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Monday, September 26, 2016

Ecosystem Engineers and the Web of Life

Goldenrod in bloom
© Beatriz Moisset

Goldenrod bunch gall
© Beatriz Moisset

This time of the year, fields and meadows are usually covered by a plethora goldenrods particularly the tall variety, known as Solidago altissima. Goldenrods nurture a huge variety of small creatures. Some feast on the rich pollen and nectar of their flowers. Others find ways to feed on the not so nutritious leaves and stems. The plants are so abundant and vigorous that they survive quite well the onslaught of all these feeders.

Rhopalomyia solidaginis
(Goldenrod bunch gall midge)
© Beatriz Moisset

Rhopalomyia solidaginis
Larva inside gall
© Beatriz Moisset

The goldenrod bunch gall midge is one of a number of goldenrod feeders that have developed interesting techniques to feed and stay safe from predators at the same time. The larva of this midge injects special substances into the tips of the goldenrod stems. These substances stimulate an unusual vigorous sprouting of the growing stem and leaves. A tight bunch or cluster of leaves with a nutritious, tender center develops. These clusters can be quite numerous in a field of goldenrods. They are easy to spot and they are known by the name of bunch galls. They provide both nourishment and shelter to the insect.

Parasitic wasps, Platygaster sp
© Beatriz Moisset
This story doesn't end there. The midge creates conditions favorable to other small creatures when it builds the bunch gall. Tiny beetles and wasps find a nice place to hide and even raise their families in the bunches of leaves. Curiously, the galls go beyond that. When dead, they become compost and enrich the soil in a larger scale than goldenrod plants free from galls.
Microrhopala vittata (Goldenrod Leaf Miner)
Inside bunch gall
© Beatriz Moisset
Microrhopala vittata (Goldenrod Leaf Miner)
© Beatriz Moisset
This is reminiscent of what beavers do. These animals build dams which provide habitat for fish and frogs and other animals. This have earned them the name of ecosystem engineers. The goldenrod gall midge is also an ecosystem engineer, although in smaller scale. It is surprising how such an insignificant and easily ignored tiny insect can contribute to the web of life.


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