Dead insects on Penstemon digitalis
I was walking through my pollinator garden last night and noticed that a few of my smooth penstemon (Penstemon digitalis) were covered in dead insects. The insects appeared dried out and were attached to the flowers. The plants were sourced as plugs from Minnesota Native Landscapes (MNL) last summer and should be neonicotinoid-free.
The city I live in fogs for mosquitoes a few times each summer, but I spoke with the city administrator yesterday and he told me the fogger has not been used yet this year. As far as I know, none of my immediate neighbors spray insecticides. One neighbor behind and to the right of us uses herbicide to control weeds in the alley that separates our properties, but the area they spray is more than 30 feet from the affected plants.
After checking the rest of the garden, I found that three smooth penstemon plants were covered in dead insects while three others were unaffected. Two of the affected plants were close together, while the third was roughly 20 feet away. As far as I can tell, only one other plant species in my garden had a single dead insect attached to it.
Does anyone have any ideas what might have caused this? Is it worth reaching out to MNL to ask about the sourcing or treatment history of the plugs?