Asked March 29, 2024, 12:33 AM EDT
I am a teacher interested in looking at goldenrod galls with students and opening them to see if they contain the original fly (Eurosta solidagnis as either larva or pupa) or one of their parasites instead (wasp or beetle). I read that the flies emerge in "late or mid-Spring". I have a few questions regarding the timing of their life cycle in Michigan (Lansing area). I am wondering when specifically they emerge in Michigan, so I have an idea of how late in the season I have for my class to look at them and expect they are likely to still contain pupa or larva before it is "too late." Do they emerge in May / June, or could it be as early as April? If we open galls in April, would they most likely still be inside assuming a bird didn't pull them out (for the flies, wasps, and beetles)? If they are likely to still be inside the galls, would they already be in the pupal case by April, and if so how would we know if the pupa is the fly, beetle, or the parasitic wasp? What specifically triggers their final change to the adult form and emergence from the gall... would the mild winter we had cause them to emerge sooner than usual (is it temperature), or is it more related to light or some other factor? I know the flies only live for a short time once they emerge and lay their eggs on goldenrod stems, but I am unsure of how they "know" that goldenrod stems would have sprouted and be "ready" for them. If I gather some galls in February or March, can I store them in a fridge or freezer to later look at during a lesson in April (would the cold temperatures keep them from moving to the next life cycle stage - whether that be pupa or adult?). I've read some articles about the life cycle but still need help figuring out timing and whether examining the gall contents is still possible in April since April is when we do a unit about insects so is the most suitable time to look at them in terms of my curriculum. An additional question I have - I looked at some galls in the past during September, and many of them (more than half of the 20 we looked at) did not seem to contain any larva at all (not of fly, wasp, or beetle) nor signs of an exit hole... do you think this means the larva just somehow died and decomposed, or do the galls form for other reasons not related to the insects, or is there another explanation you would suggest?
Thank you for your feedback!
Ingham County Michigan
