Hi Kathy, 

Thanks for reaching out to UVM Extension Master Gardener Helpline. 

Your question got routed up to UVM Extension Entomologist, Margaret Skinner, who had this response to your question: 

According to the literature, the American sunflower moth, Homoeosoma electellum, does not survive above the 40^th deg. N. latitude (https://library.ndsu.edu/ir/bitstream/handle/10365/9462/e1457_2010.pdf?sequence=1). 

However, it seems unusual to me that you would be seeing such mature larvae so early in the summer if they are not overwintering here. The best way to determine if they indeed overwinter here is to put out traps early in the spring next year. In the mean time I suggest you try applying Bacillus thuringiensis (Bt). Most of the factsheets on line only discuss the various chemical insecticides that can be effective, but Bt is registered for this type of pest and may be effective if applied at regular intervals. Keep in mind the larvae must feed on the Bt on plant tissue to be affected. Given how early it is in the summer, you should expect a second generation this year.

Here are additional websites:

https://bookstore.ksre.ksu.edu/pubs/sunflower-moth-kansas-crop-pests_MF3108.pdf

https://academic.oup.com/jipm/article/10/1/25/5538908?login=true

If you have additional questions, contact me directly.

Margaret Skinner, UVM Extension Entomologist

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Hope that helps!