THE HUNGRY BIRD

The Hungry Bird: Cooley Spruce Gall Adelgid DAVID LEATHERMAN We all know the Colorado State Bird is the Lark Bunting. Our State Tree is the Colorado Blue Spruce. The State Flower is the Rocky Mountain Columbine*. We also have a State Mammal, Dinosaur, Amphibian, Reptile, Cactus, Fish, Insect, Grass (no, not that one), Fossil, Soil, Mineral, Gemstone and even Rock. I will leave it up to you to figure out the specifics for official symbols not overtly named above. That is quite a list but it is not complete. Only somewhat in jest, years ago the student Gillette Entomology Club at Colorado State University proposed our State Gall should be the Cooley spruce gall. It will probably never become official, but I wager our legislature has dealt with more frivolous matters. The Cooley spruce gall adelgid, CSGA, (Adelges cooleyi), is an aphid-like insect. Members of its family Adelgidae are often referred to as “woolly aphids,” although this common name also applies to certain true aphids in the family Aphididae, that also cover their bodies in certain stages with waxy filaments. As is often the case with a common name used for more than one animal or plant, communication is best using the most specific name possible. No more “Cooley gall aphid” or “Cooley spruce gall woolly aphid.” Cooley spruce gall adelgid it is. Surely you have all seen the characteristic handiwork of CSGA – its gall. Most conspicuous are the old, brown galls which resemble, very loosely in my opinion, “pine cones” (Figure 1). Some texts even say “pineapples.” They are so common on spruce, wherever it grows at timberline to front yard specimens from Burlington to Grand Junction, they are almost an identifying characteristic of trees in the genus Picea. Colorado blue spruce is the most common host, with Engelmann and other spruces being less so. A related insect, the spruce gall adelgid (Pineus similis), makes a similar but smaller, thinner gall on Engelmann spruce (Cranshaw et al. 2014). This gall is a common source of inquiry by tree owners, who mostly fear it will lead to something else and might threaten the life of its host plant. At worst, I suppose it could be considered a cosmetic blemish to some of the bluer cultivars of Colorado blue spruce. But when one considers the galls are merely interesting patches of modified needles with the causal agent being food for birds, there are more worthy causes of concern. Hangnails come to mind. Figure 1. Dozens of old, open, brown Cooley spruce galls on a Colorado blue spruce. They feed birds and are not a threat to the overall health of host trees. Photo by David Leatherman. How these galls come to be on spruce is the result of a fairly complicated series of movements and life stage changes, often involving a second kind of tree, Douglas-fir. This alternation of hosts is the norm but is not required. That is, CSGA can persist in the absence of Douglas- fir. It cannot sustain itself indefinitely without spruce. Its populations likely do better in the long run if they alternate per their evolutionary path. Think of this as diversifying their genetic portfolio. If an environmental disturbance happens that is spruce-specific, the portion of the population hosted by Douglas-fir carries on for a time, and eventually reinvades spruce. If Douglas-fir wigs out, CSGA is content with spruce.

*Presumably this applies to Colorado Blue Columbine (Aquilegia coerulea) which occurs in all counties west of the eastern plains and not to Rocky Mountain Blue Columbine (A. saximontana) which occurs in the mountains from our northern border with Wyoming only as far south as El Paso and Chaffee counties.

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The following describes the CSGA life cycle on spruce when nearby Douglas-firs are involved. During late summer- autumn, individuals that had been feeding on needles of Douglas-fir develop wings and fly to spruce. Here they overwinter at the base of needles. They feed anew in spring and in late spring mature to adulthood. Resultant mated females lay large quantities of eggs in masses on the underside of spruce twigs. About the time spruce buds begin to open, these eggs hatch and begin to feed via sharp-tipped, “drinking straw” mouthparts called “stylets” on the newly formed spruce needles. This wounding induces formation of swollen needle bases that coalesce into conelike galls. The galls start out green, then turn a beautiful pale purple (Figure 2). As they enlarge, they envelop the feeding adelgid nymphs that then finish their development in chambers within the galls (Figure 3). The galls’ spines are simply the tips of needles with bases modified into the gall chambers.

Figure 2. Green and purple Cooley spruce gall at left forming on Colorado blue spruce. At right is a normal shoot of new growth. CSGAs enclosed within the enlarging gall are feeding on the gall walls and maturing. 29 May 2020, Grandview Cemetery, Fort Collins, CO. Photo by David Leatherman.

Figure 3. Developing Cooley spruce gall sliced lengthwise to show its internal chambers and white adelgid inhabitants. Per- haps such a view gave rise to the “pineapple” comparison. 12 June 2011, Grandview Cemetery. Photo by David Leatherman. Depending on the weather for its timing, each chamber opens to the outside world sometime in June or July. Out pour mature adelgids, some already possessing wings (Figure 4). They soon all molt into winged forms and disperse back to Douglas-fir or, in the absence of Douglas-fir, to needles of the same spruce in which they developed or most likely to other individual spruce trees (Cranshaw et al. 2014).

