Hi Karen,

1) Neem oil and Repel harmful to butterfly caterpillars - short answer is yes, they and their host plants should not be sprayed with them. Further info below:

• 1a) Neem oil is harmful to caterpillars. This article explains how: "Pest control falls into two basic categories: 1) interference with egg development, and 2) reducing the insect or mite population after hatching. In the first instance, the oil may prevent normal oxygen exchange through the egg covering, hardening of the outer membrane and preventing hatching, possibly dissolving the outer covering, by penetrating into the egg itself, oil may cause the coagulation of the protoplasm. When the oil gets in contact with the larval or adult stage of the insect or mite, it may interfere with the insect’s respiratory activity by blocking the tracheal openings on their bodies or, possibly, create imbalance in hormonal activity."

• 1b) Repel - This is an oil based product and would align with the above resource. That product lists it's active ingredient as Lemon Eucalyptus oil and p- Menthane-3,8-diol which, according to the EPA, "occurs naturally in the lemon eucalyptus plant".

2) Newspaper under mulch is not harmful to caterpillars, but it will suffocate the soil organisms by prohibiting air and water movement.