insect on milkweed

I noticed that my milkweed leaves were being eaten and I was excited to think monarch larva were on the plants [I have had lots every year; but none last year]...BUT these are not manarch larva...they are an orange beetle/grub like insect and they have eaten almost all the leaves on the milkweed...what are they I hate to think they will eat all the food that the monarch larva need