When I looked at the leaves closely it appeared that there were insect larvae inside the leaves. On infested trees most of the leaves had blotches and many of the trees in the park were infested. I have now uploaded photos of these leaves to my Birds and Nature blog plus one photo of a Townsend's Warbler that appeared to be gleaning larvae (or pupae?) from a leaf. I did some research and found that leafminers can cause symptoms like this and think this may be the family of insects causing this infestation. It certainly is a good source of food for hungry migrating warblers for which gleaning this larvae is compatible with their food habits as it seems to be for Townsend's as well as Yellow-rumped Warblers. SeEtta Moss Canon City Blogging for Birds and Blooms magazine @ http://birdsandbloomsblog.com/author/seetta-moss/ Personal blog @ BirdsAndNature.blogspot.com -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
