We do not recommend spraying with Malathion (or anything else) until an insect pest is actually identified. Would you be able to upload photos to show us the symptoms you are seeing on your tomato leaves? One possibility for the yellowing of the leaves might be early blight, which is a fungal disease active now on tomatoes. https://extension.umd.edu/growit/early-blight-vegetables We would really need to see photos in order to make a good diagnosis and recommendations for you. You can upload up to three photos.

ckc

Some does look like "early blight" to me.  Photos added.  Thanks!

Yes, it does look like your plant has symptoms of early blight. The second photo, with the leaves clipped off the stems, looks like deer browsing damage. We do not see any evidence of insect damage here, so there is no need to apply an insecticide. The web page we sent to you previously has information on how to manage this disease. Prune out and discard (in the trash, not compost) the leaves that are showing yellowing/browning symptoms.
https://extension.umd.edu/growit/early-blight-vegetables

Do not hesitate to be in touch again if you have any additional questions.

ckc

Thanks for your help!

You're very welcome!