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Figure 4. Close-up of Cooley spruce gall opening up that shows a couple winged forms and droplets of “honey- dew” excrement spilling out. Protected while inside the gall by the protruding needle tips of the gall’s exterior, they are now quite vulnerable to predation. 18 June 2012, Grandview Cemetery. Photo by David Leatherman.. The calendar of events happening on Douglas-fir is roughly the same without the formation of galls. That is, after galls on spruce open and the emerging adelgids grow wings, some fly to Douglas-fir, if available. Before winter these produce eggs which hatch and overwinter as nymphs. The following spring these mature and produce one or two generations that do not result in gall formation on Douglas-fir. Mostly, looking like tiny wads of white lint, they feed on Douglas-fir needles, causing them to yellow and bend or twist. Per above, some of the winged forms move over to spruce and a generation develops there that includes gall development. Simple, right? Suffice it to say, in locales where both spruce and Douglas-fir exist in proximity, and if there is a healthy CSGA population, one or more life stages exist on needles, twigs or are flying through the air between them. Birds know this and respond. Chickadees, nuthatches, Brown Creepers, warblers, Bushtits, Pine Siskins, Downy Woodpeckers and juncos and other sparrows like Chipping all love to nitpick around in Colorado blue spruce, and to a lesser degree, Douglas-fir. When I foolishly investigate the reason for all this meticulous avian searching, day after day, month after month, only one likely answer materializes. The only prominent prey I can find is one of the life stages of CSGA. Of course, the needles and twigs of these conifers harbor other things like scale insects, various spiders and harvestmen (“daddy-longlegs”), lacewings, various flies and many more. But in terms of reliable volume, CSGA appears to be very important to this subset of insectivorous gleaners.

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Trying to prove a chickadee just ate a CSGA nymph at the base of a spruce needle 40 feet up in the dark interior of the crown is an exercise in futility. And I have never seen a bird (or squirrel, for that matter) break open a developing green or purple gall full of adelgids. During winged dispersal, and then when heavy populations of these winged forms have settled on needles, seem to be the best times to observe birds feeding on CSGA. In the summer of 2020, the main flights were in late July-early August. This was a late year, and in more typical summers, emergence from galls more commonly occurs in June-early July. Besides staring down intently at substrates underfoot or overhead within centimeters of their roving eyes for grounded targets, birds no doubt take advantage of backlighting to detect flying insects moving across gaps in tree canopies. The wings of flying forms of CSGA are as big or bigger than their bodies and glint in various shades of red and green. Of course, when they land, and 6 or more of their gray forms contrast with the green hues of conifer needles, they are easy to spot. One anecdote in my journal from 17 July 2011 states, “Heard warblerlike chip of cowbird fledgling, then a metallic begging buzz, then saw it being fed by bedraggled ruby-crowned kinglet in Section 9 (of Grandview Cemetery in Fort Collins). The primary food was Cooley gall adelgids gleaned from recently opening galls. The feeding/begging took place in blue spruce, on bare lower limbs for the most part. Awesome to figure out.” (Figure 5). Figure 5. Parent Ruby-crowned Kinglet gives its Brown-headed Cowbird fledgling a beakful of Cooley spruce gall adelgids gleaned from needles within a few feet of this scene. 17 July 2011, Grandview Cemetery. Photo by David Leatherman. In observing Broad-tailed Hummingbird nests at this same cemetery over a period of decades, the adult females often utilize flying adelgids, or those readily plucked from needle surfaces, as food for nestlings. On 28 July 2020 the needles of Douglas-firs near heavily galled Colorado blue spruce trees were conspicuously decorated with winged adelgids (Figures 6 and 7). The primary responders were a family group of local Bushtits and Black-capped Chickadees. Figure 6. Douglas-fir needles heavily infested with CSGA winged forms arrived from a nearby Colorado blue spruce. Grandview Cemetery. Photo by David Leatherman.

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Figure 7. Two winged adelgids in the foreground (others in background) settling in to feed on a Douglas-fir nee- dle. Note, the white waxy secretions beginning to form at the head end that apparently serve to reduce moisture loss from the insect, and may be a deterrent to predators. Grandview Cemetery. Photo by David Leatherman. After the spruce galls open and give up their living contents, they go from purplish to straw-colored to medium brown (Figure 8). The brown Cooley galls that we have all seen, whether we know we have seen them or not, contain no adelgids. However, like once flourishing mansions, vacated and left to the natural designs of vermin and vines, in time the myriad chamber openings in brown galls invite other arthropods. Spiders, earwigs and many other life forms take up residence. The same set of birds mentioned above, especially those that winter, often investigate old galls for “squatters” (the technical term being “inquilines”).

Figure 8. Freshly-vacated Cooley spruce galls. Both photos taken on 30 July 2020, the one on the left giving up its contents more recently than the one at right based on its paler color. Grandview Cemetery. Photos by David Leatherman. Back in the 1990s, those Dark Ages when people could congregate, learn and have fun together, my employer, the Colorado State Forest Service, sponsored what we called a “Forestry Fair” in the Black Forest east of Monument. With the target audience being private tree and forest owners, there were booths, demonstrations, lumberjack competitions, food and all manner of woody plant information and fun. In my display area featuring specimens and damage samples of various tree insects and diseases, we made $4.50 from the sale of “porcupine eggs.” We would not have made a dime off birds. Nor you, if you can guess what they were. Hint, they should be a State symbol. LITERATURE CITED

Cranshaw, W., D. Leatherman, W. Jacobi and N. Tisserat. 2014. Insects and diseases of woody plants in Colorado. CSU Extension Bulletin 506A. Fort Collins.

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