dendroica:Eastern False Willow, a.k.a. Groundsel Bush (by…

Monday, October 17th, 2016


Eastern False Willow, a.k.a. Groundsel Bush (by me)

Fun fact: This species (Baccharis halimifolia) has become an invasive weed in Queensland, leading authorities there to import my favorite gall midge, Rhopalomyia californica, as a biological control. R. californica normally galls my plant-crush Baccharis pilularis, but in the absence of B. pilularis they’ll make do with B. halimifolia, thereby replacing flower production with midge production and slowing the spread of the unwelcome plant.

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wildflowers-of-southern-ontario: Ball Gall on a…

Thursday, May 19th, 2016


Ball Gall on a Goldenrod
Solidago spp.

Asteraceae (Aster) Family

In the photo above, you can see the hole created by a Eurosta solidaginis, Goldenrod Gall Fly. The inside is empty: if you cut it open, you will see a tunnel exiting from a central chamber with no insect inside.

Galls are abnormal growths that can arise in all
parts of a plant caused by insects. Galls usually do not injure their hosts to the point where the
entire plant is debilitated. These creatures produce
galls to provide food and shelter for themselves. [x]

Among goldenrods, there exists three types of galls – each caused by a different insect and each differ in shape. The gall shown above is a ball gall, named for its spherical shape. The ball gall is sometimes called an apple gall for its reddish-purple hue. The other two types are the spindle gall and the rosette gall. [x]

Gall Formation + Goldenrod Gall Fly Life Cycle

  • In late spring, after mating, the female Goldenrod Gall Fly (Eurosta solidaginis) deposits her eggs, via her ovipositor, onto the young leaves of a goldenrod, near the apical meristem.
  • About ten days later, the eggs hatch and the hungry larvae eat their way several millimeters from the oviposition site
    into the stem (at the apical meristem) and form a chamber where
    they spend their hours eating the plant’s living cells. The ingestion leads to the excretion of significant amounts of metabolic
    by-products that stimulate the abnormal formation of a ball gall, likened to a tumor.
  • In autumn, the growing larvae, about a quarter-inch in length, tunnel towards the gall’s exterior but do not break it, preparing an exit route come spring. They return to the main chamber where they prepare for the winter season: their metabolism slows and glycerol, an antifreeze, is synthesized (along with sorbitol and trehalose) and it replaces their internal water.
  • Come winter, the gall of the senescent goldenrod shelters the larvae, although the gall provides very little insulation (see Irwin & Lee (2000) below).
  • The warm days of spring stimulate the larvae from their slumber, pupae form, and after a few days, adult flies exit from the pre-made tunnel, through the thin-walled porthole now hard and brown (as seen above).
  • The non-feeding adult Goldenrod Gall flies live for about ten days. During that time they do not eat (they have vestigial mouthparts) and solely live to mate and lay a new batch of eggs on a goldenrod stem.

Source: x, x

Journal of Insect Physiology (2000) 46:655-661.
Mild winter temperatures reduce survival and potential fecundity of the
goldenrod gall fly, Eurosta solidaginis (Diptera: Tephritidae)
By J. T. Irwin & R. E. Lee

A low metabolic rate during the winter months conserves the energy, achieved during the past summer and autumn by continuously eating, of the Goldenrod Gall fly, enough energy to mate and lay viable eggs. The low metabolic rate is induced by cooler temperatures (around 0°C), average to the region. Winters with above average temperatures increase the insects’ metabolic rate and proves detrimental in the spring when fecundity decreases as a consequence.


Figure 1 Summary of the data from the article by J. T. Irwin & R. E. Lee (2000).

Photographs taken on Thursday, April 20, 2016 along the Applewood Hills Trail, Mississauga.

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